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h i g h l i g h t sAnthropogenic and biogenic organic compounds have been studied in PM 2.5 in Beijing. Higher levels of organic species were found in the upwind Yufa than PKU. Biogenic secondary organic carbon accounts for 3.1% of OC at PKU and 5.2% at Yufa. a r t i c l e i n f o a b s t r a c tAmbient fine aerosol samples (PM 2.5 ) were collected at an urban site (PKU) in Beijing and its upwind suburban site (Yufa) during the CAREBEIJING-2007 field campaign. Organic molecular compositions of the PM 2.5 samples were studied for seven organic compound classes (sugars, lignin/resin acids, hydroxy-/ polyacids, aromatic acids, biogenic SOA tracers, fatty acids and phthalates) using capillary GC/MS to better understand the characteristics and sources of organic aerosol pollution in Beijing. More than 60 individual organic species were detected in PM 2.5 and were grouped into different compound classes based on their functional groups. Concentrations of total quantified organics at Yufa (469e1410 ng m À3 , average 1050 ng m À3 ) were slightly higher than those at PKU (523e1390 ng m À3 , 900 ng m À3 ). At both sites, phthalates were found as the most abundant compound class. Using a tracer-based method, the contributions of the biogenic secondary organic carbon (SOC) to organic carbon (OC) were 3.1% at PKU and 5.5% at Yufa, among which isoprene-SOC was the dominant contributor. In addition, most of the measured organic compounds were higher at Yufa than those at PKU, indicating a more serious pollution in its upwind region than in urban Beijing.

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Fluorene (FL), dibenzothiophene (DBT) and dibenzofuran (DBF) and their alkylated homologues are important polycyclic aromatic compounds in crude oils and source rock extracts. They share the similar chemical structure and may have genetic relationships. The parent compounds (unsubstituted), methyl-, dimethyl- and ethyl-substituted isomers are identified by comparison with retention indices reported in literatures and correlation with co-injection of internal standards in gas chromatography-mass spectrometry (GC-MS) analysis. Therefore, their relative concentrations can be determined. Based on the large data sets, this paper preliminarily establishes a ternary diagram to interpret the depositional environment/lithology for oils and related source rocks. Five typical depositional environments/lithologies are distinguished on this ternary diagram. Data points from typical marine carbonate, fluvial/deltaic/fresh lacustrine shale and swamp fall into the DBTs, FLs and DBFs end-members, respectively. Oils from marine shale have subequal contents of FLs and DBFs and lie between the zones of fluvial/deltaic/fresh lacustrine shale and swamp, but have a little higher abundance of DBTs. The oils from brackish/saline lacustrine have intermediate contents of DBTs with a wide variety and some degree overlap with that of marine shale. On the basis of the ternary diagrams, two petroleum systems in the cratonic region of the Tarim basis are defined. The majority of discovered oils were derived from the Middle-Upper Ordovician carbonate source rocks. Whereas, some oils from wells TD2, T904, LK1 and TZ62 originated from the Cambrian and Lower Ordovician source rocks. Therefore, the ternary diagram of FLs, DBTs and DBFs is a useful method to interpret depositional environment/lithology for oils and related source rocks and to definite petroleum systems as well.

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