Future Year Ozone Source Attribution Modeling Studies for the Eastern and Western United States

摘要

The source attribution results from this study provide useful information on the important source categories and provide some initial guidance on future emission reduction strategies. However, since complete reductions of emissions from a given category are not feasible, it is useful to conduct partial reduction studies to calculate sensitivity coefficients, in order to refine these strategies. This study has shown that the various approaches used to conduct source attribution analysis yield similar results for most of the major contributors, but there are also some large differences. Some of the differences can be traced to model differences, while other differences are related to the limitations of the zero-out approach. One of the important findings from this study was that both the CMAQ and CAMx zero-out approaches tended to apportion a larger contribution to the "natural" category than the CAMx probing tools (OSAT) approach. Source-apportionment approaches like OSAT and source-sensitivity approaches like zero-out have strengths and weaknesses. The OSAT approach is suitable for looking at source contributions, while the zero-out approach is suitable for addressing questions of response to removing all emissions from a source. The zero-out approach includes the effects of non-linearities in the system because the sum of the sensitivities of all sources is not necessarily equal to the sum of their contributions in a non-perturbed environment. This may be viewed as a weakness when addressing questions of source contribution. On the other hand, zero-out may have strength in addressing questions of response to emission changes. Finally, general conclusions can be made regarding the overall and source apportionment results for the maximum and DVF 8-hour ozone concentrations. Regarding overall ozone levels, in 2018, all locations will meet a 75 ppb design value except Los Angeles and San Bernardino; while in 2030, only San Bernardino will not meet a 75 ppb design value. The source contributions in 2018 and 2030, in east and west US 8-hr ozone decrease for on-road mobile and natural; stay same for other area and boundary, and increase for point sources. Off-road mobile decreases in east, and stays the same in the west. Heavy duty diesel and light duty gas contributions decrease between 2018 and 2030, except in Los Angeles and San Bernardino, where heavy duty diesel contributions increase slightly.