This digital document is a journal article from Atmospheric Environment, published by Elsevier in 2004. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.Description: 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. PM"2"."5 and PM"1"0 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 PM"2"."5 were 9.2 and 4.1@mgm^-^3, while those in PM"1"0 were 12.3 and 5.2@mgm^-^3. Carbonaceous aerosol accounted for 38.0% of the PM"2"."5 and 32.9% of the PM"1"0. The daily average OC, EC, PM"2"."5 and PM"1"0 concentrations in PRDR were higher in winter than in summer. The average OC/EC ratio was 2.5 for PM"2"."5 and PM"1"0, suggesting the presence of secondary organic aerosols. The estimated secondary organic carbons in PM"2"."5 and PM"1"0 were 4.1 and 5.6@mgm^-^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.