Understanding the Transformation Pathway of Nitrogen-Containing Emerging Contaminants to Reactive Nitrogen Species by Ozonolysis

Nitrogen-containing emerging contaminants (N-EC) are attracting growing attention, and they show a unique transformation pathway that may contribute to atmospheric reactive nitrogen species, such as HONO and NOx. The thermal and photochemical ozonolysis of N-EC was investigated in terms of kinetics, products, mechanism, and environmental implications. O3 uptake was observed on various N-EC under dark conditions, with the average O3 uptake coefficient (γav) in the range of (0.32–1.21) × 10–5. Light generally promoted O3 uptake on N-EC, and the extent of enhancement was correlated to hydroxyl radicals (•OH) and singlet oxygen (1O2) derived from the photoexcited N-EC. However, light was found to suppress HONO production from the ozonolysis of nitenpyram (NPM), a representative N-EC. HONO can be generated from either the O3 attack or the electrophilic addition of •OH on the C═C–NO2 structure by the photochemical ozonolysis of NPM, but HONO production by the •OH attack was less efficient than that from the O3 attack. Our results indicate that the O3 uptake process on N-EC containing C═C–NO2 would contribute to the atmospheric HONO source in the range of 74–740 ppt h–1.