Time-dependent uptake of NO sub(3) 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 NO sub(3) by sea salt at room temperature and [NO sub(3)]=810 super(11)-410 super(13) molecule cm super(-3). The radical uptake coefficient gamma (t) is time dependent: its initial value ( gamma sub(ini)) decreases exponentially with the characteristic time ( tau ) to its steady-state value ( gamma sub(ss)) at given [NO sub(3)]. The parameters gamma sub(ini), gamma sub(ss) and tau depend on [NO sub(3)], whereas gamma sub(ss) is water vapor independent at [H sub(2)O]=810 super(12)-1.610 super(15) molecule cm super(-3) and RH less than or equal to 0.5 %. HCl and NO sub(2) 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 NO sub(3) (~90 ppt), the time dependence becomes important, and the gamma value averaged over the aerosol lifetime is 410 super(-3); at low NO sub(3) (~1 ppt), the radical uptake is time independent and proceeds faster with gamma sub(ini)=810 super(-3)