Enhanced formation of reactive nitrogen species by photochemical degradation of nitenpyram pesticides in the presence of halide ions

Neonicotinoid (NN) insecticides have garnered broad attention due to their extensive global usage. In this study, we demonstrate that the photochemical process of nitenpyram (NPM), a typical NN insecticide at the water surface, leads to the formation of gaseous reactive nitrogen species, such as nitrous acid (HONO) and nitrous oxides (NO_x = NO + NO₂). In this paper, we examined the effects of different halide ions (Cl⁻, IO₃⁻ and Br⁻) on the formation of reactive nitrogen from neonicotinoid photochemical reactions. Interestingly, the results of this study showed that different halogen ions had almost no effect on the photochemical degradation rate of NPM, but could significantly affect the generation rate and conversion process of reactive nitrogen species, among which Br⁻ exhibited the most significant effect on conversion of reactive nitrogen species, promoting the formation of HONO and NO₂. Furthermore, in the presence of halide ions, the excited triplet state of NPM can undergo a series of radical transformations which trigger the generation of reactive oxygen species (ROS). In particular, the redox reaction between halide ions and nitrate can also contribute to the formation of HONO and NO₂. Overall, this work unveils a previously overlooked source of atmospheric HONO and NO_x, which can modulate the global nitrogen cycle and affect the atmospheric oxidizing capacity as well as climate.