Abstract
Abstract. Biomass burning (BB) largely modifies the chemical composition of atmospheric aerosols on the globe. We collected aerosol samples (TSP) at Cape Hedo, on subtropical Okinawa Island, from October 2009 to February 2012 to study anhydrosugars as BB tracers. Levoglucosan was detected as the dominant anhydrosugar followed by its isomers, mannosan and galactosan. We found a clear seasonal trend of levoglucosan and mannosan with winter maxima and summer minima. Positive correlation was found between levoglucosan and nss-K+ (r = 0.38, p < 0.001); the latter is another BB tracer. The analyses of air mass trajectories and fire spots demonstrated that the seasonal variations of anhydrosugars are caused by long-range transport of BB emissions from the Asian continent. We found winter maxima of anhydrosugars, which may be associated with open burning and domestic heating and cooking in northern and northeastern China, Mongolia and Russia and with the enhanced westerly winds. The monthly averaged levoglucosan / mannosan ratios were lower (2.1–4.8) in May–June and higher (13.3–13.9) in November–December. The lower values may be associated with softwood burning in northern China, Korea and southwestern Japan whereas the higher values are probably caused by agricultural waste burning of maize straw in the North China Plain. Anhydrosugars comprised 0.22% of water-soluble organic carbon (WSOC) and 0.13% of organic carbon (OC). The highest values to WSOC (0.37%) and OC (0.25%) were found in winter, again indicating an important BB contribution to Okinawa aerosols in winter. This study provides useful information to better understand the effect of East Asian biomass burning on the air quality in the western North Pacific Rim.
Highlights
Biomass burning (BB) is a large source of atmospheric trace gases and aerosols
We found that the dominant anhydrosugar is levoglucosan, which showed a clear seasonal cycle with winter maximum and summer minimum
The degradation of anhydrosugars during atmospheric transport may contribute to the summer low levels, while in winter the observed levels of anhydrosugars are less influenced by degradation
Summary
Biomass burning (BB) is a large source of atmospheric trace gases and aerosols. During the burning, numerous organic and inorganic gases and particles are emitted into the atmosphere (Andreae and Merlet, 2001; Mkoma et al, 2013). Zhu et al.: Effect of biomass burning over the western North Pacific Rim burned (emission factor) (Andreae and Merlet, 2001; Akagi et al, 2011) It is difficult, to obtain either of these two emission indices because extensive measurements are needed with respect to different burning materials and emitted trace components. A recent estimate of 2.33 Tg yr−1 for non-methane volatile organic compounds is obtained from the burning of crop residues in China (Kudo et al, 2014) Emissions from such burning may be submitted to longdistance transport affecting regional air quality and climate (Mochida et al, 2010; Kawamura et al, 2012; Chen et al, 2013).
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