Heterogeneous reactivity of suspended pirimiphos-methyl particles with ozone.

Pirimiphos-methyl (PMM) is a widely used pesticide that can be released into the atmosphere in the gas phase and the condensed phase. The reaction of suspended PMM particles with ozone is investigated using an online vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and a scanning mobility particle sizer (SMPS). The reactions are conducted in an 180 L reaction chamber. The identification of particulate products detected with VUV-ATOFMS is proposed on the basis of GC-MS analysis of PMM ozonation products in methylene dichloride solution. The heterogeneous reactive rate constant of PMM with azelaic acid as matrix under room temperature (293 +/- 2 K) is (1.97 +/- 0.25) x 10(-17) cm(3) molecules(-1) s(-1). The corresponding lifetime at 100 ppbv of ozone is 5.2 +/- 0.66 h, and the reactive uptake coefficient (gamma) for ozone on PMM particles is (8.5 +/- 1.1) x 10(-4). Additionally, ozonation of PMM vapor is conducted, and the rapid formation of secondary organic aerosol (SOA) is observed in the homogeneous ozonation of gas-phase PMM. The experimental results indicate that ozone is an important atmospheric oxidant for the transformation of PMM in the atmosphere.