Satellite constraints on source-specific nitrogen oxide emissions and isoprene chemistry in the southeast united states: evaluations and implications for background ozone
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Nitrogen oxides (NOx = NO + NO2) originating from combustion, lightning and soil, are the main drivers of the tropospheric ozone formation and important precursors of secondary organic aerosols, with consequences for human health, climate and ecosystem. Isoprene, the most important biogenic volatile organic compounds (BVOCs) globally, accounts for about half of the BVOC emissions (~ 500 Tg yr-1). Its rapid oxidation in the presence of NOx is a main driver of atmospheric chemistry. Detailed and accurate estimations of NOx emissions and a better understanding of isoprene chemistry are essential for the development of emission and air pollution control policies. This dissertation extensively investigates the current estimates of source-specific anthropogenic and natural NOx emissions over the United States, explores the nocturnal isoprene and its implications on the transport and fates of nitrogen species and formation of SOA at a rural site, and evaluates the background ozone levels in the Southeast United States by employing regional modeling and various observation analysis. We first conducted a daily retrieval inversion to estimate emissions of eight NOx sources constraint by Ozone Monitoring Instrument (OMI) observations using a source-specific 3-D Regional chEmistry and trAnsport Model (REAM). We found consistency in total NOx emissions with the prior estimations but biases in the source distributions of NOx emissions with underestimation of natural NOx emissions and overestimation of anthropogenic sources in the United States, especially onroad emissions. Then, we evaluated the isoprene chemistry in REAM and analyzed the nocturnal decline of isoprene at Centreville using the 2013 Southern Oxidant and Aerosol Study (SOAS) campaign. More than half of the isoprene is lost by transport processes at night. Ozonolysis dominates nighttime isoprene chemical processes over OH and NO3 oxidation, indicating a minor sink for NOx and resulting in a relatively small amount of aerosol masses at Centreville. We finally applied the linear relationships of O3-CO-HCHO to term and quantitatively estimate clean-background ozone in the Southeast United States. Lower than previous estimates of summertime background ozone has been found and provide further incentives to control anthropogenic emissions in ozone nonattainment areas of the Southeast.