From The Changing Illinois Environment: Critical Trends,1994, Summary Report of the Critical Trends Assessment Project

The atmosphere above Illinois is not only the source of the air we breathe and the water that sustains us but is also a vast chemical laboratory in which polluting "acid rain" and ozone are manufactured and protective ozone in upper layers is chemically dismantled.


Sulfur dioxide, carbon monoxide, particulate matter, nitrogen oxides, and lead are among the substances emitted into the air in sufficient quantities to have been targeted as pollutants. Sulfur dioxide (SO2) can be produced during petroleum refining or when fuels containing sulfur compounds are burned. Oxidized and combined with water in the atmosphere, SO2 can produce an ultrafine mist of sulfuric acid (H2SO4); its presence in air has been correlated with increased rates of human death and disease. (On the more positive side, atmospheric sulfate particles can reduce solar heating.)

Particles are solids--very small bits of metals, fibers, stone dust, ash, and soot produced by all sorts of activities. Ozone is a pulmonary irritant, a gas created when atmospheric nitrogen dioxide and volatile hydrocarbons are bombarded by ultraviolet light energy from the sun. Assorted compounds of nitrogen are produced when fossil fuels are burned; two of them, nitric oxide and nitrogen dioxide, are quite reactive and are precursors of ozone. Carbon monoxide is a product of the incomplete combustion of virtually all fuels, although most of it comes from motor vehicles.

In general, air quality in Illinois is improving, at least as judged by its concentrations of seven criteria pollutants for which national and or state standards have been set. A CTAP analysis of routine Illinois Environmental Protection Agency air quality measurements carried out from 1978 through 1990, plus a series of nonroutine measurements of certain organic compounds, showed either unchanging or decreasing concentrations of all pollutants. Statewide data were available for twelve pollutants; of these, seven showed signs of decreasing trends. Regionally, only the Metro-East area near St. Louis recorded significant pollutant increases (for iron and manganese).

Manufacturing. Historically, manufacturing has been the major source of air pollution in Illinois. But recent declines in traditionally dirty-air industries, such as steel-making, combined with enforcement of federal clean-air regulations, have measurably improved air quality in Illinois. Between 1973 and 1989, emissions of particulate matter dropped 87% in Illinois, those of sulfur oxides (SOx) 67%, nitrogen oxides (NOx) 69%, hydrocarbons (HC) 45%, and carbon monoxide (CO) 59%. (Figure 2-1 ) Between 1973 and 1989 manufacturing's environmental cost in Illinois--the pollutants produced per million dollars of factory output--declined for all pollutants, from 57% for hydrocarbons to as much as 87% for particulate matter.

As per 1986 federal legislation, certain large emitters among Illinois manufacturing facilities are required to report releases into the environment of more than 300 toxic chemicals and 20 categories of chemical compounds. The quality of the data used to compile this annual Toxic Release Inventory is not perfect, but a general picture of industrial emissions emerges. Data from 1991 show that reported releases into the air via both smokestacks and fugitive emissions amounted to 77.5 million pounds.

Nonetheless, conventional air pollution declined overall even in Illinois' factory districts. Within the Chicago area only one location stood out for its high concentrations of multiple pollutants, and that was the industrial southeast part of the city around Lake Calumet.

Nonmanufacturing Sources. While a relatively few large facilities put the most pollutants into the air, thousands of small individual sources in the wholesale and retail trades, finance and insurance, real estate, and government combine to generate tens of thousands of tons of criteria air pollutants. Trends in emissions of total suspended particles, sulfur dioxide, nitrogen oxide, total hydrocarbons, and carbon monoxide from these sources are downward, that for CO is up, and those for NOx and HC are steady or up only slightly. Over the last 20 years the Illinois services sector, which is cleaner per unit of output than the manufacturing sector, has shown the most growth (87 %) in output and employment, which explains in part the downward trend in overall emissions.

