Impact of greenhouse gas CO2 on the heterogeneous reaction of SO2 on alpha-Al2O3

Enhanced oxidative potential and SO2 heterogeneous oxidation on candle soot after photochemical aging: Influencing mechanisms of different irradiation wavelengths

Photochemistry plays a significant role in the atmospheric aging processes of soot. However, the physicochemical properties and changes in environmental and health effects of soot particles from sacrificial sources after photochemical aging remain unclear. The reaction mechanisms of soot under different irradiation wavelengths require further investigation. In this study, candle soot from sacrificial sources was subjected to photochemical aging using ultraviolet (UV) and visible light. The experimental results of oxidation potential (OP) and heterogeneous oxidation of sulfur dioxide (SO2) indicated that both UV and visible light promoted the photooxidation of candle soot, leading to significant increases in oxygen-containing functional groups, environmentally persistent free radicals, and negative charges on soot surfaces. After photochemical aging, candle soot exhibited higher OP values and enhanced SO2 oxidation and sulfate formation. UV light had a stronger photooxidation ability on candle soot than visible light. Mechanistic analysis revealed that the photochemical aging mechanisms driven by reactive oxygen species were different under these two wavelengths. Photosensitive aging induced by organic carbon under UV light was stronger than the photocatalytic oxidation induced by element carbon under visible light. Our research findings provided new insights into the photochemical aging mechanisms and health impacts of soot.

A novel pathway of atmospheric sulfate formation through carbonate radicals

Abstract. Carbon dioxide is considered an inert gas that rarely participates in atmospheric chemical reactions. Nonetheless, we show here that CO2 is involved in some important photo-oxidation reactions in the atmosphere through the formation of carbonate radicals (CO3⚫-). This potentially active intermediate CO3⚫- is routinely overlooked in atmospheric chemistry concerning its effect on sulfate formation. The present work demonstrates that the SO2 uptake coefficient is enhanced by 17 times on mineral dust particles driven by CO3⚫-. Importantly, upon irradiation, mineral dust particles are speculated to produce gas-phase carbonate radical ions when the atmospherically relevant concentration of CO2 presents, thereby potentially promoting external sulfate aerosol formation and oxidative potential in the atmosphere. Employing a suite of laboratory investigations of sulfate formation in the presence of carbonate radicals on the model and authentic dust particles, ground-based field measurements of sulfate and (bi)carbonate ions within ambient PM, together with density functional theory (DFT) calculations for single electron transfer processes in terms of CO3⚫--initiated S(IV) oxidation, a novel role of carbonate radical in atmospheric chemistry is elucidated.