Understanding the Effectiveness of Precursor Reductions in Lowering 8-Hr Ozone Concentrations—Part II. The Eastern United States

Abstract

Analyses of ozone (O 3 ) measurements in conjunction with photochemical modeling were used to assess the feasibility of attaining the federal 8-hr O 3 standard in the eastern United States. Various combinations of volatile organic compound (VOC) and oxides of nitrogen (NO x ) emission reductions were effective in lowering modeled peak 1-hr O 3 concentrations. VOC emissions reductions alone had only a modest impact on modeled peak 8-hr O 3 concentrations. Anthropogenic NO x emissions reductions of 46 -86% of 1996 base case values were needed to reach the level of the 8-hr standard in some areas. As NO x emissions are reduced, O 3 production efficiency increases, which accounts for the less than proportional response of calculated 8-hr O 3 levels. Such increases in O 3 production efficiency also were noted in previous modeling work for central California. O 3 production in some urban core areas, such as New York City and Chicago, IL, was found to be VOC-limited. In these areas, moderate NO x emissions reductions may be accompanied by increases in peak 8-hr O 3 levels. The findings help to explain differences in historical trends in 1-and 8-hr O 3 levels and have serious implications for the feasibility of attaining the 8-hr O 3 standard in several areas of the eastern United States. INTRODUCTIONRecent empirical and modeling analyses indicate that attainment of the federal 8-hr 0.08 parts per million by volume (ppmv; 84 parts per billion by volume, ppbv) ozone (O 3 ) standard may be very difficult at many locations because the occurrences of high (Ͼ0.09 ppmv) hourly average concentrations have decreased faster than those of mid-level (0.06 -0.09 ppmv) hourly average concentrations. 1 Moreover, statistically significant downward O 3 trends in the United States over the period 1980 -1995 were clustered in three metropolitan areas, Los Angeles, New York, and Chicago, with less than 15% of rural sites exhibiting significant trends. 2,3 Some locations exhibiting significant downward trends in peak hourly maximum O 3 have not shown trends in the annual fourth-highest 8-hr maximum, 2 and the trend in the composite average fourth-highest 8-hr maximum is less than the trend in the 1-hr maximum. 2,4 These reported trends appear consistent with the U.S. Environmental Protection Agency's (EPA) most recent trends analysis. 5 In previous work, analyses of ambient O 3 data and photochemical modeling were used to examine the technical feasibility of attaining the federal 8-hr O 3 standard in central California. 6,7 Various combinations of volatile organic compound (VOC) and oxides of nitrogen (NO x ) emission reductions have been effective in lowering modeled peak 1-hr O 3 concentrations. VOC emission reductions have had only a modest impact on modeled peak 8-hr O 3 concentrations. NO x emission reductions generally lowered 8-hr O 3 concentrations, but their

Precursor reductions and ground-level ozone in the Continental United States

“…Mechanistic understanding derived from field and modeling studies, complemented by studies of ambient VOC and NO x trends in specific regions, supports the conclusion that the relationship in Figure 3 depicts causal relationships (Sillman et al, 1990;Trainer et al, 1993Trainer et al, , 2000Kleinman, 2000). Modeling studies showed that lowering peak 8-hr O 3 concentrations in multiple subregions of central California and the eastern United States to values in the range of 60-70 ppbv would require NO x emission reductions in the range of 80% to over 90% from 1996-1999 emissions (Reynolds et al, 2003(Reynolds et al, , 2004. In these studies, large (>80% from late 1990s levels) reductions of NO x emissions are required for lowering peak 8-hr O 3 concentrations, in part because the effectiveness of the mass reduction of NO x is partially offset by increasing O 3 production efficiency at lower ambient concentrations of NO x (Reynolds et al, 2004).…”

Technical note: Evaluation of standard ultraviolet absorption ozone monitors in a polluted urban environment

“…For example, a report by the Instituto Nacional de Ecología (INE) in Mexico (McKinley et al, 2003) found that the implementation of several control measures could achieve a 3% reduction in daily maximum ozone concentration at the cost of approximately two billion dollars. Regulatory action is initiated by the U.S. EPA when measured O 3 concentrations in an urban area exceed a certain threshold (see Reynolds et al, 2004, for recent discussion of one-hour and eight-hour averaged daily maxima standards); this is referred to as "non-attainment". Hundreds of U.S. counties are either close to the threshold or already in non-attainment, and it has been suggested that up to half of the non-attainment Published by Copernicus GmbH on behalf of the European Geosciences Union.…”

Weekday/Weekend Differences in Ambient Air Pollutant Concentrations in Atlanta and the Southeastern United States

“…Modeling studies confirm the importance of the increase in O 3 production efficiency as NO x emissions decline. 31 The ratios of O 3 /NO y or O 3 /NO x were also higher on weekends than on Wednesdays at other monitoring sites. Ratios of O 3 /CO were greater on Sundays compared with Wednesdays at the three locations having CO data (Jefferson Street, Yorkville, and DeKalb), and on Saturdays relative to Wednesdays at Jefferson Street and DeKalb.…”