Heterogeneous ozonation of suspended malathion and chlorpyrifos particles

Abstract

a b s t r a c tThe heterogeneous ozonation of suspended malathion and chlorpyrifos particles are studied in real-time with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The pesticide particles with the diameter of hundreds of nanometers are generated by the homogeneous nucleation method using azelaic acid as nucleus. The reactions are carried out in an aerosol reaction chamber under ambient pressure (1 atm) and room temperature (298 K), respectively. The time-of-flight mass spectra of the solid-state ozonation products of malathion and chlorpyrifos are obtained. The assignments of the mass spectra reveal that the major ozonation products of malathion particles are s-(1,2-diethoxycarbonyl)ethyl-O,O-dimethylphosphorothioate (malaoxon), 2-mercapto-succinic acid diethylester, 1,2-dicarbethoxyethyl-dimethoxyphosphinyldisulfide and bis(1,2-bis-ethoxycarbonylethyl)disulfide. The experimental results reveal that water vapor can enhance the formation of malaoxon, 2-mercapto-succinic acid diethylester and bis(1,2-bis-ethoxycarbonyl-ethyl)disulfide. In the case of chlorpyrifos, the sole ozonation product observed is 3,5,6-trichloro-2-pyridyl-diethylphosphate (chlorpyrifos oxon). The pathways of heterogeneous ozonation of malathion and chlorpyrifos particles are proposed. The atmospheric lifetimes of malathion and chlorpyrifos particles towards ozone reaction are estimated based on the time-dependent mass spectrometric signals obtained.

Heterogeneous reaction of particulate chlorpyrifos with NO 3 radicals: Products, pathways, and kinetics

“…The PIII and PIV are also observed in the reaction between chlorpyrifos-methyl with OH radicals [38]. The proposed formation mechanism of the disulfide compound is in accordance with the previous reports on the phosphinyl disulfides formed from thiols [33,37,40]. The similar disulfide compounds have also been observed in the heterogeneous reaction of suspended malathion particles with NO 3 radicals and ozone in previous studies [33,41].…”

“…The proposed formation mechanism of the disulfide compound is in accordance with the previous reports on the phosphinyl disulfides formed from thiols [33,37,40]. The similar disulfide compounds have also been observed in the heterogeneous reaction of suspended malathion particles with NO 3 radicals and ozone in previous studies [33,41]. Some differences are found between the proposed pathways in this study and those of chlorpyrifos in aqueous solution by ultrasonic irradiation and in a cranberry bog by soil microorganism [10,19].…”

“…One reaction pathway is the transformation of the P S double bond into the P O double bond, which is similar to the heterogeneous reaction mechanism of many organothiophosphorus pesticides with NO 3 radicals [29,33,41]. Hydrolysis plays a vital part in the heterogeneous reaction of chlorpyrifos particles with NO 3 radicals.…”

“…The acquisition time for each mass spectrum was 10 s and each mass spectrum was normalized to its most intense mass peak. The mass peaks at m/z 349, 351, and 353 in Figure 2A are assigned to the molecular ions of chlorpyrifos with isotopic combinations of 35 [33], respectively. These peak intensities are consistent with the natural isotope abundances of the chlorine atom.…”

Products and kinetics of the heterogeneous reaction of particulate ametryn with NO3radicals

“…4 In the previous studies, the heterogeneous reaction rates of pesticides with O 3 were reported to be in the order of $10 À18 cm 3 molecule À1 s À1 . 42,43 Compared to the results obtained in this study, the effective rate constant of ametryn with NO 3 radicals was $5 orders of magnitude faster than those of particulate pesticides with O 3 . Compared with NO 3 radicals, the effect of OH radicals on the degradation of atmospheric particulate organic compounds may not be remarkable due to its lower concentration in the atmosphere.…”