Reactive uptake of NO₃ on pure water and ionic solutions

The reactive uptake coefficients (γ) of NO 3 onto pure water and dilute solutions of NaCl, NaBr, and NaNO 2 were measured using a wetted‐wall flow‐tube setup combined with a long‐path absorption cell for the detection of NO 3 . The measured γ values were in the range 1.5 × 10 −4 – 6 × 10 −3 , depending on the salt concentration in the water. By measuring γ as a function of salt concentration, H D 𝓁 0.5 for NO 3 in water was determined to be (1.9 ± 0.4) × 10 −3 M atm −1 cm s −0.5 at 273 K, assuming that the rate coefficient for the reaction of NO 3 with Cl − is 2.76 × 10 6 M −1 s −1 at 273 K. The Henry's law coefficient for NO 3 in water is estimated to be 0.6 ± 0.3 M atm −1 , assuming that the diffusion coefficient of NO 3 in water is D 𝓁 = (1.0 ± 0.5) × 10 −5 cm 2 s −1 . Uptake of NO 3 on pure water is interpreted as due to reaction of NO 3(aq) with H 2 O (𝓁) to produce HNO 3 and OH in the liquid phase. Implications of these findings to the chemistry of NO 3 in the troposphere are also discussed.