Heterogeneous reaction of N₂O₅ on sodium nitrate aerosol

The heterogeneous reactive uptake coefficients of N 2 O 5 on metastable and deliquescent 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 ∼1 order of magnitude smaller than the uptake coefficients of N 2 O 5 on other aqueous surfaces. This effect is explained by the ionic hydrolysis mechanism of N 2 O 5 and the influence of the significantly enhanced recombination reaction NO 2 + + NO 3 − ⇒ N 2 O 5 due to the large molality of NO 3 − in the metastable aerosols. About 70% of the heterogeneously hydrolyzed N 2 O 5 are found to be released as HNO 3 into the gas phase. The results present experimental support for the ionic hydrolysis mechanism of N 2 O 5 . The low reaction probabilities lead to lower heterogeneous NO x turnover in specific areas of the atmosphere as assumed so far.