Chemistry Assignment/ Civic Engagement

21.8 Indoor Pollution

Difficult as it is to avoid air pollution outdoors, it is no easier to avoid pollution indoors. The air quality in homes and in the workplace is affected by human activities, by construction materials, and by other factors in our immediate environment. The common indoor pollutants are radon, carbon monoxide, carbon dioxide, and formaldehyde.

The Risk from Radon

In a highly publicized case in 1984, an employee reporting for work at a nuclear power plant in Pennsylvania set off the plant's radiation monitor. Astonishingly, the source of his contamination turned out not to be the plant, but radon in his home!

A lot has been said and written about the potential dangers of radon as an air pollutant. Just what is radon? Where does it come from? And how does it affect our health?

Radon is a member of Group 8A (the noble gases). It is an intermediate product of the radioactive decay of uranium-238 (see Figure 20.3). All isotopes of radon are radioactive, but radon-222 is the most hazardous because it has the longest half-life—3.8 days. Radon, which accounts for slightly over half the background radioactivity on Earth, is generated mostly from the phosphate minerals of uranium (Figure 21.27).

Figure 21.27 Figure 21.27 (a) Sources of background radiation. (b) Radon occurrence in the United States.

Since the 1970s, high levels of radon have been detected in homes built on reclaimed land above uranium mill tailing deposits. The colorless, odorless, and tasteless radon gas enters a building through tiny cracks in the basement floor. It is slightly soluble in water, so it can be spread in different media. Radon-222 is an ɑ-emitter. When it decays, it produces radioactive polonium-214 and polonium-218, which can build up to high levels in an enclosed space. These solid radioactive particles can adhere to airborne dust and smoke, which are inhaled into the lungs and deposited in the respiratory tract. Over a long period of time, the ɑ particles emitted by polonium and its decay products, which are also radioactive, can cause lung cancer.

What can be done to combat radon pollution indoors? The first step is to measure the radon level in the basement with a reliable test kit. Short-term and long-term kits are available (Figure 21.28). The short-term tests use activated charcoal to collect the decay products of radon over a period of several days. The container is sent to a laboratory where a technician measures the radioactivity (ɣ rays) from radon-decay products lead-214 and bismuth-214. Knowing the length of exposure, the lab technician back-calculates to determine radon concentration. The long-term test kits use a piece

ALEKS 360 https://www-awn.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lB...

1 of 5 5/28/2020, 4:03 PM

of special polymer film on which an ɑ particle will leave a “track.” After several months' exposure, the film is etched with a sodium hydroxide solution and the number of tracks counted. Knowing the length of exposure enables the technician to calculate the radon concentration. If the radon level is unacceptably high, then the house must be regularly ventilated. This precaution is particularly important in recently built houses, which are well insulated. A more effective way to prevent radon pollution is to reroute the gas before it gets into the house (e.g., by installing a ventilation duct to draw air from beneath the basement floor to the outside).

Figure 21.28 Figure 21.28 Home radon detector. Credit: © David A. Tietz/Editorial Image, LLC. Page 975

Currently there is considerable controversy regarding the health effects of radon. The first detailed studies of the effects of radon on human health were carried out in the 1950s when it was recognized that uranium miners suffered from an abnormally high incidence of lung cancer. Some scientists have challenged the validity of these studies because the miners were also smokers. It seems quite likely that there is a synergistic effect between radon and smoking on the development of lung cancer. Radon decay products will adhere not only to tobacco tar deposits in the lungs, but also to the solid particles in cigarette smoke, which can be inhaled by smokers and nonsmokers. More systematic studies are needed to evaluate the environmental impact of radon. In the meantime, the Environmental Protection Agency (EPA) has recommended remedial action where the radioactivity level due to radon exceeds 4 picocuries (pCi) per liter of air. [A curie corresponds to 3.70 × 1010 disintegrations of radioactive nuclei per second; a picocurie is a trillionth of a curie, or 3.70 × 10−2 disintegrations per second (dps).]

SAMPLE PROBLEM 21.3

The half-life of Rn-222 is 3.8 days. Starting with 1.0 g of Rn-222, how much will be left after 10 half- lives?

Strategy All radioactive decays obey first-order kinetics, making the half-life independent of the initial concentration.

Setup Because the question involves an integral number of half-lives, we can deduce the amount of Rn-222 remaining without using Equation 14.3.

