Characteristics and sources of the fine carbonaceous aerosols in Haikou, China

Abstract

Ambient PM2.5 samples were collected from January to September 2015 in Haikou. The carbonaceous fractions included OC, EC, OC1, OC2, OC3, OC4, EC1, EC2, EC3, Char-EC (EC1 minus POC) and Soot-EC (EC2 plus EC3) were analysed in this study. The results indicate that the mean concentrations of OC and EC are 5.6 and 2.5μg/m3 during the sampling period, respectively; and the concentrations of most of carbonaceous fractions are the highest in winter and the lowest in spring. The seasonal variations of Soot-EC and Char-EC concentrations show distinct differences. The concentrations of Char-EC are higher in winter and lower in spring; while those of Soot-EC are lower in winter and higher in summer. Compared to Char-EC, the concentrations of Soot-EC show smaller seasonal-variation in Haikou. The Char-EC has the higher correlations with OC and EC (r=0.91 and 0.95, P<0.01), while the correlation between the Soot-EC and either OC or EC is absent (r=0.15 and 0.11, P>0.05). The average ratios of Char-EC/Soot-EC are in the order of winter (15.9)>autumn (4.9)>summer (4.0)>spring (3.6), with an average value of 7.1. According to error estimation (EE) diagnostics analysis, four factors are revealed in Positive Matrix Factorization (PMF) analysis during each season. The combined gasoline/diesel vehicle exhaust, coal combustion, biomass burning and specific diesel vehicle exhaust are identified as the major sources of carbonaceous aerosols, and their contributions during the whole year are up to 29.3%, 27.4%, 17.9% and 15.9%, respectively. The transport trajectories of the air masses illustrate distinct differences during different seasons, and the transport trajectories are mainly derived from the mainland China (i.e. Jiangxi, Fujian and Guangdong provinces) in winter, likely caused by higher contribution of coal combustion.