Oxidation and sources of atmospheric NOx during winter in Beijing based on δ18O-δ15N space of particulate nitrate.

Abstract The determination of both stable nitrogen (δ15N–NO3-) and stable oxygen (δ18O–NO3-) isotopic signatures of nitrate in PM2.5 has shown potential for an approach of assessing the sources and oxidation pathways of atmospheric NOx (NO+NO2). In the present study, daily PM2.5 samples were collected in the megacity of Beijing, China during the winter of 2017–2018, and this new approach was used to reveal the origin and oxidation pathways of atmospheric NOx. Specifically, the potential of field δ15N–NO3- signatures for determining the NOx oxidation chemistry was explored. Positive correlations between δ18O–NO3- and δ15N–NO3- were observed (with R2 between 0.51 and 0.66, p