study guide

EHST 3600: Air Pollution 1

METEOROLOGY, PART 2

EHST 3600: Air Pollution

SESSION OBJECTIVES

• Know the chemical composition of the atmosphere

• Know the physical composition of the atmosphere

• Know how atmospheric factors affect air quality and air pollution

SESSION OUTLINE

• Atmosphere

• Solar radiation

• Wind circulation

• Lapse rate

• Stability conditions

• Wind velocity profile

• Maximum mixing depth

• Wind rose

• Turbulence

• General characteristics of stack plumes

WIND VELOCITY PROFILE

• Nature of terrain

• Location and density of trees

• Location and size of lakes, rivers, hills and buildings

Different wind velocity

gradients in the vertical

direction

• Planetary boundary layer

• Air layer that is influenced by friction

• Extends from a few hundred meter

to several kilometers above the surface of the earth

WIND VELOCITY PROFILE

• Height of 600 m

• Wind is affected by friction

• Height of >600 m

• Frictional effect is negligible

• Wind speed = gradient wind

• More stable atmosphere at night

Fig. 3-12. Change of wind speed profile with stability

WIND VELOCITY PROFILE

Fig. 3-13. Effect of terrain roughness on the wind

speed profile. Values along curves represent

percentages of gradient

wind value.

EHST 3600: Air Pollution 2

MAXIMUM MIXING DEPTH

Fig. 3-14

Environmental lapse rate

Adiabatic lapse rate

Rawinsonde

measurements

MAXIMUM MIXING DEPTH

Fig. 3-15. MMD values in 100s of meters

Winter mornings Winter afternoons

HORIZONTAL DISPERSION OF POLLUTANTS

• Depends on wind speed and direction

• Concentration of air pollutants decreases with increasing wind speed

• Pollutants are more rapidly separated and dispersed

• What determines our winds?

• Combined effects of temperature gradients

• Rotation of the earth

• How do we organize data on prevailing wind speed and direction?

WIND ROSE

Fig. 3.16. Hypothetical wind rose for data in Table 3-4

13-18

WIND ROSE

Fig. 3-17

a) A typical wind

rose

presentation of

wind speed

data

b) A day-night

wind rose for

New York City

showing diurnal

effect of the sea

breeze

EHST 3600: Air Pollution 3

• What is the most frequent wind direction?

• What the least frequent wind direction?

• What is the most frequent wind speed?

• How frequent in terms of percentage?

• How frequent is the wind speed of 15-25 mph (in %)?

• How frequent is the wind

speed of 0-5 mph (in %)?

http://www.mtav alanche.com/weather/windrose

• What is the most frequent wind direction?

• What the least frequent wind direction?

• In what directions was wind speed of 3.34-5.40 m/s found?

• 8.49-11.05 m/s?

• >11.05 m/s?

http://www.wcc.nrcs.usda.gov /ftpref/downloads/climate/windrose/iowa/des_moines/des_moines_jul.gif

https://windroseexcel.com/guides/how-to-interpret-a-wind-rose-diagram/

• What is the most frequent wind

direction?

• What the least frequent wind

direction?

• How frequent is the wind speed

of 2-3 knots in WSW (in %)?

• How frequent is the wind speed

of 17-22 mph in SE (in %)?

ATMOSPHERIC TURBULENCE

• Thermal turbulence

• Cause by atmospheric heating, resulting to natural convection currents

• Thermal eddies are prevalent on sunny days when light winds occur and temp gradient is highly negative.

• Mechanical turbulence

• Results from wind shear effects

• Mechanical eddies predominate with neutral stability on windy nights

• Resulting from air movement over the earth’s surface and is influenced by the location of buildings and the relative roughness of the terrain

MECHANICAL TURBULENCE

Downwash associated with mechanical turbulence

GENERAL CHARACTERISTICS OF STACK PLUMES

Fig. 3-18

Looping

Coning

Fanning

Fumigation

Lofting

Trapping

EHST 3600: Air Pollution 4

PLUME BEHAVIOR

• Characteristics of the terrain surrounding a stack

• Location and nature of buildings relative to a stack

Fig. 3-19. General arrangement of flow pattern around a sharp-edged building

Plume

behavior

PLUME BEHAVIOR

• Characteristics of the terrain surrounding a stack

• Location and nature of buildings relative to a stack

Fig. 3-20. Aerodynamic effect on pollutant dispersion

Plume

behavior

CLIMATE

• Refers to long time periods

• Seasons, years or decade

• Characteristics of atmospheric

conditions

• Urban microclimate

• Industries and pollutants hinder the ability to flush out or ventilate

• Traps infrared radiation

• Cities are less windy

• Buildings reduce wind by 20-30%

URBAN HEAT ISLAND EFFECT

• When built up areas that are hotter than nearby rural areas

• Annual mean city air temperature of a city  1.8–5.4°F (1–3°C) warmer

than its surroundings • Can affect communities by:

