The photoconversion of 4-chlorophenol (4-CP) in a simulated sunlight-Fenton system was investigated in ice and aqueous solution. It was found that the hydroxyl radical ((OH)-O-center dot) had an important effect on the photoconversion of 4-CP in both phases, but the effects of Cl-, SO42-, NO3-, and HCO3- were different. In aqueous solution, the photoconversion efficiency of 4-CP was proportional to the (OH)-O-center dot concentration, and hence, Cl- and HCO3- as (OH)-O-center dot scavengers prohibited the photoconversion: SO42- had little effect: NO3- promoted the process under certain conditions owing to (OH)-O-center dot being generated by the photolysis of NO3-. In ice, however, the photoconversion efficiency of 4-CP was not proportional to the concentration of (OH)-O-center dot. The photoconversion efficiency of 4-CP increased with increasing concentrations of all ions, although the (OH)-O-center dot remained almost constant, only increasing or decreasing slightly. This provides new evidence for the presence of a quasi-liquid layer (QLL). Hydroxylation products were detected in both phases. All photoproducts in aqueous solution contained only a single benzene ring, whereas in ice, dimers were also detected. (C) 2013 Elsevier B.V. All rights reserved.