ENV330

· Chapter Introduction

· Core Case Study Los Angeles Air Pollution

· 18.1 The Atmosphere

· 18.1a The Atmosphere Consists of Several Layers

· 18.1b The Troposphere and Stratosphere

· 18.2 Outdoor Air Pollution

· 18.2a Natural and Human Sources of Air Pollution

· 18.2b Major Outdoor Air Pollutants

· 18.2c Industrial Smog

· 18.2d Factors Affecting Outdoor Air Pollution

· 18.3 Acid Deposition

· 18.3a Acid Deposition

· 18.3b Harmful Effects of Acid Deposition

· 18.3c Reducing Acid Deposition

· 18.4 Indoor Air Pollution

· 18.4a Indoor Air Pollution Is a Serious Problem

· 18.5 Health Effects of Air Pollution

· 18.5a Overwhelming Our Body’s Natural Air Pollution Defenses

· 18.5b Air Pollution Is a Big Killer

· 18.6 Reducing Air Pollution

· 18.6a Laws and Regulations

· 18.6b Using the Marketplace to Reduce Outdoor Air Pollution

· 18.6c Reducing Outdoor Air Pollution

· 18.6d Reducing Indoor Air Pollution

· 18.7 Ozone Layer Depletion

· 18.7a Chemical Threats to the Ozone Layer

· 18.7b Why Does Ozone Depletion Matter?

· 18.7c Reversing Stratospheric Ozone Depletion

· Tying It All Together Los Angeles Air Pollution and Sustainability

· Chapter Review

· Critical Thinking

· Doing Environmental Science

· Data Analysis

18.1aThe Atmosphere Consists of Several Layers

Life exists under a thin blanket of gases surrounding the earth, called the atmosphere. It is divided into several spherical layers defined mostly by temperature differences (Figure 18.2). Our focus in this chapter is on the atmosphere’s two innermost layers: the troposphere and the stratosphere.

Figure 18.2

Natural capital: The earth’s atmosphere is a dynamic system that has four layers. The average temperature of the atmosphere varies with altitude (red line) and with differences in the absorption of incoming solar energy.

Critical Thinking:

1. Why do you think most of the planet’s air is in the troposphere?

An important atmospheric variable is density, the number of gas molecules per unit of air volume. It varies throughout the atmosphere because gravity pulls harder on gas molecules near the earth’s surface than it does on molecules high up in the atmosphere. This means that lower layers have more gases (more weight) in them than upper layers do, and are more densely packed with molecules. Thus, the air we breathe at sea level has a higher density than the air we would inhale on top of a high mountain.

Another important atmospheric variable is atmospheric pressure—the force, or mass, per unit area of a column of air. This force is caused by the continuous bombardment of a surface such as your skin by the molecules in air. Atmospheric pressure varies with density. It decreases with altitude (see black line in Figure 18.2) because there are fewer gas molecules at higher altitudes. The density and pressure of the atmosphere are important because they play major roles in the weather.

8.1bThe Troposphere and Stratosphere

About 75–80% of the earth’s air mass is found in the  troposphere , the atmospheric layer closest to the earth’s surface (Figure 18.2). This layer extends about 17 kilometers (11 miles) above sea level at the equator and 6 kilometers (4 miles) above sea level over the poles. If the earth were the size of an apple, this lower layer containing the air we breathe would be no thicker than the apple’s skin.

Take a deep breath. About 99% of the volume of air you inhaled consists of two gases: nitrogen (78%) and oxygen (21%). The remainder is 0.93% argon (Ar), 0.040% carbon dioxide , smaller amounts of water  vapor, dust and soot particles, and other gases, including methane , ozone , and nitrous oxide .

Several gases in the troposphere, including , , , and , are called greenhouse gases because they absorb and release energy that warms the troposphere and the earth’s surface. Without this natural greenhouse effect, the earth would be too cold for life as we know it to exist. Rising and falling air currents, winds, and concentrations of  and other greenhouse gases in the troposphere play major roles in the planet’s short-term weather and long-term climate.

The atmosphere’s second layer is the stratosphere, which extends from about 17 to about 48 kilometers (from 11 to 30 miles) above the earth’s surface (Figure 18.2). The stratosphere contains less matter than the troposphere but its chemical composition is similar, with two notable exceptions. The stratosphere has a much lower volume of water vapor and a much higher concentration of ozone .

Most of the atmosphere’s ozone is concentrated in a portion of the stratosphere called the  ozone layer , found roughly 17–26 kilometers (11–16 miles) above sea level (Figure 18.2). Most of the ozone in this layer is produced when oxygen molecules interact with ultraviolet (UV) radiation emitted by the sun.

The UV filtering effect of ozone in the lower stratosphere acts as a “global sunscreen” that keeps about 95% of the sun’s harmful UV radiation from reaching the earth’s surface. The stratosphere’s ozone layer allows life to exist on land and helps to protect us from sunburn, skin and eye cancers, cataracts, and damage to our immune systems. It also prevents much of the oxygen in the troposphere from being converted to ground-level ozone, a harmful air pollutant. In other words, preserving the life-sustaining stratospheric ozone layer should be one of humanity’s top priorities.

18.2aNatural and Human Sources of Air Pollution

Air pollution  is the presence of chemicals in the atmosphere in concentrations high enough to harm organisms, ecosystems, or human-made materials, or to alter climate. Almost any chemical in the atmosphere can become a pollutant if it occurs in a high enough concentration. The effects of air pollution range from annoying to lethal.

Air pollutants come from natural and human sources. Natural sources include wind-blown dust, solid and gaseous pollutants from wildfires and volcanic eruptions, and volatile organic chemicals released by some plants. Most natural air pollutants spread out over the globe and become diluted or are removed by chemical cycles, precipitation, and gravity. However, pollutants emitted by volcanic eruptions and forest fires can temporarily reach harmful levels.

Most human inputs of outdoor air pollutants occur in industrialized and urban areas where people, cars, and factories are concentrated. These pollutants are generated mostly by the burning of fossil fuels in power plants and industrial facilities (stationary sources) and in motor vehicles (mobile sources). Thus, urban areas such as Los Angeles (Core Case Study) normally have higher outdoor air pollution levels than rural areas. However, prevailing winds can spread long-lived primary and secondary air pollutants from urban and industrial areas to the countryside and to other urban areas. In fact, satellite measurements show that long-lived air pollutants from anywhere on the planet can circle the entire globe in about two weeks (Science Focus 18.1).

Science Focus 18.1

Atmospheric Brown Clouds

Air pollution is no longer viewed as primarily a localized urban problem. Annual satellite images and studies by the United Nations Environment Programme (UNEP) have found massive, dark brown clouds of pollution—called atmospheric brown clouds. At various times, these clouds stretch across much of India (Figure 18.A), Bangladesh, and the industrial heart of China, as well as parts of the western Pacific Ocean.

Figure 18.A

Air pollution in Delhi, India. In 2017, breathing the air in Delhi was the equivalent of smoking more than two packs of cigarettes a day.

Saurav022/ Shutterstock.com

In most years, these clouds cover an area about the size of the continental United States. They contain small particles of dust, smoke, and ash resulting from wind erosion due to drought and from the clearing and burning of forests for planting crops. They also contain particles of soot, or black carbon, and toxic metals such as mercury and lead. These various particles enter the atmosphere from wildfires, the burning of wood and animal dung for heat and cooking, diesel engine exhaust, motor vehicle exhaust, ocean ships burning heavy oil, coal-burning power and industrial plants, metal smelters, and waste incinerators.

These enormous pollution clouds can move across the Asian continent within three to four days. Satellites have tracked the spread of pollutants from the atmospheric brown clouds over northern China across the Pacific Ocean to the West Coast of the United States. Measurements made by atmospheric scientists show that large portions of the particulate matter, soot, and toxic mercury in the skies above Los Angeles, California (Core Case Study), can be traced to China.

Researchers estimate that the atmospheric brown clouds are directly linked to the deaths of more than 380,000 people a year in China and India. They also affect global weather patterns. Long-term studies on the effects of the brown clouds on weather were carried out by an international team of scientists led by V. Ramanathan of the Scripps Institution of Oceanography. Their findings include decreases in the summer monsoon rainfall in some areas, a north-south shift in rainfall patterns in eastern China, accelerated melting of Himalayan glaciers that feed major Asian rivers, and increased levels of ozone in the lower atmosphere in many areas. These weather effects have helped reduce water supplies and crop yields and have damaged human health.

The researchers also found that soot and some of the other particles that fall onto Himalayan glaciers from the atmospheric brown clouds absorb sunlight and heat the air above those glaciers. This soot also decreases the ability of the glaciers to reflect sunlight back into space. The glaciers then absorb more solar energy and experience increased melting. This adds to the warming of the air above them, which in turn further increases the rate of glacial melting in a runaway positive feedback cycle (see Chapter 2). The researchers projected that at the current rate of melting, the Himalayan glaciers could shrink by as much as 75% before 2050 and pose “a grave danger to the region’s water security.”

Critical Thinking

1. Do you think that dealing with pollution that crosses borders is the responsibility of the source country or of the countries that are affected?

Scientists classify outdoor air pollutants into two categories (Figure 18.3).  Primary pollutants  are chemicals emitted directly into the air from natural processes and human activities at concentrations high enough to cause harm. While in the atmosphere, some primary pollutants react with one another and with other natural components of air to form new harmful chemicals, called  secondary pollutants .

Figure 18.3

Human inputs of air pollutants come from mobile sources (such as cars) and stationary sources (such as industrial, power, and cement plants). Some primary air pollutants react with one another and with other chemicals in the air to form secondary air pollutants.

Since the 1970s, the quality of outdoor air in most of the more-developed countries has improved, thanks mostly to grassroots pressure from citizens in the 1960s and 1970s. This led governments in the United States and in most European countries to pass and enforce air-pollution-control laws (Core Case Study).

90%

Percentage of the people living in the world’s largest cities who breathe polluted air

Despite such efforts, air pollution is one of the world’s most serious environmental and health problems. In 2018, 134 million Americans or 41% of the U.S. population lived in areas where air pollution reached dangerous levels during parts of the year, according to the American Lung Association. According to a 2017 survey of 4,000 cities in 100 countries by the World Health Organization (WHO), 90% of the people living in the world’s largest cities breathe polluted air. Most people who are exposed to dangerous levels of air pollutants live in densely populated cities in less-developed countries where air-pollution-control laws do not exist or are poorly enforced. For example, 9 of the world’s 10 most polluted cities are in India, according to the WHO.

Prolonged high exposure to air pollutants overloads the body’s natural defense mechanisms. Fine and ultrafine particles can get lodged deep in the lungs and contribute to cancer, asthma, heart attack, and stroke.

18.2bMajor Outdoor Air Pollutants

Hundreds of different chemicals and substances can pollute outdoor air. Here we focus on six major groups of air pollutants.

