Air Pollution

This report provides information on the recently enacted Border Smog Reduction Act of 1998. GAO is required to study the potential impact of the act, which now applies only to the San Diego metropolitan area and amends the Clean Air Act to prohibit certain foreign-registered, noncommercial vehicles from entering the area more than twice a month. GAO focuses on measured ozone levels and the impact of the North American Free Trade Agreement on ozone in the San Diego area.

GAO noted that: (1) the California Air Resources Board, a state agency that regulates air quality, estimated that the Border Smog Reduction Act would reduce ozone-causing chemicals in San Diego County by less than 0.5 percent annually; (2) this calculation was based on an estimated number of foreign-registered vehicles that would be subject to the act's provisions; (3) the act's impact is difficult to estimate because data are not available on the number and condition of foreign-registered vehicles entering the United States and a variety of factors influence measured ozone levels; (4) the trend in commercial truck crossings into the United States from Mexico was generally upward both before and after NAFTA was implemented in January 1994; (5) at the same time, the trend in measured ozone levels in the San Diego area was generally downward; (6) several factors contributed to the decrease in ozone levels, including efforts by San Diego County and California state officials to tighten the standards for passenger vehicle emissions and to encourage the use of cleaner formulations of gasoline; and (7) because a number of factors affect measured ozone levels, it is difficult to isolate the impact of a single factor, such as commercial truck traffic.