scholarly journals Vertical variation of optical properties of mixed Asian dust/pollution plumes according to pathway of airmass transport over East Asia

2015 ◽  
Vol 15 (3) ◽  
pp. 3381-3413 ◽  
Author(s):  
S.-K. Shin ◽  
D. Müller ◽  
K. H. Lee ◽  
D. Shin ◽  
Y. J. Kim ◽  
...  
Keyword(s):  
Optical Properties ◽  
Asian Dust ◽  
Optical Characteristics ◽  
Vertical Position ◽  
Depolarization Ratio ◽  
Dust Pollution ◽  
Transport Time ◽  
Lidar Measurements ◽  
The Mean ◽  
532 Nm

Abstract. We use five years (2009–2013) of multiwavelength Raman lidar measurements at Gwangju, Korea (35.10° N, 126.53° E) for the identification of changes of optical properties of East Asian dust in dependence of its transport path over China. Profiles of backscatter and extinction coefficients, lidar ratios, and backscatter-related Ångström exponents (wavelength pair 355/532 nm) were measured at Gwangju. Linear particle depolarization ratios were used to identify East Asian dust layers. We used backward trajectory modelling to identify the pathway and the vertical position of dust-laden air masses over China during long-range transport. Most cases of Asian dust events can be described by the emission of dust in desert areas and subsequent transport over highly polluted regions of China. The Asian dust plumes could be categorized into two classes according to the height above ground in which these plumes were transported: (I) the dust layers passed over China at high altitude levels until arrival over Gwangju, and (II) the Asian dust layers were transported near the surface and the lower troposphere over industrialized areas before they arrived over Gwangju. We find that the optical characteristics of these mixed Asian dust layers over Gwangju differ in dependence of their vertical position above ground over China and the change of height above ground during transport. The mean linear particle depolarization ratio was 0.21 ± 0.06 (at 532 nm), the mean lidar ratios were 52 ± 7 sr at 355 nm and 53 ± 8 sr at 532 nm, and the mean Ångström exponent was 0.74 ± 0.31 in case I. In contrast, plumes transported at lower altitudes (case II) showed low depolarization ratios, and higher lidar ratio and Ångström exponents. The mean linear particle depolarization ratio was 0.13 ± 0.04, the mean lidar ratios were 63 ± 9 sr at 355 nm and 62 ± 8 sr at 532 nm, respectively, and the mean Ångström exponent was 0.98 ± 0.51. These numbers show that the optical characteristics of mixed Asian plumes are more similar to optical characteristics of urban pollution. We find a decrease of the linear depolarization ratio of the mixed dust/pollution plume in dependence of transport time if the pollution layer travelled over China at low heights, i.e., below approximately 3 km above ground. In contrast we do not find such a trend if the dust plumes travelled at heights above 4 km over China. We need a longer time series of lidar measurements in order to determine the change of optical properties of dust with transport time in a quantitative way.

scholarly journals Vertical variation of optical properties of mixed Asian dust/pollution plumes according to pathway of air mass transport over East Asia

2015 ◽  
Vol 15 (12) ◽  
pp. 6707-6720 ◽  
Author(s):  
S.-K. Shin ◽  
D. Müller ◽  
C. Lee ◽  
K. H. Lee ◽  
D. Shin ◽  
...  
Keyword(s):  
Optical Properties ◽  
East Asian ◽  
Asian Dust ◽  
Optical Characteristics ◽  
Vertical Position ◽  
Dust Pollution ◽  
Transport Time ◽  
Lidar Measurements ◽  
The Mean ◽  
532 Nm

