Studies on the atmospheric fate of propachlor (2-chloro-N-isopropylacetanilide) in the gas-phase

Abstract

The gas-phase degradation of propachlor (2-chloro-N-isopropylacetanilide), a widely used herbicide, was investigated under atmospheric conditions at the large outdoor European simulation chamber (EUPHORE) in Valencia, Spain. The rate coefficient for the reaction of hydroxyl radicals with propachlor was measured using a conventional relative rate technique. A value of the rate coefficient for the reaction of OH radicals with propachlor, kOH(propachlor) = (1.5 ± 0.3) × 10−11 cm3 molecule−1 s−1 was determined at 300 ± 5 K and atmospheric pressure. Rate coefficient data for the reaction of OH radicals with N,N-diisopropylaniline and N-methylacetanilide, which have structural similarities to propachlor, were also obtained using the relative rate method, kOH(N,N-diisopropylaniline) = (4.4 ± 0.5) × 10−11 cm3 molecule−1 s−1 and kOH(N-methylacetanilde) = (2.7 ± 0.2) × 10−11 cm3 molecule−1 s−1, respectively. The rate coefficients for photolysis of propachlor, J(propachlor) < 2.0 × 10−5 s−1, and reaction of ozone with propachlor, kO3(propachlor) < 1.5 × 10−19 cm3 molecule−1 s−1, under atmospheric conditions were also determined. The available kinetic data suggest that the gas-phase tropospheric degradation of propachlor will be mainly controlled by reaction with OH and possibly NO3 radicals, and provide the basis of an estimate for the propachlor tropospheric lifetime of approximately 20 h. The atmospheric implications of the use of this species as a herbicide are discussed.