Proposal Summary. We will apply OMI remote sensing information to air quality issues in the eastern US, where NO2 and SO2 are key precursors to O3 and particulate matter (PM) - USEPA designated health and environmental problems. The goal of this research is a deeper understanding of the emissions, atmospheric chemistry, sinks, and surface deposition of NOx, SO2, and related aerosols through a combination of remote and in situ observations with numerical models. This proposal was written in partnership with the proposal ""Next Generation Operational Aura/OMI NO2 and SO2 Products"" (N. Krotkov, PI.) dedicated to maintaining datasets as well as satellite retrieval evaluation and improvement. This alliance of in situ aircraft and sonde measurements by UMD and VU scientists with algorithm improvements by NASA investigators has been highly successful - yielding OMI SO2 measurements over China with temporal and spatial resolution sufficient to characterize air pollution at the episode level. We will expand these efforts to encompass NO2 and SO2 over the eastern US where concentrations are lower. UMD will support improvements in remote sensing through observations of NO2, SO22, and aerosol profiles, as well as with surface reflectance information. Our project will address NASA’s stated intent of ""merging the activities of the atmospheric composition research community and air quality monitoring activities of other agencies within the United States."" One objective is to promote satellite-based observational science by making it useful to the State Agencies that must develop abatement scenarios to comply with the EPA National Ambient Air Quality Standards for O3, NO2, SO2, and PM. This will be accomplished by integrating in situ and remotely-sensed data with numerical models such as CMAQ (a regulatory model) or WRF-Chem to constrain emissions and lifetimes as well as diel and seasonal cycles of NOx and SO2. CMAQ, for example, generates NO2 concentrations that are too high in urban areas and too low in rural areas when compared to surface and OMI measurements over the eastern US. We will investigate a number of possible causes for this discrepancy including missing NOx reservoir species, multiphase chemistry that recycles N2O5, and subgrid scale convection that vents the PBL. The model currently attributes too much ozone formation to local sources relative to regional sources, but will be improved to provide more reliable guidance for pollution control strategies. By working closely with State Agencies, the result of this project will be compliance policy based on the best science extant.