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

For several decades, dinitrogen pentoxide (N 2 O 5 ) 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 N 2 O 5 , 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 N 2 O 5 dynamics within the tropospheric aerosol. An up-to-date summary of N 2 O 5 chemistry and major loss mechanisms are provided. Furthermore, techniques for measuring ambient N 2 O 5 and an overview of typical N 2 O 5 levels in the troposphere are described. In addition, model representations of N 2 O 5 chemistry are reviewed along with key features of N 2 O 5 vertical profiles based on numerical simulations. Lastly, the article provides the outstanding uncertainties and needs for further research into the atmospheric chemistry of N 2 O 5 . These include the need for better characterization of N 2 O 5 heterogeneous uptake under temperature conditions characteristic of mid- and high-latitude winter seasons; greater understanding of the influence of individual aerosol components on N 2 O 5 uptake and representation of these components in atmospheric models; and comprehensive descriptions of nighttime vertical profiles of N 2 O 5 and related pollutants.