Study on the Concentrations of Photochemical Oxidant and Nitric Oxide at Tajima Monitoring Station in Kawasaki City

Abstract

To understand the recent increase in the concentrations of photochemical oxidant (O_x), we analyzed the concentrations of O_x and its precursor substances measured at Tajima monitoring station (MS) near seaside industrial area in Kawasaki city, from 1985 to 2005. In results, it was found that the annual mean concentrations of O_x were increasing and those of nitric oxide (NO) were decreasing, and in August the relation between monthly mean concentrations of O_x and those of NO was characteristic of trade-off. Also, it was found that daily maximum concentrations of O_x were high in the day of low concentrations of NO at 5:00 before dawn and in the day of high concentrations of non-methane hydrocarbon (NMHC), in August, 1985, 1995 and 2005. These results showed that, at Tajima MS in August, daily maximum concentrations of O_x were under the influence of both NO's effect of restraining O_x concentrations and NMHC's effect of increasing O_x concentrations, and also inferred that the decrease of NO concentrations was one of the possible factors causing the increase of O_x concentrations at Tajima MS in August.