Uptake coefficients of NO3 radicals on solid surfaces of sea-salts

Uptake coefficients of nitrate radicals (gamma(NO3)) have been measured by a technique involving a coated-wall flow tube with radical detection by E.P .R. spectrometry. The variation of NO3 concentration in the gas phase was f ollowed indirectly by monitoring OH radicals produced by the titration reac tion H + NO3. The mean initial value of gamma(NO3) measured on solid NaCl s urfaces was (1.7 +/- 1.2) x 10(-2) in the temperature range 258-301 K, whil e for solid NaBr surfaces the value was (0.11+/- 0.06) at 293 K. In each ca se, errors limits correspond to one standard deviation. For NaBr, a slight negative temperature dependence was observed over the investigated range, 2 43-293 K, which can be represented by gamma(NO3)(NaBr) = 1.6((+1.8)(-0.9)) x 10(-3) exp[(1210 +/- 200) /T]. An analysis of the results shows that unde r some conditions the heterogeneous loss of nitrate radicals on sea-salt ae rosol particles at ambient temperature could be competitive with their loss by homogeneous reaction in the marine troposphere at night.