Abstract. We use five years (2009–2013) of multiwavelength Raman lidar measurements at Gwangju, South Korea (35.10° N, 126.53° E) for the identification of changes of optical properties of East Asian dust depending on its transport path over China. Profiles of backscatter and extinction coefficients, lidar ratios, and backscatter-related Ångström exponents (wavelength pair 355/532 nm) were measured at Gwangju. Linear particle depolarization ratios were used to identify East Asian dust layers. We used backward trajectory modeling to identify the pathway and the vertical position of dust-laden air masses over China during long-range transport. Most cases of Asian dust events can be described by the emission of dust in desert areas and subsequent transport over highly polluted regions of China. The Asian dust plumes could be categorized into two classes according to the height above ground at which these plumes were transported: (case I) the dust layers passed over China at high altitude levels (> 3 km) until arrival over Gwangju, and (case II) the Asian dust layers were transported near the surface and within the lower troposphere (< 3 km) over industrialized areas before they arrived over Gwangju. We find that the optical characteristics of these mixed Asian dust layers over Gwangju differ depending on their vertical position above ground over China and the change of height above ground during transport. The mean linear particle depolarization ratio was 0.21 ± 0.06 (at 532 nm), the mean lidar ratios were 52 ± 7 sr at 355 nm and 53 ± 8 sr at 532 nm, and the mean Ångström exponent was 0.74 ± 0.31 for case I. In contrast, plumes transported at lower altitudes (case II) showed low depolarization ratios (0.13 ± 0.04 at 532 nm), and higher lidar ratio (63 ± 9 sr at 355 nm and 62 ± 8 sr at 532 nm) and Ångström exponents (0.98 ± 0.51). These numbers show that the optical characteristics of mixed Asian plumes are more similar to optical characteristics of urban pollution. We find a decrease of the linear depolarization ratio of the mixed dust/pollution plume depending on transport time if the pollution layer traveled over China at low heights, i.e., below approximately 3 km above ground. In contrast, we do not find such a trend if the dust plumes traveled at heights above 3 km over China. We need a longer time series of lidar measurements in order to determine in a quantitative way the change of optical properties of dust with transport time.

scholarly journals Profiling Aerosol Optical Properties at the Central Asian Site of Dushanbe, Tajikistan: Pure Dust Cases

2020 ◽  
Vol 237 ◽  
pp. 02027
Author(s):  
Julian Hofer ◽  
Dietrich Althausen ◽  
Sabur F. Abdullaev ◽  
Abduvosit N. Makhmudov ◽  
Bakhron I. Nazarov ◽  
...  
Keyword(s):  
Optical Properties ◽  
Central Asia ◽  
Asian Dust ◽  
Aerosol Optical Properties ◽  
Central Asian ◽  
The Mean ◽  
Ground Based Lidar ◽  
First Time ◽  
532 Nm

Tajikistan is often affected by atmospheric mineral dust originating from various surrounding deserts. The direct and indirect radiative effects of that dust play a sensitive role in the Central Asian climate system and therefore need to be quantified. The Central Asian Dust Experiment (CADEX) provides for the first time an aerosol climatology for Central Asia based long-term aerosol profiling by ground-based lidar (PollyXT type) in Dushanbe, Tajikistan. For pure dust cases, mean depolarization(lidar) ratios of 0.23±0.03(44±3 sr) at 355 nm and 0.32±0.02(38±3 sr) at 532 nm wavelength have been measured. The mean extinction-related Ångström exponent was 0.18±0.15.

scholarly journals Comparison of the optical properties of pure and transported anthropogenic dusts measured by ground-based Lidar

2017 ◽  
Author(s):  
Zhijuan Zhang ◽  
Bin Chen ◽  
Jianping Huang ◽  
Jingjing Liu ◽  
Jianrong Bi ◽  
...  
Keyword(s):  
Optical Properties ◽  
Spherical Shape ◽  
Threshold Value ◽  
Dual Band ◽  
Depolarization Ratio ◽  
Color Ratio ◽  
Lidar Measurements ◽  
Ground Based Lidar ◽  
Two Peaks ◽  
532 Nm

