Air Pollution

Chapter 17

Atmospheric ChemistryCycles and Residence Times

• Atmosphere composition mostly Nitrogen (76.6 %), Oxygen (23.1 %), and other gases

• Chemical materials cycle through the atmosphere as they do in other reservoirs– Residence Times (Table 17.1)– Influenced by amounts present in a given

reservoir• CO2 – 4 years• O2 - 7 million years• N2 – 44 million years

Figure 17.1 The Global carbon cycle

Cost of Air Pollution• Air pollution is costly• $40 billion – Worldwide annual expense of

forest-product harvest reduction due to air pollution

• $16 billion annual U.S. expense (direct costs)• Medical costs are enormous:

– Illness– Medical treatment– Absenteeism– Loss of production

Types of Air Pollution• Gaseous pollutants

– CO and CO2

– SO2

– NO, NO2

– Ozone and CFCs

• Particulates– Soot– Smoke– Ash (from burning coal)– Dust (released from industrial processes)– Other solids release by burning– From 35 million tons/year (mainly combustion) to 180

million tons/year (mostly industrial)

Figure 17.2 Principal sources of U.S. air pollutants, 1998

Figure 17.3 U.S. particulate emissions were controlled

Carbon Gases• CO – carbon monoxide

– Not very abundant in the atmosphere but deadly– Odorless, tasteless and invisible – toxic to animals– Very short residence time but easily added to the

atmosphere by common anthropogenic sources (automobiles)

• CO2 - carbon dioxide– Essential for life of plants (photosynthesis)– Product of plant respiration, combustion, and

volcanic eruptions– Short residence time and easily fluxes between

oceans and atmosphere

Figure 17.1 The Global carbon cycle

Figure 17.4 a Emissions of carbon monoxide

Sulfur Gases

• More than 50 million tons of sulfur dioxide (SO2) are emitted worldwide each year mainly from coal combustion

• SO2 - sulfur dioxide forms acid rain– very short residence time (days or hours)– By product from combusting coal– SO2 + H2O + ½ O2 = H2SO4 (sulfuric acid) and

will lower the pH scale for rain– Can contribute to acid rain causing lung and

eye irritation– Becomes a contributor to water pollution

Figure 17.4 b Emissions of sulfur dioxide

Nitrogen Gases and “Smog Ozone”• Complex geochemistry

– oxygen and nitrogen are very abundant in the atmosphere

– high temperatures cause nitrogen and oxygen to form nitrogen oxide compounds

• 2NO2 + H2O + ½ O2 = 2HNO2 (nitric acid)• NO2 + strong sun light will produce photochemical

smog• NO2 can breakdown in sun light to NO and will

react with common oxygen (O2) to form ozone (O3)• Ozone inhibits photosynthesis in plants and can

cause severe medical problems to people in urban areas where abundant automobiles are in operation

Figure 17.5 Nitrogen-gas emissions

Fig. 17.06 substandard and near-ground ozone

The Ozone Layer and Chlorofluorocarbons (CFCs)

• Ozone (O3) is a ‘chemically out of place pollutant’– In upper atmosphere (stratosphere) the ozone layer

absorbs harmful ultraviolet radiation– Ozone forms as O2 + ½ O2 = O3

– At ground level it is very harmful to plants and animals– A thick ozone layer is beneficial to life on earth– Periodically, an ozone hole forms over either pole. This

allows more ultra violet radiation to enter the lower atmosphere

– CFCs attack ozone and can destroy, or thin, the ozone layer

– CFCs build up their concentration in the upper atmosphere, have a residence time of about 100 years, and breakdown into various by-products including chlorine monoxide (ClO)

– One ClO can destroy many ozone molecules

Figure 17.7 Ozone layer

Figure 17.8 a

Figure 17.8 b

Figure 17.9

Figure 17.10

Figure 17.11

Figure 17.12

Figure 17.13

Figure 17.14

Particulate Pollutants

• Lead - once a serious pollutant– Used in gasoline as an antiknock additive,

tons of lead were released into the atmosphere by internal combustion engines

– Unleaded fuels have reduced lead in air pollution

• High doses of lead can cause brain damage, depression, apathy, and other psychological disorders

Figure 17.15 a

Figure 17.15 b

Acid Rain• Acidity is reported on the pH scale.

– An acid solution has more Hydrogen-ions (H+)– A basic solution would have fewer

• Acid rain has more acid than normal rain– Certain gases in the atmosphere will complex with

atmospheric water plus oxygen to form acids• Acid rain is harmful to plants, health of rivers and

lakes, and animals• Acid rain causes increases in the build up of heavy

metals (lead, zinc, selenium, copper, and aluminum) leached from rocks and soils

• Toxic levels are then found in our waterways, fish, and fish eaters

Figure 17.16

Figure 17.17

Regional Variations in Rainfall Acidity and Impacts

• Rain down wind of an industrial or populated areas have greater acidic conditions– Generally, industrial areas have notably higher sulfur

dioxide emissions than non-industrial areas– Urban areas, with automobiles, generally have higher

nitrogen oxide emissions than areas without autos

• Local geology can reduce the acidity of waterways that receive acid rain.– Limestone can neutralize acidic water; granite can not

Figure 17.18

Air Pollution and Weather• Thermal Inversion

– Pollutants released from ground sources generally are warmer than the surrounding air and tend to rise

– As an air mass these plumes will rise and cool– In certain situations a cool air mass will have a warm

air mass overlying it, it will trap the rising warm pollutant-bearing air mass; this condition is made worse by an air mass with stagnant conditions

– As more pollutants are dumped into the cooler air mass they will become concentrated below the warm air mass

– Eventually, the concentrations of pollutants may become very high and cause a health concern

– Local topography – mountains, basins, valleys, and local wind patterns may amplify the situation also

Figure 17.19 a

Figure 17.19 b

Figure 17.20

Figure 17.21 a

Figure 17.21 b

Air Pollution and Weather

• Air pollution can impact local weather– Reduce visibility– Reduce air quality– Modify air temperature– Produce acid rain– Produce abnormal rain

Figure 17.22

Air Pollution Control• Air Quality Standards – Clean Air Act (1970)

– Designed to protect public health, clear the visible pollution in the air, and prevent damage to crops

• Control Methods– Trapping or scrubbing emissions– conversion techniques that reduce the emission of

harmful compounds to less harmful ones • Automobile Emissions – strong legislation creates

the Environmental Protection Agency (EPA)– Goal to reduce automobile emissions– Limited success achieved by requiring the use of catalytic

converters in new cars and increased fuel economy standards for all new cars

• Cost and Effects – it has increased abatement and control cost while limited areas of success have occurred

Fig. 17.23

Figures 17.24 a and b