Chicago and Metro-East do not, however, meet federal Clean Air Act standards for ozone. Ozone precursors include volatile organic compounds (VOC) emitted from paints, solvents, glues, inks, etc., emissions of which have leveled off or declined in recent years. Ozone precursors also include NOx, which is emitted from home furnaces, vehicles (including construction equipment), structure fires, and lawn mowers.

Output of NOx and CO in the Chicago area increased overall since 1970, although both fell in Cook County after peaking in 1980. Furnaces and heavy construction equipment produce an overwhelming share of the NOx (97 %) from smaller sources, and construction and lawn equipment generate about 90% of the CO. (Such machinery is not subject to the strict emissions standards applied to cars and trucks.) High emissions of both would be expected in rapidly building suburban residential areas such as DuPage County, where construction employment increased 444% between 1967 and 1989; unlike factory-related emissions, however, these high concentrations are short-lived.

A majority of Illinois hospitals, crematoriums, veterinary clinics, and other medical facilities continue to burn their wastes on-site, mainly to reduce waste volume prior to landfilling. In addition to criteria pollutants, hospital incinerators tend to emit relatively more dioxins and acid gases such as hydrogen chloride than do municipal incinerators, in part because of the high concentrations of plastics in hospital waste streams. Currently Illinois regulates only the amount of particulate matter and CO emitted; these incinerators, however, will have to comply with additional medical waste incinerator emission standards expected to be proposed in 1995 under the amended Clean Air Act. Standards will be proposed for particulate matter, sulfur dioxide, hydrogen chloride, oxides of nitrogen, carbon monoxide, lead, cadmium, mercury, dioxins, and dibenzofurans.


Because most of the byproducts--heat, gases, and particles--are released into the atmosphere, the burning of fossil fuels for transportation and electricity generation has a substantial impact on air quality.

Transportation. Highway vehicles in Illinois are the most substantial source of NOx, VOC, and CO. The number of vehicle miles traveled (VMT) in Illinois has grown steadily in the last 20 years, from 61 billion miles in 1973 to 86 billion in 1991. (Figure 2-2) Federal clean-air regulations and mileage standards imposed in the 1970s, however, have combined to cut air emissions from cars dramatically. VOC and CO emission rates from cars and light trucks dropped 75% between 1973 and 1991.

Figure 2-2. Number of Vehicle Miles Traveled (VMT) in Illinois 1970-1991

Source: Sources of Environmental Stress, ENR Office of Research and Planning, 1994

The cumulative effect of cleaner, more efficient vehicle engines on transportation air emissions has been positive. Even though VMT grew by 40% between 1973 and 1991, CO emissions dropped 47% (two million tons), VOC emissions were down 47% (315,000 tons), and NOx emissions (for which strict standards have been in place only since 1983) were down 8% (25,000 tons). (Figure 2-3)

Figure 2-3. Percentage Change in Transportation Emissions 1973-1992

*U.S. Census Bureau Metropolitan Statistical Area, other than Cook and Collar Counties. Source: Sources of Environmental Stress, ENR Office of Research and Planning, 1994

The reduction in car and truck emissions contributed to a reduction in total transportation emissions from 1973 to 1991. (Figure 2-4) Rail generates only 1/100 of the common engine pollutants that highway vehicles generate, although the reductions are due more to reduced freight hauling than new efficiencies. Emissions from airplanes are up overall since 1973, but are down or steady since 1982 in spite of increases in passenger-miles flown. By far the largest percentage increase in VOC and CO emissions came from boats, much of it on Lake Michigan and the Chain-O-Lakes. However, water-based sources remain a tiny part (2%) of total vehicle emissions.

Figure 2-4. Vehicle Emissions Statewide 1973-1991

Source: Sources of Environmental Stress, ENR Office of Research and Planning, 1994

Utilities. The burning of fossil fuels to make electricity is a major source of air pollution in the form of sulfur dioxide, nitrous oxides, carbon monoxide, and particulate matter. In 1973, for example, 1.7 million tons of SO2 were emitted from Illinois utility smokestacks along with approximately 356,000 tons of NOx, 17,000 tons of CO, and 96,000 tons of particulate matter.

