Spatio-Temporal Variations and Source Apportionment of Carbonaceous Species in PM2.5 Across Multiple Sampling Locations in the Chengdu Plain

Abstract

To understand the characteristics and sources of carbonaceous aerosols, one-year PM2.5 samples were analyzed for their organic carbon (OC) and elemental carbon (EC) content, following the thermal/optical transmission protocol in three cities[Deyang (DY), Chengdu (CD), and Meishan (MS)] in the Chengdu Plain. The observed annual average concentrations (μg·m-3) were in the following order:MS (15.8±9.6 OC and 6.6±5.3 EC) > CD (13.0±7.5 OC and 4.7±3.6 EC) > DY (9.6±6.1 OC and 3.4±2.6 EC). Organic matter (1.6OC) and EC was regarded as the total carbonaceous aerosols (TCA) amount, and the TCA/PM2.5 ratios at the three above-mentioned cities were 36%, 34%, and 30% respectively. The EC-trace method was used to estimate secondary organic carbon (SOC), which accounted for 38%, 46%, and 47% of total OC in MS, CD, and DY. Daily variations of OC and EC concentrations exhibited significant daily variations, with simultaneous peaks on Oct. 12th to 13th, 2013, Dec. 2nd to 7th, 2013, and mid-to-late Jan., 2014. The surging concentrations of K+ during the pollution period implied the contribution of biomass burning to heavy pollution. Six sources were resolved by the positive matrix factorization (PMF) model, whose contributions to the total carbon (TC) were:biomass burning (46%-56%), secondary aerosols (26%-38%), vehicle emission (9%-12%), fugitive dust (3%-4%), coal combustion (2%-3%), and industry emission (1%-2%). Biomass burning activities presented a significant influence on TC throughout the year, especially in autumn and winter.