Comparative assessment of GRASP algorithm for a dust event over Granada (Spain) during ChArMEx-ADRIMED 2013 campaign
Abstract. In this study, vertical profiles and column integrated aerosol properties retrieved by GRASP (Generalized Retrieval of Atmosphere and Surface Properties) algorithm are evaluated with in-situ airborne measurements made during the ChArMEx-ADRIMED field campaign in summer 2013. In the framework of this campaign, two different flights took place over Granada (Spain) during a desert dust episode on 16th and 17th June. GRASP algorithm combining lidar and sun-sky photometer data measured at Granada, has been used for retrieving aerosol properties. Two sun-photometers datasets are used: one co-located with the lidar system and a second one in the Cerro Poyos station, approximately 1200 m higher than the lidar system, but at a short horizontal distance. Column integrated aerosol microphysical properties retrieved by GRASP are compared with AERONET products showing a good agreement. Differences between GRASP retrievals and airborne extinction profiles are in the range 15 % to 30 %, depending on the instrument onboard the aircraft used as reference. On 16th June, a case where the dust layer was coupled to the aerosol layer close to surface, the total volume concentration differences between in-situ data and GRASP retrieval are 15 % and 36 % for Granada and Cerro Poyos retrievals, respectively. On the other hand, on 17th June the dust layer was decoupled from the aerosol layer close to surface, the differences are around 17 % for both retrievals. In general, all the discrepancies found are within the uncertainly limits, showing the robustness and reliability of GRASP algorithm. However, the better agreement found for Cerro Poyos retrieval with the aircraft data and the vertical homogeneity of certain properties retrieved with GRASP, such as the scattering - Angström Exponent, for cases with aerosol layers characterized by different aerosol types show that uncertainties in the vertical distribution of the aerosol properties have to be considered.