Spatial and seasonal variations of atmospheric organic carbon and elemental carbon in Pearl River Delta Region, China

The concentrations of organic carbon (OC) and elemental carbon (EC) in atmospheric particles were investigated at eight sites in four cities (Hong Kong, Guangzhou, Shenzhen and Zhuhai) of the Pearl River Delta Region (PRDR), China, during winter and summer 2002. The comparison of summer and winter results was made in order to investigate spatial and seasonal variations. PM2.5 and PM10 samples were collected on pre-fired quartz filters with mini-volume samplers and analyzed by the thermal optical reflectance (TOR) method following the Interagency Monitoring of PROtected Visual Environments (IMPROVE) protocol. During summer, the average OC and EC concentrations in PM2.5 were 9.2 and 4.1 μg m–3, while those in PM10 were 12.3 and 5.2 μg m–3. Carbonaceous aerosol accounted for 38.0% of the PM2.5 and 32.9% of the PM10. The daily average OC, EC, PM2.5 and PM10 concentrations in PRDR were higher in winter than in summer. The average OC/EC ratio was 2.5 for PM2.5 and PM10, suggesting the presence of secondary organic aerosols. The estimated secondary organic carbons in PM2.5 and PM10 were 4.1 and 5.6 μg m–3, respectively. The OC and EC were found to be correlated in winter (correlation coefficient r=0.82) and summer (r=0.64), which implied that motor vehicle sources contributed to the ambient carbonaceous particles. The distribution of eight carbon fractions in OC and EC at eight sites was first reported in ambient samples in Asia, which also indicated that motor vehicle exhaust was the dominant contributor to carbonaceous particles.