Organic nitrates in coastal aerosols: Seasonal dynamics, influencing factors, and formation pathways

Abstract

Particulate organic nitrates (pON) are important nitrogen-containing compounds in ambient aerosols that have considerable impacts on air quality, nutrient inputs, and biogeochemical cycle of nitrogen. pON, estimated via the fragmentation ratios of NO₂⁺ and NO ⁺ ions detected by the quadrupole aerosol chemical speciation monitor, was investigated at a coastal site in Shanghai. Among organic aerosols, more-oxidized oxygenated organic aerosol (MO-OOA) was the dominate group throughout the whole year. pON accounted for considerable fractions of OA and the total nitrate with strong seasonal variations. Receptor modeling apportioned the nitrate-related production as the largest source of pON, indicating the significance of secondary formation pathway. Analysis of various influencing factors on pON indicated that aqueous-phase chemistry played the most significant role in the formation of pON in four seasons, while the photochemical pathway was also contributing in summer. Reactions among the nitrogenous precursors and VOCs (mainly alkanes and aromatics) facilitated by aerosol liquid water promoted the formation of pON. Under high humidity conditions, the mass yield of pON was particularly favored compared to its inorganic counterpart. This study signified the importance of accurate quantification of pON in the future research, which has scientific implications on the formation mechanisms of organic aerosols, nitrogen deposition, and biogeochemical cycle of key elements in the coastal environment.