Carbon Oxides

Carbon monoxide (CO) is a colorless, odorless, and highly toxic gas that forms during the incomplete combustion of carbon-containing materials ( Table 18.1 ). Major sources are motor vehicle exhaust, the burning of forests and grasslands, the smokestacks of fossil fuel–burning power plants and industries, tobacco smoke, and open fires and inefficient stoves used for cooking or heating.

Table 18.1

Chemical Reactions that Form Major Air Pollutants

Pollutant	Chemical Reaction
Carbon monoxide (CO)
Carbon dioxide
Nitric oxide (NO)
Nitrogen dioxide
Sulfur dioxide

In the body, CO can combine with hemoglobin in red blood cells, which reduces the ability of blood to transport oxygen to body cells and tissues. Long-term exposure can trigger heart attacks and aggravate lung diseases such as asthma and emphysema. At high levels, CO can cause headache, nausea, drowsiness, confusion, collapse, coma, and death, which is why it is important to have CO detectors in your home.

Carbon dioxide  is a colorless, odorless gas. About 93% of the  in the atmosphere is the result of the natural carbon cycle (see  Figure 3.20 ). The rest comes from human activities such as the burning of fossil fuels, which adds  to the atmosphere, and the removal of forests and grasslands that help remove excess  from the atmosphere.  is classified as an air pollutant because it has reached high enough levels to warm the atmosphere and bring about climate change that affects human health. However, there is political pressure from the U.S. fossil fuel industry to reverse the Environmental Protection Agency (EPA) ruling that  is an air pollutant, despite overwhelming scientific evidence that it is.

Nitrogen Oxides and Nitric Acid

Nitric oxide (NO) is a colorless gas that forms when nitrogen and oxygen gases react under high temperatures in automobile engines and coal-burning power and industrial plants ( Table 18.1 ). Lightning and certain bacteria in soil and water also produce NO as part of the nitrogen cycle (see  Figure 3.21 ).

In the air, NO reacts with oxygen to form nitrogen dioxide , a reddish-brown gas. Collectively, NO and  are called nitrogen oxides . Some of the  reacts with water vapor in the air to form nitric acid  and nitrate salts , components of harmful acid deposition, discussed later in this chapter. Both NO and  play a role in the formation of photochemical smog—a mixture of chemicals formed under the influence of sunlight in cities with heavy traffic ( Core Case Study ). Nitrous oxide , a greenhouse gas, is emitted from fertilizers and animal wastes and is produced by the burning of fossil fuels.

At high enough levels, nitrogen oxides can irritate the eyes, nose, and throat, and aggravate lung ailments such as asthma and bronchitis. They can also suppress plant growth and reduce visibility in the atmosphere when they are converted to nitric acid and nitrate salts.

Sulfur Dioxide and Sulfuric Acid

Sulfur dioxide ( is a colorless gas with an irritating odor. About one-third of the  in the atmosphere comes from natural sources such as volcanoes. The other two-thirds (and as much as 90% in highly industrialized urban areas) comes from human sources—mostly combustion of sulfur-containing coal in power and industrial plants ( Table 18.1 ), oil refining, and the smelting of sulfide ores.

In the atmosphere,  can be converted to aerosols, which consist of microscopic suspended droplets of sulfuric acid  and suspended particles of sulfate  salts that return to the earth as a component of acid deposition. Sulfur dioxide, sulfuric acid droplets, and sulfate particles reduce atmospheric visibility and aggravate breathing problems. They can damage crops, trees, soils, and aquatic life in lakes. They also corrode metals and damage paint, paper, leather, and the stone used to build walls, statues ( Figure 18.4 ), and monuments.

Figure 18.4

Sulfuric acid and other air pollutants have damaged this statue in Rome, Italy. The nose and part of the forehead have been restored.

O. LOUIS MAZZATENTA/National Geographic Image Collection

Particulates

Suspended particulate matter (SPM) consists of a variety of solid particles and liquid droplets that are small and light enough to remain suspended in the air for long periods. The U.S. EPA classifies particles as fine, or PM-10 (with diameters less than 10 micrometers, or less than one-fifth the diameter of a human hair); and ultrafine, or PM-2.5 (with diameters less than 2.5 micrometers). About 62% of the SPM in outdoor air comes from natural sources such as dust, wildfires, and sea salt. The other 38% comes from human sources such as coal-burning power and industrial plants ( Figure 18.5 ), motor vehicles, wind-blown dust from exposed topsoil, road construction, and microplastics. The EPA has found that fine particles can travel for thousands of kilometers in the atmosphere, while ultrafine particles have been shown to travel for up to 10 kilometers (6 miles) from their sources.

Figure 18.5

Severe air pollution from burning coal in an iron and steel factory in Czechoslovakia.

JAMES P. BLAIR/National Geographic Image Collection

Fine particulate matter has a major impact on human health because it is present everywhere and can travel deep into our lungs. Particulate matter can irritate the nose and throat, damage the lungs, aggravate asthma and bronchitis, and shorten life spans. According to the WHO, particulate matter is a major worldwide cause of deaths from lung cancer, chronic obstructive pulmonary disease (COPD), strokes, and heart disease.

Toxic particulates such as lead (see the Case Study that follows), cadmium, and polychlorinated biphenyls (PCBs) can cause genetic mutations, reproductive problems, and cancer. Particulates also reduce atmospheric visibility, corrode metals, and discolor clothing and paints.

Ozone

A major ingredient of photochemical smog is ozone , a colorless and highly reactive gas. Ozone can cause coughing and breathing problems, aggravate lung and heart diseases, reduce resistance to colds and pneumonia, and irritate the eyes, nose, and throat. Ozone also damages plants, rubber in tires, fabrics, and paints.

Research shows that ozone in the troposphere near ground level can be harmful at high levels, but ozone in the stratosphere is beneficial because it protects us from harmful UV radiation. Scientific measurements show that human activities have decreased the amount of beneficial ozone in the stratosphere and increased the amount of harmful ground-level ozone—especially in some urban areas. We examine the serious issue of decreased stratospheric ozone in the next section of this chapter.

Volatile Organic Compounds (VOCs)

Organic compounds that exist as gases in the atmosphere or that evaporate from sources on the earth’s surface into the atmosphere are called volatile organic compounds (VOCs). Examples are hydrocarbons emitted by the leaves of many plants, and methane . As a greenhouse gas,  is 25 times more effective per molecule than  is at warming the atmosphere. About a third of global methane emissions come from natural sources such as plants, wetlands, and termites. The rest come from human sources such as rice paddies, landfills, leaking natural gas wells and pipelines, and cows (mostly from their belching) raised for meat and dairy production.

Other VOCs are liquids that can evaporate quickly into the atmosphere. Examples are benzene and other industrial solvents, dry-cleaning fluids, and various chemicals in gasoline, plastics, and other products. In 2018, researchers at the University of Colorado found that chemicals found in paints, pesticides, hair spray, deodorant, soap, perfumes, household chemicals, and other commercial products account for about half of the emissions of VOCs in major U.S. cities such as Los Angeles ( Core Case Study ). This is more than the 32% of the VOC emissions from gasoline and engine exhaust in these cities. Many of these VOCs are emitted indoors where people spend most of their time.

An important priority for many public health officials and scientists is to continually improve the monitoring of outdoor air for the presence of dangerous pollutants ( Science Focus 18.2 ).

Science Focus 18.2

Detecting Air Pollutants and Monitoring Air Quality

Chemical instruments and satellites armed with various sensors can detect and measure levels of pollutants in the air. The scientists who discovered the components and effects of the atmospheric brown clouds ( Science Focus 18.1 ) used small, unmanned aircraft carrying miniaturized instruments to measure chemical concentrations, temperatures, and other variables within the clouds.

Aerodyne Research in the U.S. city of Boston, Massachusetts, has developed a mobile laboratory that uses sophisticated instruments to make instantaneous measurements of primary and secondary air pollutants from motor vehicles, factories, and other sources. This laboratory can also monitor changes in concentrations of the pollutants throughout a day and under different weather conditions, and it can measure the effectiveness of various air pollution control devices used in cars, trucks, and buses. Scientists are also using nanotechnology (see  Science Focus 14.1 ) to try to develop inexpensive detectors for various air pollutants.

In partnership with the EPA, some Google Street View cars are equipped with state-of-the-art sensors that measure atmospheric levels of a number of pollutants, including soot, ozone, and nitrogen oxide gases. If expanded, these data would allow individuals to use Google Earth and Google Maps to monitor air quality on the block where they live.

Biological indictors can also detect air pollutants. For example, a lichen is an organism consisting of a fungus and an alga living together, usually in a mutualistic relationship. These hardy pioneer species are good biological indicators of air pollution because they continually absorb air as a source of nourishment. A highly polluted area around an industrial plant might have only gray-green crusty lichens or none at all. An area with moderate air pollution might support only orange crusty lichens ( Figure 18.B ) and areas with clean air can support a variety of lichens.

Figure 18.B

Lichens such as these growing on a rock can act as biological indicators of air pollution.

Mr Doomits/ Shutterstock.com

Some lichen species are sensitive to specific air-polluting chemicals. Old man’s beard and yellow Evernia lichens, for example, can sicken and die in the presence of excessive sulfur dioxide , even if the pollutant originates far away. Scientists used Evernia lichens to discover  pollution on Isle Royale, Michigan (USA), in Lake Superior, an island where no car or smokestack has ever intruded, and traced it to coal-burning facilities in and around the Canadian city of Thunder Bay, Ontario.

Using daily information about air pollution, the EPA has created an air quality indicator called the Air Quality Index (AQI) for informing citizens about unsafe levels of pollution in any given area of the country. Scientists collect daily data on the levels of five major pollutants—ground-level ozone, particulates, CO, , and —using instruments at more than 1,000 locations around the United States. They use these data to compute a daily AQI for each pollutant and an overall AQI for any particular region. AQI values run from 0 to 500, with higher numbers indicating poorer air quality. Values of 200 and over are considered very unhealthy or hazardous for all people.

Critical Thinking

1. Who should pay for the science and technology of air pollution detection and air quality monitoring? Explain.

Learning from Nature

The atmosphere has a self-cleaning mechanism involving sunlight and naturally occurring ozone, which when mixed with polluting gasses, cause pollutants to clump together to form particles which are then washed out of the air by precipitation. Chemist Matthew Johnson has invented a device called the atmospheric photochemical accelerator that mimics this process, cleansing indoor and outdoor air of pollutants, especially VOCs, without the use of toxic substances or high-temperature processes common to most air filtering devices.

Case Study

Lead: A Highly Toxic Pollutant

Lead (Pb) is a soft gray metal used to make various products including lead–acid batteries and bullets, and it was once a common ingredient of gasoline and paints. It is also a particulate pollutant found in air, water, soil, plants, and animals.

Because it is a chemical element, lead does not break down in the environment. This indestructible and potent neurotoxin can harm the nervous system, especially in young children. Children with severe lead poisoning can suffer from palsy, partial paralysis, blindness, and mental retardation.

Children under age 6 and unborn fetuses, even with low blood levels of lead, are especially vulnerable to nervous system impairment, lowered IQ (by 2 to 5 points), shortened attention span, hyperactivity, hearing damage, and various behavior disorders. According to many scientists, there is no safe level of lead in children’s blood, and they call for sharply reducing the currently allowed levels for lead in the air and water.

