A novel approach for the characterization of transport and optical properties of aerosol particles near sources – Part I: Measurement of particle backscatter coefficient maps with a scanning UV lidar (original) (raw)
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Atmospheric …, 2011
The physical and chemical properties of aerosols emitted from a livestock farm were determined by a novel approach which combines high-resolution lidar measurements (0.33 s, 30 m) with simulations of a microphysicsechemistryetransport model. This first of two companion papers describes the scanning lidar measurements of optical particle properties. The lidar system employed laser radiation at a wavelength of 355 nm with a power of 9 W and a pulse repetition rate of 30 Hz. The laser beam was expanded before transmission to the atmosphere so that it became eye-safe at distances >270 m to the lidar. The elastic backscatter signal was detected with a resolution of 0.033 s and 3 m. A receiving telescope with a primary-mirror diameter of 40 cm was used. For this system, we developed a novel method for twodimensional retrievals of the particle backscatter coefficient. With this set up and approach, the lidar was able to identify the aerosol plume up to a range of w2.5 km from the source, a farm in northern Germany, in daytime. The measurements confirm that the optical particle properties of the emission plume vary largely with distance from the source and that the maximum particle backscatter coefficient is found away from the source. Within a close-to-horizontal scan (elevation angle of 2.3 ), we found a mean particle backscatter coefficient of 1.5$10 À5 m À1 sr À1 inside the plume between 1.5 and 2.0 km distance from the source. Subtraction of the mean particle backscatter coefficient of the background aerosol present in this case (4.1$10 À6 m À1 sr À1 ) yields a particle backscatter coefficient of the livestock aerosols of 1.1$10 À5 m À1 sr À1 . The limited extend of the plume is revealed with the scanning lidar: Scans with a slightly higher elevation angle of 4.8 did not pick up the plume.
LIDAR investigation of properties of atmospheric aerosol
The European Physical Journal Special Topics, 2007
In the paper application of lidars for investigation of aerosol particle size distribution and for observation of aerosol consisting of solid state particles is presented. For size distribution the multiwavelength lidar and original method of data analysis was applied. For registration of dust transported to Central Europe from Sahara and Middle East deserts analysis of depolarization of the backscattered signals was used. In order to solve the lidar equation measurements of total atmospheric optical depth by means of Microtops sun photometer was done. Mean size and the aspect ratio of dust particles were determined by comparing of lidar observations with data from T-matrix calculations.
Atmospheric Environment, 2011
A new high-resolution microphysicsechemistry-transport model (LES-AOP) was developed and applied for the investigation of aerosol transformation and transport in the vicinity of a livestock facility in northern Germany (PLUS1 field campaign). The model is an extension of a Large-Eddy Simulation (LES) model. The PLUS1 field campaign included the first deployment of the new eye-safe scanning aerosol lidar system of the University of Hohenheim. In a combined approach, model and lidar results were used to characterise a faint aerosol source. The farm plume structure was investigated and the absolute value of its particle backscatter coefficient was determined. Aerosol optical properties were predicted on spatial and temporal resolutions below 100 m and 1 min, upon initialisation by measured meteorological and size-resolved particulate matter mass concentration and composition data. Faint aerosol plumes corresponding to a particle backscatter coefficient down to 10 À6 sr À1 m À1 were measured and realistically simulated. Budget-related quantities such as the emission flux and change of the particulate matter mass, were estimated from model results and ground measurements.
THE EUROPEAN PHYSICAL JOURNAL LIDAR investigation of properties of atmospheric aerosol a
In the paper application of lidars for investigation of aerosol particle size distribution and for observation of aerosol consisting of solid state particles is presented. For size distribution the multiwavelength lidar and original method of data analysis was applied. For registration of dust transported to Central Europe from Sahara and Middle East deserts analysis of depolarization of the backscattered signals was used. In order to solve the lidar equation measurements of total atmospheric optical depth by means of Microtops sun photometer was done. Mean size and the aspect ratio of dust particles were determined by comparing of lidar observations with data from T-matrix calculations.
