1991

1975 1980

I I Transportation

1985 1987

I I Fuel Combustion

I I Industrial Processes -M/zypA/Scellaneous

FIG. 5.1.5 U.S. emissions of sulfur oxides by^ou^ce,^970—1991. (Reprinted from Council on Environmental Quality 1993.)

the removal of lead from most gasoline. In addition, the gradual phase in of cleaner automobiles and powerplants reduced atmospheric levels of carbon monoxide by 30%, nitrogen oxides by 6%, ozone by 8%, and sulfur dioxide by 20%. Levels of fine particulate matter (PM-10, otherwise known as dust and soot) dropped 10% since the PM-10 standard was set in 1987 (Council on Environmental Quality 1993).

Despite this progress, 86 million people live in U.S. counties where the pollution levels in 1991 exceeded at least one national air quality standard, based on data for a single year. Figure 5.1.3 shows this data. Urban smog continues to be the most prevalent problem; 70 million people live in U.S. counties where the 1991 pollution levels exceeded the standard for ozone.

Many areas release toxic pollutants into the air. The latest EPA toxics release inventory shows a total of 2.2 billion lb of air toxics released nationwide in 1990 (Council on Environmental Quality 1993).

The primary sources of major air pollutants in the United States are transportation, fuel combustion, industrial processes, and solid waste disposal. Figures 5.1.4 through 5.1.9 show the relative contribution of these sources on a nationwide basis for particulates, sulfur oxides, nitrogen oxides, VOCs, carbon monoxide, and lead. Table 5.1.1 contains statistics on the emissions from key sources of these six major pollutants.

Figure 5.1.10 shows anthropogenic sources of carbon dioxide emissions, mainly fuel combustion, from 1950-1990. Table 5.1.2 contains information on the source contributions. Solid and liquid fuel combustion have been the major contributors.

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