Since the 1970s, the percentage of U.S. children under age 6 with blood lead levels above the safety standard dropped from 85% to less than 1%, which prevented at least 9 million childhood lead poisonings, according to the U.S. Centers for Disease Control and Prevention (CDC). The primary reason for this drop was that after a decade-long fight with the oil and lead industries, the federal government banned leaded gasoline in 1976. Leaded gasoline was completely phased out by 1986. The government also greatly reduced the allowable levels of lead in paints. This is an example of the effectiveness of pollution prevention.

However, in 2012, the CDC used the latest scientific data to come up with stricter guidelines for identifying children who have potentially dangerous blood lead levels. These guidelines more than doubled the estimated number of young children at risk from lead poisoning in the United States, raising it to about 535,000. In 2018, the CDC found that at least 4 million U.S. households—about 1 in every 30—had children exposed to high levels of lead.

The major source of lead exposure is peeling lead-based paint and lead-contaminated dust in some older U.S. homes. Children can inhale or ingest paint particles from these sources when they put dust-covered hands or toys into their mouths. Another source is soils contaminated with lead emitted by motor vehicles before leaded gasoline was banned. Lead can also leach from water pipes and faucets containing lead parts or lead solder (a water pollution problem that we examine in  Chapter 20 ). Other sources are older coal-burning power plants that have not been required to meet the emission standards of new plants, as well as lead smelters and waste incinerators.

Connections

Lead and Urban Gardening

Health officials and scientists urge people who plant urban vegetable gardens to have their garden soils tested for lead. For decades, lead particles fell from the air into urban soils, primarily from the exhaust fumes of vehicles burning leaded gasoline. Soil found to have lead in it can be treated or removed from urban gardens and replaced with uncontaminated soil.

By 2017, all of the world’s countries, except Algeria, had banned the use of leaded gasoline. Most of the world’s more developed counties banned the use of lead for painting the inside or outside of homes and other buildings over 40 years ago. However, 55 countries including China, India, Russia, most South America countries, and several African countries, still allow the sale of lead-based paints. This exposes millions of young children to toxic lead.

Children and adults in China and several African countries are also exposed to dangerous levels of lead when they work in recycling centers extracting lead and other valuable metals from electronic waste (e-waste)—discarded computers, TV sets, cellphones, and other electronic devices. Globally in 2016, exposure to lead killed about 540,000 people, mostly in less-developed countries, according to Institute for Health Metrics and Evaluation. Health scientists have proposed a number of ways to help protect children from lead poisoning ( Figure 18.6 ).

Figure 18.6

Ways to help protect children from lead poisoning.

Critical Thinking:

1. Which two of these solutions do you think are the best ones? Why?

Top: ssuaphotos/ Shutterstock.com. Center: Mark Smith/ Shutterstock.com. Bottom: Dmitry Kalinovsky/ Shutterstock.com.

18.2cIndustrial Smog

Seventy-five years ago, cities such as London, England, and the U.S. cities of Chicago, Illinois, and Pittsburgh, Pennsylvania, burned large amounts of coal in power plants and factories. People in such cities also burned coal to heat their homes and to cook food. Often, especially during winter, they were exposed to  industrial smog , consisting mostly of an unhealthy mix of sulfur dioxide , suspended droplets of sulfuric acid, and a variety of suspended solid particles in outside air. People who burned coal inside their homes were often exposed to dangerous levels of particulates and other indoor air pollutants.

When coal or oil is burned, the sulfur compounds they contain react with oxygen to produce  gas (Figure 18.7, left), some of which is converted to tiny suspended droplets of sulfuric acid . Some of these droplets react with ammonia  in the atmosphere to form solid particles of ammonium sulfate, or . In addition, during combustion of coal and oil, most of the carbon they contain is converted to carbon monoxide (CO) and carbon dioxide . Unburned carbon in coal also ends up in the atmosphere as soot or black carbon. Suspended particles of such salts and soot give the resulting smog a gray color (Figure 18.5), which is why it is sometimes called gray-air smog.

Figure 18.7

Simplified model of how pollutants are formed when coal and oil are burned. The result is industrial smog.

Today, urban industrial smog is rarely a problem in most of the more-developed countries where coal is burned only in large power and industrial plants with reasonably good air pollution control. However, many of these facilities have tall smokestacks that send the pollutants high into air where prevailing winds carry them downwind to rural areas, and can cause air pollution problems that we deal with later in this chapter.

However, industrial smog remains a problem in industrialized urban areas of China, India, Ukraine, Czechoslovakia (Figure 18.5), Poland (which has 33 of the European Union’s 50 most polluted cities), and other countries where large quantities of coal are still burned in houses, power plants, and factories with inadequate pollution controls. Because of its heavy reliance on coal, China has high levels of industrial smog in many of its cities, including Beijing (see chapter opening photo). China is making some progress in lessening its dependence on coal and in reducing air pollution in Beijing and 27 other cities but has a long way to go.

Another type of smog is  photochemical smog . It is a brownish mixture of primary and secondary pollutants formed when certain gases in the atmosphere mostly those emitted by automobiles and trucks react with UV radiation from the sun. The formation of photochemical smog (Figure 18.8) begins when exhaust from morning commuter traffic releases large amounts of NO and VOCs into the air over a city. The NO is converted to reddish-brown , which is why photochemical smog is sometimes called brown-air smog (Figure 18.1) .  When exposed to UV radiation from the sun, some of the  reacts with VOCs released by certain trees (such as certain species of oak, sweet gum, and poplar), motor vehicles, and businesses (especially bakeries and dry cleaners). The resulting photochemical smog is a mixture of secondary pollutants, dominated by ground-level ozone. Hotter days lead to higher levels of ozone and other smog components. The smog usually reaches peak levels in late morning and causes eye irritation and breathing problems.

Figure 18.8

Simplified model of how the pollutants that make up photochemical smog are formed mostly from gases emitted by automobiles and trucks.

Photo: ssuaphotos/ Shutterstock.com

All modern cities have some photochemical smog, but it is much more common in cities with sunny and warm climates, and a large number of motor vehicles. Examples are Los Angeles, California (Core Case Study and Figure 18.1), and Salt Lake City, Utah, in the United States; Sydney, Australia; São Paulo, Brazil; Bangkok, Thailand; and Mexico City, Mexico.

Connections

Short Driving Trips and Air Pollution

About 60% of the pollution from motor vehicle emissions occurs in the first minutes of operation before pollution control devices are working at top efficiency. Yet 40% of all U.S. car trips take place within 3 kilometers (2 miles) of drivers’ homes, and half of the U.S. working population drives 8 kilometers (5 miles) or less to work. Did you drive a car today, and if so, how far did you drive?

18.2dFactors Affecting Outdoor Air Pollution

Five natural factors help reduce outdoor air pollution. First, gravity causes particles heavier than air to settle out of the atmosphere. Second, rain and snow partially cleanse the air of pollutants. Third, salty sea spray from the oceans washes out many pollutants from air that flows from land over the oceans. Fourth, winds sweep pollutants away and dilute them by mixing them with cleaner air. Fifth, natural chemical reactions remove some pollutants. For example,  can react with  in the atmosphere to form , which reacts with water vapor to form droplets of  that fall out of the atmosphere as acidic precipitation.

Six other factors can increase outdoor air pollution. First, urban buildings slow wind speed and reduce the dilution and removal of pollutants. Second, hills and mountains reduce the flow of air in valleys below them and allow pollutant levels to build up at ground level. Third, high temperatures promote the chemical reactions leading to the formation of photochemical smog. Fourth, emissions of volatile organic compounds (VOCs) from certain trees and plants in urban areas can promote the formation of photochemical smog.

The fifth factor that increases air pollution has to do with the vertical movement of air. During the day, the sun warms air near the earth’s surface. Normally, this warm air and most of the pollutants it contains rise and mix with the cooler air above it and are dispersed. However, under certain atmospheric conditions layer of warm air can temporarily lie atop a layer of cooler air nearer the ground. This is called a  temperature inversion . Because the cooler air near the surface is denser than the warmer air above, it does not rise and mix with the air above. If this condition persists, pollutants can build up to harmful and even lethal concentrations in the trapped layer of cool air near the ground.

Two types of areas are especially susceptible to prolonged temperature inversions. The first is a town or city located in a valley surrounded by mountains where the weather turns cloudy and cold during part of the year ( Figure 18.9 , left). In such cases, the clouds block much of the winter sunlight that causes air to heat and rise, and the mountains block winds that could disperse the pollutants. As long as these stagnant conditions persist, pollutants in the valley below will continue to build up.

Figure 18.9

A temperature inversion can take place in either of the two sets of topography and weather conditions shown here. Polluted air can be trapped between mountain ranges and under the inversion layer (left), or it can be blown by sea breezes and trapped against a mountain range and under the conversion layer (right).

The other type of area vulnerable to temperature inversions is a city with many motor vehicles in an area with a sunny climate, mountains on three sides, and an ocean on the fourth side ( Figure 18.9 , right). Here, the conditions are ideal for the formation of photochemical smog, worsened by frequent thermal inversions. The surrounding mountains prevent the polluted surface air from being blown away by breezes coming off the sea. This describes several cities, including heavily populated Los Angeles, California ( Core Case Study ), which has prolonged temperature inversions.

The sixth factor is that air pollution can move from one country to another, as discussed in  Science Focus 18.1 .

18.3aAcid Deposition

Most coal-burning power plants, metal ore smelters, oil refineries, and other industrial facilities emit sulfur dioxide , suspended particles, and nitrogen oxides  into the atmosphere. In more-developed countries, these facilities often use tall smokestacks to vent their exhausts high into the atmosphere where wind can dilute and disperse these pollutants ( Figure 18.10 ). This reduces local air pollution, but it can increase regional air pollution, because prevailing winds can transport the  and  pollutants as far as 1,000 kilometers (600 miles). During their trip, these compounds form secondary pollutants such as droplets of sulfuric acid , nitric acid vapor , and particles of acid-forming sulfate  and nitrate  salts ( Figure 18.3 ).

Figure 18.10

Tall smokestacks can reduce local air pollution from burning coal, but they help transfer sulfur dioxide and particulates to downwind areas.

JAMES P. BLAIR/National Geographic Image Collection

These acidic substances remain in the atmosphere for 2 to 14 days. They descend to the earth’s surface in two forms. The first is wet deposition, consisting of acidic rain, snow, fog, and cloud vapor, with a pH of less than 5.6—the acidity level of unpolluted rain ( Figure 2.6 ). The second is dry deposition, consisting of acidic particles. The resulting mixture is called  acid deposition  ( Figure 18.11 )—often called acid rain. Most dry deposition occurs within 2 to 3 days of emission, relatively close to the industrial sources, whereas most wet deposition takes place within 4 to 14 days in more distant downwind areas.

Figure 18.11

Natural capital degradation: Acid deposition, which consists of rain, snow, dust, or gas with a pH lower than 5.6, is commonly called acid rain.

