AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Water Solubility of Primary and Secondary Organic Aerosols in an Urban Atmosphere in Hong Kong
Bin Yu Kuang, Peng Lin, X. H. Hilda Huang, Yee Ka Wong, JIAN ZHEN YU, Hong Kong University of Science and Technology
Abstract Number: 254 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Sources of organic aerosols in an urban atmosphere in Hong Kong were investigated by applying the Positive Matrix Factorization (PMF) analysis to PM2.5 chemical composition data set covering two years. The data set includes PM2.5 major inorganic constituents, elements, organic carbon (OC), elemental carbon (EC), organic tracers, as well as water-soluble organic carbon (WSOC) and humic-like substances. Seven factors were resolved by PMF, consisting of two secondary formation processes factors, three primary combustion emissions factors (vehicle, ship, and biomass burning), and two non-combustion primary emission factors (dust and sea salt). Separation of primary and secondary organic aerosols into water-soluble and water-insoluble fractions was obtained by reconstructing the concentration of WSOC and water-insoluble OC (WISOC) from the PMF-resolved source factors. The two major primary OC sources, vehicular exhaust (1.88±0.83 micro-gram-C/m$^3) and ship emission (0.64±0.59 micro-gram-C/m$^3), were mainly water-insoluble, with WISOC taking up more than 70% of OC. The other major primary OC source, biomass burning (0.91±1.10 micro-gram-C/m$^3), had comparable amounts of WSOC and WISOC. The secondary sulfate formation process (2.93±3.05 micro-gram-C/m$^3) was found to have a considerable fraction (42%) of OC apportioned as water-insoluble while the dominate fraction (92%) of OC in the secondary nitrate formation process factor (1.28±1.27 micro-gram-C/m$^3) was water-insoluble. The apportionment implies that off-line chemical characterization of the full range of secondary OC needs to go beyond water extraction to solvent-extraction based methods. Secondary WISOC had a stronger correlation with the hydrophobic fractions of WSOC (i.e., HULIS) (r = 0.81) than the hydrophilic fraction of WSOC (r = 0.57), and moderate correlations with EC fractions evolved at or before 700ºC during thermal analysis (r: 0.72-0.78) while no correlation with the higher temperature step (EC4) at 775ºC. These correlation data suggest that aging of the primary OC might be the dominate source of secondary WISOC.