Persistence of pesticides in the atmosphere: Heterogeneous degradation by ozone and OH radicals and its impact on long-range transport

Abstract

This study investigates the heterogeneous atmospheric reactivity of nine commonly used pesticides (Boscalid, Cypermethrin, Cyprodinil, Deltamethrin, Folpet, Pendimethalin, Spiroxamine, Tebuconazole, and Trifloxystrobin) toward ozone and OH radicals, aiming to improve predictions of their persistence in the atmosphere. Pesticides were adsorbed onto hydrophobic silica to simulate atmospheric particles and were exposed to oxidants under controlled conditions (55% relative humidity, 25 °C). Degradation rate constants were determined, revealing atmospheric half-lives of pesticides ranging from 6 days (Cyprodinil) to 220 days (Folpet) for ozone, and from 7 days (Cyprodinil) to 54 days (Folpet) for OH radicals. These experimental degradation rates were compared to those estimated by the AOPWIN model for gas-phase OH radical reactions, highlighting significantly slower degradation in the particulate phase, with rate constants up to 132 times lower. This study also compares the gas-particle partitioning of the pesticides using three models: Junge-Pankow, Octanol-Air, and Mackay. This research emphasizes the importance of accounting for particulate-phase reactivity in risk assessments, as it significantly affects pesticide persistence and their potential for long-range atmospheric transport.