Pollution characteristics of organic and elemental carbon in PM2.5 in Xiamen, China

Xiamen, located on the southeastern coastal line of China, is undergoing rapid urbanization and industrialization, so its air quality has a trend of degradation. However, studies on level, temporal and spatial changes of fine particles (PM2.5) and their carbonaceous fractions are scarce. In this article, abundance, sources, seasonal and spatial variations, distribution of organic carbon (OC) and elemental carbon (EC) in PM2.5, were studied at suburban, urban and industrial sites in Xiamen during four season-representative months in 2009-2010. PM2.5 samples were collected with middle volume sampler and were analyzed for OC and EC with thermal optical transmittance (TOT) method. Results showed that the annual average PM2.5 concentrations were 63.88-74.80 microg/m3 at three sites. While OC and EC concentrations were in the range of 15.81-19.73 microg/m3 and 2.74-3.49 microg/m3, respectively, and clearly presented the summer minima and winter maxima in this study. The carbonaceous aerosol accounted for 42.8%-47.3% of the mass of PM2.5. The annual average of secondary organic carbon (SOC) concentrations in Xiamen were 9.23-11.36 micro/m3, accounting for approximately 56% of OC. Strong correlations between OC and EC was found in spring (R2 = 0.50) and autumn (R2 = 0.73), suggesting that there were similar emission and transport processes for carbonaceous aerosols in these two seasons, while weak correlations were found in summer (R2 = 0.33) and winter (R2 = 0.41). The OC/EC ratios in PM2.5 varied from 2.1 to 8.7 with an annual average of 5.7, indicating that vehicle exhaust, coal smoke and biomass burning were main source apportionments of carbonaceous fractions in Xiamen.