Uptake coefficients of NO_3 radicals on solid surfaces of sea-salts

摘要

Uptake coefficients of nitrate radicals (#gamma#NO_3) have been measured by a technique involving a coated-wall flow tube with radical detection by E.P.R. spectrometry. The variation of NO_3 concentration in the gas phase was followed indirectly by monitoring OH radicals produced by the titration reaction H + NO_3. The mean initial value of #gamma#NO_3 measured on solid NaCl surfaces was (1.7 +- 1.2) * 10~(-2) in the temperature range 258-301 K, while for solid NaBr surfaces the value was (0.11 +- 0.06) at 293 K. In each case, errors limits correspond to one standard deviation. For NaBr, a slight negative temperature dependence was observed over the investigated rang, 243-293 k, which can be represented by #gamma#_(NO_3)~(NaBr) = 1.6_(-0.9)~(+0.8) * 10~(-3) exp[(1210 +- 200) / T]. An analysis of the results shows that under some conditions the heterogeneous loss of nitrate radicals on sea-salt aerosol particles at ambient temperature could be competitive with their loss by homogeneous reaction in the marine troposphere at night.