Is the near-spherical shape the new black for smoke?

Abstract. We examine the capability of near-spherical-shaped particles to reproduce the non-typical Particle Linear Depolarization Ratio (PLDR) values measured over Europe for stratospheric smoke originating from Canadian wildfires. The smoke layers were detected both in the troposphere and the stratosphere, though in the latter case the particles presented PLDR values of almost 18 % at 532 nm as well as a strong spectral dependence from the UV to the Near-IR. The assumption that the smoke particles have a near-spherical shape allows for the reproduction of the observed PLDR and Lidar Ratio (LR), whereas this was not possible when using more complicated shapes. The results presented here are supported by recent findings in the literature, showing that up to now the near-spherical shape (or closely similar shapes) is the only morphology found capable of reproducing the observed intensive optical properties of stratospheric smoke, as well as their spectral dependence.

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Is the near-spherical shape the “new black” for smoke?

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-14005-2020 ◽

2020 ◽

Vol 20 (22) ◽

pp. 14005-14021

Author(s):

Anna Gialitaki ◽

Alexandra Tsekeri ◽

Vassilis Amiridis ◽

Romain Ceolato ◽

Lucas Paulien ◽

...

Keyword(s):

Spectral Dependence ◽

Spherical Shape ◽

Simulation Studies ◽

Particle Characterization ◽

Additional Insight ◽

Near Ir ◽

Lidar Measurements ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

532 Nm

Abstract. We examine the capability of near-spherical-shaped particles to reproduce the triple-wavelength particle linear depolarization ratio (PLDR) and lidar ratio (LR) values measured over Europe for stratospheric smoke originating from Canadian wildfires. The smoke layers were detected both in the troposphere and the stratosphere, though in the latter case the particles presented PLDR values of almost 18 % at 532 nm as well as a strong spectral dependence from the UV to the near-IR wavelength. Although recent simulation studies of rather complicated smoke particle morphologies have shown that heavily coated smoke aggregates can produce large PLDR, herein we propose a much simpler model of compact near-spherical smoke particles. This assumption allows for the reproduction of the observed intensive optical properties of stratospheric smoke, as well as their spectral dependence. We further examine whether an extension of the current Aerosol Robotic Network (AERONET) scattering model to include the near-spherical shapes could be of benefit to the AERONET retrieval for stratospheric smoke cases associated with enhanced PLDR. Results of our study illustrate the fact that triple-wavelength PLDR and LR lidar measurements can provide us with additional insight when it comes to particle characterization.

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Is Near-Spherical Shape “the New Black” for Smoke ?

EPJ Web of Conferences ◽

10.1051/epjconf/202023702017 ◽

2020 ◽

Vol 237 ◽

pp. 02017

Author(s):

Anna Gialitaki ◽

Alexandra Tsekeri ◽

Vassilis Amiridis ◽

Romain Ceolato ◽

Lucas Paulien ◽

...

Keyword(s):

Spherical Shape ◽

Wavelength Dependence ◽

Depolarization Ratio ◽

Smoke Particles ◽

Near Ir ◽

Lidar Measurements ◽

Lidar Ratio ◽

T Matrix ◽

Linear Depolarization Ratio

We present smoke lidar measurements from the Canadian fires of 2017. The advected smoke layers over Europe are detected at both tropospheric and stratospheric heights, with the latter presenting non-typical values of the Particle Linear Depolarization Ratio (PLDR) with strong wavelength dependence from the UV to the Near-IR. Specifically, the PLDR values are of the order of 22, 18 and 4% at 355, 532 and 1064 nm respectively. In an attempt to interpret these results, we apply the hypothesis that smoke particles have near-spherical shapes. Scattering calculations with the T-matrix code support other findings in the literature ([1]- [2]), showing that the near-spherical shape (or closely similar shapes as in [2]), is the only shape that has been shown to reproduce the observed PLDR and Lidar Ratio (LR) values of the stratospheric smoke particles at the three measurement wavelengths.

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Smoke of extreme Australian bushfires observed in the stratosphere over Punta Arenas, Chile, in January 2020: optical thickness, lidar ratios, and depolarization ratios at 355 and 532 nm

10.5194/acp-2020-96 ◽

2020 ◽

Author(s):

Kevin Ohneiser ◽

Albert Ansmann ◽

Holger Baars ◽

Patric Seifert ◽

Boris Barja ◽

...

