Physicochemical model and kinetics of pesticide constituent evaporation out of multi-ingredient polydisperse aerosols

Contamination of the atmosphere by pesticides is an inevitable consequence of their application for plant protection, and a substantial part of pesticide pollutants exists as airborne particles. Evaporation of particulate matter is often the main pathway that provides the removal of intraparticle pesticide, and, thus, the detoxication of aerosol pollutants occurs. On the other hand, evaporation causes entry of pesticide vapour into the air, and may result in pesticide contamination of the atmosphere. The known models of particle evaporation cannot be directly used for realistic multi‐ingredient pesticide formulations because the data on the physico‐chemical properties of particle constituents are usually absent or unavailable. A simplified model is derived which describes the evaporation of the pesticide out of both an individual particle and a polydisperse aerosol mixture, taking into account the pesticide vapour pressure‐temperature dependence, initial content of pesticide in particles, aerosol sizes, and degree of particle polydispersity, etc. The temperature dependencies of evaporation rates for both the polydisperse aerosol mixtures, and the particles of diameter dm≈2 μm, and, then, of an arbitrary diameter were determined for malathion, parathion‐methyl, phosalone, propiconazole, and ethaphos formultions. The unknown vapour concentration or pressure‐temperature dependencies were evaluated for some pesticides, and the evaporation life‐times of particles were estimated under ambient conditions. ©1998 SCI