Heterogeneous atmospheric degradation of pesticides by ozone: Influence of relative humidity and particle type

In the atmosphere pesticides can be adsorbed on the surface of particles, depending on their physico-chemical properties. They can react with atmospheric oxidants such as ozone but parameters influencing the degradation kinetics are not clear enough. In this study the heterogeneous ozonolysis of eight commonly used pesticides (i.e., difenoconazole, tetraconazole, cyprodinil, fipronil, oxadiazon, pendimethalin, deltamethrin, and permethrin) adsorbed on hydrophobic and hydrophilic silicas, and Arizona dust at relative humidity ranging from 0% to 80% was investigated. Under experimental conditions, only cyprodinil, deltamethrin, permethrin and pendimethalin were degraded by ozone. Second-order kinetic constants calculated for the pesticides degraded by ozone ranged from (4.7 ± 0.4) × 10−20 cm3 molecule−1 s−1 (pendimethalin, hydrophobic silica, 55% RH) to (2.3 ± 0.4) × 10−17 cm3 molecule−1 s−1 (cyprodinil, Arizona dust, 0% RH). Results obtained can contribute to a better understanding of the atmospheric fate of pesticides in the particulate phase and show the importance of taking humidity and particle type into account for the determination of pesticides atmospheric half-lives. [Display omitted] •Investigation of atmospheric ozonolysis of pesticides in the particle phase•Pesticides of the same chemical family have the same reactivity toward ozone.•Hydrophobicity of the particle surface influences the ozonolysis of pesticides.•Heterogeneous ozonolysis is slower when relative humidity increases.