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Regional Differences on Sources for Ozone and Particle Pollution
Region 9: Arizona, California, Hawaii and Nevada
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%). Other fuel combustion 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. This is not surprising, given the highway presence in California. NOx generated off-highway 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% v 12% nationwide). NOx emissions in Region 9 totaled 2.25 million tons in 1999, the fourth highest in the nation. Two-thirds of the NOin Region 9 is produced in California.
Local sources of Particle Pollution (PM 2.5)
Region 9 produced 445,590 short tons of particle pollution in 1999, as reported in its inventory. Lower than the national average of 47 percent, miscellaneous sources of particle pollution from other combustion and agriculture and forestry contributed 40 percent of the particle pollution emissions in this region. Other fuel combustion from activities such as residential wood burning comprised the second largest source of particle pollution at 15 percent. Other major sources of particle pollution include off-highway vehicles (11%), other industrial processes (10%), and waste disposal and recycling (9%).
Trends
California has historically led the way in reducing ozone levels in the nation. Their success is reflected in the steep decline in Region 9’s ozone levels from 1983 to 2002, when the monitored levels dropped by 29 percent, the greatest reduction in any region of the nation and over twice the national rate (14%). Furthermore, between 1991 and 2000 when 3 of the 10 regions increased ozone levels, this region had the third highest rate of decline, reducing ozone levels by 14.4 percent in that decade.
Growth and dependence on the car will continue to challenge the region in reaching 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.17
Comparable trend data are not available for PM2.5 levels.
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