Critical Thinking:

1. What are three ways in which your daily activities contribute to acid deposition?

Acid deposition has been occurring since the Industrial Revolution began in the mid-1700s. In 1872, British chemist Robert A. Smith coined the term acid rain after observing that rain was eating away stone in the walls of buildings in major industrial areas. Acid deposition is the result of human activities that disrupt the natural nitrogen cycle (see  Figure 3.21 ) and sulfur cycle by adding excessive amounts of  and  to the atmosphere.

Acid deposition is a regional air pollution problem in areas that lie downwind from coal-burning facilities and from urban areas with large numbers of cars. The map in  Figure 18.12  shows areas of the world where acid deposition is, or is likely to be, a problem. In some areas, soils contain basic compounds such as calcium carbonate  or limestone that can react with and help neutralize, or buffer, some inputs of acids. The areas most sensitive to acid deposition are those with thin, acidic soils that provide no natural buffering ( Figure 18.12 , all green and most red areas) and those where the buffering capacity of soils has been depleted by decades of acid deposition.

Figure 18.12

This map shows regions where acid deposition is now a problem and regions with the potential to develop this problem. Such regions have large inputs of air pollution (mostly from power plants, industrial facilities, and ore smelters) or are sensitive areas with naturally acidic soils and bedrock that cannot neutralize (buffer) additional inputs of acidic compounds.

(Compiled by the authors using data from World Resources Institute and U.S. Environmental Protection Agency.)

In the United States, older coal-burning power and industrial plants without adequate pollution controls, especially in the Midwest, emit the largest quantities of  and other pollutants that cause acid deposition. Because of these emissions and those of other urban industries and motor vehicles, as well as the prevailing west-to-east winds, typical precipitation in the eastern United States is at least 10 times more acidic than natural precipitation is. One of the first experiments to determine this took place in the Hubbard Brook Experimental Forest (see  Chapter 2   Core Case Study ), located in the northeastern United States. There, researchers found that precipitation was several hundred times more acidic than natural rainwater.

Many acid-producing chemicals generated in one country are exported to other countries by prevailing winds. For example, acidic emissions from the United Kingdom and Germany blow south and east into Switzerland and Austria, and north and east into Norway and other neighboring countries. The worst acid deposition occurs in Asia, especially in China, which in 2017 got 60% of its total energy and 75% of its electricity from burning coal, according to the International Energy Agency. According to its government, China is the world’s top emitter of .

18.3bHarmful Effects of Acid Deposition

Acid deposition damages stone and metals in buildings and statues ( Figure 18.4 ), contributes to human respiratory diseases, and can leach toxic metals such as lead and mercury from soils and rocks into lakes used as sources of drinking water. These toxic metals can accumulate in the tissues of fish eaten by people (especially pregnant women) and other animals. Currently, 45 U.S. states have issued warnings telling people to avoid eating fish caught from waters that are contaminated with toxic mercury (see  Chapter 17 ,  Core Case Study ).

Acid deposition also harms aquatic ecosystems. Most fish cannot survive in water with a pH less than 4.5. In addition, as acid precipitation flows through soils, it can release aluminum ions  attached to minerals in the soils and carry them into lakes, streams, and wetlands. There these ions can suffocate many kinds of fish by stimulating excessive mucus formation, which clogs their gills. Because of excess acidity, several thousand lakes in Norway and Sweden, and 1,200 lakes in Ontario, Canada, contain few if any fish. In the United States, several hundred lakes (most in the Northeast) are similarly threatened.

A combination of acid deposition and other air pollutants (such as ozone) can harm crops and reduce plant productivity, especially when the soil pH is below 5.1. Low pH reduces plant productivity and the ability of soils to buffer or neutralize acidic inputs. An estimated 30% of China’s cropland suffers from excess acidity.

A combination of acid deposition and other air pollutants can also affect forests in two ways ( Figure 18.13 ). One is by leaching essential plant nutrients such as calcium and magnesium from forest soils. They also cause soils to release ions of aluminum, lead, cadmium, and mercury, which are toxic to trees. These effects rarely kill trees directly, but they can weaken them and leave them vulnerable to stresses such as severe cold, diseases, insect attacks, and drought.

Figure 18.13

Natural capital degradation: Air pollution is one of several interacting stresses that can damage, weaken, or kill trees and pollute surface and groundwater. The inset photo shows trees in a German forest that have died due to exposure to acid deposition and other air pollutants.

Anticiclo/ Shutterstock.com

Mountaintop forests are the terrestrial areas hit hardest by acid deposition. These areas tend to have thin soils without much buffering capacity and some of these areas are bathed almost continuously in highly acidic fog and clouds. Some mountaintop forests in the eastern United States, as well as east of Los Angeles, California ( Core Case Study ), are bathed in fog and dews that are as acidic as lemon juice—with about 1,000 times the acidity of unpolluted precipitation.

18.3cReducing Acid Deposition

Figure 18.14 lists ways to reduce acid deposition. According to most scientific experts on acid deposition, the best solutions are preventive approaches that reduce or eliminate emissions of sulfur dioxide , nitrogen oxides , and particulates. Since 1994, acid deposition has decreased sharply in the United States and especially in the eastern half of the country. This is partly the result of significant reductions in  and  emissions from coal-burning facilities under the 1990 amendments to the U.S. Clean Air Act. Even so, soils and surface waters in many areas are still acidic because of the accumulation of acids over decades of acid deposition.

Figure 18.14

Ways to reduce acid deposition and its damage.

Critical Thinking:

1. Which two of these solutions do you think are the best ones? Why?

Top: Brittany Courville/ Shutterstock.com. Bottom: racorn/ Shutterstock.com.

Implementing acid deposition prevention solutions is politically difficult. One problem is that the people and ecosystems affected by acid deposition often are quite far downwind from the sources of the problem. In addition, countries with large supplies of coal (such as China, India, Russia, Australia, and the United States) have a strong incentive to use it. Owners of coal-burning power plants also resist adding the latest pollution control equipment to their facilities and using low-sulfur coal, arguing that these measures increase the cost of electricity for consumers.

However, in the United States, the use of affordable and cleaner-burning natural gas (see Chapter 15) and wind (see Chapter 16) for generating electricity is on the rise, and has reduced the use of coal. Environmental scientists point out that including the largely hidden, harmful health and environmental costs of burning coal in its market prices, in keeping with the full-cost pricing principle of sustainability, would further reduce coal use, spur the use of cleaner ways to generate electricity, and help prevent acid deposition.

Large amounts of limestone or ground lime can be used to neutralize some acidified lakes and surrounding soils. However, this expensive and temporary remedy usually must be repeated annually. It can also kill some types of plankton and aquatic plants and harm certain wetland plants that need acidic water.

According to the EPA, between 1980 and 2017, air pollution laws in the United States helped to reduce  emissions from all sources by 90% and nitrogen oxide emissions by 60%. This has helped reduce the acidity of rainfall in parts of the Northeast, Mid-Atlantic, and Midwest regions. However, scientists call for more reductions of these and other harmful emissions from older coal-burning power and industrial plants.

China, the world’s largest emitter of , has one of the world’s most serious acid deposition problems. China’s  emissions have declined slightly because of some reduction in coal use since 2011, but the country has a long way to go in curtailing acid deposition.

Connections

Low-Sulfur Coal, Atmospheric Warming, and Toxic Mercury

Some U.S. power plants have lowered  emissions by switching from high-sulfur to low-sulfur coals such as lignite (see Figure 15.10). However, because low-sulfur coal has a lower heat value, more coal must be burned to generate a given amount of electricity. This has led to increased  emissions, which contribute to atmospheric warming and climate change. Because low-sulfur coal also has higher levels of toxic mercury and other trace metals, burning it emits more of these hazardous chemicals into the atmosphere.

18.4aIndoor Air Pollution Is a Serious Problem

3.8 Million

Annual number of global deaths due to indoor air pollution

Indoor air pollution has become a major health concern all over the world. In less-developed countries, the indoor burning of wood, charcoal, dung, crop residues, coal, and other fuels in open fires ( Figure 18.15 ) and in unvented or poorly vented stoves exposes people to dangerous levels of particulate air pollution. The WHO has estimated that indoor air pollution kills about 3.8 million people per year—an average of 10,410 deaths per day—mostly in less-developed countries.

Figure 18.15

Burning wood to cook food inside this dwelling in Nepal exposes this woman and other occupants to dangerous levels of indoor air pollution.

Alain Lauga/ Shutterstock.com

Indoor air pollution is also a serious problem in the United States and in more-developed areas of all countries. According to the EPA and public health officials, the three most dangerous indoor air pollutants in such areas are tobacco smoke (see  Chapter 17 , Case Study); formaldehyde emitted from many building materials and various household products; and radioactive radon-222 gas, which can seep into houses from underground rock deposits (see the  Case Study  that follows).

Case Study

Radioactive Radon Gas

Radon-222 is a colorless, odorless, radioactive gas produced by the natural radioactive decay of uranium-238, small amounts of which are contained in most rocks and soils. However, this isotope is much more concentrated in underground deposits of minerals such as uranium, phosphate, shale, and granite.  Figure 18.17  compares the potential geological risk of exposure to radioactive radon across the United States.

Figure 18.17

The potential for radon exposure varies across the United States, depending on the types of underlying soils and bedrock. (Expressed in terms of concentrations of radioactive radon in picocuries per liter (pCi/L).

Question:

1. What is the average risk level of exposure to radioactive radon where you live or go to school?

(Compiled by the authors using data from U.S. Geological Survey and U.S. Environmental Protection Agency.)

When radioactive radon gas from such deposits seeps upward through the soil and is released outdoors, it disperses quickly in the air and decays to harmless levels of radioactivity. However, in buildings above such deposits, radon gas can enter through cracks in a foundation’s slab and walls, as well as through well water, openings around sump pumps and drains, and hollow concrete blocks ( Figure 18.18 ). Once inside, it can build up to high levels, especially in unventilated lower levels of homes and buildings.

Figure 18.18

Ways that radon-222 gas can enter homes and other buildings.

Question:

1. Has anyone tested the indoor air where you live for radon-222?

(Compiled by the authors using data from U.S. Environmental Protection Agency.)

Radon-222 gas quickly decays into solid particles of other radioactive elements such as polonium-210, which can expose lung tissue to large amounts of radioactivity. This exposure can damage lung tissue and lead to lung cancer over the course of a 70-year lifetime. Your chances of getting lung cancer, the leading cancer killer in both men and women in the United States, from radon depend mostly on how much radon is in your home, how much time you spend in your home, and whether you are a smoker or have ever smoked. About 90% of radon-related lung cancers occur among current or former smokers.

According to the EPA, radioactive radon is the second-leading cause of lung cancer after smoking. Each year, according to the National Cancer Institute, radon-induced lung cancer kills about 20,000 people in the United States. Despite this risk, less than 20% of U.S. households have followed the EPA’s recommendation to conduct radon tests, which can be done with inexpensive testing kits. Many schools and day-care centers also have not tested for radon, and only a few states have laws that require radon testing for schools.

