Experimental studies on the heterogeneous reaction of NO3 radicals with suspended carbaryl particles

Carbaryl, a widely used pesticide, can be released into atmosphere in the gas phase and condensed phase, but its atmospheric fate is not yet well understood. In this study, the reaction between suspended carbaryl particles and NO3 radicals is investigated, and the sequential nitration of carbaryl is observed in real time with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). Four nitro- and/or hydroxy-substituted products are detected, which are different from degradation products of carbaryl in aqueous environments. The apparent reaction rate of particulate carbaryl with NO3 radicals is measured by a relative rate method. The decays of carbaryl and the reference compound isoprene are synchronously monitored online with VUV-ATOFMS and an atmospheric gas analysis mass spectrometer. The apparent reaction rate of condensed-phase carbaryl with NO3 radicals under experimental conditions is 4.4 × 10−13 cm3 molecule−1 s−1, which corresponds to an approximate lifetime of 1.3 h in the atmosphere for the same particle surface area and carbaryl coating as used in the experiments.