Marginal PM25: Nonlinear Aerosol Mass Response to Sulfate Reductions in the Eastern United States |
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| Authors: | J Jason West Asif S Ansari Spyros N Pandis |
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| Institution: | 1. Departments of Civil and Environmental Engineering and Engineering and Public Policy , Carnegie Mellon University , Pittsburgh , Pennsylvania , USA;2. Department of Chemical Engineering , Carnegie Mellon University , Pittsburgh , Pennsylvania , USA;3. Departments of Chemical Engineering and Engineering and Public Policy , Carnegie Mellon University , Pittsburgh , Pennsylvania , USA |
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| Abstract: | ABSTRACT Reductions in airborne sulfate concentration may cause inorganic fine particulate matter (PM25) to respond nonlinearly, as nitric acid gas may transfer to the aerosol phase. Where this occurs, reductions in sulfur dioxide (SO2) emissions will be much less effective than expected at reducing PM2.5. As a measure of the efficacy of reductions in sulfate concentration on PM , we define marginal PM2.5 as the local change in PM2.5 resulting from a small change in sulfate concentration. Using seasonal-average conditions and assuming thermodynamic equilibrium, we find that the conditions for PM2.5 to respond nonlinearly to sulfate reductions are common in the eastern United States in winter, occurring at half of the sites considered, and uncommon in summer, due primarily to the influence of temperature. Accounting for diurnal and intraseasonal variability, we find that seasonal-average conditions provide a reasonable indicator of the time-averaged PM2.5 response. These results indicate that reductions in sulfate concentration may be up to 50% less effective at reducing the annual-average PM2.5 than if the role of nitric acid is neglected. Further, large reductions in sulfate will also cause an increase in aerosol nitrate in many regions that are the most acidic. |
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