Abstract
The Chiba Prefectural government issued an alert based on the provisional standard on November 4th, 2013, due to the possibility of the daily average of the PM2.5 mass concentration exceeding 70 μg/m3 at the general ambient air monitoring stations located in Ichihara city, Chiba. This paper presents analytical results to investigate the possible causes of this PM2.5 episode. From the data of air pollutants obtained at the monitoring stations, and the chemical analysis results of the PM2.5 components, a high concentration of NH4NO3 was measured, which was probably due to the influence of oxidative atmospheric conditions assumed from a high concentration of Ox on November 3rd. Also, levoglucosan, that is commonly used as the tracer of biomass burning, WSOC and Char-EC tended to exhibit high concentrations during the corresponding period, which demonstrated the high impact of biomass burning. V and Ni were the elemental components that showed relatively higher concentrations on November 4th, which could be attributed as the effect of oil combustion sources. The prevention of air mass diffusion under the nocturnal inversion layer and high relative humidity led the PM2.5 mass concentration change. Furthermore, the creation of wind convergence, which includes the concentrated PM2.5 mass, and that of advection to the Ichihara district contributed to the PM2.5 episode.
