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 NO 3 by sea salt at room temperature and [NO 3 ] = 8⋅10 11 − 4⋅10 13 molecule cm −3 . The radical uptake coefficient γ ( t ) is time dependent: its initial value ( γ ini ) decreases exponentially with the characteristic time ( τ ) to its steady-state value ( γ ss ) at given [NO 3 ]. The parameters γ ini , γ ss and τ depend on [NO 3 ], whereas γ ss is water vapor independent at [H 2 O] = 8⋅10 12 − 1.6⋅10 15 molecule cm −3 and RH ≤ 0.5 %. HCl and NO 2 are uptake products detected in the gas phase. We used these findings to estimate γ values under tropospheric conditions for urban coastal and remote marine environments: at high NO 3 (~90 ppt), the time dependence becomes important, and the γ value averaged over the aerosol lifetime is 4⋅10 −3 ; at low NO 3 (~1 ppt), the radical uptake is time independent and proceeds faster with γ ini = 8⋅10 −3