Atmospheric Environment 38 (2004) 4447–4456 Spatial and seasonal variations of atmospheric organic carbon and elemental carbon in Pearl River Delta Region, China J.J. Cao a,b , S.C. Lee a, *, K.F. Ho a , S.C. Zou c , Kochy Fung d , Y. Li b , John G. Watson e , Judith C. Chow e a Department of Civil and Structural Engineering, Research Center for Environmental Technology and Management, The Hong Kong Polytechnic University, Hung Hum, Kowloon, Hong Kong, China b State Key Laboratory of Loess & Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China c Department of Chemistry, Zhongshan University, Guangzhou, China d AtmAA Inc., 23917 Craftsman Road, Calabasas, CA, USA e Desert Research Institute, Reno, NV, USA Received 16 January 2004; accepted 26 May 2004 Abstract 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 10 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 10 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 10 . The daily average OC, EC, PM 2.5 and PM 10 concentrations in PRDR were higher in winter than in summer. The average OC/EC ratio was 2.5 for PM 2.5 and PM 10 , suggesting the presence of secondary organic aerosols. The estimated secondary organic carbons in PM 2.5 and PM 10 were 4.1 and 5.6 mgm –3 , respectively. The OC and EC were found to be correlated in winter (correlation coefficient r ¼ 0:82) and summer (r ¼ 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. r 2004 Elsevier Ltd. All rights reserved. Keywords: Organic carbon; Elemental carbon; Urban aerosol; Pearl River Delta Region 1. Introduction Atmospheric particulates are one of the main air pollutants in urban areas. Particulate matter (PM) is considered to be a health hazard since it can be absorbed into human lung tissue during breathing. Previous study has demonstrated that urban and industrial air pollution could inhibit precipitation from clouds (Rosenfeld, 2002). Therefore, much research has focused on the chemical composition of atmospheric suspended PM. Carbonaceous particles, usually classified into two categories—organic carbon (OC) and elemental carbon (EC)—are the most important constituents of the fine fraction of PM, especially in highly industrialized and urbanized areas (Nunes and Pio, 1993). OC represents a large variety of organic compounds that can be classified ARTICLE IN PRESS AE International – Asia *Corresponding author. Tel.: +86-852-27666011; fax: +86- 852-23346389. E-mail address: ceslee@polyu.edu.hk (S.C. Lee). 1352-2310/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2004.05.016