Heterogeneous Reactions of HNO3(g) + NaCl(s) .fwdarw. HCl(g) + NaNO3(s) and N2O5(g) + NaCl(s) .fwdarw. ClNO2(g) + NaNO3(s)

Abstract

The heterogeneous reactions of HNO3(g) + NaCl(s) -HCl(g) + NaNOs(s) (eq 1) and N205(g) + NaCl(s) -ClN02(g) + NaNO3(s) (eq 2) were investigated over the temperature range 223-296 K in a flow-tube reactor coupled to a quadrupole mass spectrometer. Either a chemical ionization mass spectrometer (CIMS) or an electron-impact ionization mass spectrometer (EIMS) was used to provide suitable detection sensitivity and selectivity. In order to mimic atmospheric conditions, partial pressures of HN03 and N2O5 in the range 6 x Torr were used. Granule sizes and surface roughness of the solid NaCl substrates were determined by using a scanning electron microscope. For dry NaCl substrates, decay rates of HN03 were used to obtain y(1) = 0.013 f 0.004 (lo) at 296 K and '0.008 at 223 K, respectively. The error quoted is the statistical error. After all corrections were made, h e overall error, including systematic error, was estimated to be about a factor of 2. HC1 was found to be the sole gas-phase product of reaction 1. The mechanism changed from heterogeneous reaction to predominantly physical adsorption when the reactor was cooled from 296 to 223 K. For reaction 2 usingdry salts, y(2) was found to be less than 1.0 x at both 223 and 296 K. The gas-phase reaction product was identified as ClN02 in previous studies using an infrared spectrometer. An enhancement in reaction probability was observed if water was not completely removed from salt surfaces, probably due to the reaction of N2O5(g) + H2O(s) -2HN03(g). Our results are compared with previous literature values obtained using different experimental techniques and conditions. The implications of the present results for the enhancement of the hydrogen chloride column density in the lower stratosphere after the El Chichon volcanic eruption and for the chemistry of HCl and HN03 in the marine troposphere are discussed.

Knudsen cell studies of the reactions of N2O5 and ClONO2 with NaCl: development and application of a model for estimating available surface areas and corrected uptake coefficients

“…The mass spectra of the species of interest in this study share common fragment peaks when using electron impact ionization ( Based on previous studies of the gaseous products of the HNO 3 -NaCl reaction, 12,13,17,18,29,32 HNO 3 generated in the N 2 O 5 hydrolysis reacts on the salt surface to form gaseous HCl. We denote the HCl produced in reaction (4) …”

“…However, if chloride ions are present, there is a competition between the reactions of NO 2 + with water and Cl À , and ClNO 2 is generated: 3,5,8,[10][11][12][13][14][15][16] …”

“…In the former case, the HNO 3 product can react further with NaCl [11][12][13][14][15][16][17][18]20,[22][23][24][25][26][27][28][29][30][31][32][33][34] to generate HCl.…”

Ozone decomposition on Saharan dust: an experimental investigation

“…Keyser and co-workers have developed a model for ice surfaces Leu, 1991, 1993) which in principle can also be applied to granular surfaces (e.g. Timonen et al, 1994;Leu et al, 1995). This model predicts a linear dependence of the uptake coefficient on the sample mass if the sample height is much less than the diffusion depth of the gas molecules into the bulk sample.…”

Reactive uptake coefficients for heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with submicron aerosols of NaCl and natural sea salt

“…There have been a number of investigations (Livingstone and Finlayson-Pitts 1991; Leu et al, 1995;Fenter et al, 1996) of the kinetics of N 2 O 5 reaction with solid NaCl crystals at low humidity, to represent the marine aerosol. These studies show small uptake coefficients of <1×10 −3 , when corrected for sample porosity and crystal presentation.…”