scholarly journals Monitoring Atmospheric Aerosols Over the Urmia Lake by CALIPSO and a Ground Based Depolarized Lidar

2020 ◽  
Vol 237 ◽  
pp. 02025
Author(s):  
Hamid R. Khalesifard ◽  
Hossein Panahifar ◽  
Fatemeh Ghomashi ◽  
Salar Alizadeh ◽  
Ruhollah Moradhaseli
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Urmia Lake ◽  
Hypersaline Lake ◽  
Depolarization Ratio ◽  
Hysplit Model ◽  
Aerosol Source

The Urmia Lake, a hypersaline lake in Northwest Iran is facing a severe drying scenario. We have installed an azimuthal scanning depolarized backscatter lidar in the coast of the lake to monitor the atmospheric aerosols that may originate from the dried lake bed. We also used the CALIPSO recordings to monitor the aerosol optical depth and particulate depolarization ratio just over the lake. Recordings of the lidar and CALIPSO both show that dry salt particles can be found in the atmospheric boundary layer over the lake especially in summer times. Also CALIPSO data in synergy with HYSPLIT model show that the lake is not an intense aerosol source comparing to neighboring sources like the Mesopotamia region but it is under their influence.

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – A lidar study during SALTRACE

2016 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Depolarization Ratio ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Lidar Ratio ◽  
The Caribbean ◽  
Linear Depolarization Ratio ◽  
532 Nm

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high accurate measurements of the linear depolarization ratio down to about 150–200 m above ground level, the dust volume fraction and the dust mass concentration within the Caribbean boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information of the boundary layer height and the meteorological situation within the boundary layer. We investigate the lidar derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find over all mean values and mean uncertainties of 0.04 ± 0.03 and 0.05 ± 0.04 at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and 26 ± 5 sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the Caribbean boundary layer we find that most values are between 20 and 50 g/m3, and that on most days the dust contribution to total aerosol volume is about 30–40 %. Comparing the dust contribution to the columnintegrated sun-photometer measurements we see a correlation of high dust contribution, high total aerosol optical depth and a corresponding low Angström exponent, and of low dust contribution with low total aerosol optical depth and corresponding high Angström exponent. The relative humidity within the boundary layer was high with values around 80 % on most of the days.

scholarly journals Saharan dust contribution to the Caribbean summertime boundary layer – a lidar study during SALTRACE

2016 ◽  
Vol 16 (18) ◽  
pp. 11535-11546 ◽  
Author(s):  
Silke Groß ◽  
Josef Gasteiger ◽  
Volker Freudenthaler ◽  
Thomas Müller ◽  
Daniel Sauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Marine Boundary Layer ◽  
Volume Fraction ◽  
Saharan Dust ◽  
Depolarization Ratio ◽  
Mean Values ◽  
Lidar Ratio ◽  
Linear Depolarization Ratio

Abstract. Dual-wavelength lidar measurements with the small lidar system POLIS of the Ludwig-Maximilians-Universität München were performed during the SALTRACE experiment at Barbados in June and July 2013. Based on high-accuracy measurements of the linear depolarization ratio down to about 200 m above ground level, the dust volume fraction and the dust mass concentration within the convective marine boundary layer can be derived. Additional information from radiosonde launches at the ground-based measurement site provide independent information on the convective marine boundary layer height and the meteorological situation within the convective marine boundary layer. We investigate the lidar-derived optical properties, the lidar ratio and the particle linear depolarization ratio at 355 and 532 nm and find mean values of 0.04 (SD 0.03) and 0.05 (SD 0.04) at 355 and 532 nm, respectively, for the particle linear depolarization ratio, and (26 ± 5) sr for the lidar ratio at 355 and 532 nm. For the concentration of dust in the convective marine boundary layer we find that most values were between 20 and 50 µgm−3. On most days the dust contribution to total aerosol volume was about 30–40 %. Comparing the dust contribution to the column-integrated sun-photometer measurements we see a correlation between high dust contribution, high total aerosol optical depth and a low Angström exponent, and of low dust contribution with low total aerosol optical depth.