Abstract. In this study, the optical properties of pure dust (PDU) and transported anthropogenic dust (TDU) (also defined as polluted dust) are compared by using ground-based Lidar data for the period from October 2009 to June 2013. The total attenuated backscattering coefficient at 532 nm, the linear volume depolarization ratio and the color ratio are derived from the L2S-SM-II dual-band polarization Lidar. We found that the TDU has a spherical shape, a small linear volume depolarization ratio and a large color ratio which representing its large particle sizes. The threshold value delineating PDU and TDU was approximately 0.2, which is the same as the threshold value used in the CALIPSO CAD algorithm. The histogram of the attenuated backscattering coefficients and the color ratios of pure dust shows two peaks, but that for the transported anthropogenic dust shows no significant peak and a nearly uniform distribution. The ground-based Lidar results confirm that both the transported anthropogenic dust and pure dust can be detected by air-borne or ground-based Lidar measurements.

scholarly journals Properties of biomass burning aerosol mixtures derived at fine temporal and spatial scales from Raman lidar measurements: Part I optical properties

2019 ◽  
Author(s):  
Lucja Janicka ◽  
Iwona S. Stachlewska
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Spatial Scales ◽  
Depolarization Ratio ◽  
Data Set ◽  
Lidar Ratio ◽  
Biomass Burning Aerosol ◽  
The Mean ◽  
Temporal And Spatial ◽  
532 Nm

Abstract. The analysis of the aerosol optical properties derived at fine temporal and spatial scales were performed based on measurements obtained during heat wave event in vicinity of a cold weather front in Warsaw on August 9th–11th, 2015. The signals collected by the PollyXT-UW lidar allowed for the calculation of 23 sets of so-called 3β + 2α + 2δ + wv profiles averaged by 30-minutes periods during 2 nights. The total number of 11 different aerosol types and aerosol mixtures were identified with reference to properties within 116 sub-layers in the profiles and were characterized by the mean values. The statistical sample of various optical properties being in agreement for consecutive profiles allowed to assess the spatio-temporal extent of aerosol/mixture types. The mean lidar ratio values of 53–73 sr (355 nm) and 31–45 sr (532 nm) in the layers dominated by the anthropogenic pollution were found. For the layers dominated by the biomass burning aerosol (fresh, moderately fresh, moderately aged) mean lidar ratio was of 69–114 sr (355 nm) and 57–85 sr (532 nm). The colour ratio of lidar ratio (532 / 355) higher than 1, characteristic for aged biomass burning aerosol, was found only in one scattered layer, accompanying with low value of extinction related Ångström exponent of 0.60 ± 0.32 and low particle depolarization ratio. The maximum of the particle depolarization ratio of 4.8–5.0 % at 532 nm were observed in a layer likely contaminated with pollen and in a layer dominated by fresh biomass burning aerosol. This study provides an excellent data set for exploration of separation algorithms, aerosol typing algorithms and microphysical inversion.

scholarly journals Benefit of depolarization ratio at λ = 1064 nm for the retrieval of the aerosol microphysics from lidar measurements

2014 ◽  
Vol 7 (11) ◽  
pp. 3773-3781 ◽  
Author(s):  
J. Gasteiger ◽  
V. Freudenthaler
Keyword(s):  
Optical Properties ◽  
Mass Concentration ◽  
Volcanic Ash ◽  
Single Scattering ◽  
Depolarization Ratio ◽  
Complex Relation ◽  
Microphysical Properties ◽  
Lidar Measurements ◽  
Increased Sensitivity ◽  
Linear Depolarization Ratio

