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. Humic-like substances (HULIS) are a mixture of high-molecular-weight,water-soluble organic compounds that are widely distributed in atmosphericaerosol. Their sources are rarely studied quantitatively. Biomass burning isgenerally accepted as a major primary source of ambient humic-like substances(HULIS) with additional secondary material formed in the atmosphere. However,the present study provides direct evidence that residential coal burning isalso a significant source of ambient HULIS, especially in the heating seasonin northern China based on source measurements, ambient sampling andanalysis, and apportionment with source-oriented CMAQ modeling. Emissiontests show that residential coal combustion produces 5 % to 24 % of theemitted organic carbon (OC) as HULIS carbon (HULISc). Estimation of primaryemissions of HULIS in Beijing indicated that residential biofuel and coalburning contribute about 70 % and 25 % of annual primary HULIS,respectively. Vehicle exhaust, industry, and power plant contributions arenegligible. The average concentration of ambient HULIS in PM 2.5 was7.5  µ g m −3 in urban Beijing and HULIS exhibited obvious seasonal variationswith the highest concentrations in winter. HULISc accounts for 7.2 % ofPM 2.5 mass, 24.5 % of OC, and 59.5 % of water-soluble organic carbon. HULISare found to correlate well with K+ , Cl− , sulfate, andsecondary organic aerosol, suggesting its sources include biomass burning,coal combustion, and secondary aerosol formation. Source apportionment basedon CMAQ modeling shows residential biofuel and coal burning and secondaryformation are important sources of ambient HULIS, contributing 47.1 %,15.1 %, and 38.9 %, respectively.

atmospheric chemistry and physics

Quantifying primary and secondary humic-like substances in urban aerosol based on emission source characterization and a source-oriented air quality model