Abstract
Abstract. The influence of smoke on the aerosol loading in the free troposphere over Thessaloniki, Greece is examined in this paper. Ten cases during 2001–2005 were identified when very high aerosol optical depth values in the free troposphere were observed with a UV-Raman lidar. Particle dispersion modeling (FLEXPART) and satellite hot spot fire detection (ATSR) showed that these high free tropospheric aerosol optical depths are mainly attributed to the advection of smoke plumes from biomass burning regions over Thessaloniki. The biomass burning regions were found to extend across Russia in the latitudinal belt between 45° N–55° N, as well as in Eastern Europe (Baltic countries, Western Russia, Belarus, and the Ukraine). The highest frequency of agricultural fires occurred during the summer season (mainly in August). The data collected allowed the optical characterization of the smoke aerosols that arrived over Greece, where limited information has so far been available. Two-wavelength backscatter lidar measurements showed that the backscatter-related Ångström exponent ranged between 0.5 and 2.4 indicating a variety of particle sizes. UV-Raman lidar measurements showed that for smoke particles the extinction to backscatter ratios (so-called lidar ratios) varied between 40 sr for small particles to 100 sr for large particles. Dispersion model estimations of the carbon monoxide tracer concentration profiles for smoke particles indicate that the variability of the optical parameters is a function of the age of the smoke plumes. This information could be useful on the lidar community for reducing uncertainty in the aerosol backscatter coefficient determination due to the lidar ratio assumption, starting from a simply elastic backscatter lidar as the first satellite-borne lidar CALIPSO.
Highlights
Biomass burning is a major source of air pollution and the second largest source of anthropogenic aerosols (IPCC, 2001)
Raman lidar measurements for ten selected cases during 2001–2005, when air masses were advected over Thessaloniki from regions with intense fire activity, have been presented, in terms of extinction (355 nm) and backscatter coefficient (355 and 532 nm) and the corresponding lidar ratio (355 nm) and backscatter-related Angstrom exponent (355/532 nm)
Lidar ratios in the range of 32–103 sr were observed for smoke particles, while the backscatterrelated Angstrom exponent varied between 0.5 and 2.4
Summary
Biomass burning is a major source of air pollution and the second largest source of anthropogenic aerosols (IPCC, 2001). The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Forster et al, 2007) reports a contribution of roughly +0.04 W/m2 of biomass burning aerosol to the global radiative forcing (RF) with a standard deviation of 0.07 W/m2. This estimate of the direct RF is more positive than that of the Third Assessment Report (IPCC, 2001) and it is linked with improvements in the models in representing the absorption properties of biomass burning aerosol and the effects of their vertical distribution. A considerable body of research using in situ measurement techniques has been published on the optical properties of smoke
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