When radon is detected, homeowners need to seal all cracks in the foundation’s slab and walls. They can also increase ventilation by cracking a window, installing vents in the basement, and using a fan to create cross ventilation.

Formaldehyde  is a colorless, extremely irritating chemical that is considered a carcinogen. It is commonly used to make furniture, drapes, carpeting, foam insulation, and other products. It can also be present in plywood, particleboard, paneling, and high-gloss wood used to make flooring and cabinets. According to the EPA and the American Lung Association, 20 to 40 million Americans suffer from chronic breathing problems, dizziness, headaches, sore throats, sinus and eye irritation, and other ailments caused by daily exposure to low levels of formaldehyde emitted from these materials and products. Many manufactured (mobile) homes have been found to have high levels of formaldehyde. The EPA estimates that 1 of every 5,000 people who live for more than 10 years in such homes will likely develop cancer from formaldehyde exposure.

Other common sources of indoor air pollution, according to the EPA, include the following:

· Pesticide residues in the 75% of U.S. homes where pesticides are used indoors at least once a year

· Lead particles brought indoors on shoes and collecting in carpets and furnishings

· Dust mites and cockroach droppings found in some homes, thought to play a role in asthma attacks

· Airborne spores of molds and mildew that can cause headaches, allergic reactions, and asthma attacks

· Candles, almost all of which emit fine-particle soot when burned

· Clothes dryer sheets that emit an ammonium salt, linked to asthma

· Gas stoves that emit nitrogen dioxide

· Cleaning products that contain alcohol, chlorine, ammonia, and VOCs

· Air fresheners that emit glycol ethers, which can contribute to fatigue, nausea, and anemia

· Air purifiers that emit ozone

Figure 18.16  summarizes these and other sources of indoor air pollution in a modern home.

Figure 18.16

Numerous indoor air pollutants are found in most modern homes.

Question:

1. To which of these pollutants are you likely exposed?

(Compiled by the authors using data from U.S. Environmental Protection Agency.)

Danish and U.S. EPA studies have linked various air pollutants found in buildings to a number of health effects, a phenomenon known as the sick-building syndrome. Such effects include dizziness, headaches, coughing, sneezing, shortness of breath, nausea, burning eyes, sore throats, skin irritation, and respiratory infections. EPA and Labor Department studies indicate that almost one of every five U.S. commercial buildings exposes employees to such health risks.

EPA studies have revealed some alarming facts about indoor air pollution in the United States. First, levels of several common air pollutants generally are two to five times higher inside U.S. homes and commercial buildings than they are outdoors. In some cases, they are as much as 100 times higher. Second, pollution levels inside cars in traffic-clogged urban areas can be up to 18 times higher than outside levels. Third, the health risks from exposure to such chemicals are growing because most people in more-developed urban areas spend up to 90% of their time indoors or inside vehicles. Smokers, children younger than age 5, the elderly, the sick, pregnant women, people with respiratory or heart problems, and factory workers are especially at risk from indoor air pollution. GREEN CAREER: Indoor air pollution specialist

18.5aOverwhelming Our Body’s Natural Air Pollution Defenses

Your respiratory system ( Figure 18.19 ) helps protect you from air pollution in various ways. Hairs in your nose filter out large particles. Sticky mucus in the lining of your upper respiratory tract captures smaller (but not the smallest) particles and dissolves some gaseous pollutants. Hundreds of thousands of tiny, mucus-coated, hair-like structures, called cilia, also line your upper respiratory tract. They continually move back and forth and transport mucus and the pollutants it traps to your throat where they are swallowed or expelled through sneezing and coughing.

Figure 18.19

Major components of the human respiratory system can help protect us from air pollution, but these defenses can be overwhelmed or breached.

Prolonged or acute exposure to air pollutants can overload or break down these natural defenses. Fine and ultrafine particulates can lodge deep in the lungs and contribute to lung cancer, asthma, heart attack, and stroke. Years of smoking or breathing polluted air can lead to other lung ailments such as chronic bronchitis and emphysema, ( Figure 17.23 ) which lead to acute shortness of breath.

Recent research, including a study done at the University of Southern California, indicates that fine and ultrafine particles in the air can bypass this defense system by moving directly from our nostrils to our brains along neural pathways. Researchers say that once in the brain, these pollutants could be initiating or accelerating degenerative diseases such as Parkinson’s and Alzheimer’s.

18.5bAir Pollution Is a Big Killer

8 Million

Annual global number of deaths due to outdoor and indoor air pollution

The WHO has dubbed air pollution “the world’s largest single environmental health risk.” In 2017, the WHO estimated that outdoor and indoor air pollution kills about 8 million people each year—an average of about 913 deaths every hour. According to a 2017 study by the U.S. Health Effects Institute, outdoor air pollution annually kills about 1.8 million people in India, 1.6 million people in China, and 780,000 in Africa. The leading direct causes of death related to air pollution are heart attacks, stroke, chronic obstructive pulmonary disease (COPD), and lung cancer.

Steven Barrett and other researchers at the Massachusetts Institute of Technology (MIT) estimate that outdoor air pollution, mostly fine-particle pollution, contributes to the deaths of roughly 200,000 Americans every year ( Figure 18.20 ). About half of these deaths are blamed on car and truck exhaust and the other half on coal-burning power and industrial plants. Millions more suffer from asthma attacks and other respiratory disorders brought on or aggravated by air pollution, especially from fine-particle pollutants. In 2018, the EPA, led by a former lobbyist for coal companies, proposed weakening the air pollution standards for burning coal.

Figure 18.20

Distribution of premature deaths from air pollution in the United States, mostly from very small, fine, and ultrafine particles added to the atmosphere by older coal-burning power plants that have been exempted from air pollution standards for new power plants.

Critical Thinking:

1. Why do the highest death rates occur in the eastern half of the United States? If you live in the United States, what is the risk at your home or where you go to school?

(Compiled by the authors using data from U.S. Environmental Protection Agency.); GaViAl/ Shutterstock.com

According to EPA studies, each year, more than 125,000 Americans get cancer primarily from breathing soot-laden diesel fumes emitted by buses, trucks, tractors, bulldozers and other construction equipment, trains, and ships. A large diesel truck emits as much particulate matter as 150 cars. A study led by Daniel Lack found that the world’s 100,000 or more diesel-powered oceangoing ships emit almost half as much particulate pollution as do the world’s 1 billion motor vehicles.

Each year, about 10,000 people in the United States die from breathing smoke from wildfires. This number is projected to increase to 44,000 deaths per year by 2100, mostly because of the projected increase in wildfires caused by the drying of forests that are suffering from prolonged drought.

18.6aLaws and Regulations

The United States provides an example of how government can reduce air pollution. The U.S. Congress passed the Clean Air Acts of 1970, 1977, and 1990. With these laws, the federal government established air pollution regulations for key outdoor air pollutants to be enforced by states and major cities.

Congress directed the EPA to establish air quality standards for six major outdoor pollutants—carbon monoxide (CO), nitrogen dioxide , sulfur dioxide , suspended particulate matter (SPM, smaller than PM-10), ozone , and lead (Pb). One limit, called a primary standard, was set to protect human health. Another limit, called a secondary standard, was intended to prevent environmental and property damage. Each standard specifies the maximum allowable level for a pollutant, averaged over a specific period.

The EPA has also established national emission standards for more than 188 hazardous air pollutants (HAPs)—pollutants that can cause serious health and ecological effects. Most of these chemicals are chlorinated hydrocarbons, volatile organic compounds, or compounds of toxic metals. An important public source of information about HAPs is the annual Toxic Release Inventory (TRI). The TRI law (passed in 1990 as part of the Pollution Prevention Act) requires more than 20,000 refineries, power plants, mines, chemical manufacturers, and factories to report their releases and waste management methods for 667 toxic chemicals. The TRI, which is available on the internet, lists this information by community. Since the first TRI report was released in 1988, reported emissions of toxic chemicals have dropped sharply.

In 2015, the EPA issued the first federal rules to limit emissions of  on existing coal-fired power plants beginning in 2022 with full compliance by 2030. According to the EPA, these plants are responsible for nearly 40% of  emissions in the United States. In addition to slowing climate change, measures to control  emissions will also result in reduced emissions of other air pollutants. The EPA projected that by 2030 these new regulations will have the effect of cutting nitrogen oxides by 72% and sulfur dioxides by 90%, compared to 2005 levels. The agency also projected that these cuts would prevent 3,600 premature deaths, 1,700 heart attacks, 90,000 asthma attacks, and 300,000 missed work days and school days.

Coal and utility companies and 18 states with older polluting coal-fired power plants have succeeded in putting off stricter air pollution standards for existing coal-burning power plants for almost 40 years. They have challenged these new regulations in the courts, charging the EPA with a power grab designed to put coal companies out of business. In 2016, the U.S. Supreme Court put a hold on implementing the new standards even though they do not start taking effect until 2022 while the legal challenges make their way through 30 lawsuits in the courts. Since 2017, the EPA, under pressure from coal producers, has been studying ways to weaken these standards.

In 2013, the EPA proposed stricter motor vehicle emission standards that would reduce emissions of VOCs and nitrogen oxides by 80% and particulate emissions by 70%. The EPA estimated that each year, these new standards would cut the death toll from outdoor air pollution by 2,000 and reduce the number of cases of respiratory ailments in children by 23,000. They would also lead to estimated savings of $7 in health-care costs for every $1 spent to implement the new standards. The resulting increase in the cost of a gallon of gasoline would be 1 cent. Oil companies oppose the new standards, saying they would cost too much and would hinder economic growth. In 2018, the EPA, under pressure from car and truck producers, was considering weakening these air pollution standards.

According to the EPA, there were significant declines in the annual atmospheric levels of lead (98% drop), sulfur dioxide (88% drop), carbon monoxide (77% drop), nitrogen dioxide (56% drop), and ozone (22 % drop) between 1980 and 2017 ( Figure 18.21 ). According to a 2018 EPA report on the nation’s air quality, the combined emissions of the six major outdoor air pollutants decreased by about 73% between 1970 and 2017, even with significant increases during the same period in gross domestic product, vehicle miles traveled, population, and energy consumption.

Figure 18.21

Trends in reduction of levels of major air pollutants between 1990 and 2017.

Data Analysis:

1. Which of the pollutants declined by the greatest percentage between 1990 and 2017?

Compiled by the authors using data from the U.S. Environmental Protection Agency.

This significant reduction of outdoor air pollution in the United States since 1990 is due mostly to two factors. First, during the 1960s and early 1970s, U.S. citizens insisted that laws be passed and enforced to improve air quality. Prior to 1970, when Congress passed the Clean Air Act, air-pollution-control equipment did not exist but was widespread in the 1980s. Second, the country was affluent enough to afford such controls for factories, power plants, and motor vehicles. Today, a new car in the United States emits 75% less air pollution than did a pre-1970 car.