Over the subsequent 16 years, however, emissions of all four pollutants dropped dramatically. Annual SO2 emissions in 1989 were down roughly one-half compared to 1973 levels, to 870,000 tons. Those of NOx were down almost 20%, those of CO were down by 35%, and those of particulate matter were down 81%. These reductions occurred in spite of the fact that electricity generation (measured in kilowatt-hours) grew by 52% over the same period.

Two trends explain these results. One was the switch to nuclear plants by Illinois' two largest utilities. In 1973, 22% of the state's electricity was generated by nuclear energy; by 1989 the figure was 59%.

The other trend noted was toward cleaner generation, the result mainly of regulations imposed under the federal Clean Air Act. Between 1973 and 1989 the amount of SO2 emitted per unit of electricity dropped by roughly 32%. Particles showed an even more substantial decline--77%.


Human health. Ozone is a reactive gas that has been shown to cause damage to both human and plant tissues (including human lungs) and to other exposed materials. For these reasons both ozone and the chemical "precursors" in the lower atmosphere that create ozone are monitored. (Ozone high in the atmosphere shields the earth's surface from potentially damaging ultraviolet radiation.) Ozone pollution in particular is a product of cities; in recent years ozone concentrations exceeded standards only in seven urbanized counties.

In the 1950s and 1960s, concentrations of atmospheric lead were six to ten times higher in cities than in rural areas. In 1967-69, at least 27 areas of the state registered average maximum lead concentrations higher than two milligrams per cubic meter on a quarterly basis, roughly one-third higher than the legal standard. Most of these readings occurred near busy streets traveled by vehicles using leaded motor fuel.

Human exposure to criteria air pollutants has declined significantly in Illinois since the 1970s. The lead standard has not been exceeded anywhere in the state since sales of leaded gasoline were banned in 1982 (Figure 2-5), and the SO2 standard not since 1988. The CO standard has been exceeded only once since 1985. Since 1978 exposure to above-standard levels of ozone also has declined in Illinois, although sunny summer weather created unusually high levels in 1983, 1987, and 1988.

Figure 2-5. Statewide Trends in Airborne Lead Concentrations in Illinois 1979-1990

Source: Air Resources, Illinois State Water Survey, 1994

Traditional air pollution controls seek to reduce concentrations of criteria pollutants in outdoor air, but these pollutants occur indoors as well. Carbon monoxide and nitrogen dioxide can be emitted by unvented space heaters or leaking furnaces, for example, and lead can be present in the form of lead-based paint. Indoor air also can be fouled by viruses, molds, and fungal spores; smoke from tobacco, fireplaces, or wood stoves; assorted volatile organic compounds from paints, solvents, and cleaners; pesticides and asbestos; and formaldehyde from pressed wood products.

While it is possible to state that the problem exists, data are inadequate to identify trends in indoor air pollution in Illinois. Consider for example the problem of radon. Radon is the term commonly used to describe radon-222, an isotope of radioactive radium-226 and uranium-238. It occurs in trace amounts in most geologic materials, including soils. Radon enters most houses via gases escaping from these soils (for example from crawl spaces) and can build up to potentially unhealthful levels, especially in winter, when houses are tightly sealed against weather. Various surveys by Illinois and U.S. government agencies have come to varying conclusions about the extent of indoor radon levels in Illinois--that concentrations of radon exceeded the U.S. EPA's "action level" in anywhere from 19% to 31% of Illinois homes, that most of the state has a high or moderate potential for elevated radon readings, that only a few areas in Illinois (about 25 zip code areas) show radon concentrations high enough to be called high-risk.

