Characteristics of atmospheric intermediate volatility organic compounds (IVOCs) in winter and summer under different air pollution levels

Intermediate volatility organic compounds (IVOCs) in outdoor air have been reported in recent years with focus on characterizing IVOCs and their contributions to the formation of secondary organic aerosol (SOA). Little has been studied on the different behaviors of IVOCs in particulate matter (PM) dominated winter pollution weather and ozone (O-3) dominated summer pollution weather. In this study, we collected and analyzed outdoor airborne IVOCs in an urban location in Shanghai during PM dominated pollution events in winter (ten samples) and O-3 dominated pollution events in summer (22 samples). IVOCs were categorized into n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and unspeciated complex mixture (UCM) that includes unspeciated branched alkanes (b-alkanes) and other unidentified IVOCs. In winter samples total IVOCs concentrations were up to 114 mu g/m(3) and UCM IVOCs accounted for 91% +/- 3%, while in summer samples total IVOCs concentrations were only up to 17.2 mu g/m(3) and UCM accounted for 69% +/- 14%. The average concentration of primary IVOCs which are directly from emission sources, was 35.1 +/- 16.1 mu g/m(3) and 4.0 +/- 2.2 mu g/m(3) in winter and summer, respectively. IVOCs were found to have statistically significant positive correlations with PM (PM2.5, PM10) but not with O-3 in both winter and summer samples. Statistically significantly inverse relationships between O-3 and C-12-C-14 n-alkanes and between O-3 and two to three rings PAHs in summer samples were observed, indicating that these relatively more volatile IVOCs might be actively involved in atmospheric photochemical reactions in the atmosphere in summer. Our study revealed different behaviors of IVOCs in winter and summer pollution events in Shanghai; however, more research is needed to better understand the contribution of IVOCs to SOA, and the underlying photochemical reactions of IVOCs during O-3 dominated air pollution events.