Time-dependent uptake of NO3 by sea salt

Using a coated-insert flow tube reactor coupled to a low-energy electron-impact mass spectrometer with molecular beam sampling, we studied uptake of NO3 by sea salt at room temperature and [NO3] = 8a <...10(11) -aEuro parts per thousand 4a <...10(13) molecule cm(-3). The radical uptake coefficient gamma(t) is time dependent: its initial value (gamma (ini)) decreases exponentially with the characteristic time (tau) to its steady-state value (gamma (ss)) at given [NO3]. The parameters gamma (ini), gamma (ss) and tau depend on [NO3], whereas gamma (ss) is water vapor independent at [H2O] = 8a <...10(12) -aEuro parts per thousand 1.6a <...10(15) molecule cm(-3) and RH a parts per thousand currency sign 0.5 %. HCl and NO2 are uptake products detected in the gas phase. We used these findings to estimate gamma values under tropospheric conditions for urban coastal and remote marine environments: at high NO3 (similar to 90 ppt), the time dependence becomes important, and the gamma value averaged over the aerosol lifetime is 4a <...10(-3); at low NO3 (similar to 1 ppt), the radical uptake is time independent and proceeds faster with gamma (ini) = 8.10(-3).