Heterogeneous photochemical conversion of chlorobenzene on γ-Al2O3: A chamber experiment study

Abstract

Atmospheric photochemical conversion of chlorinated volatile organic compounds (CVOCs) is crucial for secondary aerosol formation and tropospheric chlorine chemistry. However, their corresponding conversion pathways and the reaction products are lack of sufficient exploration. Herein, the photochemical conversion of chlorobenzene (CB) on the mineral γ-Al2O3 particulates was chosen as a model reaction to unveil the atmospheric chemistry of CVOCs. Chamber experiments were performed to determine the decay rates of CB with/without SO2 or NH3 under light irradiation. Reaction products were evaluated, along with the in situ diffuse reflectance infrared Fourier transform spectroscopy measurements, to explore the CB conversion pathways under different conditions. We showed that the CB could be greatly degraded by γ-Al2O3 under light irradiation, and the added SO2 significantly inhibited this conversion owing to surface acidification. However, the presence of NH3 was shown to facilitate the CB conversion by immobilizing Cl− as NH4Cl, and recovering surface oxygen vacancies for oxygen activation. In particular, we found that polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) could be generated from the photochemical CB conversion over γ-Al2O3, regardless of SO2 or NH3 coexistence, indicating a potential origin of PCDD/Fs on the atmospheric particulates from the heterogeneous photochemical CVOC conversion.