Environmental Problems, Their Causes, and Sustainability 1

SolarradiationUltraviolet radiationNONitric oxideH 2 OWaterNO 2Nitrogen dioxideOAtomicoxygenO 2Molecular oxygenHydrocarbonsHNO 3Nitric acidPANsPeroxyacyl nitratesAldehydes(e.g., formaldehyde)O 3OzonePhotochemical smogFigure 20-5 Natural capital degradation: simplified scheme of the formation of photochemical smog. Theseverity of smog generally is associated with atmospheric concentrations of ozone at ground level.Because of trees’ ecological and aesthetic benefits,environmentalists support their widespread plantingin urban areas. But they say the emphasis should be ontree species that emit low levels of VOCs.How Does Industrial Smog Form, and HowBig a Problem Is It? Gray-Air Smog Is aDanger in Some Developing CountriesIndustrial smog is a mixture of sulfur dioxide,droplets of sulfuric acid, and a variety of suspendedsolid particles emitted by burning coal and oil.Fifty years ago, cities such as London, England, andChicago and Pittsburgh in the United States burnedlarge amounts of coal and heavy oil (which containsulfur impurities) in power plants and factories andfor heating homes and cooking food. During winter,people in such cities were exposed to industrial smogconsisting mostly of sulfur dioxide, aerosols containingsuspended droplets of sulfuric acid formed fromsulfur dioxide, and a variety of suspended solid particles(Figure 20-6).The chemistry of industrial smog is fairly simple.When burned, the carbon in coal and oil is convertedto carbon dioxide (C O 2 CO 2 ) and carbonmonoxide (2 C O 2 2 CO). Some of the unburnedcarbon also ends up in the atmosphere as suspendedparticulate matter (soot), another ingredient ofindustrial smog.The sulfur compounds in coal and oil also reactwith oxygen to produce sulfur dioxide (SO 2 ), a colorless,suffocating gas. Sulfur dioxide also is emitted intothe troposphere when metal sulfide ores are roasted orsmelted to convert a metal ore (such as lead sulfide,PbS) to a free metal (such as Pb).In the troposphere, some of the sulfur dioxide reactswith oxygen to form sulfur trioxide (SO 3 ), whichthen reacts with water vapor in the air to produce tiny440 CHAPTER 20 Air Pollution