Ozone depletion. Substances produced when chlorofluorocarbons (CFCs) are broken down in the atmosphere have the potential to react with and destroy ozone in the upper atmosphere that protects living things from the sun's ultraviolet rays. (Ozone-destroying chemicals also are emitted from such natural sources as volcanoes.) CFCs are used in foam packaging, insulation, various kinds of containers and cartons, and refrigeration equipment; halons (chemicals used in fire-fighting equipment) are present in much smaller amounts than CFCs but have a much higher ozone-depleting potential per molecule. An estimated 2,105 tons of CFCs and halons are emitted in Illinois each year.

The manufacture of CFCs will soon cease in the U.S. but many CFCs and halons remain in the environment. They are "stored" in appliances and materials that constitute a sizeable CFC and halon "bank." It is estimated that more than 35,000 tons are banked. This inventory is expected to remain unchanged for some years, as the equipment and materials they are part of (such as insulation) tend to be replaced slowly.

Acid rain. Illinois precipitation is a dilute solution of sulfuric and nitric acids. However, these acids are partially neutralized by ammonium and calcium particles from soil and from rock-surfaced roads. In the 1980s, acid-buffering airborne calcium decreased, but decreases in sulfate compounds occurring at the same time were even larger. The result, tests suggest, was a decrease in the acidity of precipitation.


Weather records tend to confirm popular opinion that, over time, the only thing that is predictable about Illinois weather is its variability. Records of temperature and precipitation that in some cases date to the mid-19th century suggest that long-term average temperatures in Illinois increased by four to five degrees Fahrenheit from the mid-to late 1800s to the 1930s and then cooled by about half that amount to the present, consistent with global temperature trends. (Figure 2-6) The 1980s departed from this general trend toward cooler and more benign summers; for example, the 1988 growing season drought in Illinois has been equaled in severity in only two other years since the turn of the century. Episodes of extreme cold were far more frequent from about 1930 until the late 1970s and early 1980s. Tornado frequency over the past three decades has varied dramatically but shows no upward or downward trend.

Figure 2-6. Statewide Average Annual Temperatures for Illinois 1840-1992

Source: Air Resources, Illinois State Water Survey, 1994

The possibility that human activity may affect Illinois weather has profound implications. Some research suggests that cities affect weather in areas downwind of them. Cities create "heat islands" that disrupt normal temperature and precipitation patterns. Jet airplane contrails have been linked to recent significant increases in the number of cloudy days in cities. Smoky or hazy days were reported at Illinois' major weather stations only a few tens of days each year prior to the 1930s; since then their frequency has been on the order of 100 days per year or more. (Figure 2-7) The source of this atmospheric turbidity may be industrial smoke or increased dust from more extensive or more frequent plowing of farm fields.

Figure 2-7. Number of Days When Smoke and/or Haze Was Reported at Chicago, St. Louis and Evansville

Source: Air Resources, Illinois State Water Survey, 1994

Global warming. Five common air pollutants are thought to contribute to global warming--carbon dioxide, methane, nitrous oxide, nitrogen oxides, and carbon monoxide. These gases are produced variously by the burning of fossil fuels and agricultural wastes, by the decomposition of organic matter from livestock and in landfills, by releases from underground mines, and by fertilizer use.

By far the most significant of these sources is fossil fuel combustion. Because it is an industrial state, Illinois' share of the global CO2 production (237 million tons per year, or 1% of the world total) exceeds by fivefold its proportion of the world's population.

Emissions of greenhouse gases are sometimes measured in "CO2 equivalents" to adjust for their different heat-trapping potentials. Adjusted emissions of the three major greenhouses gases (methane, CO2, and N2O) from Illinois sources in 1990 were some 260 million tons, down 18% since 1970. (Figure 2-8 ) The decline has several causes, from increased use of nuclear energy to more efficient use of energy overall to recent downturns in the economy; small (and inadvertent) reductions in methane emissions have resulted from more recent bans on the disposal of yard wastes in overburdened landfills. Projections of CO2 from energy use forecast either small decreases in CO2 emissions or modest (0.08%) annual increases through 2000.

Doing More With Less | Rivers and Streams

Return to Table of Contents