. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. Figure 4. Population distribution (percentage of total) in urban areas, 1960-1990. Most economic and population growth is taking place in the collar counties around Chicago, spurring slight increases in emissions of ozone precursors — volatile organic compounds, nitrogen dioxide and carbon monoxide — in these areas. Land is rapidly being developed in these growth areas, decreasing urban density but
. The changing Illinois environment : critical trends : technical report of the Critical Trends Assessment Project. Man; Pollution; Environmental protection; Ecology; Environmental impact analysis. Figure 4. Population distribution (percentage of total) in urban areas, 1960-1990. Most economic and population growth is taking place in the collar counties around Chicago, spurring slight increases in emissions of ozone precursors — volatile organic compounds, nitrogen dioxide and carbon monoxide — in these areas. Land is rapidly being developed in these growth areas, decreasing urban density but increasing the stress on surrounding ecosystems and agricultural lands. The trend to lower urban density is particularly evident in the residential sector, as larger houses are being built for fewer people per household. Over 30 years, the median number of rooms per housing unit has increased from to , while the number of persons per unit has declined from to Although point emissions of criteria air pollutants from urban sources are small compared to other sectors, such as manufacturing and utilities, some are large enough to require a permit and be included in lEPA's Total Air System (TAS) database. Figure 5 shows statewide trends in these urban sector point source emissions (taken from the TAS) of five criteria air pollutants. Overall, only carbon monoxide increases slightly in each three-year period, with the most significant change occurring in the service sector. From 1983 to 1989 service sector CO emis- sions grew from 21% to 33% of the Total TSP Total S02 Total NQx Total HC Total CO 101963 a 1986 11989 Figure 5. Statewide urban point source emissions, 1983,1986 and 1989. To estimate trends in municipal wastewater dis- charge, the Illinois Environmental Protection Agency provided a data analysis from the Permit Compliance System. The analysis only included those major facilities which reported an equivalent number of sample measurements for a s
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