Heterogeneous Atmospheric Chemistry, Ambient Measurements, and Model Calculations of N2O5: A Review

For several decades, dinitrogen pentoxide (N2O5) has been recognized as an important reactive intermediate in the atmospheric chemistry of nitrogen oxides and nitrate aerosol, especially during nighttime. However, due to the lack of ambient observations of N2O5, the nocturnal nitrogen oxide chemistry could not be quantified until recent years. The objective of the present article is to assess the current state-of-the-art knowledge of N2O5 dynamics within the tropospheric aerosol. An up-to-date summary of N2O5 chemistry and major loss mechanisms are provided. Furthermore, techniques for measuring ambient N2O5 and an overview of typical N2O5 levels in the troposphere are described. In addition, model representations of N2O5 chemistry are reviewed along with key features of N2O5 vertical profiles based on numerical simulations. Lastly, the article provides the outstanding uncertainties and needs for further research into the atmospheric chemistry of N2O5. These include the need for better characterization of N2O5 heterogeneous uptake under temperature conditions characteristic of mid-and high-latitude winter seasons; greater understanding of the influence of individual aerosol components on N2O5 uptake and representation of these components in atmospheric models; and comprehensive descriptions of nighttime vertical profiles of N2O5 and related pollutants.