Abstract. A better quantification of aerosol properties is required for improving the modelling of aerosol effects on weather and climate. This task is methodologically demanding due to the diversity of the microphysical properties of aerosols and the complex relation between their microphysical and optical properties. Advanced lidar systems provide spatially and temporally resolved information on the aerosol optical properties that is sufficient for the retrieval of important aerosol microphysical properties. Recently, the mass concentration of transported volcanic ash, which is relevant for the flight safety of aeroplanes, was retrieved from measurements of such lidar systems in southern Germany. The relative uncertainty of the retrieved mass concentration was on the order of ±50%. The present study investigates improvements of the retrieval accuracy when the capability of measuring the linear depolarization ratio at 1064 nm is added to the lidar setup. The lidar setups under investigation are based on those of MULIS and POLIS of the Ludwig-Maximilians-Universität in Munich (Germany) which measure the linear depolarization ratio at 355 and 532 nm with high accuracy. The improvements are determined by comparing uncertainties from retrievals applied to simulated measurements of this lidar setup with uncertainties obtained when the depolarization at 1064 nm is added to this setup. The simulated measurements are based on real lidar measurements of transported Eyjafjallajökull volcano ash. It is found that additional 1064 nm depolarization measurements significantly reduce the uncertainty of the retrieved mass concentration and effective particle size. This significant improvement in accuracy is the result of the increased sensitivity of the lidar setup to larger particles. The size dependence of the depolarization does not vary strongly with refractive index, thus we expect similar benefits for the retrieval in case of measurements of other volcanic ash compositions and also for transported desert dust. For the retrieval of the single scattering albedo, which is relevant to the radiative transfer in aerosol layers, no significant improvements were found.

scholarly journals Airborne pollen observations using a multi-wavelength Raman polarization lidar in Finland: characterization of pure pollen types

2020 ◽  
Author(s):  
Xiaoxia Shang ◽  
Elina Giannakaki ◽  
Stephanie Bohlmann ◽  
Maria Filioglou ◽  
Annika Saarto ◽  
...  
Keyword(s):  
Optical Properties ◽  
Airborne Pollen ◽  
Pollen Grains ◽  
Wavelength Dependence ◽  
Depolarization Ratio ◽  
Mean Values ◽  
Pollen Types ◽  
Pine Pollen ◽  
Significant Wavelength ◽  
532 Nm

Abstract. We present a novel algorithm for characterizing the optical properties of pure pollen particles, based on the depolarization values obtained in lidar measurements. The algorithm was first tested and validated through a simulator, and then applied to the lidar observations during a four-month pollen campaign from May to August 2016 at the European Aerosol Research Lidar Network (EARLINET) station in Kuopio (62°44′ N, 27°33′ E), in Eastern Finland. Twenty types of pollen were observed and identified from concurrent measurements with Burkard sampler; Birch (Betula), pine (Pinus), spruce (Picea) and nettle (Urtica) pollen were most abundant, contributing more than 90 % of total pollen load, regarding number concentrations. Mean values of lidar-derived optical properties in the pollen layer were retrieved for four intense pollination periods (IPPs). Lidar ratios at both 355 and 532 nm ranged from 55 to 70 sr for all pollen types, without significant wavelength-dependence. Enhanced depolarization ratio was found when there were pollen grains in the atmosphere, and even higher depolarization ratio (with mean values of 25 % or 14 %) was observed with presence of the more non-spherical spruce or pine pollen. The depolarization ratio at 532 nm of pure pollen particles was assessed, resulting to 24 ± 3 % and 36 ± 5 % for birch and pine pollen, respectively. Pollen optical properties at 1064 nm and 355 nm were also estimated. The backscatter-related Ångström exponent between 532 and 1064 nm was assessed as ~ 0.8 (~ 0.5) for pure birch (pine) pollen, thus the longer wavelength would be better choice to trace pollen in the air. The pollen depolarization ratio at 355 nm of 17 % and 30 % were found for birch and pine pollen, respectively. The depolarization values show a wavelength dependence for pollen. This can be the key parameter for pollen detection and characterization.

scholarly journals Airborne measurements of aerosol optical properties related to early spring transport of mid-latitude sources into the Arctic

2010 ◽  
Vol 10 (11) ◽  
pp. 5011-5030 ◽  
Author(s):  
R. A. de Villiers ◽  
G. Ancellet ◽  
J. Pelon ◽  
B. Quennehen ◽  
A. Schwarzenboeck ◽  
...  
Keyword(s):  
Optical Properties ◽  
The Arctic ◽  
Depolarization Ratio ◽  
Aerosol Optical Properties ◽  
Accumulation Mode ◽  
Color Ratio ◽  
Aerosol Sources ◽  
Aerosol Backscatter ◽  
532 Nm