• Increasing summertime peak energy demand, air conditioning

costs • Increasing air pollution and

greenhouse gas emissions • Increasing heat-related illness

and mortality, and water quality

https://www.epa.gov/heat-islands

URBAN AIR CIRCULATION

• Steel, concrete and masonry absorb and hold heat

• Results of heat island effect

• Will encompass the city at night

• Will have its own circulation pattern

• Pollutants cannot readily escape

• Resulting in the haze layer seen over a large urban area

Urban air circulation pattern associated

with the heat island effect https://www.epa.gov/heat-islands

EHST 3600: Air Pollution 5

AIR QUALITY & PAVED SURFACES

https://www.nsf.gov /news/mmg/media/images/air_quality2_h.jpg

HUMAN IMPACT ON THE EARTH-ATMOSPHERE SYSTEM

1. Depletion of the ozone layer

2. Rising levels of atmospheric CO2

OZONE LAYER DEPLETION

• Depletion of the ozone layer by stable chemicals that react with and destroy ozone molecules

• CFCs – chlorofluorocarbons; synthetic chemicals used as refrigerants and aerosol propellants; one million tons produced annually during the 1970s

• Halons – bromofluorocarbons; fire suppressant; widespread use in 1960s–1970s

• 1978 – nationwide ban on ozone-depleting gases

• 1985 – hole in ozone represented 40% decline in ozone concentration; continues to increase

• 1987 – Montreal Protocol

OZONE LAYER DEPLETION

• “Antarctic ozone hole” was almost twice the area of the Antarctic continent

EFFECTS OF OZONE LAYER DEPLETION

• Health effects

• Sunburn

• Cataracts

• Skin cancer

• Basal cell carcinoma

• Squamous cell carcinoma

• Melanoma

• Ecological effects

• Biological changes in phytoplankton in the food chain

• Wildlife

CHLOROFLUOROCARBONS (CFCS)

• Suspect in depletion of the ozone layer

• Developed by Thomas Midgley in 1930 to replace ammonia used in refrigerators during the 1920s

• Were considered safe

• Did not react with other substances

• Did not breakdown easily (below the stratosphere)

• Reactions in the stratosphere was not seen

EHST 3600: Air Pollution 6

CHLOROFLUOROCARBONS (CFCS)

• Main cause of ozone layer depletion

• Altitude: 10-20 miles  Cl released when CFCs break down

• O2  no sun-blocking properties

Cl + O3 O2

WHERE DO CFCs COME FROM?

• Propellants in products (hair sprays and bathroom cleaners in aerosol containers)

• Refrigeration units in appliances and air conditioners

WHERE DO CFCs COME FROM?

• Minor by-products from the production of

• Foam coffee cups

• Egg cartons

• Furniture cushions

• Building insulation

• Nonflammable gas used in hospitals for sterilization of medical

equipment

HUMAN IMPACT ON THE EARTH-ATMOSPHERE SYSTEM

• Rising levels of atmospheric CO2 • Global warming well documented – upward trend begins early

1900s; more pronounced since 1976

• Fossil fuel use releases large amounts of CO2 as byproduct; 1 ton coal releases 3 tons CO2

• Widescale destruction of natural vegetation releases CO2 during burning

• Other greenhouse gases

• Methane

• Nitrous oxide

• Halocarbons

• Water vapor

GLOBAL LAND-OCEAN TEMPERATURE ANOMALY

EHST 3600: Air Pollution 7

TOP CO2 EMITTERS EVIDENCE FOR CLIMATE CHANGE

• Ice core analyses

• Melting sea ice and mountain glaciers

• Ocean waters heating up and acidifying

• Increasing height of the tropopause

• Shifting range of biological species and temporal advancement of spring events

IMPACTS OF GLOBAL WARMING

• Shifting rainfall patterns

• Extreme weather events more common

• Rising sea levels

• Diminishing crop yields due to hotter drier weather

• Loss of biodiversity

• Human illness—spread of tropical diseases

• Collapse of thermohaline circulation in North Atlantic

• National security concerns

Increase flooding

Polar bear habitat reduction http://www.epa.gov/climatechange/

SUMMARY

• Wind velocity profile is affected by the nature of terrain, location and density of trees, and location and size of lakes, rivers, hills and buildings.

• Planetary boundary layer is the air layer that is influenced by friction;

extends from a few hundred meter to several kilometers above the surface of the earth.

• Wind speed above the planetary boundary layer is equivalent to the gradient wind.

• The maximum mixing depth is the depth of the convective mixing layer in the atmosphere, and is affected by the atmospheric stability.

• Wind rose is the graphical representation of the local wind speed and direction.

SUMMARY

• Atmospheric turbulence can be classified into thermal and mechanical turbulence.

• Stack plume characteristics may be classified as looping, coning, fanning, fumigation, lofting and trapping.

• Plume behavior may be influenced by the general characteristics of the terrain surrounding a stack, and the location and nature of buildings relative to a stack.

• Urban heat island effect is when built up areas (urban areas) are hotter than nearby rural areas.

• The human impact on the earth-atmosphere system is manifested in 2 main events: depletion of the ozone layer and rising levels of CO2.