Changes in the Distribution of Air Pollution Exposure in the Los Angeles Basin from 1990 to 1999

I. INTRODUCTION Throughout the decade of the 1990s, pollution levels fell substantially throughout the South Coast Air Basin of California (hereafter, the basin), continuing a trend of significant reductions from the mid-1970s to 1990. Table 1 shows the population-weighted average ozone and particulate (P[M.sub.10]) levels, by county, ethnicity, and income for 1990 and 1999. Clearly the entire basin population has benefited from the considerable commitment that the region has made to reducing pollution levels. Table 1 shows that population-weighted ozone levels decreased overall by 24 percent, while particulate levels fell about 22 percent over the 10-year period. However, these overall gains in air quality are not distributed evenly across the basin. As Table 1 also shows, there is significant variation among the counties in the percentage change in average pollution levels, with Orange County experiencing the smallest improvements in both pollutants, while San Bernardino and Riverside Counties had the largest reductions for particulates, and San Bernardino and Los Angeles Counties for ozone. In addition, the table also shows that while these benefits have impacted the various ethnic and income groups of the basin by roughly the same proportions, Hispanic residents enjoyed slightly larger declines in ozone exposures, as did people in the lower income quintile groups, while non-Hispanic whites experienced the largest reduction in particulate exposure. (1) Further, as Table 2 shows, for ozone there is also a large difference in the number of days exceeding the federal standard. Such days have fallen by more than 90 percent at the most polluted locations in Orange, Riverside, and Los Angeles Counties, but by only 70 percent in the areas of San Bernardino County with the most exceedences. At the same time, while overall population grew, for each ethnic group the proportion in each county shifted, as seen in Table 3. Different socioeconomic groups are differentially exposed to ozone and particulate levels, but over time groups also become larger or smaller proportions of the population in subregions. As pollution levels decrease, the question arises of how exposure patterns change, given concurrent demographic shifts within the basin. Significant reductions in emissions of ozone precursors occurred during the decade. The majority of these reductions resulted from an aggressive and successful state program to jointly require cleaner gasoline and cleaner gasoline-powered vehicles, but local controls on solvents and coatings and fuel combustion in stationary sources were also important. Particulate emissions were also reduced, but to a lesser degree, because controls on particulate emissions were adopted later in the interval or are still pending. Reductions in nitrogen oxide emissions also reduce particulates because they reduce the formation of the nitrate component of particulates. An important step in the assessment of these on-going cleanup programs is the assessment of "equity" effects--that is, which socioeconomic groups may have benefited the most (or the least). Over the past decade, a growing body of environmental justice literature has sought to determine whether minorities are more likely to be exposed to a variety of pollutants than are nonminorities. At the same time, regulatory focus on environmental justice has increased at the regional level, with the Environmental Justice Initiatives instituted by the Board of the South Coast Air Quality Management District (SCAQMD) in 1997 (SCAQMD 1997). An earlier study by Brajer and Hall (1992) examined the statistical associations between basin pollution levels (ozone and particulate matter) and a variety of socioeconomic variables (income, ethnicity, age, and education), measured at the city level. In that study, which relied on a powerful pollution exposure model known as REHEX, results indicated that relatively younger, poorer, black or Hispanic residents suffered from poorer air quality than did non-Hispanic whites and Asian residents, or those families in the top 40 percent of the income distribution. …