scholarly journals Evolution of Aerosols in the Atmospheric Boundary Layer and Elevated Layers during a Severe, Persistent Haze Episode in a Central China Megacity

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 152
Author(s):  
Yunfei Zhang ◽  
Yunpeng Zhang ◽  
Changming Yu ◽  
Fan Yi
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
Atmospheric Boundary Layer ◽  
Optical Depth ◽  
Distinct Pattern ◽  
Central China ◽  
Pollution Level ◽  
Hysplit Model ◽  
Convective Boundary ◽  
Anthropogenic Pollutants

Aerosol vertical profiling is crucial to understand the formation mechanism and evolution processes of haze, which have not yet been comprehensively clarified. In this study, we investigated a severe, persistent haze event in Wuhan (30.5° N, 114.4° E), China during 5–18 January 2013 by the use of a polarization lidar, a Cimel sun photometer, meteorological datasets, and the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model, focusing on the time–height evolution of aerosols in both the atmospheric boundary layer (ABL) and elevated layers. During the haze period, the integrated particle depolarization ratio was 0.05 ± 0.02, and the fine mode fraction reached 0.91 ± 0.03, indicating haze particles were rather spherical and predominately submicron, that is, of anthropogenic nature. Compared with the clear period, columnar aerosol optical depth at 500 nm tripled to 1.32 ± 0.31, and the strongest enhancement in aerosol concentration occurred from near the ground to an altitude of 1.2 km during the haze period. The daytime evolution of aerosol vertical distribution in the ABL exhibited a distinct pattern under haze weather. Abundant particles accumulated below 0.5 km in the morning hours due to stable meteorological conditions, including a strong surface-based inversion (4.4–8.1 °C), late development (from 1000–1100 LT) of the convective boundary layer, and weak wind (<4 m∙s−1) in the lowermost troposphere. In the afternoon, improved ventilation delivered an overall reduction in boundary layer aerosols but was insufficient to eliminate haze. Particularly, the morning residual layer had an optical depth of 0.29–0.56. It influenced air quality indirectly by weakening convective activities in the morning and directly through the fumigation process around noon, suggesting it may be an important element in aerosol–ABL interactions during consecutive days with haze. Our lidar also captured the presence of the elevated aerosol layers (EALs) embodying regional/long-range transport. Most of the EALs were observed to subside to <1.2 km and exacerbate the pollution level. Backward trajectory analysis and lidar data revealed the EALs originated from the transport of anthropogenic pollutants from the Sichuan Basin, China, and of dust from the deserts in the northwest. They were estimated to contribute ~19% of columnar aerosol-loading, pointing to a non-negligible role of transport during the intense pollution episode. The results could benefit the complete understanding of aerosol–ABL interactions under haze weather and air quality forecasting and control in Wuhan.

scholarly journals Retrieval of aerosol single-scattering albedo and polarized phase function from polarized sun-photometer measurements for Zanjan's atmosphere

2013 ◽  
Vol 6 (10) ◽  
pp. 2659-2669 ◽  
Author(s):  
A. Bayat ◽  
H. R. Khalesifard ◽  
A. Masoumi
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Phase Function ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Sun Photometer ◽  
Ångstrom Exponent

Abstract. The polarized phase function of atmospheric aerosols has been investigated for the atmosphere of Zanjan, a city in northwest Iran. To do this, aerosol optical depth, Ångström exponent, single-scattering albedo, and polarized phase function have been retrieved from the measurements of a Cimel CE 318-2 polarized sun-photometer from February 2010 to December 2012. The results show that the maximum value of aerosol polarized phase function as well as the polarized phase function retrieved for a specific scattering angle (i.e., 60°) are strongly correlated (R = 0.95 and 0.95, respectively) with the Ångström exponent. The latter has a meaningful variation with respect to the changes in the complex refractive index of the atmospheric aerosols. Furthermore the polarized phase function shows a moderate negative correlation with respect to the atmospheric aerosol optical depth and single-scattering albedo (R = −0.76 and −0.33, respectively). Therefore the polarized phase function can be regarded as a key parameter to characterize the atmospheric particles of the region – a populated city in the semi-arid area and surrounded by some dust sources of the Earth's dust belt.

