Chapter 12: Air Chapter 12: Air PollutionPollution

A brief history of air pollutionA brief history of air pollution Types and sources of air pollutantsTypes and sources of air pollutants Factors that affect air pollutionFactors that affect air pollution Air pollution and the urban environmentAir pollution and the urban environment Acid depositionAcid deposition

A Brief History of Air A Brief History of Air PollutionPollution

disastrous London smog event of 1952 disastrous London smog event of 1952 smog: smoke and fog;smog: smoke and fog; 5 days, nearly 4000 deaths; 5 days, nearly 4000 deaths; Clean Air Act in 1956Clean Air Act in 1956 Los Angeles: photochemical smog Los Angeles: photochemical smog forms in sunny weather and irritates the eyesforms in sunny weather and irritates the eyes U.S. Clean Air Act, 1970, 1990U.S. Clean Air Act, 1970, 1990 set federal emission standards for states to set federal emission standards for states to

implement implement and enforceand enforce

Types and Sources of Air Types and Sources of Air PollutantsPollutants

Air pollutants are airborne substances (either solids, liquids, or gases) that occur in concentrations high enough to threaten the health of people and animals,to harm vegetation and structures, or to toxify a givenenvironment.

They come from natural sources and human activities:Natural: dust, volcano, forest fire, ocean waves, …Human: fixed sources (power plants, homes, …) mobile sources (cars, ships, …)

Principal Air PollutantsPrincipal Air Pollutants primary and secondary pollutantsprimary and secondary pollutants particulate matter: particulate matter: a group of solid particles a group of solid particles

and liquid droplets that are small enough to remain and liquid droplets that are small enough to remain suspended in the airsuspended in the air

PM10, PM2.5: PM10, PM2.5: <10 or 2.5 micrometer in <10 or 2.5 micrometer in diameter diameter

Carbon monoxide: Carbon monoxide: colorless, odorless, colorless, odorless, poisonouspoisonous• Globally, a large percentage of air pollution sources are Globally, a large percentage of air pollution sources are

natural. Within localized areas, however, human-natural. Within localized areas, however, human-caused sources are often the largest contributors.caused sources are often the largest contributors.

Over U.S.

Principal Air PollutantsPrincipal Air Pollutants Volatile organic compounds (VOCs): Volatile organic compounds (VOCs):

represent a class of organic compounds that are mainly represent a class of organic compounds that are mainly hydrocarbons – individual organic compounds composed of hydrocarbons – individual organic compounds composed of hydrogen and carbonhydrogen and carbon

nitrogen oxides: nitrogen oxides: nitrogen dioxide (NOnitrogen dioxide (NO22) and ) and nitric oxide (NO), together called NOnitric oxide (NO), together called NOxx

• Along with ozone, VOCs and NOx are major Along with ozone, VOCs and NOx are major components of photochemical smog.components of photochemical smog.

• Photochemical smog is a problem on most Photochemical smog is a problem on most major cities of the world.major cities of the world.

Ozone in the Ozone in the TroposphereTroposphere

Photochemical smog: Photochemical smog: in the presence of sunlightin the presence of sunlight Ozone: Ozone: unpleasant odor, irritates eyes and hurt unpleasant odor, irritates eyes and hurt

human health, reduce crop yieldhuman health, reduce crop yield

Ozone in the Ozone in the StratosphereStratosphere

relationship to ultraviolet radiationrelationship to ultraviolet radiation chlorine compoundschlorine compounds chlorofluorocarbons (CFCs); a single chlorofluorocarbons (CFCs); a single chlorine removes as many as 100,000 chlorine removes as many as 100,000 ozone moleculesozone molecules

Montreal ProtocolMontreal Protocol• When scientists first measured When scientists first measured

extremely low ozone values in the extremely low ozone values in the Antarctic stratosphere, they Antarctic stratosphere, they thought the instruments were thought the instruments were malfunctioning.malfunctioning.

Figure 1, p. 337

Ozone hole in 2006;mainly due to changes inpolar stratospheric temperatures

Air Pollution: Trends and Air Pollution: Trends and PatternsPatterns

Air Quality Index (AQI): Air Quality Index (AQI): includes the pollutants CO, SOincludes the pollutants CO, SO22, , NONO22, particulate matter, and O, particulate matter, and O33

• Secondary air pollutants (e.g., OSecondary air pollutants (e.g., O33)) are particularly difficult to control, are particularly difficult to control, because they are not emitted because they are not emitted directly into the atmosphere.directly into the atmosphere.

Fig. 12-11, p. 338

Factors affecting air Factors affecting air pollutionpollution

dilutiondilution turbulenturbulen

cece mixingmixing

• ““Dilution is the solution to pollution” - in the 1950s this motto Dilution is the solution to pollution” - in the 1950s this motto led to the construction of tall smokestacks for large factories. led to the construction of tall smokestacks for large factories. Pollution was released higher in the atmosphere where winds Pollution was released higher in the atmosphere where winds were stronger. Air quality improved locally but suffered were stronger. Air quality improved locally but suffered downwind.downwind.

The role of the wind

The Role of Stability and The Role of Stability and InversionsInversions

temperature lapse ratestemperature lapse rates inversionsinversions mixing depthmixing depth

• The mixing layer can often be The mixing layer can often be easily seen from an airplane.easily seen from an airplane.

The Role of TopographyThe Role of Topography cold air drainagecold air drainage air blockage by mountain rangesair blockage by mountain ranges

Severe Air Pollution Severe Air Pollution PotentialPotential

Sources Sources (clustered close together)(clustered close together) high pressure high pressure (for inversion and weak wind)(for inversion and weak wind) Inversions Inversions Stagnation Stagnation (unable to disperse pollutants) (unable to disperse pollutants) A valley A valley (for accumulation of pollutants)(for accumulation of pollutants)

• Some locations, like Los Angeles and Mexico City, have an Some locations, like Los Angeles and Mexico City, have an unfortunate combination of surrounding topography, unfortunate combination of surrounding topography, frequent inversions, abundant emissions and plentiful frequent inversions, abundant emissions and plentiful sunlight - perfect conditions for photochemical smog.sunlight - perfect conditions for photochemical smog.

Air Pollution and the Air Pollution and the Urban EnvironmentUrban Environment

urban heat islandurban heat island country breezecountry breeze

Acid DepositionAcid Deposition pHpH wet depositionwet deposition dry depositiondry deposition acid fog: acid fog: SOSO22 and and

NONOxx acid rain effectsacid rain effects

Precipitation pH values