Regional Differences in Ozone
Region 10: Washington, Oregon, Idaho and Alaska

Local Sources of VOCs
In this section of the country, off-highway vehicles dominate the VOC sources from all human activity, contributing nearly two fifths (39%) of the total. By contrast, the nation’s off-highway section is less than half that at 18 percent. Highway vehicles represent only16 percent, about half the national rate of 29 percent. Solvent use also contributes less than half the rate seen nationally, at 13 percent versus 27 percent. Other VOC sources are more similar to the national rates, though industrial sources are half (2% v 4%) of the nationwide rate. Region 10 produced 1.3 million tons of VOCs in 1999.

Local Sources of NOx
Highway vehicles contribute the largest amount of NOx in the region—41 percent of the 892,073 tons generated in 1999. This is the second lowest NOx total of all regions in the nation. The percentage of highway vehicle NOx emissions in Region 10 is higher than it is in the nation as a whole, where it makes up 33 percent of emissions. Off-highway vehicles contribute 31 percent of NOx, higher than the national rate of 22 percent. Electric utilities emit only 5 percent of total NOx in this region, compared with 23 percent nationwide. Miscellaneous sources are an unusually high percentage at 11 percent. Industrial fuel combustion is only 7 percent compared with 12 percent nationally. Industrial emissions that are not fuel combustion account for 3 percent, slightly less than the national rate of 5 percent.

Trends
Ozone monitors show the second greatest drop in ozone readings (21%) in Region 10 among the 10 regions in the nation during the period 1982-2001. During the same period the nation dropped by only 11 percent. During the 1990s, when many areas in the nation had increased ozone levels, the northwest and Alaska saw the greatest drop, by 21 percent.