Dissertation Defense: Calum Wilson

Title: Reactive Greenhouse Gas Chemistry in Urban and Industrial Pollution Plumes from South Korea

Abstract: Recent industrialisation across Asia has produced increased air pollution emissions, altering the chemistry of reactive greenhouse gases (GHGs) in the troposphere. We compute the additional loss of methane (L-CH4) and net production of ozone (P-O3) attributable to urban and industrial emissions from South Korea during the May-June Korea-US Air quality (KORUS-AQ) mission. We build a three-stage hybrid modelling system (HMS) equipped with detailed chemical mechanisms to simulate the full life-cycle of emissions over >120 days (Chapter 3). The first stage processes the fresh emissions in the well-mixed boundary layer over terrestrial South Korea. The 4D model fields of O3, carbon monoxide, and nitrogen oxides are compared with surface observation data, which are interpolated and gridded in Chapter 2 to match the model discretisation. The second stage integrates the chemistry of the transboundary pollution plumes transported offshore, and the final stage disperses the residual pollutants. We find that the KORUS-AQ summertime emissions cause +4.3 Gmol CH4 loss and +31.2 Gmol net O3 production, which are about 0.1% and 0.3% of the respective global budget terms during an equivalent time period. These reactivities are greatly amplified when pollution plumes are dispersed more rapidly. A parallel study using the UCI chemistry-transport model (CTM) reveals a similar integrated O3 enhancement in both models, but with lower total P-O3 and L-CH4 by factors of 2/3 and 1/2 respectively (Chapter 4). The lower CTM values are attributed to insufficient organic nitrate formation in the pollution on account of simplified chemical mechanisms.