Evaluation of the Transport and Deposition of Fugitive Dust Using Lidar
2002
Ambient measurements suggest that source inventories of PM 10 from geologic sources are overestimated by 50 percent or more. This discrepancy may be due to inaccurate emission calculations and/or due to the rapid deposition of PM 10 after entrainment into the atmosphere. Tests were conducted during December 2000 and December 2001 using a two-wavelength scanning backscatter lidar to investigate PM 10 deposition rates from artificially generated fugitive dust. Dust was generated by vehicles on unpaved roads and with a blower dispersing known amounts of finely ground calcium carbonate (paint pigment) or native soil. The size and concentration of the resulting dust plumes were monitored for up to a half-hour and a distance of several kilometers. The changes in these dust plumes' characteristics with time, including particle size and density, were estimated from the relationship between backscatter and extinction for the two wavelengths used. The lidar was calibrated using dust of known size distribution and concentration generated in a contained volume during a set of tests conducted in December 2001. An approximation of the backscatter and extinction signals has been obtained using model calculations that are based upon Mie theory for spherical particles. These models show that the backscatter signal does not depend strongly on the particle density but does depend strongly upon size and wavelength of the scattering radiation. However, the extinction depends strongly on the concentration and size of the scattering particles but not on the wavelength. Therefore, simultaneous measurements of the backscatter and extinction at two different wavelengths should permit analysis to reveal the approximate settling rates for the various types (i.e., sources) of fugitive dust.
Atmospheric Chemistry and Physics, 2003
Single wavelength polarization lidar observations collected at Mt. Cimone (44.2 • N, 10.7 • E, 1870 m a.s.l.) during the June 2000 MINATROC campaign are analyzed to derive tropospheric profiles of aerosol extinction, depolarization, surface area and volume. Lidar retrievals for the 2170-2245 m level are compared to the same variables as computed from in situ measurements of particles size distributions, performed at the mountain top Station (2165 m a.s.l.) by a differential mobility analyzer (DMA) and an optical particle counter (OPC). A sensitivity analysis of this closure experiment shows that mean relative differences between the backscatter coefficients obtained by the two techniques undergo a sharp decrease when hygroscopic growth to ambient humidity is considered for the DMA dataset, otherwise representative of dry aerosols. Minimization of differences between lidar and size distribution-derived backscatter coefficients allowed to find values of the "best" refractive index, specific to each measurement. These results show the refractive index to increase for air masses proceeding from Africa and Western Europe. Lidar depolarization was observed to minimize mainly in airmasses proceeding from Western Europe, thus indicating a spherical, i.e. liquid nature for such aerosols. Conversely, African, Mediterranean and East Europe aerosol showed a larger depolarizing fraction, mainly due to coexisting refractory and soluble fractions. The analysis shows average relative differences between lidar and insitu observations of 5% for backscatter, 36% for extinction 41% for surface area and 37% for volume. These values are well within the expected combined uncertainties of the lidar and in situ retrievals. Average differences further decrease during the Saharan dust transport event, when a lidar signal inversion model considering non-spherical scatterers is employed. The quality of the closure obtained between particle counter and lidar-derived aerosol surface area and volume observations constitutes a validation of the technique
Atmospheric Research, 2004
Functional relationships linking at k 0 = 351 nm aerosol extinction a k 0 aer and backscatter coefficient b k 0 aer of maritime and desert type aerosols are determined to allow for inversion of the singlewavelength lidar signals. Such relationships are derived as mean behavior of 20,000 extinction versus backscatter computations, performed for aerosol size distributions and compositions whose describing parameters are randomly chosen within the naturally observed variability. For desert-type aerosols, the effect of the particle non-sphericity is considered and it is shown that the extinction to backscatter ratio of non-spherical dust particles can be up to 60% larger than the values obtained for spherical particles. Aerosol extinction and backscatter coefficient profiles obtained inverting the single-wavelength lidar signal with the modeled relationships are then compared to the same profiles measured by a combined elastic-Raman lidar operating at 351 nm. Analytical back trajectories and satellite images are used to characterize advection patterns during lidar measurements and to properly choose the modeled functional relationship. A good accordance between the two techniques is found for advection patterns over the lidar site typical of maritime and dust conditions. Maximum differences between the model-based a k 0 aer and b k 0 aer vertical profiles and the corresponding ones measured by the combined elastic-Raman lidar technique are of 30% and 40% in maritime and desert dust conditions, respectively. The comparison of elastic-Raman lidar measurements and model-based results also reveals that particle non-sphericity must be taken into account when mineral dust-type aerosols are directly advected over the measurement site.
