Study on the mechanisms of the 2〜3 year variation in the increasing trend of oxidant in the urban air

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(1) Collection and analyses of datasets for atmospheric pollutants and meteorological elementsWe obtained the atmospheric pollutants datasets of Aichi prefecture from 1991 to 2001 as well as the meteorological datasets at Nagoya. We identified the period when this variation was well defined (1985-1998). Since temporal variation in the oxidant concentration in Nagoya was closely related with that in ozone (O_3), this 2-3 year variation in oxidant can be regarded as that in O_3 in Nagoya. In addition, the precursors of O_3 such as NO_x and NMHC (total) were also collected and analyzed to find the similar variations in their trends.(2) Analyses of 03 dataset in the free troposphere over Japan and in the marine boundary layer over the western North PacificSurface O_3 concentration is controlled by in-situ photochemical reactions and transport of the O_3 in the overlying free troposphere. In summer, O_3 in Nagoya can be also affected by the transport of O_3 from the North Pacific. Therefore we analyzed the behaviors in the O_3 concentrations in the free troposphere and at the Ogasawara Island between 1994 and 1997.(3) Measurements of C_2~C_<11> NMHCs in NagoyaTo understand the variation in the photochemical processes in O_3 production, it is required to variation in the individual component of NMHCs. We developed the continuous measurement system of each NMHC component (C_2-C_<11>) with GC/FID and air sampling device, and obtained the NMHC data fro C_2-C_<11>. In particular, the ratio of NMHC/NOx increased in spring and summer could be explained by an increase emission of biogenic NMHC (isoprene), and this result will be helpful to investigate the mechanism.We have not yet revealed the mechanisms of 2-3 year variation in oxidant in urban air. Now we are investigating the differences in the processes between the well-defined periods and the not defined periods to reveal the factors controlling this variation.