Environmental scientists applaud this success, but they point out that the rate of decline for emissions of CO and  has been slowing since 2011. They call for strengthening U.S. air pollution laws by doing the following:

· Putting much greater emphasis on pollution prevention. The power of prevention was made clear by the 99% drop in U.S. atmospheric lead emissions after lead in gasoline was banned in 1976.

· Sharply reducing emissions from approximately 20,000 older coal-burning power and industrial plants, cement plants, oil refineries, and waste incinerators that have not been required to meet the air pollution standards for new facilities under the Clean Air Acts.

· Reducing atmospheric emissions of toxic pollutants such as mercury (see  Figure 17.13 ).Continuing to improve fuel efficiency standards for motor vehicles, one of the most important steps needed to slow climate change and ocean acidification.

· Strict regulation of emissions from motorcycles and two-cycle gasoline engines used in devices such as chainsaws, lawnmowers, generators, scooters ( Figure 18.22 ), and snowmobiles. The EPA estimates that running a gas-powered riding lawn mower for an hour creates as much VOC air pollution as driving 34 cars for an hour.

Figure 18.22

Many of the motorized scooters so commonly found on most college campuses, especially those with two-cycle engines, produce more nitrogen oxides and hydrocarbons—pollutants that contribute to photochemical smog—per unit of distance driven than the average car produces. Older scooters and poorly maintained scooters emit many times more of these pollutants than cars emit. Thus, even though they are more fuel-efficient than most cars, as a group, scooters are major contributors to urban air pollution.

ZRyzner/ Shutterstock.com

· Setting much stricter air pollution regulations for airports and oceangoing ships.

· Sharply reducing indoor air pollution.

However, there is strong political pressure to weaken—not strengthen—U.S. air pollution laws. Executives of companies that would be affected by implementing stronger air pollution regulations claim that they would cost too much and would hinder economic growth. Proponents of stronger regulations contend that history has shown that most industry cost estimates for implementing U.S. air pollution control standards have been much higher than the costs actually proved to be. In addition, implementing such standards has helped some companies and created jobs by stimulating these companies to develop new pollution control technologies.

In 2018, the American Lung Association pointed to threats to the nation’s important progress toward healthier and cleaner air that could result from seven key policy changes being considered by the EPA:

· Weakening the Clean Air Act

· Repealing plans to reduce climate-changing  emissions from power plants

· Eliminating limits on climate-changing  emission from natural gas and oil operations

· Reducing efforts to raise the air pollution emission standards and increase fuel economy standards for cars and trucks

· Relaxing the health standards for emissions of microscopic (PM2.5) particulates, even though research has revealed that they are one the world’s greatest health threats.

· Exempting farmers from reporting air pollutant emissions from animal feedlots ( Figure 12.10 ) and combined animal feeding operations for pigs and chickens ( Figure 12.11 )

· Cutting EPA funding for staff and independent scientific advisers needed to implement air pollution and other environmental laws.

· 18.6bUsing the Marketplace to Reduce Outdoor Air Pollution

· One approach to reducing pollutant emissions has been to allow producers of air pollutants to buy and sell government air pollution allotments in the marketplace. For example, with the goal of reducing  emissions, the Clean Air Act of 1990 authorized an emissions trading, or cap-and-trade program, which enables the 110 most polluting coal-fired power plants in 21 states to buy and sell  air pollution rights.

· Under this system, each plant is annually given a number of pollution credits, which allow it to emit a certain amount of . A utility that emits less than its allotted amount at one its plants has a surplus of pollution credits. It can use these credits to offset  emissions at its other plants, keep them for future plant expansions, or sell them to other utilities or private citizens or groups. Between 1990 and 2017, this emissions trading program helped to reduce  emissions from power plants in the United States by 79%, at a cost of less than one-tenth of the cost projected by the utility industry, according to the EPA. The 2015 Clean Power Plan gives states the option of allowing power plant companies to use emissions trading to meet the new  reduction standards.

· Proponents of this market-based approach say it is cheaper and more efficient than government regulation of air pollution. Critics of this approach contend that it allows utilities with older, dirtier power plants to buy their way out of their environmental responsibilities and to continue to pollute. The ultimate success of any emissions trading approach depends on two factors: how low the initial cap is set and how often it is lowered in order to promote continuing innovation in air pollution prevention and control.

18.6cReducing Outdoor Air Pollution

Figure 18.23 summarizes several ways to reduce emissions of sulfur oxides, nitrogen oxides, and particulate matter from stationary sources such as coal-burning power plants and industrial facilities—the primary contributors to industrial smog.

Figure 18.23

Ways to prevent, reduce, or disperse emissions of sulfur oxides, nitrogen oxides, and particulate matter from stationary sources, especially coal-burning power plants and industrial facilities.

Critical Thinking:

1. Which two of these solutions do you think are the best ones? Why?

Top: Brittany Courville/ Shutterstock.com. Bottom: racorn/ Shutterstock.com.

One commonly used technological solution is the electrostatic precipitator (Figure 18.24, left). It is simple to maintain and can remove up to 99% of the particulate matter it processes. However, it uses a lot of electricity and produces a toxic dust that must be disposed of safely. Another is the wet scrubber (Figure 18.24, right), which uses a stream of water droplets to dissolve and remove up to 98% of  and 98% of the particulate matter in smokestack emissions. However, it produces waste in the form of sludge that must be disposed of in a landfill.

Figure 18.24

An electrostatic precipitator (left) and a wet scrubber (right) are used to reduce particulate and  emissions from coal-burning power and industrial plants.

Learning from Nature

A team of biomimicry researchers called Refish has developed a portable, energy-efficient device that removes particulates from air and can be mounted anywhere. It is based on certain plant leaves that have hair-like growths on their surfaces that trap particulates. When rain falls on these leaves, it dissolves the particulate matter, some of which is then absorbed by the plant and used as a nutrient.

Figure 18.25 lists several ways to prevent and reduce emissions from motor vehicles, the primary contributors to photochemical smog. In more-developed countries, many of these solutions have been successful (see the Case Study that follows). However, the already poor air quality in urban areas of many less-developed countries is worsening because of the sharp increase in the number of motor vehicles without use of adequate pollution control technology.

Figure 18.25

Ways to prevent or reduce emissions from motor vehicles.

Critical Thinking:

1. Which two of these solutions do you think are the best ones? Why?

Top: egd/ Shutterstock.com. Bottom: Tyler Olson/ Shutterstock.com.

Case Study

Revisiting Air Pollution in Los Angeles

In 2018, Los Angeles (LA) (Core Case Study) was ranked highest among all U.S. cities in ozone pollution (as it has for 18 years) and in the number of unhealthy air days, according to the American Lung Association.

The factors contributing to air pollution in LA have not gone away. LA has had the worst smog for 19 of the 20 years that the American Lung Association has been evaluating its annual air pollution. Currently, the area’s largest sources of pollutants are the ports of Los Angeles and Long Beach. Most of the ships that use these ports burn dirty diesel fuel—a major source of particulate pollution. In addition, the number of motor vehicles in this urban area has grown dramatically and the city has a high concentration of power plants.

Greater LA’s location also affects its air pollution levels. It is an urban area surrounded by mountains on three sides and an ocean on the fourth side. Prevailing westerly ocean breezes blow pollution inland where it becomes trapped against the mountain ranges and builds up during thermal inversions (Figure 18.9, right). Another factor is climate change, which is projected to make its air pollution problems worse by increasing the number of hot, sunny days that increase the rate of ozone formation.

Even with these challenges, LA has managed to cut its pollution to the point where in 2017, it could report the lowest pollution levels since 1999 when the American Lung Association began reporting annually on overall urban air quality in the United States. Consequently, the city sees more clear days than it saw in the 1960s and 1970s. (Compare Figure 18.26 with Figure 18.1)

Figure 18.26

A clear day in downtown Los Angeles.

Gerry Boughan/ Shutterstock.com

How did LA manage to make such improvements? Several analysts argue that the key development was the passage of the Clean Air Act of 1970. Others cite the fast-growing grassroots citizen efforts of the 1960s and 1970s, which ultimately led to the passage of that landmark legislation. The strength of the law—a reflection of the strength of the grassroots effort—forced specific and meaningful changes that led to cleaner air in LA and in urban areas throughout the United States.

For example, as LA air worsened in the 1960s, carmakers were dragging their feet in developing pollution control technology. In 1975, more than two decades after anti-smog protests began in Los Angeles, carmakers were finally required to install catalytic converters in all new cars. This was a key technological development, according to the California Air Resources Board, and it would not have come about if the Clean Air Act had not been passed.

The Los Angeles and Long Beach ports also reduced their contributions to air pollution in compliance with the law. Since 2005, they reduced their emissions of particulate matter from the burning of diesel fuel by more than 73%. The ports accomplished this mostly by using cleaner-burning cranes, machinery, and trucks, and cleaner, low-sulfur fuel.

In the United States, Canada, and a number of European counties cars and trucks are required to have catalytic converters, which reduce tailpipe emissions of carbon monoxide, nitrogen oxides, and hydrocarbons. However, thieves are removing catalytic converters from cars to extract and sell its highly valuable palladium. Over the next 10 to 20 years, new technologies could help all countries have cleaner air through improved engine and emission systems and hybrid-electric, plug-in hybrid, and all-electric vehicles (see  Figure 16.4 ).

18.6dReducing Indoor Air Pollution

Little effort has been devoted to reducing indoor air pollution, even though it poses a greater threat to human health than does outdoor air pollution. Air pollution experts suggest several ways to prevent or reduce indoor air pollution, as shown in Figure 18.27.

Figure 18.27

Ways to prevent or reduce indoor air pollution.

Critical Thinking:

1. Which two of these solutions do you think are the best ones? Why?

Top: Tribalium/ Shutterstock.com. Bottom: PATSTOCK/AGE Fotostock.

In less-developed countries, indoor air pollution from open fires (Figure 18.15) and inefficient stoves that burn wood, charcoal, or coal could be reduced. More people could use inexpensive clay or metal stoves that burn fuels more efficiently and vent their exhausts to the outside, or they could use stoves that use solar energy to cook food (see Figure 16.16) in sunny areas.

One way to reduce indoor air pollution in a home is to have plenty of houseplants. Studies show that they can reduce more than 80% of indoor toxins within a few days. Plants that do a good job of purifying air include Devil’s Ivy, English Ivy, African Violets, and Peace Lily. Figure 18.28 lists some ways in which you can reduce your exposure to indoor air pollution.

Figure 18.28

Individuals matter: Ways to reduce your exposure to indoor air pollution.

Critical Thinking:

Which three of these actions do you think are the most important ones to take? Why? 18.7aChemical Threats to the Ozone Layer

The ozone layer in the stratosphere (Figure 18.2) is a vital form of natural capital that supports all life on land and in shallow aquatic environments by keeping 95% of the sun’s harmful ultraviolet (UV-A and UV-B) radiation from reaching the earth’s surface and harming us and many other species.

However, measurements taken by researchers revealed a considerable seasonal depletion, or thinning, of ozone concentrations in the stratosphere above Antarctica (Figure 18.29) and above the Arctic since the 1970s. Similar measurements reveal slight overall ozone thinning everywhere except over the tropics. The loss of ozone over Antarctica has been called an ozone hole. A more accurate term is ozone thinning because the ozone depletion varies with altitude and location.

