Characterization of organic aerosols from a Chinese Mega-City during winter : 1 predominance of fossil fuel combustion 2 3

6 1 Yale-NUIST Center on Atmospheric Environment, Department of Applied 7 Meteorology, Nanjing University of Information Science and Technology, Nanjing 8 210044, China 9 2 Chubu Institute for Advanced Studies, Chubu University, Kasugai 487-8501, Japan 10 3 Key Laboratory of Meteorological Disaster, Ministry of Education & Collaborative 11 Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing 12 University of Information Science and Technology, Nanjing 210044, China 13 14


Introduction
Particulate matter (PM) comprised a wide variety of chemical components, 55 which are derived from a broad range of sources and processes in the atmosphere 56 (Seinfeld and Pandis, 2006). Organic aerosol (OA) is one of the major constituents of  The large emissions of atmospheric particles from China have a major effect on 88 regional and global climate changes (Huebert et al., 2003). Atmospheric pollution in 89 China is a serious problem due to its rapid industrialization and urbanization. Globally, 90 one-fourth of anthropogenic POA are originated in China (Cooke et al., 1999). Many  (Table S1). Filter aliquots (6.28 cm 2 ) were 131 extracted three times with 5 mL of dichloromethane/methanol mixture (2:1) under ultra-  than 80% for target compounds. The field blank filters (n = 5) were analyzed by the 157 procedures as described above. The target species were not noticed in the blank filters.

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Fascinatingly, NO2 showed high concentration during E1, whereas relative humidity 223 (RH) and ozone (O3) levels were not high ( Figure S1). Our results suggest that NO2 January (1.6 km), which might be due to the haze formation. It is remarkable that the 233 levels of organics were not high during these periods (Figures 3 and S1). These results

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imply that NO2 derived from fossil fuel combustion plays an important role in the 235 formation of OAs in the Nanjing atmosphere.

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The results of OC, EC, and WSOC are mentioned in    followed by C16 and C24 fatty acids, and C29 n-alkane (Table S1).  2003), where n-alkanes were mainly originated from terrestrial higher plant waxes.

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Plant wax derived n-alkanes are estimated as the excess of odd homologues minus 303 adjacent even homologues (Simoneit et al., 1991b(Simoneit et al., , 2004c, which is attributable to 304 vascular plant waxes (Tables 1 and S1). Concentrations ranges of higher plant wax 305 derived n-alkanes were 2.12-48.1 ng m -3 (ave. 15.5 ng m -3 ) in daytime and 0.86-58.9 ng 306 m -3 (17.6 ng m -3 ) in nighttime, both of which are much lower than total n-alkanes, 307 indicating that n-alkanes in Nanjing urban area are derived mainly from fossil fuel 308 combustion.

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A homologous series of C12:0-C32:0 saturated fatty acids, including two  (Table S1 328 and Figure 2). Their molecular distributions are characterized by a strong even-to-odd 329 carbon number predominance with Cmax at C28 or C30 (Figure 4c). We found that the  level in this study is 4-6 times lower than that of a previous study in Nanjing (Table 2) 366 (Wang and Kawamura, 2005). This result implies that biomass-burning emissions have 367 been decreased significantly in the last decade in the Nanjing area during winter. 368 We detected four lignin and resin products, i.e., 4-hydroxybenzoic, vanillic,    The diagnostic ratios of hopanes can differentiate their sources (Table 3). The     (Table S1). Glycerol is a primary product of a metabolic reaction of soil organisms,  (Table S1 and