scholarly journals Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

2020 ◽  
Author(s):  
Stephanie P. Rusli ◽  
Otto Hasekamp ◽  
Joost aan de Brugh ◽  
Guangliang Fu ◽  
Yasjka Meijer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Zenith Angle ◽  
Atmospheric Aerosols ◽  
Solar Zenith Angle ◽  
Added Value ◽  
Aerosol Layer ◽  
Satellite Mission ◽  
Measurement Uncertainties ◽  
Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus candidate mission for anthropogenic CO2 monitoring (CO2M). To this end, we compare aerosol-induced XCO2 errors from standard retrievals using spectrometer only (without MAP) with those from retrievals using both MAP and spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm, and a spread (defined as half of the 15.9th to the 84.1th percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to a worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. Adopting the derived MAP requirements, a retrieval exercise using both MAP and spectrometer measurements of the synthetic scenes delivers XCO2 errors with an overall bias of −0.004 ppm and a spread of 0.54 ppm, implying compliance with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument onboard the CO2M mission.

scholarly journals The regime of Aerosol Optical Depth and Ångström exponent over Central and South Asia

2019 ◽  
Vol 99 ◽  
pp. 01003
Author(s):  
Athina Avgousta Floutsi ◽  
Marios Bruno Korras Carraca ◽  
Christos Matsoukas ◽  
Nikos Hatzianastassiou ◽  
George Biskos
Keyword(s):  
South Asia ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Aerosols ◽  
Dust Particles ◽  
Desert Dust ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Dust Load ◽  
Ångstrom Exponent

Central and South Asia are regions of particular interest for studying atmospheric aerosols, being among the largest sources of desert dust aerosols globally. In this study we use the newest collection (C061) of MODIS - Aqua aerosol optical depth (AOD) at 550 nm and Ångström exponent (a) at 412/470 nm over the 15-year period between 2002 and 2017, providing the longest analyzed dataset for this region. According to our results, during spring and summer, high aerosol load (AOD up to 1.2) consisting of coarse desert dust particles, as indicated by a values as low as 0.15, is observed over the Taklamakan, Thar and Registan deserts and the region between the Aral and Caspian seas. The dust load is much lower during winter and autumn (lower AOD and higher a values compared to the other seasons). The interannual variation of AOD and a suggests that the dust load exhibits large decreasing trends (AOD slopes down to -0.22, a slopes up to 0.47 decade-1) over the Thar desert and large increasing trends between the Aral and Caspian seas (AOD and a slopes up to 0.23 decade-1 and down to -0.61 decade-1, respectively.) The AOD data are evaluated against AERONET surface-based measurements. Generally, MODIS and AERONET data are in good agreement with a correlation coefficient (R) equal to 0.835.

scholarly journals Retrieval of Fine-Resolution Aerosol Optical Depth (AOD) in Semiarid Urban Areas Using Landsat Data: A Case Study in Urumqi, NW China

2020 ◽  
Vol 12 (3) ◽  
pp. 467 ◽  
Author(s):  
Xiangyue Chen ◽  
Jianli Ding ◽  
Jingzhe Wang ◽  
Xiangyu Ge ◽  
Mayira Raxidin ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Urban Areas ◽  
Lookup Table ◽  
Atmospheric Environment ◽  
Sustainable Urban Development ◽  
Long Distance ◽  
Hysplit Model ◽  
Variation Characteristics ◽  
Fine Resolution

