UC Irvine

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 several months (Chapter 3). The first stage processes the fresh emissions in the well-mixed boundary layer over terrestrial South Korea. The 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 71% and 46% respectively (Chapter 4). The lower CTM values are attributed to insufficient organic nitrate formation near emission sources on account of simplified chemical mechanisms.