Particulate Matter and Ozone: Remote Sensing and Source Attribution

Particulate matter (PM) and tropospheric ozone are air pollutants that are harmful to human health and have broad implications for climate. Despite their importance, there remain large uncertainties related to their sources, evolution in the atmosphere, and impact downwind. In this thesis, I work to address some of these uncertainties through integrated analysis of ground, aircraft, and satellite observations and using both forward and inverse modeling approaches. A new, high-resolution database of ozone-CO correlations was developed from two separate satellite platforms and was validated against in-situ profiles of the trace gases from commercial aircraft. These correlations were interpreted with a state-of-the-science global chemical transport model (CTM) to infer constraints on ozone sources. The observations supported the major source representation in the model for polluted North American outflow in June-July-August (combustion sources) and for the observed ozone maximum in the South Atlantic during December-January-February (lightning). A major model discrepancy was revealed over the North Pacific in summer and fall that was related to an overestimate of the natural lightning source and an underestimate of East Asian anthropogenic emissions. Land clearing by fire in Equatorial Asia pollutes the air shed of one of the most densely populated regions in the world, but fires set in different areas have very different public health implications depending on the population downwind. Smoke exposure sensitivity to Equatorial Asian fires for several receptor locations was calculated with the adjoint of a global CTM. Peatswamp fires in southern Sumatra were found to be particularly detrimental to public health for all years studied, implying that an effective land management policy protecting the remaining peatswamp forests would be of great air quality benefit. This approach can be used to estimate PM exposure for any future fire emission scenario and can be used to provide guidance for targeted land conservation in Equatorial Asia. We use an ensemble of surface, aircraft, and satellite observations over the Southeast US during the summer-fall of 2013 together with the GEOS-Chem CTM at high resolution to better understand aerosol sources in the region and the relationship between surface PM and aerosol optical depth (AOD). Sulfate and organic aerosol (OA) are the main contributors to surface PM2.5 (mass concentration of PM finer than 2.5 μm aerodynamic diameter) and AOD over the Southeast US, with OA acquiring an increasing role over the past decade as anthropogenic emissions have declined. Biogenic isoprene and monoterpenes are the dominant source of OA, and may contribute to sulfate formation through the production of Criegee intermediates as SO2 oxidants. The vertical profile of aerosol extinction over the Southeast US follows closely that of aerosol mass. The SEAC4RS aircraft data demonstrate that the AODs measured from space are fundamentally consistent with surface PM2.5. This implies that satellites can be used reliably to infer PM2.5 air quality if a good CTM representation of the aerosol vertical distribution is available.Earth and Planetary Science