Saharan aerosol sensed over Warsaw by backscatter depolarization lidar
2010
The estimates of the optical properties of mineral dust aerosol observed on April 13th and 14th, 2005 during SAWA (Saharan aerosol over Warsaw) experiment are described. Lidar signals at 532 and 1064 nm wavelengths were inverted with a modified Klett -Fernald algorithm. Aerosol optical depth measured with a sun-photometer allowed to reduce uncertainties in the inversion procedure. Further improvement of the estimation came from distinguishing three aerosol layers in the atmosphere on the basis of vertical profiles of optical properties. Having calculated vertical distributions of aerosol extinction coefficients, profiles of local Angstrom exponent were estimated. Independent information on depolarisation of 532 nm lidar returns, together with the assumption about the spheroidal shape and random orientation of aerosol particles, allowed to estimate the aspect ratio and size of particles on the basis of numerical calculations with transition matrix (T-matrix) algorithm by M. Mishchenko. Results indicate the mode radii of spheroids in the range of 0.15 -0.3 μm, and their aspect ratio in the range of 0.6 -0.8 or 1.3 -2.2 (two solutions are allowed). Small size of the particles is explained by dust deposition and mixing with boundary layer aerosol in the Mediterranean region.
Journal of Geophysical Research, 2002
1] During the Lindenberg Aerosol Characterization Experiment (LACE 98) simultaneous measurements with ground-based and airborne lidars and with two aircraft equipped with aerosol in situ instrumentation were performed. From the lidar measurements, particle backscatter coefficients at up to eight wavelengths between 320 and 1064 nm and particle extinction coefficients at 2-3 wavelengths between 292 and 532 nm were determined. Thus, for the first time, an extensive set of optical particle properties from several lidar platforms was available for the inversion into particle microphysical quantities. For this purpose, two different inversion algorithms were used, which provide particle effective radius, volume, surface-area, and number concentrations, and complex refractive index. The single-scattering albedo follows from Mie-scattering calculations. The parameters were compared to the ones from airborne measurements of particle size distributions and absorption coefficients. Two measurement cases were selected. During the night of 9 -10 August 1998 measurements were taken in a biomass-burning aerosol layer in the free troposphere, which was characterized by a particle optical depth of about 0.1 at 550 nm. Excellent agreement between remote-sensing and in situ measurements was found. In the center of this plume the effective radius was approximately 0.25 m, and all methods showed rather high complex refractive indices, ranging from 1.56 -1.66 in real part and from 0.05-0.07i in imaginary part. The single-scattering albedo showed low values from 0.78 -0.83 at 532 nm. The second case, taken on 11 August 1998, presents the typical conditions of a polluted boundary layer in central Europe. Optical depth was 0.35 at 550 nm, and particle effective radii were 0.1-0.2 m. In contrast to the first case, imaginary parts of the refractive index were below 0.03i. Accordingly, the single-scattering albedo ranged from 0.87-0.95. Optical and microphysical characterization of biomass-burning and industrial-pollution aerosols from multiwavelength lidar and aircraft measurements,
Optical Properties of Aerosols from Lidar Data and Other Ground-based Instruments Near Bucharest
Chemical engineering transactions, 2008
The aerosols in the lower troposphere are one of the major issues studied by scientific community mainly because of their effect on human health and their role in climate change. They have also a determining effect on visibility and contribute to the soiling of monuments. Observations and model calculations show that the increase in the atmospheric aerosol burden is delaying the global warming expected from the increase in greenhouse gasses. The aim of present paper is to analyze the aerosol characteristics of aerosol in 0-5 km altitude interval, at Magurele-Bucharest, Romania (44.35 N, 26.03 E) during 2007, using ground-based Lidar (Light Detection and Ranging) and Sun-photometer data. The optical thickness show seasonal variation resulting from different aerosol sources, long range transport and local atmospheric environment. Saharan dust and biomass burning can be identified using back trajectories analysis.