Kinetic Mechanism of ClONO₂ Uptake on Polycrystalline Film of NaCl

Abstract

Kinetic studies and the mechanism determination of ClONO2 uptake on polycrystalline NaCl were carried out using a coated-insert flow tube reactor combined with high-resolution, low-energy electron-impact mass spectrometer under the following conditions: p = 1-2 Torr, linear flow velocity v = 3.5-75 m s(-1), T = 293 and 387 K, [ClONO2] = (0.5-25) x 10(12) molecules cm(-3). The salt was deposited as a film from nonsaturated aqueous solution on the sliding rod. The temporal dependences of the uptake coefficient and the partial uptake coefficients leading to a formation of the prime Cl2 and HOCl products were measured for different ClONO2 concentrations. These dependences are established to be described by gamma = gamma0 exp(-t/tau) + gamma(s), gamma(0,s)(-1) = a(0,s) + b(0,s)[ClONO2]. In the framework of the proposed kinetic model, the data are explained and the main elementary kinetic parameters of the uptake are evaluated. The model is based on a combination of Langmuir adsorption, formation of surface complexes on initial active sites, Z(ch), followed by their unimolecular decomposition. Decomposition is proposed to proceed concurrently in two channels, one of which is a released surface site that conserves the properties of the initial site. In the other channel, the initial Z(ch) transforms into Z(ph) followed by steady-state uptake and reproduction of final Z(ph). The model gives an analytical expression for experimental parameters gamma0, gamma(s), and tau in terms of elementary rate constants and the reactant volume concentration. The final objective of the proposed model is the extrapolation of gamma0, gamma(s), and tau parameters to real tropospheric conditions.

Production and Release of Molecular Bromine and Chlorine from the Arctic Coastal Snowpack

“…Analogous reactions R1, R2, and R5−R8, involving production of ClONO 2 and subsequent reaction with Cl − , can also produce Cl 2 . 46 During elevated ozone (>10 ppb) periods of the two experiments, BrCl mole ratios were factors of 7−8 greater than Cl 2 mole ratios.…”

“…However, Wren et al concluded that initial Cl 2 production resulted from photolysis of BrCl to produce HOCl, which reacted with Cl – to produce Cl 2 (reactions –, , and ). Analogous reactions , , and –, involving production of ClONO 2 and subsequent reaction with Cl – , can also produce Cl 2 . During elevated ozone (>10 ppb) periods of the two experiments, BrCl mole ratios were factors of 7–8 greater than Cl 2 mole ratios.…”

Adsorption and heterogeneous reactions of ClONO2 and N2O5 on/with NaCl aerosol

“…2,3 During the last few decades, growing interest has been given to understanding of the fundamental chemical and physical processes in the marine boundary layer, especially in the heterogeneous reactions of nitrogen oxides such as NO 2 , N 2 O 5 and ClONO 2 with sea salt aerosols, with the goal to reveal the role they play in atmospheric chemistry. [4][5][6][7] It has been proposed that the heterogeneous reactions taking place on or in sea salt aerosols may provide the main possible sources for gaseous chlorinecontaining species (including HCl, Cl 2 , ClNO 2 , and HOCl etc.). Upon photolysis, the inert halogen reservoir species can convert into active halogen atoms, which may affect the ozone balance and oxidative potential of the local atmosphere, specically in the marine boundary layer.…”

“…Two possible reaction paths were taken into consideration when water was present, ClONO 2 could react with NaCl to form Cl 2 and NaNO 3 , or hydrolyze on the surface to generate HOCl and HNO 3 . 5,13 The heterogeneous reaction of N 2 O 5 with NaCl has been investigated by different techniques. 10,11,14,15 Results indicated that the uptake coefficients (g) were in a wide range of 10 À4 to 10 À2 , and increased with increase in relative humidity (RH).…”

“…4,10 In order to assess the source and role of halogen atoms, it is important to elucidate the kinetics, products, and mechanisms for reactions of nitrogen oxides with sea salt, especially for its major component, NaCl. However, while the overall kinetics and products are well-known by experiments, 4,5,[10][11][12][13][14][15] there have been no studies conducted to the interaction mechanisms between ClONO 2 or N 2 O 5 and NaCl. The experimental analysis helped to establish that the (100) surface of NaCl is dominant.…”