A model evaluation of coarse-mode nitrate heterogeneous formation on dust particles

The significance of the heterogeneous formation of particulate nitrate, rarely included in chemistry-transport models (CTMs), is investigated. According to several field campaigns, particulate nitrate in a coarse particle (2-10 μm) can be obtained by reaction of nitric acid with calcium and magnesium carbonates. This process significantly contributes to the total nitrate mass concentration over land, particularly in summer. We introduce this heterogeneous reaction in the CHIMERE CTM and analyze its impact on total nitrate, nitric acid and aerosol particles, by statistical comparison of one-year long simulations with EMEP measurements over Europe. Several values of the nitric acid uptake coefficient are tested in order to investigate the sensitivity to this parameter, and we propose an optimal value for our study. The model performance in simulating nitrates and PM₁₀ significantly improves when the heterogeneous nitrate formation is included. This process also greatly improves the simulation of coarse nitrate by comparison with field campaign measurements near Paris city.