Figure 18.29

Natural capital degradation: The colorized satellite image shows ozone thinning over Antarctica during October of 2018 at its annual peak extent. Ozone depletion of 50% or more occurred in the center blue area.

NASA Ozone Watch/Katy Mersmann

When the seasonal thinning ends each year, huge masses of ozone-depleted air above Antarctica flow northward, and these masses linger for a few weeks over parts of Australia, New Zealand, South America, and South Africa. This has raised biologically damaging UV-B levels in these areas by 3–10%, and in some years by as much as 20%.

Based on ozone-level measurements and on mathematical and chemical models, the overwhelming consensus of researchers in this field is that ozone depletion in the stratosphere poses a serious threat to humans, other animals, and some primary producers (mostly plants) that use sunlight to support the earth’s food webs.

In 1988, scientists discovered that similar but usually less severe ozone thinning occurs over the Arctic from February to June, resulting in a typical ozone loss of 11–38% (compared to a typical 50% loss above Antarctica). When this body of air above the Arctic breaks up each year, large masses of ozone-depleted air flow south to linger over parts of Europe, North America, and Asia. However, models indicate that the Arctic is unlikely to develop the large-scale ozone thinning found over the Antarctic.

The origin of this dangerous environmental threat began in 1930 with the accidental discovery of the first chlorofluorocarbon (CFC), a compound that contains carbon, chlorine, and fluorine. Chemists soon developed similar compounds to create a family of highly useful CFCs, known by their trade name Freons™.

These chemically unreactive, odorless, nonflammable, nontoxic, and noncorrosive compounds were thought to be dream chemicals. Inexpensive to manufacture, they became popular as coolants in air conditioners and refrigerators, propellants in aerosol spray cans, cleansers for electronic parts such as computer chips, fumigants for granaries and ships’ cargo holds, and gases used to make insulation and packaging.

It turned out that CFCs were too good to be true. Starting in 1974 with the work of chemists Sherwood Rowland and Mario Molina (Individuals Matter 18.1), scientists showed that CFCs are persistent chemicals that reach the stratosphere and destroy some of its protective ozone. Satellite data and other measurements and models indicate that 75–85% of the observed ozone losses in the stratosphere since 1976 resulted from people releasing CFCs and other ozone-depleting chemicals into the troposphere from human activities beginning in the 1950s.

Individuals Matter 18.1

Sherwood Rowland and Mario Molina—A Scientific Story of Expertise, Courage, and Persistence

Hal Garb/AFP/Getty Images; Donna Cove, Mit/University of California, San Diego

In 1974, calculations by the late Sherwood Rowland (left photo) and Mario Molina (right photo), chemists at the University of California–Irvine, indicated that chlorofluorocarbons (CFCs) were lowering the average concentration of ozone in the stratosphere. They also found that CFCs are persistent, remaining in the stratosphere for hundreds of years. During that time, they noted, each CFC molecule can breakdown hundreds of ozone molecules.

These scientists decided they had an ethical obligation to go public with the results of their research. They shocked both the scientific community and the $28-billion-per-year CFC industry by calling for an immediate ban of CFCs in spray cans, for which substitutes were available.

The CFC industry (led by DuPont) was a powerful, well-funded adversary with a lot of profits and jobs at stake. It attacked Rowland’s and Molina’s calculations and conclusions, but the two researchers held their ground, expanded their research, and explained their results to other scientists, elected officials, and the media. After 14 years of delaying tactics, DuPont officials acknowledged in 1988 that CFCs were depleting the ozone layer, and they agreed to stop producing them and to sell higher-priced alternatives that their chemists had developed.

In 1995, Rowland and Molina received the Nobel Prize in chemistry for their work on CFCs.

Rowland and Molina came to four major conclusions. First, once CFCs are put into the atmosphere, these persistent chemicals remain there for a long time. Second, over 11–20 years, these compounds rise into the stratosphere through convection, random drift, and the turbulent mixing of air in the lower atmosphere. Third, once they reach the stratosphere, the CFC molecules break down under the influence of high-energy UV radiation. This releases highly reactive chlorine atoms (Cl), as well as atoms of fluorine (F) and bromine (Br), all of which accelerate the breakdown of ozone  into  and O in a cyclic chain of chemical reactions. This process destroys ozone faster than it forms in some parts of the stratosphere.

Fourth, after entering the troposphere, these long-lived chemicals eventually reached the stratosphere. There they began destroying ozone faster than it was being formed. Each CFC molecule can last in the stratosphere for 65–385 years, depending on its type. During that time, each chlorine atom released during the breakdown of CFCs can break down hundreds of  molecules. Such ozone depletion is a disruption of one of the earth’s most important forms of natural capital that helps sustain life and the world’s economies.

CFCs are not the only ozone-depleting chemicals. Others are halons and hydrobromofluorocarbons (HBFCs) (used in fire extinguishers), methyl bromide (a widely used fumigant), hydrogen chloride (emitted into the stratosphere by the launches of certain space vehicles), and cleaning solvents such as carbon tetrachloride, methyl chloroform, n-propyl bromide, and hexachlorobutadiene. While in the troposphere, CFCs also act as greenhouse gases that help to warm the lower atmosphere and contribute to climate change.

8.7cReversing Stratospheric Ozone Depletion

According to researchers in this field, we should immediately stop producing all ozone-depleting chemicals. However, models and measurements indicate that even with immediate and sustained action, it will take 35 to 60 years for the earth’s ozone layer to recover the levels of ozone it had in the 1960s and it could take about 100 years for it to recover to pre-1950 levels.

In 1987, representatives of 36 nations met in Montreal, Canada, and developed the Montreal Protocol. This treaty’s goal was to cut emissions of CFCs (but no other ozone-depleting chemicals) by about 35% between 1989 and 2000. After hearing more bad news about seasonal ozone thinning above Antarctica in 1989, representatives of 93 countries had more meetings and in 1992 adopted the Copenhagen Amendment, which accelerated the phase-out of CFCs and added some other key ozone-depleting chemicals to the agreement.

The Montreal Protocol is viewed as the world’s most successful global environmental agreement. It set an important precedent because nations and companies worked together and used a prevention approach to solve a serious environmental problem.

This approach worked for three reasons. First, there was convincing and dramatic scientific evidence of a serious problem. Second, CFCs were produced by a small number of international companies and this meant there was less corporate resistance to finding a solution. Third, the certainty that CFC sales would decline over a period of years because of government bans unleashed the economic and creative resources of the private sector to find even more profitable substitute chemicals.

Substitutes are available for most uses of CFCs. However, the most widely used substitutes are hydrofluorocarbons (HFCs), which also act as greenhouse gases during their trip to the stratosphere. An HFC molecule can be up to 10,000 times more potent in warming the atmosphere than a molecule of . The Intergovernmental Panel on Climate Change (IPCC) has warned that global use of HFCs is growing rapidly and that they need to be quickly replaced with substitutes that do not deplete ozone in the stratosphere or act as greenhouse gases while they are in the troposphere. Several companies have developed HFC substitutes that need to be evaluated.

In addition, there is a growing consensus among scientists that the Montreal Protocol should also be used to regulate the greenhouse gas nitrous oxide , which is released from fertilizers and livestock manure. It remains in the troposphere for about 100 years and then migrates to the stratosphere where it can destroy ozone.

Researchers led by Martyn Chipperfield of the University of Leeds, using in new atmospheric chemistry modeling, calculated that, without the benefit of the Montreal Protocol, the Antarctic ozone hole would likely have grown by another 40% by 2013 and that the ozone layer around the globe would have been thinned by 15%. Deaths other harmful effects of ozone thinning would also have been much worse.

These international agreements on protecting stratospheric ozone are working. According to NASA scientists, between 2000 and 2018, ozone thinning in the stratosphere above Antarctica ( Figure 18.29 ), which peaks in September and October, had shrunk by an area equal to about one-third the area of the continental United States. If this trend continues, the ozone layer over Antarctica could return to 1980 levels by 2050. However, a 2018 study by 22 scientists at various research centers in the United States and Europe found that concentration of ozone in the portion of the ozone layer over the mid-latitudes where most of the world’s people live has not risen since the 1990s.

The landmark international agreements on stratospheric ozone, now signed by all 196 of the world’s countries, are important examples of successful global cooperation in response to a serious global environmental problem. This is also an example of the win-win principle of sustainability in action. However, more needs to be done to stop companies in China and other East Asian countries from illegally producing a banned chlorofluorocarbon (CFC-11).

Big Ideas

1. Outdoor air pollution, in the form of industrial smog, photochemical smog, and acid deposition, and indoor air pollution are serious global problems.

2. Each year, about 8 million people die from the effects of outdoor and indoor air pollution, with around half of these deaths occurring in less-developed countries.

3. We need to give top priority to preventing outdoor and indoor air pollution throughout the world and ozone depletion in the stratosphere.

Doing Environmental Science

4. Find out whether or not the buildings at your school have been tested for radon. If so, what were the results? What has been done about any areas with unacceptable levels of radon? If this testing has not been done, talk with school officials about having it done. You could also complete this exercise for the house or building where you live and run a test for the presence of radon there. (Radon testing kits are available at affordable prices in most hardware stores, drug stores, and home centers.)

5.

Data Analysis

Coal often contains sulfur (S) as an impurity that is released as gaseous  during combustion, and  is one of six primary air pollutants monitored by the EPA. The U.S. Clean Air Act limits sulfur emissions from large coal-fired boilers to 0.54 kilograms (1.2 pounds) of sulfur per million Btus (British thermal units) of heat generated. (; .)

1. Given that coal burned in power plants has a heating value of 27.5 million Btus per metric ton (25 million Btus per ton), determine the number of kilograms (and pounds) of coal needed to produce 1 million Btus of heat.

2. If all of the sulfur in the coal is released to the atmosphere during combustion, what is the maximum percentage of sulfur that the coal can contain and still allow the utility to meet the standards of the Clean Air Act?

3. Tying It All TogetherLos Angeles Air Pollution and Sustainability

4.

5. barteverett/ Shutterstock.com

6. In the chapter’s Core Case Study, we learned about how human activities can create massive and harmful air pollution that builds up over time, especially over urban areas such as Los Angeles, California. We saw how a grassroots movement of people concerned about the resulting problems led to a process that has improved air quality over LA. We saw how important it was to pass strict legislation to limit emissions from various sources of pollution. In this chapter, we learned that in passing such limits, we can help prevent not only air pollution, but also acid deposition and the further thinning of the stratospheric ozone layer.

7. We can apply the six principles of sustainability to help reduce the harmful effects of air pollution, acid deposition, and stratospheric ozone depletion. We can reduce emissions of pollutants and ozone-depleting chemicals by relying more on direct and indirect forms of solar energy than on fossil fuels; recycling and reusing matter resources much more widely than we do now; and mimicking biodiversity by using a variety of often locally available renewable energy resources in place of fossil fuels, especially coal. We can advance toward these goals by including the harmful environmental and health costs of fossil fuel use in market prices; seeking win-win solutions that will benefit both the economy and the environment; and giving high priority to passing along to future generations an environment in which they too can thrive.

