Online measurement of aerosol inorganic and organic nitrogen based on thermal evolution and chemiluminescent detection

Abstract

Nitrogenous aerosols, including inorganic nitrogen (IN) and organic nitrogen (ON), are relevant to ecosystem evolution, secondary aerosol formation, and biotoxicity. While analytical method for aerosol IN species is achievable, a direct quantification method of bulk ON is so far unavailable, hindering the quantitative assessment of atmospheric nitrogenous aerosols. In this study, we develop the first online instrument method for simultaneous quantification of aerosol IN and ON. The instrument is based on programmed thermal evolution and chemiluminescent detection of nitrogenous aerosols coupled with multivariate curve resolution analysis. Atmospheric abundances of IN and ON at a suburban site in Hong Kong were quantified using the online technique, which was validated through comparing with IN measured by ion chromatography analysis of offline filters. The average mass concentrations of TN, IN, and ON were 1.84 ± 0.99, 1.59 ± 0.93, and 0.24 ± 0.09 μgN/m3, respectively. ON accounted for 13.0% of aerosol TN during the measurement period. Examination of the online IN and ON measurements during hours of aerosol nitrogen episodes revealed that biomass burning emissions and secondary formation processes could be important sources of aerosol ON. This method breakthrough enables the quantitative assessment of aerosol nitrogen at the diurnal scale, providing an effective tool to study sources and environmental impacts of nitrogenous aerosols.