Influence of boundary conditions and anthropogenic emission inventories on simulated O₃ and PM_2.5 concentrations over Lebanon

This study investigates the influence of boundary conditions and anthropogenic emission inventories on the simulated O₃ and PM_2.5 concentrations over a middle-eastern country – Lebanon. The Polyphemus chemical transport model (CTM) is used over Lebanon to simulate O₃ and PM_2.5 concentrations. Comparisons to measurements at a sub-urban site of Beirut between 2 and 13 July 2011 show that O₃ is largely over-estimated when concentrations from a large-scale model are used as boundary conditions, as used in Waked et al. (2013). A global anthropogenic emission inventory (EDGAR-HTAP) is used with Polyphemus, in order to provide anthropogenic emissions for the Middle-East domain. Over Lebanon, sensitivity to emissions and to boundary conditions have been investigated. The comparison of EDGAR-HTAP to Waked et al. (2012) over Lebanon highlights high discrepancies between the inventories both in terms of emission estimates and spatial distribution. However, when studying the sensitivity to boundary conditions, O₃ is well modeled when a Middle-East domain and the Lebanon domain are nested and thus achieves better statistics. The observed concentration is 48.8 μg m⁻³ and the respective concentrations for the simulation using MOZART4 and the one using the Polyphemus/Middle-East are 154.8 and 65.1 μg m⁻³. As for PM_2.5 which is less sensitive to regional transport than O₃, the influence of the boundary conditions on the PM_2.5 concentrations at the site of comparison is low. The observed concentration is 20.7 μg m⁻³, while the modeled concentrations are 20.7 and 20.1 μg m⁻³ respectively.