Regional Differences in Ozone
Region 5: Ohio, Indiana, Michigan, Illinois, Wisconsin and Minnesota
Local Sources of VOCs
The Midwest produced the nation’s second highest VOC emissions—3.5 million tons—in 1999. The largest human activity generating VOCs in the Midwest is the use of solvents, which contributes 34 percent, much higher than the U.S. nationally (27%). Highway vehicles and off-highway vehicles are about the same as the nation as a whole (28% and 19% respectively, compared to 29% and 18% nationwide). Other sources are about the same as nationwide, with industry contributing 5 percent, fuel combustion contributing 4 percent, storage and transport 7 percent and waste disposal and recycling 3 percent.
Local Sources of NOx
The Region produced the nation’s second highest NOx emissions—4.98 million tons— in 1999. Highway vehicles generate the largest amount of NOx in the Midwest, followed by electric utilities and off-highway vehicles. Highway vehicles generate about one-third of the NOx, similar to their percentage nationwide. However, electric utilities generate 29 percent of the region’s NOx, compared with only 23 percent nationwide. Off-highway vehicles produce 19 percent, slightly less than the nation as a whole (22 percent). Contributions from industrial fuel combustion make up a third less in Region 5 than they do in the nation (5% compared to 12%).
Trends
Monitored ozone levels dropped by 9 percent between 1982 and 2001, a trend slightly behind the nation as a whole, which dropped 11 percent during the same period. Furthermore, the long-term decline could have been greater had not the region’s ozone levels risen by 7 percent in the 1990s.
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