Estelle Roth

Heterogeneous ozonolysis of folpet and dimethomorph: a kinetic and mechanistic study.

The research study discussed in this paper concerns determination of the kinetic rate constants for heterogeneous degradation of the pesticides folpet and dimethomorph by ozone at room temperature. The study also involves identification of the degradation products of the analyzed compound in the condensed phase by solid-phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS). The heterogeneous O3 reactivity of the identified degradation product of dimethomorph, 4-chlorophenyl 3,4-dimethoxyphenyl methanone (CPMPM), is also evaluated experimentally. The obtained results show that the rate constant values of the analytes are (1.7 ± 0.5) × 10(-19), (2.1 ± 0.8) × 10(-19), (2.6 ± 0.2) × 10(-20), and (2.7 ± 0.2) × 10(-20) cm(3)·molecule(-1)·s(-1) for (Z)-dimethomorph, (E)-dimethomorph, folpet, and CPMPM, respectively. Such values implicate heterogeneous ozone lifetimes that vary from a few days to several months, meaning that, depending on their reactivity with respect to other atmospheric oxidants, these compounds might be relatively persistent and may be transported to regions far from their point of application.

A mechanistic and kinetic study of the heterogeneous degradation of chlorpyrifos and chlorpyrifos oxon under the influence of atmospheric oxidants: ozone and OH-radicals

Chlorpyrifos (CLP) is a widely used pesticide and chlorpyrifos oxon (CLPO) is one of its degradation products. They are both detected in the gas and particulate phase of the atmosphere. The kinetics and mechanism of heterogeneous oxidation of CLP and CLPO by ozone and OH radicals have been studied at room temperature using a photochemical reactor coupled to a GC/MS analytical system. CLPO and trichloropyridinol (TCP) were identified as degradation products in sample residues of both ozonolysis and OH-oxidation experiments of CLP. The yields of these products were measured and the results show that pathways producing TCP and CLPO are both of ∼50% for ozonolysis of CLP, whereas OH oxidation produces ∼50% CLPO and ∼25% TCP. Heterogeneous OH-oxidation rates of CLP and CLPO are greater than those measured for ozonolysis, and CLP is twenty times more reactive than CLPO. The calculated CLP lifetimes suggest that once emitted into the atmosphere, CLP can be degraded quite rapidly (∼2 day) by OH radicals in the heterogeneous phase. Meanwhile, CLPOs tropospheric lifetime in the heterogeneous phase towards OH-radicals is in the order of several weeks.

Kinetics of the heterogeneous photo oxidation of the pesticide bupirimate by OH-radicals and ozone under atmospheric conditions

This article is concerned with the study of the photochemical degradation of bupirimate adsorbed on a quartz surface by atmospheric oxidants, namely ozone and OH radicals. OH oxidation experiments were conducted relative to two reference compounds, terbuthylazine and (4-chlorophenyl)(3,4-dimethoxyphenyl) methanone. Meanwhile, ozone oxidation experiments were performed in the absolute mode and were interpreted by both, the Surface Layer Reaction and the Gas Surface Reaction models of heterogeneous reactions. The obtained results show that the rate constants for the reactions between bupirimate and OH radicals and ozone are (cm(3)molecule(-1)s(-1)): (1.06 ± 0.87) × 10(-12) and (5.4 ± 0.3) × 10(-20), respectively. As a consequence, for the experimental conditions used in this study, the lifetime of bupirimate at quartz like surface/atmosphere interfaces is several months against ozone and a tenth of days against OH-radical.