The aerosol optical depth (AOD) represents the light attenuation by aerosols and is an important threat to urban air quality, production activities, human health, and sustainable urban development in arid and semiarid regions. To some extent, the AOD reflects the extent of regional air pollution and is often characterized by significant spatiotemporal dynamics. However, detailed local AOD information is ambiguous at best due to limited monitoring techniques. Currently, the availability of abundant satellite data and constantly updated AOD extraction algorithms offer unprecedented perspectives for high-resolution AOD extraction and long-time series analysis. This study, based on the long-term sequence MOD09A1 data from 2010 to 2018 and lookup table generation, uses the improved deep blue algorithm (DB) to conduct fine-resolution (500 m) AOD (at 550 nm wavelength) remote sensing (RS) estimation on Landsat TM/OLI data from the Urumqi region, analyzes the spatiotemporal AOD variation characteristics in Urumqi and combines gray relational analysis (GRA) and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to analyze AOD influence factors and simulate pollutant propagation trajectories in representative periods. The results demonstrate that the improved DB algorithm has a high inversion accuracy for continuous AOD inversion at a high spatial resolution in urban areas. The spatial AOD distribution in Urumqi declines from urban to suburban areas, and higher AODs are concentrated in cities and along roads. Among these areas, Xinshi District has the highest AOD, and Urumqi County has the lowest AOD. The seasonal AOD variation characteristics are distinct, and the AOD order is spring (0.411) > summer (0.285) > autumn (0.203), with the largest variation in spring. The average AOD in Urumqi is 0.187, and the interannual variation generally shows an upward trend. However, from 2010 to 2018, AOD first declined gradually and then declined significantly. Thereafter, AOD reached its lowest value in 2015 (0.076), followed by a significant AOD increase, reaching a peak in 2016 (0.354). This shows that coal to natural gas (NG) project implementation in Urumqi promoted the improvement of Urumqi’s atmospheric environment. According to GRA, the temperature has the largest impact on the AOD in Urumqi (0.699). Combined with the HYSPLIT model, it was found that the aerosols observed over Urumqi were associated with long-range transport from Central Asia, and these aerosols can affect the entire northern part of China through long-distance transport.

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 How much of the global aerosol optical depth is found in the boundary layer and free troposphere?

2017 ◽  
Author(s):  
Quentin Bourgeois ◽  
Annica M. L. Ekman ◽  
Jean-Baptiste Renard ◽  
Radovan Krejci ◽  
Abhay Devasthale ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Climate Models ◽  
Convective Transport ◽  
Free Troposphere ◽  
Range Transport ◽  
Aerosol Classification ◽  
The Tropics ◽  
The Vertical Distribution

Abstract. The global aerosol extinction from the CALIOP space lidar was used to compute aerosol optical depth (AOD) over a nine-year period (2007–2015) and partitioned between the boundary layer (BL) and the free troposphere (FT) using BL heights obtained from the ERA-Interim archive. The results show that the vertical distribution of AOD does not follow the diurnal cycle of the BL but remains similar between day and night highlighting the presence of a residual layer during night. The BL and FT contribute 69 % and 31 %, respectively, to the global tropospheric AOD during daytime in line with observations obtained using the Light Optical Aerosol Counter (LOAC) instrument. The FT AOD contribution is larger in the tropics than at mid-latitudes which indicates that convective transport largely controls the vertical profile of aerosols. Over oceans, the FT AOD contribution is mainly governed by long-range transport of aerosols from emission sources located within neighboring continents. According to the CALIOP aerosol classification, dust and smoke particles are the main aerosol types transported into the FT. Overall, the study shows that the fraction of AOD in the FT – and thus potentially located above low-level clouds – is substantial and deserves more attention when evaluating the radiative effect of aerosols in climate models. More generally, the results have implications for process determining the overall budgets, sources, sinks and transport of aerosol particles and their description in atmospheric models.

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