Heterogeneous reaction of N2O5 on sodium nitrate aerosol

The heterogeneous reactive uptake coefficients of N2O5 on metastable and de liquescent aerosols were determined in a large aerosol chamber at different humidities to 0.0018 +/- 0.0004, 0.0032 +/- 0.0006, and 0.023 +/- 0.005 at 48, 62, and 88% relative humidity and 293 +/- 2 K. The uptake coefficients at the lower two relative humidities are similar to 1 order of magnitude s maller than the uptake coefficients of N2O5 on other aqueous surfaces. This effect is explained by the ionic hydrolysis mechanism of N2O5 and the infl uence of the significantly enhanced recombination reaction NO2+ + NO3- doub le right arrow N2O5 due to the large molality of NO3- in the metastable aer osols. About 70% of the heterogeneously hydrolyzed N2O5 are found to be rel eased as HNO3 into the gas phase. The results present experimental support fur the ionic hydrolysis mechanism of N2O5. The low reaction probabilities lead to lower heterogeneous NOx turnover in specific areas of the atmospher e as assumed so far.