A study of the uptake of NO_3 on film coatings of natural sea salt

摘要

A comparative analysis of the uptake NO_3 on natural sea salt (NSS) and Dead Sea salt (DSS) is performed using a coated-insert flow reactor coupled to an electron impact ionization mass spectrometer for detecting gas-phase reactants and products. The uptake coefficients are determined by measuring both reactant consumption and gaseous products formation at various concentrations of NO_3, from 8 · 10~(12) to 4 · 10~(13) cm~(-3), and water vapor, from 8 · 10~(12) to 1.6 · 10~(15) cm~(-3). It has been established that the uptake on a fresh coating is time-dependent, with the uptake coefficient exponentially varying with time, γ(t) = γ _a exp(-t/τ) + γ _s, from an initial value to a steady-state value, both of which depends on the type of salt and the concentration of the gaseous reactant but do not depend on [H_2O] in this range of water vapor concentrations. The dependence of the coefficient of steady-state uptake of the gaseous reactant is determined as 1/γ s = a + b[NO_3]. It is shown that the main primary products of the NO_3 uptake on NSS are HCl and Cl _(ad) formed with branching ratios of 1: 1 and 1: 2 in the initial and steady-state uptake stages, respectively. For the uptake of NO_3 on DSS, the primary products are HCl and Br, formed in proportions of 1: 0.1 and 1: 0.006 for the respective uptake stages. Chemical reactions leading to the formation of these products are proposed.