PM,, (particles < 10 y m in aerodynamic diameter) and PM,,, (particles < 2.5 y m in aerodynamic diameter) mass, elements, water-soluble nitrate, sulfate, ammonium, sodium, potassium, and organic and elemental carbon were determined in 24-h aerosol samples collected during this period. Federal and state standards for PM,, were exceeded a t both urban and nonurhan sites. PM,, concentrations were generally highest during winter and were dominated by PM,, during this time. The coarse (PM1, minus PM,.,) aerosol fraction constituted more than half of PM,, mass during the summer and fall.PM,, concentrations of secondary ammonium nitrate were elevated during the winter a t all sites. Conversely, concentrations of coarse particle iron, indicative of geologically related dust, were higher under less humid conditions during the summer and fall. Regionwide meteorological and chemical transformation processes influence the secondary (nitrate and sulfate) components of PM,,. Elevated concentrations of coarse-particle dust, however, appear to originate from local emissions, such as agricultural and transportation-related activities, as well as region-wide emissions.

Analyses of ambient measured ozone data were used in conjunction with the application of photochemical modeling to determine the technical feasibility of attaining the federal 8-hr ozone standard in central California. Various combinations of volatile organic compound (VOC) and oxides of nitrogen (NO x ) emission reductions were effective in lowering modeled peak 1-hr ozone concentrations. However, VOC emissions reductions were found to have only a modest impact on modeled peak 8-hr ozone concentrations. NO x emission reductions generally lowered 8-hr ozone concentrations, but their effectiveness was partially or, in some cases, wholly offset by the increase in the number of NO cycles and, hence, in the ozone produced per NO. As a result, substantial NO x emission reductions-70 to 90%-were required to reduce peak 8-hr ozone concentrations to the level of the standard throughout the modeling domain. These modeling results provide a possible physical explanation for recent analyses that have reported more prominent trends in peak 1-hr ozone levels than in peak 8-hr ozone concentrations or in occurrences of mid-level (60 -90 parts per billion by volume) ozone concentrations. The findings also have serious implications for the feasibility of attaining the 8-hr ozone standard in central California. Further efforts are needed to clarify the applicability of the modeling results to the full set of days with ozone levels exceeding the 8-hr ozone standard, as well as their applicability to other geographical areas. INTRODUCTIONRecent empirical and modeling analyses indicate that attainment of the new federal 8-hr 0.08 parts per million by volume (ppmv; 84 parts per billion by volume, ppbv) ozone 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 ozone 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 ozone have not shown trends in the annual fourthhighest 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 max. 2,4 A physical explanation for these various differential ozone trends has not yet been advanced.Different emission control strategies may be required for attainment of the 8-hr ozone standard than those that have successfully reduced peak hourly ozone concentrations, and very large reductions of anthropogenic emissions might be needed. To determine the technical feasibility of attaining the 8-hr standard, and to identify the best precursor reduction strategies for moving toward attainment, it is necessary to understand the physical and chemical mechanisms underlying the observed ozone trends and to use ...

The desulfurization of cisand irares-2-butene episulfides with n-butyllithium, diiron nonacarbonyl, and triiron dodecacarbonyl to the corresponding butenes was studied. These reactions proceed with complete stereospecificity, the 2-6% crossover in the cases of the iron carbonyls being attributable to subsequent olefin isomerization. The intermediacy of 2-lithio-3-alkylthiobutanes for the n-butyllithium reaction can be excluded. Independent generation of these species demonstrates considerable loss of stereochemistry under the conditions of episulfide desulfurizations. The loss of stereochemistry is a function of the thioether leaving group, the loss being considerably less for thiophenoxide than for ethyl thiolate. A consequence of these studies also demonstrates that metal-halogen exchange between an alkyl halide and an organolithium proceeds with at least 95% retention of configuration.

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

On Sept. 16,1997, the new 8-hour ozone standard replaced the previous 1-hour primary ozone standard. EPA set the new standard at 0.08 parts per million (ppm) and defined it as a concentrationbased form that averages the annual fourth highest daily maximum 8-hour ozone concentrations over three years (1). For control purposes, it is important to understand whether high-level (>0.09 ppm) or instead midlevel (0.06-0.09 ppm) ozone concentrations are mainly responsible for violations. Using information from EPA' s air quality database, we found that, for 1993-95, more than 50% of the areas that would violate the new standard were influenced by midlevel hourly average concentrations. Our analysis shows that as control strategies are implemented, violating sites that experience high daily maximum 8-hour average concentrations will realize faster declines than violating sites that experience daily maximum 8-hour average concentrations above, but near, the 8-hour 0.08-ppm standard. For most sites that violate the new standard, attainment may be difficult, and in some cases, impractical, to achieve.