Environmental Photochemistry in Surface Waters

Abstract

Abstract Photochemistry in surface waters is an important environmental process, inextricably linked to global geochemical cycles, climate, and biological activity. A wide variety of chromophores reside in natural waters and exhibit significant spectral overlap with the available incident solar flux. Potential chromophores can include dissolved organic material, inorganic nitrate and nitrite ions, metal complexes, colloidal minerals, and various small molecules. Photoexcitation of these chromophores leads to the generation of a range of reactive radical and ionic intermediates that then subsequently react with biogenic and anthropogenic material present in the water system. Possible intermediates include superoxide, singlet oxygen, hydroxyl and peroxyl radicals, redox active metal centers, and organic radical cations. In many surface waters, reactive intermediates are photoproduced with sufficient rates to influence, or even dictate, the lifetime and chemical fate of pollutants, the concentration and availability of critical nutrients and substrates for biogenic processes, and the residence time of carbon in the hydrosphere. The chromophoric starting material is itself degraded in the process, which can significantly influence the optical properties of the surface water as well as the photochemical activity. A brief description of the important species and processes that play a role in environmental photochemistry in surface waters is provided, along with some estimates of relative importance.