Environmental Problems, Their Causes, and Sustainability 1

Table 20-1 Major Classes of Air PollutantsClassExamplesCarbon oxides Carbon monoxide (CO) and carbon dioxide (CO 2 )Sulfur oxides Sulfur dioxide (SO 2 ) and sulfur trioxide (SO 3 )Nitrogen oxides Nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrous oxide (N 2 O)(NO and NO 2 often are lumped together and labeled NO x )Volatile organic compounds (VOCs)Methane (CH 4 ), propane (C 3 H 8 ), chlorofluorocarbons (CFCs)Suspended particulate matter (SPM)Solid particles (dust, soot, asbestos, lead, nitrate, and sulfate salts),liquid droplets (sulfuric acid, PCBs, dioxins, and pesticides)Photochemical oxidantsOzone (O 3 ), peroxyacyl nitrates (PANs), hydrogen peroxide(H 2 O 2 ), aldehydesRadioactive substances Radon-222, iodine-131, strontium-90, plutonium-239 (Table 3-1, p. 49)Hazardous air pollutants (HAPs), which cause health Carbon tetrachloride (CCl 4 ), methyl chloride (CH 3 Cl), chloroformeffects such as cancer, birth defects, and nervous(CHCl 3 ), benzene (C 6 H 6 ), ethylene dibromide (C 2 H 2 Br 2 ), formaldehydesystem problems (CH 2 O 2 )and carbon monoxide. While in the troposphere, someof these primary pollutants may react with one anotheror with the basic components of air to form new pollutants,called secondary pollutants (Figure 20-4).With their concentration of cars and factories,cities normally have higher outdoor air pollution levelsthan rural areas. However, prevailing winds canspread long-lived primary and secondary air pollutantsfrom urban and industrial areas to the countrysideand to other urban areas.Indoor air pollutants come from infiltration of pollutedoutside air and various chemicals used or pro-Primary PollutantsCOCO 2Secondary PollutantsSourcesNaturalSO 2 NO NO 2Most hydrocarbonsSO 3Most suspended particlesHNO 3 H 3 SO 4H 2 O 2 O 3 PANs– 2–Most NO 3 and SO 4 saltsStationaryMobileFigure 20-4 Natural capital degradation: sources and types of air pollutants. Human inputs of air pollutantsmay come from mobile sources (such as cars) and stationary sources (such as industrial and power plants).Some primary air pollutants may react with one another or with other chemicals in the air to form secondary airpollutants.436 CHAPTER 20 Air Pollution