Regional Differences in Ozone
Region 6: Texas, Oklahoma, Arkansas, Louisiana, and New Mexico
Local Sources of VOCs
VOCs generated by human activity in this region include highway vehicles (32% compared with 29% nationally); off-highway vehicles (13% compared with 18% nationally); and solvents (20% regionally compared with a national rate of 27%). Region 6 had a higher rate of VOCs from petroleum and related products (10% regionally compared with 2% nationally), and storage and transport (9% regionally, compared with a national rate of 7%). This difference probably reflects the concentration of the petroleum industry in the region. Total VOCs produced in Region 6 were 2.5 million tons in 1999, the third highest.
Local Sources of NOx
Highway vehicles represented the largest source of NOx in this region at 27 percent, lower than national rate of 33 percent. The next highest source of NOx in the region is industrial fuel combustion, which, at 24 percent, is very high compared with the national percentage (12%). Off-highway vehicles produce 23 percent of NOx regionally, compared with 22 percent nationally. Electric utilities represented 18 percent regionally, compared with 23 percent nationally. Petroleum and related NOx, at 2 percent, is twice the national rate (1%), and probably reflects concentration of the petroleum industry in the region. Total NOx produced in Region 6 was 4.2 million tons in 1999 (the third highest region).
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 remained unchanged from 1990-1999.
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