Molecular Characteristics of Dissolved Organic Nitrogen in PM_2.5 from Shanghai by FT-ICR Mass Spectrometry

School of Chemical Engineering, University of Science and Technology Liaoning, Anshan 114051, China

^* Corresponding author: 312146@ustl.edu.cn

Abstract

Dissolved organic nitrogen (DON) is a significant contributor to atmospheric organic nitrogen, and it can influence the global nitrogen cycle. However, its composition and sources remain largely unknown. We collected atmospheric fine particulate matter (PM_2.5) in Shanghai and analyzed the molecular compositions of DON using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that 902 dissolved organic nitrogen molecular formulas were identified in PM_2.5 during the summer in Shanghai. The molecular weight of DON ranged from 200 to 600 Da. The DON compounds included CHON₁ and CHON₂, with CHON₂ having a higher O/C ratio. The DON was mainly composed of lipid-like compounds, aliphatic/peptide-like compounds, and carbohydrate-like compounds, with their contributions being 37.3%, 35.9%, and 11.2%, respectively. A total of 95% of the CHON compounds had an O/N≥3, indicating that these compounds carried the -ONO₂ functional group and might be organonitrate compounds. Source apportionment analysis revealed that dissolved organic nitrogen mainly comprised semi-volatile oxidized organic aerosol, low volatile oxidized organic aerosol , and biomass burning organic aerosol.