Heterogeneous Interaction of N2O5 with HCl Doped H2SO4 under Stratospheric...

Talukdar, R. K., J. Burkholder, J. M. Roberts, R. W. Portmann, and A. R. Ravishankara (2012), Heterogeneous Interaction of N2O5 with HCl Doped H2SO4 under Stratospheric Conditions: ClNO2 and Cl2 Yields, J. Phys. Chem. A, 116, 6003-6014, doi:10.1021/jp210960z.

The reaction of dinitrogen pentoxide, N2O5, with hydrogen chloride, HCl, in sulfuric acid solutions was studied at temperatures and compositions relevant to the upper troposphere/lower stratosphere. Experiments were performed using a rotating wetted wall flow tube reactor coupled to a chemical ionization mass spectrometer for the gas-phase detection of reactants (N2O5 and HCl) and products (nitryl chloride, ClNO2, and Cl2) using I− as the reagent ion. Uptake coefficients, γ, were measured under stratospheric conditions: 205 < T < 225 K; 50 and 60 wt % H2SO4 solutions; 5.8 × 10−5 < [HCl]liq < 0.1 M. Uptake coefficients of N2O5 on pure H2SO4/H2O (50 and 60 wt % H2SO4) and HCldoped H2SO4 were found to be independent of temperature and sulfuric acid composition (weight percent of H2SO4 and HCl concentration) consistent with previous studies. ClNO2 was observed to be a major gas-phase product with its yield strongly dependent on the liquid-phase HCl concentration (5.8 × 10−5 to 0.1 M HCl) and with a maximum yield of nearly unity at 0.005 M HCl in both 50 and 60 wt % sulfuric acid solutions. The Cl2 yield was <1% under all conditions studied. ClNO2 production was attributed to the heterogeneous reaction of NO2+(aq), or H2NO3+(aq) (formed in the dissociative ionization of N2O5), with Cl−. The variation of the ClNO2 yield with HCl concentration was attributed to the competition between the reaction of NO2+(aq), or H2NO3+(aq) with Cl− and H2O. Using our measured yields as a function of HCl concentrations in 50 and 60 wt % H2SO4 solutions at different temperatures, we calculated the variation of the ClNO2 yield under stratospheric conditions. The atmospheric implications of these findings were examined using a 2D atmospheric model. The contribution of this chemistry to ozone depletion was found to be a minor process under nonvolcanic background aerosol levels.

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Upper Atmosphere Research Program (UARP)