Abstract
Routine monitoring of hourly PM2.5 mass concentrations by local governments started in the 2011 fiscal year in Japan. The levels and temporal variation pattern of PM2.5 mass concentrations were summarized nationwide. Data from a total of 71 monitoring sites from 36 municipalities was investigated. The annual mean concentration ranged from 9.7-22.7 μg m-3, and 39 sites exceeded 15 μg m-3 (Japanese annual average air quality standard value). The daily concentrations, ranging from - 35.1-105.5 μg m-3 tended to exceed 35 μg m-3 (24-hour average air quality standard value) when Asian Dust and/or anthropogenic sulfate aerosols from East Asia were transported to Japan. However, high concentration events sometimes occurred on urban scale, implying the strong influence from domestic sources. Diurnal variation patterns of PM2.5 were multifarious compared to those of NOx, which exhibited a clear bimodal pattern. A day-of-week variation increasing on weekdays and decreasing on weekends was detected, suggesting anthropogenic influence on the PM2.5 levels. The monthly maxima tended to appear in spring or autumn, while the minima generally appeared in September or in December.
