Characterization of organic aerosol at a rural site in North China Plain: sources, volatility and organonitrates

Abstract:

The North China Plain (NCP) is the region that experience serious aerosol pollution. A number of studies focus on aerosol pollution in urban regions in NCP, however, research on characterizing aerosols in rural NCP areas is comparatively limited. In this study, we deployed a thermodenuder high-resolution aerosol mass spectrometer (TD-HR-AMS) system at a rural site in NCP region in summer 2013 to characterize the chemical compositions and volatility of submicron aerosols (PM₁). The average PM₁ mass concentration was 51.2 ± 48.0µg m^-3 and organic aerosol (OA) contributed most (35.4%) to PM₁. Positive matrix factorization (PMF) analysis of OA measurements identified four OA factors including hydrocarbon-like OA (HOA, accounting for 18.4%), biomass burning OA (BBOA, 29.4%), less-oxidized oxygenated OA (LO-OOA, 30.8%) and more-oxidized oxygenated OA (MO-OOA, 21.4%). The volatility sequence of the OA factors was HOA > BBOA > LO-OOA > MO-OOA, consistent with their oxygen-to-carbon (O:C) ratios. In addition to the general species that most aerosol studies focus on, we paid attention to organonitrates (ON). The mean concentration of ON was 1.48–3.39 µg m^-3, contributing 8.1–19% of OA based on cross validation of two estimated methods with the HR-ToF-AMS measurement. The correlation analysis showed that ON were more correlated with BBOA and black carbon emitted from biomass burning but poorly correlated with LO-OOA. The diurnal pattern, volatility and size distribution characteristics from this study further suggested that particulate ON formation might be highly relevant to aerosol aging process and largely influenced by biomass burning in rural NCP.