The heterogeneous photo-oxidation of difenoconazole in the atmosphere

A photo-chemical reactor coupled to a UV spectrometer was used to investigate the degradation of difenoconazole deposited on a quartz surface by atmospheric oxidants, namely ozone and OH radicals. OH-oxidation experiments were conducted relative to a reference compound, the terbuthylazine. The rate constant of heterogeneous OH-oxidation of difenoconazole was found to be (7.1 ± 0.8) 10−14 cm3 molecule−1 s−1. Meanwhile, ozone oxidation experiments were performed in the absolute mode and were interpreted by both, the Langmuir–Rideal (LR) and the Langmuir-Hinshelwood (LH) models of heterogeneous reactions. In the case of ozonolysis, a comparison between both models shows that, within the range of ozone concentration employed in this study, both models fit the experimental data correctly. The obtained results show that the atmospheric life-time of difenoconazole with respect to both oxidants is in the order of several months, meaning that this pesticide is relatively persistent, and may be transported over long distances.

► Heterogeneous reactivity.
► LH and LR models.
► Atmospheric life-time.