Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 5 11 2005 10.5194/acp-5-3127-2005 http://www.atmos-chem-phys.net/5/3127/2005/ http://www.atmos-chem-phys.net/5/3127/2005/acp-5-3127-2005.html http://www.atmos-chem-phys.net/5/3127/2005/acp-5-3127-2005.pdf 3127 3137 2005-11-22 Characterization and source apportionment of atmospheric organic and elemental carbon during fall and winter of 2003 in Xi'an, China J. J. Cao F. Wu J. C. Chow S. C. Lee Y. Li S. W. Chen Z. S. An K. K. Fung J. G. Watson C. S. Zhu S. X. Liu SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China The Graduate School of Chinese academy of Sciences, Beijing 100049, China Desert Research Institute, Reno, Nevada, USA The Hong Kong Polytechnic University, Hong Kong, China Tongji University, Shanghai 200092, China Atmoslytic, Inc., Calabasas, CA, USA Continuous measurements of atmospheric organic and elemental carbon (OC and EC) were taken during the high-pollution fall and winter seasons at Xi'an, Shaanxi Province, China from September 2003 through February 2004. Battery-powered mini-volume samplers collected PM_2.5 samples daily and PM₁₀ samples every third day. Samples were also obtained from the plumes of residential coal combustion, motor-vehicle exhaust, and biomass burning sources. These samples were analyzed for OC/EC by thermal/optical reflectance (TOR) following the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. OC and EC levels at Xi'an are higher than most urban cities in Asia. Average PM_2.5 OC concentrations in fall and winter were 34.1±18.0 μg m^−3 and 61.9±;33.2 μg m^−3, respectively; while EC concentrations were 11.3±6.9 μg m^−3 and 12.3±5.3 μg m^−3, respectively. Most of the OC and EC were in the PM_2.5 fraction. OC was strongly correlated (R>0.95) with EC in the autumn and moderately correlated (R=0.81) with EC during winter. Carbonaceous aerosol (OC×1.6+EC) accounted for 48.8%±10.1% of the PM_2.5 mass during fall and 45.9±7.5% during winter. The average OC/EC ratio was 3.3 in fall and 5.1 in winter, with individual OC/EC ratios nearly always exceeding 2.0. The higher wintertime OC/EC corresponded to increased residential coal combustion for heating. Total carbon (TC) was associated with source contributions using absolute principal component analysis (APCA) with eight thermally-derived carbon fractions. During fall, 73% of TC was attributed to gasoline engine exhaust, 23% to diesel exhaust, and 4% to biomass burning. During winter, 44% of TC was attributed to gasoline engine exhaust, 44% to coal burning, 9% to biomass burning, and 3% to diesel engine exhaust.