Studies on strategic control of photochemical oxidants in mega-cities

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We have developed instruments for precise measurements of ozone precursors (NOx,HNO_3,PAN,VOCs, and CO), OH and HO_2 radicals, and actinic flux. Measurement campaigns using these instruments were conducted in different seasons in 2003-2005. Especially, in July-August 2004, intensive measurements were made at two sites ; one in Tokyo and the other in Kisai-city in Saitama. At the same time, aerosol chemical composition at each size range was measured using an Aerodyne Aerosol Mass Spectrometer. Air mass which left Tokyo reaches Saitama in the afternoon, providing ideal conditions for investigationg chemical processes during transport. In mid-August, sea-land breeze developed under the influence of stable high pressure system. Under these conditions, O_3 reached high levels in northern Tokyo around 1300 LT. This O_3 levels further increased while the air mass was transported to Saitama by sea breeze. During the transport, NOx oxidation and O_3 formation occurred simultaneously. Organic aerosol was observed to be formed efficiently under high O_3 conditions. 3D-CTM has been developed taking into account the chemical and transport processes. This model well reproduces O_3 and precursors in Kanto area. By this model, it is indicated that O_3 was produced within a few hours near noon.