REACTIVE UPTAKE OF NO3 ON PURE WATER AND IONIC-SOLUTIONS

The reactive uptake coefficients (gamma) of NO3 onto pure water and di lute solutions of NaCl, NaBr, and NaNO2 were measured using a wetted-w all flow-tube setup combined with a long-path absorption cell for the detection of NO3. The measured gamma values were in the range 1.5x10(- 4)-6x10(-3), depending on the salt concentration in the water. By meas uring gamma as a function of salt concentration, HDl0.5 for NO3 in wat er was determined to be (1.9+/-0.4)x10(-3) M atm(-1) cm s(-0.5) at 273 K, assuming that the rate coefficient for the reaction of NO3 with CP is 2.76x10(6) M(-1) s(-1) at 273 K. The Henry's law coefficient for N O3 in water is estimated to be 0.6+/-0.3 M atm(-1), assuming that the diffusion coefficient of NO3 in water is D-l=(1.0+/-0.5)x10(-5) cm(2) s(-1). Uptake of NO3 on pure water is interpreted as due to reaction o f NO3(aq) with H2O(l) to produce HNO3 and OH in the liquid phase. Impl ications of these findings to the chemistry of NO3 in the troposphere are also discussed.