Abstract. Airborne lidar and in-situ measurements of the aerosol properties were conducted between Svalbard Island and Scandinavia in April 2008. Evidence of aerosol transport from Europe and Asia is given. The analysis of the aerosol optical properties based on a multiwavelength lidar (355, 532, 1064 nm) including volume depolarization at 355 nm aims at distinguishing the role of the different aerosol sources (Siberian wild fires, Eastern Asia and European anthropogenic emissions). Combining, first aircraft measurements, second FLEXPART simulations with a calculation of the PBL air fraction originating from the three different mid-latitude source regions, and third level-2 CALIPSO data products (i.e. backscatter coefficient 532 nm,volume depolarization and color ratio between 1064 and 532 nm in aerosol layers) along the transport pathways, appears a valuable approach to identify the role of the different aerosol sources even after a transport time larger than 4 days. Optical depth of the aerosol layers are always rather small (<4%) while transported over the Arctic and ratio of the total attenuated backscatter (i.e. including molecular contribution) provide more stable result than conventional aerosol backscatter ratio. Above Asia, CALIPSO data indicate more depolarization (up to 15%) and largest color ratio (>0.5) for the northeastern Asia emissions (i.e. an expected mixture of Asian pollution and dust), while low depolarization together with smaller and quasi constant color ratio (≈0.3) are observed for the Siberian biomass burning emissions. A similar difference is visible between two layers observed by the aircraft above Scandinavia. The analysis of the time evolution of the aerosol optical properties revealed by CALIPSO between Asia and Scandinavia shows a gradual decrease of the aerosol backscatter, depolarization ratio and color ratio which suggests the removal of the largest particles in the accumulation mode. A similar study conducted for a European plume has shown aerosol optical properties intermediate between the two Asian sources with color ratio never exceeding 0.4 and moderate depolarization ratio being always less than 8%, i.e. less aerosol from the accumulation mode.

scholarly journals Benefit of depolarization ratio at λ = 1064 nm for the retrieval of the aerosol microphysics from lidar measurements

2014 ◽  
Vol 7 (5) ◽  
pp. 5095-5115
Author(s):  
J. Gasteiger ◽  
V. Freudenthaler
Keyword(s):  
Optical Properties ◽  
Mass Concentration ◽  
Single Scattering ◽  
Sufficient Information ◽  
Depolarization Ratio ◽  
Aerosol Composition ◽  
Microphysical Properties ◽  
Lidar Measurements ◽  
Increased Sensitivity ◽  
Linear Depolarization Ratio

Abstract. A better quantification of aerosol microphysical and optical properties is required to improve the modelling of aerosol effects on weather and climate. This task is methodologically demanding due to the huge diversity of aerosol composition and of their shape and size distribution, and due to the complexity of the relation between the microphysical and optical properties. Lidar remote sensing is a valuable tool to gain spatially and temporally resolved information on aerosol properties. Advanced lidar systems provide sufficient information on the aerosol optical properties for the retrieval of important aerosol microphysical properties. Recently, the mass concentration of transported volcanic ash, which is relevant for the flight safety of airplanes, was retrieved from measurements of such lidar systems in Southern Germany. The relative uncertainty of the retrieved mass concentration was on the order of ±50%. The present study investigates improvements of the retrieval accuracy when the capability of measuring the linear depolarization ratio at 1064 nm is added to the lidar setup. The lidar setups under investigation are based on the setup of MULIS and POLIS of the LMU in Munich which measure the linear depolarization ratio at 355 nm and 532 nm with high accuracy. By comparing results of retrievals applied to simulated lidar measurements with and without the depolarization at 1064 nm it is found that the availability of 1064 nm depolarization measurements reduces the uncertainty of the retrieved mass concentration and effective particle size by a factor of about 2–3. This significant improvement in accuracy is the result of the increased sensitivity of the lidar setup to larger particles. However, the retrieval of the single scattering albedo, which is relevant for the radiative transfer in aerosol layers, does hardly benefit from the availability of 1064 nm depolarization measurements.

