Chemical Characteristics and Source Apportionment of Biogenic Primary and Secondary Organic Aerosols in an Alpine Ecosystem of Tibetan Plateau

The knowledge about the chemical characteristics of organic aerosols in alpines were still limited. Fifty samples were collected in an alpine site in Tibetan Plateau during May 2015 and April 2016 to measure the concentrations of sugar and biogenic secondary organic aerosol (BSOA) compounds. The annual mean concentrations of anhydrosugar, primary sugars, and sugar alcohols in Mt. Gongga were 86.6 ± 43.1, 168 ± 40.0 and 204 ± 62.9 ng/m³, respectively. All of the anhydrosugars displayed the highest concentrations in winter, followed by spring, autumn, and the lowest ones in summer, which was contributed by dense biomass burning (BB) in winter. In contrast, nearly all of the primary sugar and sugar alcohol levels peaked in summer, which might be associated with the higher rates of vegetation growth and microbial metabolic activities during the warming season. The levels of BSOA tracers also suffered from markedly seasonal variations. The sesquiterpene SOA displayed the highest level in winter (27.3 ± 16.8 ng/m³), which might be associated with the biomass burning in the surrounding regions. However, most of the species of isoprene and monoterpene SOA tracers suffered from the higher levels in summer, which was contributed by the higher biogenic volatile organic compounds (BVOC) emission and reaction rates. Based on source apportionment result, BB (26%) was the dominant contributor to sugar and BSOA species in Mt. Gongga, followed by airborne pollen (24%), plant release (19%), soil emission (13%), fungal spore (9%), and isoprene oxidation (8%). The result of this study reveals mixed contributions of BB and vegetation emission promote the formation of biogenic organic aerosols in Tibetan Plateau.