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Acrylic acid (AA), a short-chain fatty acid found in the ocean, is derived from the microbial cleavage of dimethylsulfoniopropionate in addition to terrestrial input. The aqueous photochemical transformation of AA in natural seawater, artificial seawater, and Milli-Q water was studied under artificial light (using a photochemical reactor) and natural light (by exposure to sunlight). A degradation study on field seawater was conducted inside and outside Jiaozhou Bay, which is located in the north of China. Kinetic studies showed that the degradation and reaction rate of AA in natural seawater were obviously higher than those in the other aqueous media under artificial and natural light, with the degradation characteristics in artificial seawater and Milli-Q water being similar. The degradation and reaction rate of AA in natural seawater significantly increased with decreased concentration. AA in different media exhibited relatively lower reaction rates under natural light than those under artificial light. However, AA at different concentrations had similar degradation and reaction rates under these two irradiation types. Visible light seemed more efficient for the degradation reaction than ultraviolet A and ultraviolet B rays. The concentrations and degradation of AA inside and outside the Jiaozhou Bay showed significantly seasonal variations, and the photochemical and microbial degradation both showed the maximum rates in autumn. The photochemical reaction rates were found to be lower than the microbial degradation rates in four seasons. The photochemical degradation inside the bay was always lower than that outside. The photochemical transformation of AA depended on seawater composition and field conditions. [ABSTRACT FROM AUTHOR]