Heterogeneous reaction of ClONO2(g) + NaCl(s) .fwdarw. Cl2(g) + NaNO3(s)

Abstract

The heterogeneous reaction of ClONOz + NaCl -Cl2 + NaN03 (eq 1) was investigated over a temperature range 220-300 K in a flow-tube reactor interfaced with a differentially pumped quadrupole mass spectrometer. Partial pressures of ClONOz in the range 10-8-10-5 Torr were used. Granule sizes and surface roughness of the NaCl substrates were determined by using a scanning electron microscope, and in separate experiments, surface areas of the substrates were measured by using BET analysis of gas-adsorption isotherms. For dry NaCl substrates, both the decay rates of ClONO2 and the growth rates of Cl2 were used to obtain reaction probabilities, y1 = (4.6 f 3.0) x at 296 K and (6.7 f 3.2) x at 225 K, after considering the internal surface area. The error bars represent 1 standard deviation. The C12 yield based on the ClONO2 reacted was measured to be 1.0 f 0.2. In order to mimic the conditions encountered in the lower stratosphere, the effect of water vapor pressures between 5 x and 3 x Torr on reaction 1 was also studied.With added H20, reaction probabilities, y l = (4.1 f 2.1) x at 225 K, were obtained. A trace of HOC1, the reaction product from the ClON02 4-H20 -HOC1 i-HNO3 reaction, was observed in addition to the Cl2 product from reaction 1. The implications of this result for the enhancement at 296 K and (4.7 f 2.9) x of hydrogen chloride in the stratosphere after the El Chichon volcanic eruption and for the marine troposphere are discussed.

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.…”

The uptake of SO<sub>2</sub> on Saharan dust: a flow tube study

“…This expression derives from the solution of the diffusion equation for Fick's Law with a specified mean diffusion depth L. More explicit models of pore diffusion do exist and have been used successfully to correct uptake coefficients in a number of studies, but these are either concerned with time independent uptake (Keyser et al, 1991;Timonen et al, 1994) or uptake into multiple layers of particles (Goodman et al, 2001). D 0.5 s /L was used as an adjustable parameter.…”

Uptake study of ClONO<sub>2</sub> and BrONO<sub>2</sub> by Halide containing droplets

“…It has been proposed that ClONO 2 reacts with NaCl according to Aguzzi and Rossi (1999) and Timonen et al (1994):…”

“…The heterogeneous reactions of ClONO 2 with solid NaCl and KBr have already been studied in a fast flow reactor (Timonen et al, 1994) and a Knudsen cell (Aguzzi and Rossi, 1999;Caloz et al, 1996;Gebel and Finlayson-Pitts, 2001;Wingenter et al, 1996) and the primary reaction products on NaCl were HOCl and Cl 2 while BrCl was observed on KBr.…”

“…All these experiments were conducted over different solid substrates corresponding to powders (Timonen et al, 1994;Caloz et al, 1996;Gebel et al, 2001), spray deposited films, grains of various sizes and also single crystals (Caloz et al, 1996 ;Aguzzi and Rossi, 1999). Most of these experiments were also performed at low pressure (e.g.…”