A parameterization of the heterogeneous hydrolysis of N2O5 for mass-based aerosol models: improvement of particulate nitrate prediction.

The heterogeneous hydrolysis of N₂O₅ on the surface of deliquescent aerosol leads to HNO₃ formation and acts as a major sink of NO_x in the atmosphere during nighttime. The reaction constant of this heterogeneous hydrolysis is determined by temperature (T ), relative humidity (RH), aerosol particle composition, and the surface area concentration (S). However, these parameters were not comprehensively considered in the parameterization of the heterogeneous hydrolysis of N₂O₅ in previous mass-based 3-D aerosol modelling studies. In this investigation, we propose a sophisticated parameterization (NewN₂O₅) of N₂O₅ heterogeneous hydrolysis with respect to T, RH, aerosol particle compositions, and S based on laboratory experiments. We evaluated closure between NewN₂O₅ and a state-of-the-art parameterization based on a sectional aerosol treatment. The comparison showed a good linear relationship (R D0.91) between these two parameterizations. NewN₂O₅ was incorporated into a 3-D fully online coupled model, COSMO- MUSCAT, with the mass-based aerosol treatment. As a case study, we used the data from the HOPE Melpitz campaign (10-25 September 2013) to validate model performance. Here, we investigated the improvement of nitrate prediction over western and central Europe. The modelled particulate nitrate mass concentrations ([NO^-₃ ]) were validated by filter measurements over Germany (Neuglobsow, Schmücke, Zingst, and Melpitz). The modelled [NO^-₃ ] was significantly overestimated for this period by a factor of 5-19, with the corrected NH3 emissions (reduced by 50 %) and the original parameterization of N₂O₅ heterogeneous hydrolysis. The NewN₂O₅ significantly reduces the overestimation of [NO^-₃ ] by ~35 %. Particularly, the overestimation factor was reduced to approximately 1.4 in our case study (12, 17-18 and 25 September 2013) when [NO^-₃ ] was dominated by local chemical formations. In our case, the suppression of organic coating was negligible over western and central Europe, with an influence on [NO^-₃ ] of less than 2% on average and 20% at the most significant moment. To obtain a significant impact of the organic coating effect, N₂O₅, SOA, and NH3 need to be present when RH is high and T is low. However, those conditions were rarely fulfilled simultaneously over western and central Europe. Hence, the organic coating effect on the reaction probability of N₂O₅ may not be as significant as expected over western and central Europe. [ABSTRACT FROM AUTHOR]