Source identification and characterization of organic nitrogen in atmospheric aerosols at a suburban site in China

Despite the fact that atmospheric particulate organic nitrogen (ON) can significantly affect human health, ecosystems and the earth's climate system, qualitative and quantitative chemical characterization of ON remains limited due to its chemical complexity. In this study, the Aerodyne soot particle - high-resolution time-of-flight aerosol mass spectrometer (SP-AMS) was deployed for ambient measurements in Nanjing, China. Positive matrix factorization (PMF) was applied to the ON data to quantify the sources of ON in submicron aerosols. The averaged ON concentration was 1.24 μg m^-3, while the averaged total nitrogen (TN) in the aerosol was 20.26 μg m^-3. From the PMF ON analysis, a 5-factor solution was selected as the most representative and interpretable solution for the investigated dataset, including oxygenated OA (OOA_ON), amine-related OA_ON (AMOA_ON), hydrocarbon-like OA (HOA_ON), industry OA (IOA_ON), and local primary OA (POA_ON) factors. The quantified ON ions were separated into families, including C_xHN, C_xH_yNO, C₃H_<6N, C_xH_2x+2N, C_xH_2xN and Others, consistent with their contribution to each factor. The C_xH_yNO family mainly contributed to the OOA_ON factor and suggested the presence of amides or amino acids. The C_xH_2x+2N family likely mostly originated from amines only contributing to the AMOA_ON and HOA_ON factors. The IOA_ON and POA_ON factors were resolved due to significant tracers in the mass spectra. Further, compared with regular organic PMF analysis, PMF ON analysis gave more insights due to improved source separation and interpretability of the OA components, which could be a role model for further atmospheric ON research.