Products and kinetics of the heterogeneous reaction of particulate ametryn with NO3 radicals

Abstract

As a renowned s-triazine herbicide, ametryn is worldwide emitted into the atmosphere in both gaseous and particulate phases via spray drifts from treatments and post application emissions, but its chemical degradation in the atmosphere has not been well characterized. In this study, the heterogeneous kinetics of particulate ametryn with NO₃ radicals were investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and an atmospheric gas analysis mass spectrometer were synchronously used to online monitor the decays of particulate ametryn and gas-phase isoprene. The reactive uptake coefficient of NO₃ radicals on ametryn particles was calculated to be 2.9 × 10⁻², according to the measured ametryn loss ratio and the average NO₃ concentration. The effective rate constant for the heterogeneous reaction of particulate ametryn with NO₃ radicals measured under experimental conditions was 8.4 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. In addition, atraton, ametryn sulfoxide and ametryn sulfone were identified as the reaction products by gas-chromatography-mass spectrometry (GC-MS) analysis. The experimental results might shed light on the chemical behavior of atmospheric ametryn at night-time.