Impact of the heterogeneous hydrolysis of N₂O₅ on chemistry and nitrate aerosol formation in the lower troposphere under photosmog conditions

The impact of the heterogeneous hydrolysis of N_2O5 on tropospheric gas phase and particle phase chemistry was investigated by performing model simulations with two comprehensive model systems and taking into account recent findings on the heterogeneous reaction probability of N_2O5. Hereby, we focused on photosmog conditions in the lower troposphere. Chemistry box model runs were carried out neglecting transport and deposition processes. The heterogeneous hydrolysis of N_2O5 leads to a decrease of ozone under low-NO_x conditions and to a strong increase of ozone under high-NO_x conditions. One-dimensional simulations were performed to take into account vertical mixing processes, deposition, and temporal changes of the emissions. The rate constant for the heterogeneous hydrolysis was determined depending on the simulated aerosol surface area density. A large impact of the heterogeneous hydrolysis on the nocturnal concentrations of N_2O5, NO₃, HNO₃, and the surface area density and nitrate content of the aerosol is found. However, the effect of the hydrolysis of N_2O5 on ozone decreases considerably compared to the box model simulations. Three-dimensional simulations for a typical summer smog situation for the southwestern part of Germany and on the European scale, which cover variety of atmospheric and emission conditions, confirm these findings. The impact of heterogeneous hydrolysis on ozone is small, but it causes remarkable changes in the nocturnal concentrations of nitrogen-containing species and on aerosol properties such as surface area density and nitrate content.