Aerosol optical and microphysical properties observed by the lidar technique from a forest-fire smoke event over Madrid

On 27 August 2012, a wildfire occurred in the western zone of the Madrid region. Consequently, a significant release of smoke and aerosols was injected into the free troposphere and advected by the synoptic circulation in trajectories that passed over the capital. This event was detected by the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT; Research Centre for Energy, Environment and Technology), Madrid lidar station at about 5 km height. While the main aerosol plume did not pass over the lidar station, the eastern portion of the dispersed emissions did. No aerosol layers were detected by lidar in the free-troposphere for the next few days. Since few observations of fresh biomass burning aerosol have been carried out by lidar so far, this study contributes to previous studies on biomass burning aerosols, in particular regarding the first stages of the smoke transport.This article studies the optical and microphysical properties of the smoke aerosols retrieved by the lidar technique along with the recently developed Lidar/Radiometer Inversion Code (LiRIC), which combines both lidar and sun–sky photometer data. The sun–sky photometer data are provided by the Agencia Estatal de Meteorología (AEMET; Spanish Meteorological Agency) station close to the CIEMAT site. We suggest that the aerosol properties retrieved might be linked to the water uptake phenomenon in view of the fact that simultaneous water vapour lidar measurements exhibited a close relationship with backscatter coefficient profiles. This article is concerned not only with showing the capability of combining different remote-sensing techniques and the LiRIC code to provide aerosol vertical distribution for fine and coarse modes, but also with providing signs about the plausible interaction between aerosols and humidity that leads fresh biomass burning aerosols to act as cloud condensation nuclei. This key role, known as the indirect effect, remains the major source of uncertainty when the global radiation budget is assessed.