Inhibition of Imidacloprid Photolysis by Particulate Matter: Experimental and Computational Evidence.

Neonicotinoid insecticides have been consistently detected in atmospheric particulate matter (PM), highlighting the possible critical role of PM in shaping their environmental persistence and ecological impact. This study investigates the influence of PM on the photolysis of imidacloprid (IMI), a representative neonicotinoid, using computational simulations and laboratory experiments. Results reveal that the adsorption of IMI onto soot particles significantly suppresses its photolysis, reducing its photolysis rate by ∼39-fold and increasing its atmospheric half-life from 7.1 to 279.5 h under simulated conditions. Computational modeling attributes this decrease in the IMI photolysis rate to IMI-soot van der Waals interactions, energy transfer from IMI to soot, and particle shading. Field measurements reveal that IMI undergoes considerable degradation during the daytime, and direct photolysis appears to be a minor loss pathway under the examined ambient conditions. Our findings highlight the important role of PM in altering the atmospheric photolysis of IMI and provide a quantitative assessment of the contribution of IMI photolysis to its outdoor loss, offering a valuable reference for future investigations on its environmental fate.