GAW Report No. 205 - IGAC Project

CHAPTER 7 – OVERVIEW OF INTERNATIONAL COLLABORATIVE RESEARCH ACTIVITIES7.8 IMPACT1. O 3 and aerosol studies in the Tokyo Metropolitan Area (TMA)Large amounts of reactive gases and aerosol are emitted from urban areas. Megacities,including the Tokyo Metropolitan Area (TMA), are very large, concentrated sources of thesespecies, which affect O 3 and aerosol levels on local, regional, and global scales [Molina and Molina,2004; Ramanathan et al., 2007]. The uncertainties in emission estimates of these air pollutants aregenerally large for Asia [Streets et al., 2006; Ohara et al., 2007] or do not assess the TMA [Kannariet al., 2007].The increased levels of pollutants have a large impact on regional air quality, nutrientdeposition patterns, and climate. In order to assess the impacts of anthropogenic species emittedfrom these megacities on surrounding areas, we need to understand quantitatively the keyprocesses involved in the oxidation of primary species and the fate of the oxidized species near thesource regions (Figure 11). In addition, clusters of megacities lead to accumulation of O 3 andaerosol through large-scale mixing. Reactive species with elevated concentrations in urbanoutflows can also interact with species emitted from natural sources surrounding the megacities. Itshould be noted here that O 3 and aerosol are coupled due to similar sources, photochemicalinteractions (e.g., UV changes by aerosol), and transport.Figure 11 - Schematic diagram of key processes of O3, aerosols, and their precursor gases near megacity regions2. Integrated Measurement Programme for Aerosol and oxidant Chemistry in Tokyo(IMPACT)Studies on characterizing primary emission and secondary formation of aerosols in theTokyo Metropolitan Area (TMA) have to date been very limited. Further observational studies ofaerosols, especially organic aerosol, near source areas are needed in order to improve theunderstanding of the amounts and chemical composition of aerosols emitted from these largesource areas. As a result, the Integrated Measurement Programme for Aerosol and oxidantChemistry in Tokyo (IMPACT) campaign was conducted. The specific goal of IMPACT was toimprove the understanding of atmospheric chemistry in the TMA [Kondo et al., 2010]. IMPACT wasconducted within the framework of the International Global Atmospheric Chemistry Project (IGAC),Mega-Cities: Asia. The major objectives of IMPACT were to:• Characterize the temporal and spatial changes of aerosols, oxidants, and their precursors,primarily through surface measurements near and downwind of urban centres• Characterize the composition, mixing state, and physical properties of aerosols in urban air• Evaluate emission inventories of trace gases (e.g., NO X , SO 2 , NH 3 , and VOCs) throughcomparisons of ratios of concentrations of trace species observed in urban air267