Japan Geoscience Union

We examined the contribution from Siberian forest fires to PM2.5 pollution in Japan using a regional chemical transport model. In May 2003, several events resulting in PM2.5 concentrations exceeding Japan's air quality standard for daily mean value (35 μg/m³) were observed at Rishiri in northern Japan. The model generally well reproduced the temporal variations of PM2.5 including the elevated events. The simulations demonstrated that the PM2.5 enhancements during the events were mostly attributed to biomass burning in Siberia, suggesting that the contribution from Siberian forest fires had a critical impact on the high PM2.5 days (>35 μg/m³). The contributions from Siberian biomass burning to the monthly mean PM2.5 concentrations were estimated to be 64% at Rishiri and 45% at both Nonodake and Oki located in eastern and western Japan, respectively, suggesting that Siberian forest fires had a large impact on air quality for the whole of Japan. Especially at Rishiri, the observed PM2.5 concentrations and aerosol optical depth (AOD) from MODIS in May 2003 were much larger than those of the 10-year average in May from 2001 to 2010. The trend in horizontal distribution for May 2003 was opposite to the long-term average; PM2.5 and AOD in May 2003 were the highest in northern Japan.