Uptake coefficients of O3 on NaCl and synthetic sea salt (SSS) were found to be enhanced from < 10-5 to ~ 3.5 ¿ 10-2 in the presence of water-soluble Fe3+ in the Fe/Na weight ratio larger than 0.1 %. Cl2 release was observed without radiation in the reaction of O3 and a FeCl3/NaCl mixture with surface adsorbed water at the yields of 0.48 and 0.28 for Fe/Na ratio of 1.0 and 0.5 weight %, respectively. Only Br2 release was observed for a FeCl3/SSS sample. These results imply that when bromide is deficient in sea salt, Cl2 would be released from the sea salt with the coexistence of Fe3+. The estimate was made to show that the Cl2 releasing rate can be high enough to explain sporadically observed Cl2 at nighttime in a coastal area. ¿ 2001 American Geophysical Union