Abstract
Biomass burning for domestic heating and cooking in winter is common in northern and northeastern China. Emissions from biomass burning largely affect the regional air quality. We collected aerosol samples (TSP) at Cape Hedo, subtropical Okinawa Island in October 2009 to February 2012 and analyzed for levoglucosan and its isomers (mannosan and galactosan) as tracers of biomass burning. Higher levels of levoglucosan and mannosan were found in winter whereas lower levels were in summer. Air mass trajectories and fire spots indicated that the seasonal variations of anhydrsosugsars were related to the long-range transport of biomass burning emissions from the Asian Continent. The monthly averaged levoglucosan/mannosan (L/M) ratio increased from 2.1?4.8 in May?June to 13.3?13.9 in November?December, suggesting that the burning substrates are changing depending on seasons and air mass origins. Total anhydrosugars in aerosols were found to contribute on average 0.22% of water-soluble organic carbon (WSOC) and 0.13% of total organic carbon (OC). We also found that contributions of anhydrosugars to WSOC (0.37%) and OC (0.25%) maximized in winter, indicating a strong influence of biomass burnings on regional air quality in cold season. Two event analyses for high abundances of anhydrosugars indicated a long-range transport of open burning and domestic heating emissions from northern and northeastern China, Mongolia, and Russia over the sampling site in Okinawa. These results provide the information to better understand the effect of biomass burning on regional air quality in East Asia.