Solution After one half-life, the amount of Rn left is 0.5 × 1.0 g, or 0.5 g. After two half-lives, only 0.25 g of Rn remains. Generalizing the fraction of the isotope left after n half-lives as (1/2)n, where n = 10, we write

ALEKS 360 https://www-awn.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lB...

2 of 5 5/28/2020, 4:03 PM

THINK ABOUT IT

An alternative solution is to calculate the first-order rate constant from the half-life and use Equation 14.3:

where N is the mass of Rn-222. Try this and verify that your answers are the same. (Since most of the kinetics problems we encounter do not involve an integral number of half-lives, we generally use Equation 14.3 as the first approach to solving them.)

  

Page 976

Practice Problem TTEMPT The concentration of Rn-222 in the basement of a house is 1.8 ×

10−6 mol/L. Assume the air remains static, and calculate the concentration of the radon after 2.4 days.

Answers

Practice Problem UILD How long will it take for the radioactivity due to radon to fall to a level

considered acceptable by the EPA if the starting activity is 2.25 × 103 dps/L?

Answers

Practice Problem ONCEPTUALIZE The first diagram represents a sample of radon gas. Which of the following diagrams [(i)–(iii)] best represents the system after about 10 days?

Carbon Dioxide and Carbon Monoxide

Both carbon dioxide (CO2) and carbon monoxide (CO) are products of combustion.

In the presence of an abundant supply of oxygen, CO2 is formed; in a limited supply of oxygen, both CO and CO2 are formed. The indoor sources of these gases are gas cooking ranges, woodstoves, space heaters, tobacco smoke, human respiration, and exhaust fumes from cars (in garages). Carbon dioxide is not a toxic gas, but it does have an asphyxiating effect. In airtight buildings, the concentration of CO2 can reach as high as 2000 ppm by volume (compared with 3 ppm outdoors). Workers exposed to high concentrations of CO2 in skyscrapers and other sealed environments become fatigued more easily and have difficulty concentrating. Adequate ventilation is the solution to CO2 pollution.

Like CO2, CO is a colorless and odorless gas, but it differs from CO2 in that it is highly poisonous. The toxicity of CO lies in its unusual ability to bind very strongly to hemoglobin, the oxygen carrier in

ALEKS 360 https://www-awn.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lB...

3 of 5 5/28/2020, 4:03 PM

blood. Both O2 and CO bind to the Fe(II) ion in hemoglobin, but the affinity of hemoglobin for CO is about 200 times greater than it is for O2. Hemoglobin molecules with tightly bound CO (called carboxyhemoglobin) cannot carry the oxygen needed for metabolic processes. At a concentration of 70 ppm, CO can cause drowsiness and headache; at higher concentrations, death may result when about half the hemoglobin molecules become complexed with CO. The best first-aid response to CO poisoning is to remove the victim immediately to an area with a plentiful oxygen supply or to give mouth-to-mouth resuscitation.

Formaldehyde

Formaldehyde (CH2O) is a rather disagreeable-smelling liquid used as a preservative for laboratory specimens. Industrially, formaldehyde resins are used as bonding agents in building and furniture construction materials such as plywood and particle board. In addition, urea-formaldehyde insulation foams are used to fill wall cavities. The resins and foams slowly break down to release free formaldehyde, especially under acid and humid conditions. Low concentrations of formaldehyde in the air can cause drowsiness, nausea, headaches, and other respiratory ailments. Laboratory tests show that breathing high concentrations of formaldehyde can induce cancers in animals, but whether it has a similar effect in humans is unclear. The safe standard of formaldehyde in indoor air has been set at 0.1 ppm by volume.

Because formaldehyde is a reducing agent, devices have been constructed to remove it by means of a redox reaction. Indoor air is circulated through an air purifier containing an oxidant such as Al2O3/KMnO4, which converts formaldehyde to the less harmful and less volatile formic acid (HCOOH). Proper ventilation is the best way to remove formaldehyde. However, care should be taken not to remove the air from a room too quickly without replenishment, because a reduced pressure would cause the formaldehyde resins to decompose faster, resulting in the release of more formaldehyde.

ALEKS 360 https://www-awn.aleks.com/alekscgi/x/Isl.exe/1o_u-IgNsIkr7j8P3jH-lB...

4 of 5 5/28/2020, 4:03 PM