Abstract
The diurnal variation of photochemical oxidants (Ox) over central Japan during clear summer days was investigated to clarify how it is intimately associated with the thermally-induced local circulation using hourly Ox, NO2, NOx concentrations and surface meteorological variables for the period of 1992-2009. In the Kanto plain, the peak time of the Ox concentration is gradually delayed from urban areas to inland and mountain areas. A similar situation is also evident in the Nobi plain, suggesting that air pollutants emitted in coastal areas are transported into the southeastern part of the Gifu prefecture by large-scale sea breezes. The high Ox concentrations in the inland area of the Kanto plain, which are observed before the occurrence of the large-scale sea breeze, tend to occur during successive clear summer days, and the high concentration area expands along the primary route of the large-scale sea breeze. These features might result from the nighttime accumulation of NO2 produced by the decomposition of Ox that had already been transported into the inland areas on the preceding day. In the basins of the mountain areas, the Ox concentration increases until around noon, but it remains constant or slightly decreases after that time. The second peak of the Ox concentration appears at 17JST in the Kofu basin and at 19JST in the Iida basin. Since such a decrease in the afternoon is also evident for the diurnal variation in the potential ozone (PO) concentration, it is postulated that the consumption of O3 by NO is not a major factor in the inhibition of the Ox concentration within the basin. Other factors, such as the transport of air pollutants due to the development of local circulations over the basin, should also be considered.
