LAUSR

PM2.5 samples were collected simultaneously at three urban sites including Beijing (BJ), Tianjin (TJ), Shijiazhuang (SJZ) and one background site Xinglong (XL) from June 2014 till April 2015. Typical polar organic aerosol tracers including 2-methylglyceric acid, 2-methyltetrols, 3-hydroxyglutaric acid, anhydrous saccharides and phthalic acid were analyzed by gas chromatography-mass spectrometry. Both Isoprene secondary organic aerosol (SOA) tracers and pinene SOA tracers had higher mass concentrations at background site than those at urban sites. But they showed different seasonal variations. The former had the highest mass concentration in summer while the latter had the highest mass concentration in spring. Anhydrous saccharides and phthalic acids at urban sites had higher mass concentrations than those at background site and showed higher mass concentration in autumn and winter, respectively. Corresponding estimated secondary organic carbons (SOCs) showed similar variation trends with tracers. In general, biogenic sources had more influence on background site while urban sites were more affected by anthropogenic sources.