scholarly journals The potential of elastic and polarization lidars to retrieve extinction profiles

2020 ◽  
Vol 13 (2) ◽  
pp. 893-905 ◽  
Author(s):  
Elina Giannakaki ◽  
Panos Kokkalis ◽  
Eleni Marinou ◽  
Nikolaos S. Bartsotas ◽  
Vassilis Amiridis ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Dust Particles ◽  
Depolarization Ratio ◽  
Lidar System ◽  
Lidar Measurements ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio ◽  
Aerosol Types ◽  
532 Nm

Abstract. A new method, called ElEx (elastic extinction), is proposed for the estimation of extinction coefficient lidar profiles using only the information provided by the elastic and polarization channels of a lidar system. The method is applicable to lidar measurements both during daytime and nighttime under well-defined aerosol mixtures. ElEx uses the particle backscatter profiles at 532 nm and the vertically resolved particle linear depolarization ratio measurements at the same wavelength. The particle linear depolarization ratio and the lidar ratio values of pure aerosol types are also taken from literature. The total extinction profile is then estimated and compared well with Raman retrievals. In this study, ElEx was applied in an aerosol mixture of marine and dust particles at Finokalia station during the CHARADMExp campaign. Any difference between ElEx and Raman extinction profiles indicates that the nondust component could be probably attributed to polluted marine or polluted continental aerosols. Comparison with sun photometer aerosol optical depth observations is performed as well during daytime. Differences in the total aerosol optical depth are varying between 1.2 % and 72 %, and these differences are attributed to the limited ability of the lidar to correctly represent the aerosol optical properties in the near range due to the overlap problem.

scholarly journals Assessment of aerosol's mass concentrations from measured linear particle depolarization ratio (vertically resolved) and simulations

2013 ◽  
Vol 6 (3) ◽  
pp. 5923-5957
Author(s):  
A. Nemuc ◽  
J. Vasilescu ◽  
C. Talianu ◽  
L. Belegante ◽  
D. Nicolae
Keyword(s):  
Atmospheric Model ◽  
Saharan Dust ◽  
Depolarization Ratio ◽  
Backscatter Coefficient ◽  
Regional Atmospheric Model ◽  
Lidar Measurements ◽  
Different Origins ◽  
532 Nm ◽  
Good Agreement ◽  
Mass Concentrations

Abstract. Multiwavelength depolarization Raman lidar measurements from Magurele, Romania are used in this study along with simulated mass-extinction efficiencies to calculate the mass concentrations profiles of different atmospheric components, due to their different depolarization contribution to the 532 nm backscatter coefficient. Linear particle depolarization ratio (δpart) was computed using the relative amplification factor and the system-dependent molecular depolarization. The low depolarizing component was considered as urban/smoke, with a mean δpart of 3%, while for the high depolarizing component (mineral dust) a mean δpart of 35% was assumed. For this study 11 months of lidar measurements were analyzed. Two study cases are presented in details: one for a typical Saharan dust aerosol intrusion, 10 June 2012 and one for 12 July 2012 when a lofted layer consisting of biomass burning smoke extended from 3 to 4.5 km height. Optical Properties of Aerosols and Clouds software package (OPAC) classification and conversion factors were used to calculate mass concentrations. We found that calibrated depolarization measurements are critical to distinguish between smoke-reach aerosol during the winter and dust-reach aerosol during the summer, as well as between elevated aerosol layers having different origins. Good agreement was found between lidar retrievals and DREAM- Dust REgional Atmospheric Model forecasts in cases of Saharan dust. Our method was also compared against LIRIC (The Lidar/Radiometer Inversion Code) and very small differences were observed.

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