Aqueous photochemistry of neonicotinoids unveils a major source of atmospheric reactive nitrogen impacting global climate

Neonicotinoid insecticides (NNs), widely deployed in agriculture, are now recognized as pervasive environmental contaminants. This study reveals that the photochemical degradation of nitenpyram (NPM), a prominent NN, in the aqueous phase generates substantial fluxes of gaseous reactive nitrogen species, including nitrous acid (HONO) and nitrogen oxides (NOx = NO + NO 2 ). Reaction pathways, elucidated through aqueous and gas-phase product analysis and density functional theory (DFT) calculations, demonstrate that HONO, NO 2 , and NO arise directly from the excited triplet state of NPM. Global modeling, parameterized by laboratory-derived kinetics, estimates annual emissions of 71.2 Gg N yr −1 (NOx) and 40.7 Gg N yr −1 (HONO) from NPM photodegradation. These emissions elevate boundary-layer concentrations of HONO, ozone (O 3 ), and OH by 0.54%, 0.11%, and 0.20%, respectively, globally. Our findings uncover a significant, yet overlooked, source of reactive nitrogen that perturbs global nitrogen cycling, amplifies atmospheric oxidative capacity, and influences climate dynamics.