18.7cReversing Stratospheric Ozone Depletion

According to researchers in this field, we should immediately stop producing all ozone-depleting chemicals. However, models and measurements indicate that even with immediate and sustained action, it will take 35 to 60 years for the earth’s ozone layer to recover the levels of ozone it had in the 1960s and it could take about 100 years for it to recover to pre-1950 levels.

In 1987, representatives of 36 nations met in Montreal, Canada, and developed the Montreal Protocol. This treaty’s goal was to cut emissions of CFCs (but no other ozone-depleting chemicals) by about 35% between 1989 and 2000. After hearing more bad news about seasonal ozone thinning above Antarctica in 1989, representatives of 93 countries had more meetings and in 1992 adopted the Copenhagen Amendment, which accelerated the phase-out of CFCs and added some other key ozone-depleting chemicals to the agreement.

The Montreal Protocol is viewed as the world’s most successful global environmental agreement. It set an important precedent because nations and companies worked together and used a prevention approach to solve a serious environmental problem.

This approach worked for three reasons. First, there was convincing and dramatic scientific evidence of a serious problem. Second, CFCs were produced by a small number of international companies and this meant there was less corporate resistance to finding a solution. Third, the certainty that CFC sales would decline over a period of years because of government bans unleashed the economic and creative resources of the private sector to find even more profitable substitute chemicals.

Substitutes are available for most uses of CFCs. However, the most widely used substitutes are hydrofluorocarbons (HFCs), which also act as greenhouse gases during their trip to the stratosphere. An HFC molecule can be up to 10,000 times more potent in warming the atmosphere than a molecule of . The Intergovernmental Panel on Climate Change (IPCC) has warned that global use of HFCs is growing rapidly and that they need to be quickly replaced with substitutes that do not deplete ozone in the stratosphere or act as greenhouse gases while they are in the troposphere. Several companies have developed HFC substitutes that need to be evaluated.

In addition, there is a growing consensus among scientists that the Montreal Protocol should also be used to regulate the greenhouse gas nitrous oxide , which is released from fertilizers and livestock manure. It remains in the troposphere for about 100 years and then migrates to the stratosphere where it can destroy ozone.

Researchers led by Martyn Chipperfield of the University of Leeds, using in new atmospheric chemistry modeling, calculated that, without the benefit of the Montreal Protocol, the Antarctic ozone hole would likely have grown by another 40% by 2013 and that the ozone layer around the globe would have been thinned by 15%. Deaths other harmful effects of ozone thinning would also have been much worse.

These international agreements on protecting stratospheric ozone are working. According to NASA scientists, between 2000 and 2018, ozone thinning in the stratosphere above Antarctica ( Figure 18.29 ), which peaks in September and October, had shrunk by an area equal to about one-third the area of the continental United States. If this trend continues, the ozone layer over Antarctica could return to 1980 levels by 2050. However, a 2018 study by 22 scientists at various research centers in the United States and Europe found that concentration of ozone in the portion of the ozone layer over the mid-latitudes where most of the world’s people live has not risen since the 1990s.

The landmark international agreements on stratospheric ozone, now signed by all 196 of the world’s countries, are important examples of successful global cooperation in response to a serious global environmental problem. This is also an example of the win-win principle of sustainability in action. However, more needs to be done to stop companies in China and other East Asian countries from illegally producing a banned chlorofluorocarbon (CFC-11).

Big Ideas

Outdoor air pollution, in the form of industrial smog, photochemical smog, and 18.7bWhy Does Ozone Depletion Matter?

Why should we care about ozone depletion? Figure 18.30 lists some of the harmful effects of stratospheric ozone thinning. One effect is that more biologically damaging UV-A and UV-B radiation will reach the earth’s surface. This increased UV radiation will likely lead to rising numbers of eye cataracts, damaging sunburns, and skin cancers. Figure 18.31 lists ways in which you can protect yourself from harmful UV radiation.

Figure 18.30

Harmful effects of decreased levels of ozone in the stratosphere.

Critical Thinking:

1. Which three of these effects do you think are the most threatening? Why?

Figure 18.31

Individuals matter: Ways to reduce your exposure to harmful UV radiation.

Critical Thinking:

1. Which of these precautions do you already take? Which others would you consider doing?

Another serious threat from ozone depletion and the resulting increase in UV radiation reaching the planet’s surface is the possible impairment or destruction of phytoplankton, especially in Antarctic waters. These tiny marine plants play a key role in removing  from the atmosphere and they form the base of many ocean food webs. Greatly decreasing their population would degrade the vital ecological services they provide. The loss of plankton could accelerate projected climate change and ocean acidification by reducing the capacity of the oceans to remove the  that human activities are adding to the atmosphere.

· acid deposition, and indoor air pollution are serious global problems.

· Each year, about 8 million people die from the effects of outdoor and indoor air pollution, with around half of these deaths occurring in less-developed countries.

· We need to give top priority to preventing outdoor and indoor air pollution throughout the world and ozone depletion in the stratosphere.

· 18.7aChemical Threats to the Ozone Layer

· The ozone layer in the stratosphere (Figure 18.2) is a vital form of natural capital that supports all life on land and in shallow aquatic environments by keeping 95% of the sun’s harmful ultraviolet (UV-A and UV-B) radiation from reaching the earth’s surface and harming us and many other species.

· However, measurements taken by researchers revealed a considerable seasonal depletion, or thinning, of ozone concentrations in the stratosphere above Antarctica (Figure 18.29) and above the Arctic since the 1970s. Similar measurements reveal slight overall ozone thinning everywhere except over the tropics. The loss of ozone over Antarctica has been called an ozone hole. A more accurate term is ozone thinning because the ozone depletion varies with altitude and location.

· Figure 18.29

· Natural capital degradation: The colorized satellite image shows ozone thinning over Antarctica during October of 2018 at its annual peak extent. Ozone depletion of 50% or more occurred in the center blue area.

·

· NASA Ozone Watch/Katy Mersmann

· When the seasonal thinning ends each year, huge masses of ozone-depleted air above Antarctica flow northward, and these masses linger for a few weeks over parts of Australia, New Zealand, South America, and South Africa. This has raised biologically damaging UV-B levels in these areas by 3–10%, and in some years by as much as 20%.

· Based on ozone-level measurements and on mathematical and chemical models, the overwhelming consensus of researchers in this field is that ozone depletion in the stratosphere poses a serious threat to humans, other animals, and some primary producers (mostly plants) that use sunlight to support the earth’s food webs.

· In 1988, scientists discovered that similar but usually less severe ozone thinning occurs over the Arctic from February to June, resulting in a typical ozone loss of 11–38% (compared to a typical 50% loss above Antarctica). When this body of air above the Arctic breaks up each year, large masses of ozone-depleted air flow south to linger over parts of Europe, North America, and Asia. However, models indicate that the Arctic is unlikely to develop the large-scale ozone thinning found over the Antarctic.

· The origin of this dangerous environmental threat began in 1930 with the accidental discovery of the first chlorofluorocarbon (CFC), a compound that contains carbon, chlorine, and fluorine. Chemists soon developed similar compounds to create a family of highly useful CFCs, known by their trade name Freons™.

· These chemically unreactive, odorless, nonflammable, nontoxic, and noncorrosive compounds were thought to be dream chemicals. Inexpensive to manufacture, they became popular as coolants in air conditioners and refrigerators, propellants in aerosol spray cans, cleansers for electronic parts such as computer chips, fumigants for granaries and ships’ cargo holds, and gases used to make insulation and packaging.

· It turned out that CFCs were too good to be true. Starting in 1974 with the work of chemists Sherwood Rowland and Mario Molina (Individuals Matter 18.1), scientists showed that CFCs are persistent chemicals that reach the stratosphere and destroy some of its protective ozone. Satellite data and other measurements and models indicate that 75–85% of the observed ozone losses in the stratosphere since 1976 resulted from people releasing CFCs and other ozone-depleting chemicals into the troposphere from human activities beginning in the 1950s.

· Individuals Matter 18.1

· Sherwood Rowland and Mario Molina—A Scientific Story of Expertise, Courage, and Persistence

·

· Hal Garb/AFP/Getty Images; Donna Cove, Mit/University of California, San Diego

· In 1974, calculations by the late Sherwood Rowland (left photo) and Mario Molina (right photo), chemists at the University of California–Irvine, indicated that chlorofluorocarbons (CFCs) were lowering the average concentration of ozone in the stratosphere. They also found that CFCs are persistent, remaining in the stratosphere for hundreds of years. During that time, they noted, each CFC molecule can breakdown hundreds of ozone molecules.

· These scientists decided they had an ethical obligation to go public with the results of their research. They shocked both the scientific community and the $28-billion-per-year CFC industry by calling for an immediate ban of CFCs in spray cans, for which substitutes were available.

· The CFC industry (led by DuPont) was a powerful, well-funded adversary with a lot of profits and jobs at stake. It attacked Rowland’s and Molina’s calculations and conclusions, but the two researchers held their ground, expanded their research, and explained their results to other scientists, elected officials, and the media. After 14 years of delaying tactics, DuPont officials acknowledged in 1988 that CFCs were depleting the ozone layer, and they agreed to stop producing them and to sell higher-priced alternatives that their chemists had developed.

· In 1995, Rowland and Molina received the Nobel Prize in chemistry for their work on CFCs.

· Rowland and Molina came to four major conclusions. First, once CFCs are put into the atmosphere, these persistent chemicals remain there for a long time. Second, over 11–20 years, these compounds rise into the stratosphere through convection, random drift, and the turbulent mixing of air in the lower atmosphere. Third, once they reach the stratosphere, the CFC molecules break down under the influence of high-energy UV radiation. This releases highly reactive chlorine atoms (Cl), as well as atoms of fluorine (F) and bromine (Br), all of which accelerate the breakdown of ozone  into  and O in a cyclic chain of chemical reactions. This process destroys ozone faster than it forms in some parts of the stratosphere.

· Fourth, after entering the troposphere, these long-lived chemicals eventually reached the stratosphere. There they began destroying ozone faster than it was being formed. Each CFC molecule can last in the stratosphere for 65–385 years, depending on its type. During that time, each chlorine atom released during the breakdown of CFCs can break down hundreds of  molecules. Such ozone depletion is a disruption of one of the earth’s most important forms of natural capital that helps sustain life and the world’s economies.

· CFCs are not the only ozone-depleting chemicals. Others are halons and hydrobromofluorocarbons (HBFCs) (used in fire extinguishers), methyl bromide (a widely used fumigant), hydrogen chloride (emitted into the stratosphere by the launches of certain space vehicles), and cleaning solvents such as carbon tetrachloride, methyl chloroform, n-propyl bromide, and hexachlorobutadiene. While in the troposphere, CFCs also act as greenhouse gases that help to warm the lower atmosphere and contribute to climate change.