Volume 102, Issue D3 p. 3795-3804
Papers on Atmospheric Chemistry
Free Access

Production and decay of ClNO2 from the reaction of gaseous N2O5 with NaCl solution: Bulk and aerosol experiments

First published: 01 February 1997
Citations: 1

Abstract

The chemistry of N2O5 on liquid NaCl aerosols or bulk NaCl solutions was studied at 291 K by aerosol smog chamber and wetted-wall flow tube experiments. The uptake of N2O5 on deliquescent aerosol was obtained to be (3.2±0.2)×10−2 (1σ error) from the aerosol experiments. In the wetted-wall flow tube we observed that nitryl chloride (ClNO2) is the main product of the reaction at NaCl concentrations larger than approximately 0.5 M and almost the only product at concentrations larger than 1 M. The ClNO2 yield does not depend linearly on the NaCl concentration, especially at small sodium chloride concentrations (i.e., smaller than 1 M). It appeared that a simple mechanism where N2O5 undergoes two reaction channels (hydrolysis and reaction with Cl) is unable to explain the observed concentration dependence of the product yield. We propose that N2O5 dissociates to NO2+ and NO3 (rate constant kl>104 s−1) mainly. The directly hydrolysis of N2O5 (k3[H2O]) is less than 20% of the total reaction. NO2+ reacts with water to form 2H+ and NO3 (k5) or with Cl to form ClNO2 (k4). Neglecting the influence of ionic strength we evaluate k4/k5 to be 836±32 (1σ error). Using the wetted-wall flow tube technique, we studied the uptake of nitryl chloride by aqueous solutions containing NaCl. We observed that the uptake coefficient γ decreased from (4.84±0.13)×10−6 on pure water to (0.27±0.02)×10−6 on a 4.6 M NaCl solution. The sharp decrease of γ with increasing salt concentrations is evidence of reversible hydrolysis. ClNO2 dissociates to Cl + NO2+(k6). In the absence of Cl we evaluate H ⋅ k61/2 to be 0.44±0.01 mol L−1 atm−1 s−1/2. Finally, we discuss that atomic Cl from photolysis of ClNO2 may play a role in the marine boundary layer at high northern latitudes.