Regional heterogeneities in the emission of airborne primary sugar compounds and biogenic secondary organic aerosols in the East Asian outflow: Evidence for coal combustion as a source of levoglucosan

Abstract

Abstract. Biomass burning (BB) significantly influences the chemical composition of organic aerosols (OA) in the East Asian outflow. Source apportionment of BB-derived OA is an influential factor for understanding their regional emissions, which is crucial for reducing uncertainties in their projected climate and health-effects. We analyzed here three different classes of atmospheric sugar compounds (anhydrosugars, primary sugars, and sugar alcohols) and two types of biogenic secondary organic aerosol (BSOA) tracers (isoprene- and monoterpene derived SOA products) in a year-long collected total suspended particulate matter (TSP) from an island-based receptor site in South Korea, the Gosan. We investigate seasonal variations in the source-emissions of BB-derived OA using mass concentrations of anhydrosugars and radiocarbon (14C-) isotopic composition of organic carbon (OC) and elemental carbon (EC) in ambient aerosols. Levoglucosan (Lev) is the most abundant anhydrosugar, followed by galactosan (Gal) and/or mannosan (Man). Strong correlations of Lev with Gal and Man as well as their high mass ratios such as Lev/Gal (6.7 ± 2.2) and Lev/Man (15.0 ± 6.7), indicate the contribution from hardwood burning emissions. The seasonal trends revealed that the biomass-burning impact is more pronounced in winter and fall, as evidenced from the high concentrations of anhydrosugars. Likewise, significant correlations were observed among three primary sugars (i.e., glucose, fructose, and sucrose), emphasizing the contribution from airborne pollen. The primary sugars showed higher concentrations in spring/summer than winter/fall. The fungal spore tracer compounds (i.e., arabitol, mannitol, and erythritol) correlated well with trehalose (i.e., a proxy for soil organic carbon), suggesting the origin from airborne fungal spores and soil microbes in the East Asian outflow. These sugar alcohols peaked in summer, followed by spring/fall and winter. Monoterpene-derived SOA tracers were most abundant compared to isoprene-SOA tracers. Both BSOA tracers were dominant in summer, followed by fall, spring, and winter. The source apportionment based on multiple linear regressions, diagnostic mass ratios, and positive matrix factorization analysis altogether revealed that biomass burning (41.9 %) and biogenic SOA (21.1 %) mostly dictates the OA loading in the ambient aerosols from East Asian outflow. We also found significant positive linear relationships of 14C-based nonfossil- and fossil-derived organic carbon fractions with Lev-C along with the comparable regression slopes, suggesting the importance of BB and coal combustion sources in the East Asian outflow.