Heterogeneous reactions of ozone with commonly used pesticides adsorbed on silica particles

Abstract

There is an increasing concern about the pesticides spread in the atmosphere. They can be found in the gas-phase but because of their physico-chemical properties they mostly remain adsorbed on the surface of the atmospheric particles. The kinetic data of the adsorbed pesticides towards atmospheric oxidants such as ozone and hydroxyl radicals are very scarce.Here we present the kinetic data set for the heterogeneous reactions of gas-phase ozone and eight commonly used pesticides adsorbed on silica particles. The obtained rate constants are described by both kinetic patterns, i.e., Langmuir–Rideal (L–R) and Langmuir–Hinshelwood (L–H) mechanisms. Concerning the L–R mechanism the rate constants range between 3.4 · 10−19 cm3 molecules−1 s−1 and 8.8 · 10−19 cm3 molecules−1 s−1. With respect to the L–H mechanism, the values of air–silica partitioning coefficient (K(O3)) vary between 21 · 10−16 cm3 molecules−1 and 358 · 10−16 cm3 molecules−1. The maximum rate constants range between 0.4 · 10−4 and 1.7 · 10−4 s−1. The estimated lifetimes of the selected pesticides according to both L–R and L–H mechanism span from 8 to >33 days, demonstrating that these species are very persistent with respect to ozone reactivity in the atmosphere.The results obtained in this study can contribute to better describe the atmospheric fate of pesticides in the particulate phase.