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To provide information necessary for implementation of newly-revised U.S. standards for airborne particulate matter, we have analyzed available data on PM2.5 in Illinois. A major component of PM2.5 at locations in Illinois is secondary (NH4)2SO4 that forms from the oxidation of SO2 downwind of the emission sources. Another major component of PM2.5 in Illinois is generally unmeasured, but is likely to be mostly organic and elemental carbon. The secondary oxidation of SO2 and gas-phase organic compounds is greatest during summer, and the highest concentrations of PM2.5 also occur then. Analyses of available ambient PM2.5 in Illinois indicates that the annual standard of 15 μg m-3 would likely be exceeded in the Chicago and East St. Louis metropolitan areas. Given the preponderance of secondary material in the PM2.5, such exceedances would probably be widespread. The data indicate that the 24 h standard of 65 μg m-3 would not likely be exceeded at these locations. At rural and suburban locations statewide neither standard is likely to be exceeded, but current annual means in these locations are within about 10% of the proposed standard. Future reductions in SO2 emissions may lower PM2.5 concentrations in Illinois, barring offsetting increases in other PM2.5 components and precursors. |
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