CARB reported that, in the South Coast Air Basin, average ozone levels on the smoggiest days in June and July were 18 percent lower in 1996 than in 1994 and 1995, after adjusting for differences in weather. (CARB 1996) Similar reductions were noted in Sacramento (11 percent) and in the San Francisco Bay area (10 percent). In Southern California, Stage 1 episodes,13 which are characterized as high ozone concentrations, decreased from 23 in 1994, to 14 in 1995, to 7 in 1996. Beozene levels also decreased by 36 percent in 1995 and an additional 14 percent in 1996. (Hirsch 1996)
13 Stage 1 episodes occur when the maximum daily 1-hour ozone concentration exceeds O.2 parts per million. These levels are considered very unhealthful to hazardous on EPA's Pollutant Standard Index.
Figure 4-12.
KEY: Tier I=new standards for certifying light-duty trucks and vehicles; I/M=inspection and maintenance; RFG=reformulated gasoline; VOC=volatile organic compounds; Phases I and II -see text.
NOTE: Average value used for estimated cost ranges.
SOURCE: U.S. Environmental Protection Agency estimates cited in U.S. General Accounting Office. 1996. Motor Fuels: Issues Related to Reformulated Gasoline, Oxygenated Fuels, and Biofuels, GAO/RCED-96-121. Washington, DC. June. p. 4.
● New Standards for Heavy-Duty Vehicles
Federal regulation of highway vehicles has proven effective in reducing transportation-related emissions. Although emissions from these vehicles have been regulated for many year-light-duty passenger vehicles since 1970 and heavy-duty trucks since 1980-those of many nonroad vehicles have only recently come under scrutiny. Over the past few years, EPA bas been developing emissions standards for nonroad mobile sources such as locomotives, marine vessels, aircraft, and heavy-duty on- and off-highway vehicles. Many of these standards are now finalized and will go into effect around the turn of the century.
