Photocatalysis and photosorption in the Earth's atmosphere

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The troposphere of Earth is abundant in particles of solid and liquid aerosols which have a large specific surface area and can be activated by visible light and mild ultraviolet (UV) solar radiation with wavelengths λ > 300 nm for promoting different photocatalytic and photoadsorption processes. This paper discusses possible heterogeneous photocatalytic and photosorption phenomena on the surface of solid tropospheric aerosols. These phenomena can proceed in nature at ambient conditions and can make an important contribution to the global chemistry of the Earth's atmosphere. For example, the particles of semiconductor metal oxides like TiO2, ZnO, and Fe2O3 are able to photocatalyze oxidation of organic compounds from the atmosphere by air oxygen and even mineralize them. For insulator metal oxides like SiO2, Al2O3, MgO, and CaO, which are the main components of tropospheric solid aerosols, a substantial depletion of many halogen-containing organic compounds (freons) is possible via their destructive photoadsorption. All mentioned processes appear to be driven by mild solar UV radiation and can proceed in the troposphere, in contrast to direct photochemistry which can take place only in the upper layers of the atmosphere.

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