Evaluation of modeled vertical aerosol distributions over Europe using in-situ and satellite data

As part of the EU ECLIPSE project, which aims to quantify the climate impact of short-lived climate forcers (SLCFs), including aerosols, black carbon and ozone, regional models are being used to evaluate global model performance for specific case studies. Here, we present results using regional WRF-Chem simulations run with different aerosol schemes over Europe. Results are compared to satellite data and field campaigns which took place in spring and summer 2008. The aim is to evaluate the ability of the models to simulate the aerosol physical, chemical and optical properties, with a focus on pollution layers over source regions and during transport downwind. The radiative impact of such layers over Europe is also examined as a function of their relative positions to clouds. The WRF-Chem regional model was run using MOZART gas phase chemistry and different aerosol schemes and evaluated against the measurements. The model was run using anthropogenic and fire emissions for 2008, while boundary conditions were specified using the fields from a global chemical transport model. The radiative impact of pollution aerosol layers has already been investigated but less is known about the influence of vertical layering in the atmosphere. Such layers might have different radiative impacts whether they are below or above clouds and in that sense, a better understanding of their spatial extent is critical. Information about pollution aerosol layers and clouds optical properties and positions over Europe are determined using satellite-based remote-sensing measurements (CALIPSO lidar). The radiative impact of these layers has been evaluated and compared to the observations. In addition to satellite observations, data providing information on aerosol physical, optical and chemical properties from 2008 measurements campaigns over Europe (e.g., EUCAARI and POLARCAT-France) have been used to evaluate the simulations. In this study, we assess, for exemple, aerosol total number concentrations and size distributions simulated by the model. The aerosol aging is also evaluated bu examining the ratio between elementary and organic carbon (EC:OC), while the aerosol origins and sources are investigated using Lagrangian back-trajectories and observed chemical compositions, respectively. Specific attention is given to the simulation of observed pollution aerosol layers identified by CO and aerosol total number concentration enhancements.