Sources of Pollutant Chemicals to the Atmosphere

Human activities contribute large fluxes of gases and particles to the atmosphere. Many of these fluxes are associated with combustion such fluxes date back to prehistory, when humans first built fires. Historical records of air pollution from fossil fuel combustion appear in the late I3th century, when 

Foremost among the many gases emitted by human activities is carbon dioxide. At natural levels, C02 is not an air pollutant, but an atmospheric com- 

In many industrial areas, emissions of gaseous oxides of sulfur (SOx), especially sulfur dioxide (S02), also rival natural sulfur gas emissions from volcanoes, wetlands, and oceans. SOx are produced from the oxidation of sulfur in fuels, especially coals and residual oils, and are responsible in large part for acid rain (Section 4.6.3). In fuels, sulfur typically occurs either in organic compounds (organic S) or as pyrite (FeS2). SOx also are formed from the refining of the ores of the many metals that occur in the form of metal sulfides [e.g., copper (Cu), lead (Pb), and nickel (Ni)]. 

Carbon monoxide (CO), a toxic gas, is produced during combustion, both in wildfires and in fuel-burning devices CO also can be produced and consumed by bacterial activity. The presence of CO may indirectly increase the atmospheric mixing ratios of other gases by competing for oxidant species (such as the hydroxyl radical, OH-), thereby decreasing the oxidation rates of the other gases. This competition for oxidant species is believed to be one reason for the current increase in atmospheric methane, whose major atmospheric sink is reaction with the hydroxyl radical. 

Methane (CH4), a key greenhouse gas, has many natural sources, including wetlands and termites. Methane is also released by the petroleum industry, landfills, cattle, rice cultivation, and wastewater treatment plants. (Wastewater treatment plants often burn off CH4 at the top of a tall stack in a process 

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