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

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 gamma-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 SO(2 )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 gamma-Al(2)O(3 )under light irradiation, and the added SO2 significantly inhibited this conversion owing to surface acidification. However, the presence of NH(3 )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 gamma-Al2O3, regardless of SO2 or NH(3 )coexistence, indicating a potential origin of PCDD/Fs on the atmospheric particulates from the heterogeneous photochemical CVOC conversion.

Automated summary

The atmospheric photochemical conversion of chlorinated volatile organic compounds (CVOCs) is crucial for aerosol formation and chlorine chemistry. However, the pathways and products of this conversion are not well understood. In this study, the conversion of chlorobenzene (CB) on gamma-Al2O3 mineral particles was used as a model reaction to investigate CVOC atmospheric chemistry. The results showed that CB can be degraded by gamma-Al2O3 under light, with the presence of SO2 inhibiting the conversion and NH3 facilitating it. Additionally, the study found that polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) can be generated from the photochemical CB conversion, indicating a potential source of PCDD/Fs in atmospheric particulates.