Validation of LIRIC aerosol concentration retrievals using airborne measurements during a biomass burning episode over Athens

• Validation of LIRIC algorithm for estimating fine mode particles concentration, using airborne chemical composition dataset.
• Case study of smoke layer over Athens-Greece (September 2011). Retrievals regarding aerosol optical and chemical properties.
• High AOD (0.82 at 340 nm) and Ångström exponent values (~ 1.8) have been observed in the atmospheric column with AERONET.
• In the height range of 2-4 km, fine mode particle fraction found to consist of sulphates (57.6%) and organic carbon (31.6%).
• Correlation coefficient between airborne in-situ and LIRIC values found to be 0.853 reaching even the 0.968.
• An overall good performance of LIRIC has been revealed for fine mode particles, with higher discrepancies observed below 2 km.

In this paper we validate the Lidar-Radiometer Inversion Code (LIRIC) retrievals of the aerosol concentration in the fine mode, using the airborne aerosol chemical composition dataset obtained over the Greater Athens Area (GAA) in Greece, during the ACEMED campaign. The study focuses on the 2nd of September 2011, when a long-range transported smoke layer was observed in the free troposphere over Greece, in the height range from 2 to 3 km. CIMEL sun-photometric measurements revealed high AOD (~ 0.4 at 532 nm) and Ångström exponent values (~ 1.7 at 440/870 nm), in agreement with coincident ground-based lidar observations. Airborne chemical composition measurements performed over the GAA, revealed increased CO volume concentration (~ 110 ppbv), with 57% sulphate dominance in the PM1 fraction. For this case, we compare LIRIC retrievals of the aerosol concentration in the fine mode with the airborne Aerosol Mass Spectrometer (AMS) and Passive Cavity Aerosol Spectrometer Probe (PCASP) measurements. Our analysis shows that the remote sensing retrievals are in a good agreement with the measured airborne in-situ data from 2 to 4 km. The discrepancies observed between LIRIC and airborne measurements at the lower troposphere (below 2 km), could be explained by the spatial and temporal variability of the aerosol load within the area where the airborne data were averaged along with the different time windows of the retrievals.