Exceedances of air quality standard level of PM2.5 in Japan caused by Siberian wildfires

Abstract

We revisited long-term observations of PM2.5 at ground-based stations in Japan during 2001–2012 to examine possible impacts of Siberian wildfires on regional air quality. Exceedances of Japan’s air quality standard for daily mean concentration (35 μg m−3) were observed several times at Rishiri Island in northern Japan in the spring of 2003 and 2008 when intense wildfires occurred in Siberia. Satellite observations showed that aerosols and CO originating from biomass burning were transported from Siberia toward Japan. The regional chemical transport model also demonstrated that the PM2.5 enhancements during high PM2.5 days (>35 μg m−3) were attributed to Siberian wildfires, suggesting that the contribution from Siberian biomass burning had a critical impact on exceedances of air quality standard level. The monthly (May) and annual mean PM2.5 concentrations in 2003 were about twice and 20% higher, respectively, than those of the long-term average at Rishiri Island, where the influence of Siberian wildfires was the largest in Japan. Except for 2003 and 2008, a high PM2.5 day due to Siberian wildfires was not identified. Although Siberian biomass burning does not affect the air quality standard of PM2.5 for the years without strong fires, it causes exceedance of the air quality standard level when intense fires occur.