KINETICS OF NITRIC-ACID UPTAKE BY SALT

The kinetics of the uptake of HNO3 on a series of salt powders (NaCl, NaBr, KCl, and KBr) has been studied in a Teflon-coated, low-pressure flow reactor. HCl and HBr are found to be the sole products of the reactions, and, within experimental uncertainty, all the HNO3 taken up by the salt is converted to HCl or HBr. Values for the uptake coefficients are derived from two experimental procedures: (1) Steady-state uptake of constant HNO3 flows and (2) real-time monitoring of pulsed quantities of HNO3: The two procedures yield values in good agreement, and it has been determined that all the salts studied, including the nonreactive NaNO3, are characterized by the same value of the uptake coefficient: gamma = (2.8 +/- 0.3) x 10(-2). A discussion is given for the non-negligible affinity of HNO3 for the Teflon-coated walls and how this effect is taken into account in our experiments. We develop a model of the uptake kinetics, based on our experimental results, that reproduces the observations over a broad range of experimental conditions. In addition, the uptake of HCl (gamma = 3 x 10(-2)) and H2O (gamma < 2 x 10(-4)) on NaCl powder is determined in ancillary experiments. The results may hold implications for the understanding of chloride displacement in marine aerosols.