Regional Differences in Ozone
Region 9: California, Nevada, Arizona, and Hawaii
Local Sources of VOCs
The largest source of VOCs generated by human activity was highway vehicles, at 34 percent, compared with the national rate of 29 percent. Off-highway vehicles generated 24 percent of VOCs regionally, compared with 18 percent nationally. Solvents generated less than the national rate (19% v 27%). Industrial sources generated about the same regionally and nationally (5%). Storage and transport generated much less VOCs regionally compared with the national rate (4% v 7%). Total VOCs emitted in 1999 in Region 9 was 1.51 million tons.
Local Sources of NOx
Highway vehicles generate a much greater percentage of NOx in Region 9, 42 percent versus 33 percent nationally. NOx generated offhighway is greater in Region 9 than nationwide (31% v 22%). By contrast, electric utilities are much less of a source of NOx in the region (8% v 23%.) Industrial fuel combustion is slightly less regionally (10%v12% nationwide). NOx emissions in Region 9 totaled 2.25 million tons in 1999, the fourth highest in the nation. Two-thirds of the NOx in Region 9 is produced in California.
Trends
California has led the way in reducing ozone levels in the nation. This success is reflected in the steep decline in Region 9’s ozone levels from 1982 to 2001, when the monitored levels dropped by 24 percent, the greatest reduction in any region of the nation and over twice the national rate (11%). Furthermore, in the 1990s when 4 of the 10 regions increased emissions, this region was second only to the Northwest, Region 10, in reducing ozone, dropping 13 percent in that decade.
Growth and dependence on the car will continue to challenge the region in achieving clean air. In California, for example, the population grew by 39 percent between 1981 and 2000. That growth was far outstripped by increased driving: the average daily number of vehicle miles traveled grew by 91 percent in that same period.xii
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