Abstract. Molecular composition and abundance of sugars and secondary organic aerosols (SOA) from biogenic sources over the East China Sea were investigated based on gas chromatography–mass spectrometry. Biogenic SOA tracers and sugars exhibit higher levels in the samples affected by continental air masses, demonstrating the terrestrial outflows of organic matter to the East China Sea. Glucose was the dominant sugar species (0.31–209, 18.8 ng m−3), followed by mannitol – a fungal spore tracer. All sugar compounds show generally higher average concentrations in the nighttime than in the daytime. 3-Methyl-1,2,3-butanetricarboxylic acid, one higher generation photooxidation tracer of monoterpene SOA, was found to be the most abundant species among measured biogenic SOA markers, suggesting the input of aged organic aerosols through long-range transport. Fungal-spore-derived organic carbon (OC) was the biggest contributor to total OC (0.03 %–19.8 %, 3.1 %), followed by sesquiterpene-derived secondary OC (SOC), biomass-burning-derived OC, and monoterpene- and isoprene-derived SOC. Larger carbon percentages of biogenic primary OCs and SOCs in total OC presented in the terrestrially influenced aerosols indicate significant contributions of continental aerosols through long-range transport. Positive matrix factorization results illustrate that the secondary nitrate and biogenic SOA, biomass burning, and fungal spores were the main sources of OC in marine aerosols over the East China Sea, again highlighting the importance of the Asian continent as a natural emitter of biogenic organic aerosols together with anthropogenic aerosols over the coastal marine atmosphere.

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.