An old-fashioned technology such as the "searchlight profiler", which was used in the 1960s for the early profiling of atmospheric backscatter, recently modified for its use with lasers and CCD cams1, has been revisited in the telemetric-LIDAR described here. The instrument is intended for the low-cost monitoring of urban aerosols, with a limited useful range of 100-200 meters. A modulated CW laser beam is used to probe the atmosphere, and a refractive telescope is used to collect the backscattered light on a photodiode array. Like in a telemetric system, the distance between the laser beam and the telescope axis determines the range resolution and the distance of the measurement volume corresponding to each pixel of the array. The system was used in conjunction with in-situ PM10 instruments for several months of continuous operation in Prato and Florence (Italy). The comparison between LIDAR-derived and conventional PM10 measurements is shown.
A statistically significant data set of backscattering LIDAR and ground-based information has been obtained for the planetary boundary layer (PBL) of Florence (I). The summer LIDAR backscattering data at 532 and 1064 nm have been used to estimate both the size and the number concentration of the urban aerosols in the accumulation mode. This technique seems to be relatively insensitive to the aerosol composition. The time-height evolution of the PBL [mainly the stable (SL) and the mixed (ML) layers] has been plotted, together with the meteorological and ground-based pollution data for the 200 measurement days. The ground-based hourly pollution data (NOx, CO) have been compared with the hourly-averaged 1064 nm backscattering at 25 meters above the ground. A correlation, R equals 0.65, was obtained between NOx and 1064 nm backscattering during the summer period when the traffic aerosols do not grow considerably after their production. The correlation is not significant during winter, when the growth of the particles is much faster. During winter, the RH variations are more important than aerosol number variations to determine the backscattering evolution.
Juergen Kolenda, Bernd Mielke, Patrick Rairoux, Bernhard Stein, Dirk Weidauer, Jean-Pierre Wolf, Ludger Woeste, Francesco Castagnoli, Massimo Del Guasta, Marco Morandi, V. Sacco, Leopoldo Stefanutti, V. Venturi, L. Zuccagnoli
Consideration is given to a novel inversion algorithm to determine the aerosol size distribution from lidar signals obtained at several wavelengths. This algorithm is based on a nonlinear fit of the backscattered measurements using a set of predetermined functions. Size distribution profiles of tropospheric aerosols in different meteorological conditions - clear, hazy, and cloudy atmosphere - are determined on the basis of lidar measurements made in central Switzerland, which is characterized by a specific microclimate. Measurements of stratospheric clouds and aerosols created by the Pinatubo eruption were measured above Berlin and Sodankyla, Finland. These measurements are used to characterize the size distribution of these volcanic aerosols in order to estimate their influence on radiative transfer.
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