Characterization of submicron aerosols influenced by biomass burning at a site in the Sichuan Basin, southwestern China

Severe air pollution caused by large amount of pollutants and adverse synoptic processes appears often in Asia. However, limited studies on aerosols have been conducted under high emission intensity, and unique geographical and 10 meteorological conditions. In this study, an Aerodyne high resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) and other state-of-the-art instruments were utilized at a suburban site, Ziyang, in the Sichuan Basin during December 2012 to January 2013. The chemical compositions of atmospheric submicron aerosols (PM1) were determined, the sources of organic aerosols (OA) were apportioned, and the aerosol secondary formation and aging process were explored as well. Due to high humidity and static air, PM1 was maintained at a relatively stable level during the whole campaign, with the mean concentration 15 of 59.724.1 μg m. OA was the most abundant component (36%) in PM1, characterized by a relatively high oxidation state. Positive matrix factorization analysis was applied to the high resolution organic mass spectral matrix, which deconvolved OA mass spectra into four factors: low volatility (LV-OOA) and semi-volatile oxygenated OA (SV-OOA), biomass burning (BBOA) and hydrocarbon-like OA (HOA). OOA (sum of LV-OOA and SV-OOA) dominated OA as high as 71%. In total, secondary inorganic and organic formation contributed 76% of PM1. Secondary inorganic species correlated well with relative 20 humidity (RH), indicating the humid air can favor the formation of secondary inorganic aerosols. With the increase of photochemical age, OA became more aged with higher oxidation state, and secondary organic aerosol formation contributed more significantly to OA. The slope of OOA against Ox (=O3+NO2) steepened with the increase of RH, implying that besides Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-114, 2016 Manuscript under review for journal Atmos. Chem. Phys. Published: 9 May 2016 c © Author(s) 2016. CC-BY 3.0 License.