Atmospheric concentrations of the Cl atom, CIO radical, and HO radical in the coastal marine boundary layer

Atmospheric concentrations of chlorine atom (Cl√), chlorine monoxide radical (ClO√), and hydroxyl radical (HO√) in the coastal marine boundary layer are estimated in this study. A steady-state approach to their concentrations in equilibrium with other atmospheric chemical species is used. Measurements of atmospheric trace species, HCl, Cl2, HCHO, H2O2, CH3OOH, CH4, CO, SO2, NO, NO2, and O3, were performed at four sites in Taiwan during the spring of 1999. The results indicate that the concentrations of the Cl√ atom and the ClO√ and HO√ radicals decrease significantly with cloud cover. The calculated average daytime concentrations of Cl√, ClO√, and HO√ are 3×105, 1×107, and 6×105 molecules/cm3, respectively. Due to the high reactivity of Cl√ with hydrocarbons and its concentration level competitive to that of HO√, Cl√ should be a significant sink for hydrocarbons in these cases.