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

摘要

Severe air pollution in Asia is often the consequence of acombination of large anthropogenic emissions and adverse synopticconditions. However, limited studies on aerosols have been conducted underhigh emission intensity and under unique geographical and meteorologicalconditions. In this study, an Aerodyne high-resolution time-of-flightaerosol mass spectrometry (HR-ToF-AMS) and other state-of-the-artinstruments were utilized at a suburban site, Ziyang, in the Sichuan Basinduring December 2012 to January 2013. The chemical compositions ofatmospheric submicron aerosols (PM) were determined, the sources oforganic aerosols (OA) were apportioned, and the aerosol secondary formationand aging process were explored as well. Due to high humidity and staticair, PM maintained a relatively stable level during the wholecampaign, with the mean concentration of 59.7 ± 24.1 µg m.OA was the most abundant component (36 %) in PM, characterized by arelatively high oxidation state. Positive matrix factorization analysis wasapplied to the high-resolution organic mass spectral matrix, whichdeconvolved OA mass spectra into four factors: low-volatility (LV-OOA) andsemivolatile oxygenated OA (SV-OOA), biomass burning (BBOA) andhydrocarbon-like OA (HOA). OOA (sum of LV-OOA and SV-OOA) dominated OA ashigh as 71 %. In total, secondary inorganic and organic formationcontributed 76 % of PM. Secondary inorganic species correlated well(Pearson  = 0.415–0.555,   0.01) with relative humidity(RH), suggesting the humid air can favor the formation of secondaryinorganic aerosols. As the photochemical age of OA increased with higheroxidation state, secondary organic aerosol formation contributed more to OA.The slope of OOA against O( = O+NO) steepened withthe increase of RH, implying that, besides the photochemical transformation,the aqueous-phase oxidation was also an important pathway of the OOAformation. Primary emissions, especially biomass burning, resulted in highconcentration and proportion of black carbon (BC) in PM. During theepisode obviously influenced by primary emissions, the contributions of BBOAto OA (26 %) and PM (11 %) were much higher than those(10–17 %, 4–7 %) in the clean and other polluted episodes,highlighting the significant influence of biomass burning.