Photochemical reaction of CO2 on atmospheric mineral dusts

Airborne mineral dust is a big contributor to atmospheric particulate matter. Complex chemistry of mineral dust surfaces might give rise to the conversion of some important atmospheric trace gases. Herein, for the first time we find that CO2 can be photochemically reduced to CO, which is an ozone precursor in the atmosphere, on mineral dust particles. In this study, we performed CO2 uptake experiments using a quartz reactor and investigated the uptake kinetics of CO2 on TiO2 particles and authentic mineral dust (Arizona Test Dust, illite, montmorillonite, and kaolin) under simulated atmospheric conditions using gas chromatography (GC). The impacts of different relative humidity (RH) values and irradiation intensities on CO2 photoreduction were studied. Moreover, the surface intermediate of the heterogeneous photoreduction of CO2 with mineral dust and its kinetic relevance were investigated using in situ DRIFTS and isotopic C-13 labelling. Furthermore, field observations of increased CO concentrations in a mineral dust storm were interpreted as the results of the direct uptake of CO2 on the mineral dust surface and the following photochemical reaction of CO2 on atmospheric mineral dusts under solar irradiation. In summary, we provide evidence for a pathway in which CO2 interacts with mineral dust and is converted into CO under artificial solar light. Due to the abundance of CO2 and mineral dust in the lower atmosphere, this process could cause some impacts on the atmosphere and climate.