Formation of reactive nitrogen species promoted by iron ions through the photochemistry of a neonicotinoid insecticide

Nitrous acid (HONO) and nitrogen oxides (NOx=NO+NO2) are important atmospheric pollutants and key intermediates in the global nitrogen cycle, but their sources and formation mechanisms are still poorly understood. Here, we investigated the effect of soluble iron (Fe.sup.3+) on the photochemical behavior of a widely used neonicotinoid (NN) insecticide, nitenpyram (NPM), in the aqueous phase. The yields of HONO and NO.sub.x increased significantly when NPM solution was irradiated in the presence of iron ions (Fe.sup.3+). We propose that the enhanced HONO and NO.sub.2 emissions from the photodegradation of NPM in the presence of iron ions result from the redox cycle between Fe.sup.3+ and Fe.sup.2+ and the generated reactive oxygen species (ROS) by electron transfer between the excited triplet state of NPM and molecular oxygen (O.sub.2). Using the laboratory-derived parameterization based on kinetic data and gridded downward solar radiation, we estimate that the photochemistry of NPM induced by Fe.sup.3+ releases 0.50 and 0.77 Tg N yr.sup.-1 of NO.sub.x and HONO, respectively, into the atmosphere.