Keyword(s):

Optical Thickness ◽

Stratospheric Aerosol ◽

Data Sets ◽

Depolarization Ratio ◽

Smoke Particles ◽

Important Input ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

532 Nm ◽

Depolarization Ratios

Abstract. We present particle optical properties of stratospheric smoke layers observed over Punta Arenas (53.2° S, 70.9° W), Chile, at the southernmost tip of South America in January 2020. The smoke originated from the record-breaking bushfires in Australia. The stratospheric aerosol optical thickness reached values up to 0.7 at 532 nm in mid January 2020. The measured smoke extinction-to-backscatter ratios (lidar ratios) and linear depolarization ratios at 355 and 532 nm wavelength indicate shape, size, and light-absorption properties and are important input parameters in the analysis of spaceborne lidar observations of the CALIPSO and Aeolus missions. They are also of key importance regarding the homogenization of the overall Aeolus (355 nm wavelength) and CALIPSO (532 nm wavelength) smoke data sets and interpretation of the observations with respect to the spread of the smoke particles across the southern hemisphere and decay of the stratospheric perturbation. We found typical values and spectral dependencies of the lidar ratio and linear depolarization ratio for aged stratospheric smoke. At 355 nm, the lidar ratio and depolarization ratio ranged from 53–97 sr and 0.2–0.26, respectively. At 532 nm, the lidar ratios were higher (76–104 sr) and the depolarization ratios were lower with values around 0.15. The found lidar ratio and depolarization ratio values for Australian smoke are in good agreement with respective ones obtained from observations of stratospheric smoke layers over central Europe originating from the record-breaking Canadian wildfires in the summer of 2017. The higher 532 nm lidar ratios, however, indicate stronger absorption by the Australian smoke particles.

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The potential of elastic/polarization lidars to retrieve extinction profiles

10.5194/amt-2019-271 ◽

2019 ◽

Author(s):

Elina Giannakaki ◽

Panos Kokkalis ◽

Eleni Marinou ◽

Nikolaos S. Bartsotas ◽

Vassilis Amiridis ◽

...

Keyword(s):

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Dust Particles ◽

Depolarization Ratio ◽

Dust Component ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

Aerosol Types ◽

532 Nm

Abstract. In this study we estimate the particle extinction profiles at Finokalia, Crete, using only the information provided by the elastic and polarization channels of a PollyXT lidar system. Most of the time Finokalia site is affected by only two aerosol types, i.e. marine and dust particles. These two aerosol types, having different optical properties, permit the separation of aerosol mixture. The proposed method 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 taken from literature. The total extinction profile is then estimated and compared well with Raman retrievals. Any difference between the proposed methodology and Raman extinction profiles indicates that the non-dust component could be probably attributed to polluted marine or polluted continental aerosols. Comparison with sun-photometric aerosol optical depth observations is performed as well during daytime with reasonable differences between the two instruments. Differences in the total aerosol optical depth is attributed to the limited ability of the lidar to correctly represent the aerosol optical properties in the near range due to overlap problem.

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The potential of elastic and polarization lidars to retrieve extinction profiles

Atmospheric Measurement Techniques ◽

10.5194/amt-13-893-2020 ◽

2020 ◽

Vol 13 (2) ◽

pp. 893-905 ◽

Cited By ~ 5

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.

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The characterization of Taklamakan dust properties using a multi-wavelength Raman polarization lidar in Kashi, China

10.5194/acp-2020-375 ◽

2020 ◽

Cited By ~ 1

Author(s):

Qiaoyun Hu ◽

Haofei Wang ◽

Philippe Goloub ◽

Zhengqiang Li ◽

Igor Veselovskii ◽

...

Keyword(s):

Fine Particles ◽

Depolarization Ratio ◽

Taklamakan Desert ◽

Multi Wavelength ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

Dust Events ◽

532 Nm ◽

Depolarization Ratios

Abstract. The Taklamakan desert is an important dust source for the global atmospheric dust budget and a cause of the dust weather in Eastern Asia. The characterization of the properties and vertical distributions of Taklamakan dust in the source region is still very limited. To fill this gap, the DAO (Dust Aerosol Observation) was conducted in Kashi, China in 2019. Kashi site is about 150 km to the west rim of the Taklamakan desert and is strongly impacted by desert dust aerosols, especially in spring time, i.e. April and May. Apart from dust, fine particles coming from local anthropogenic emissions or/and transported aerosols are also a non-negligible aerosol component. In this study, we provide the first profiling of the 2α + 3β + 3δ lidar profiles of Taklamakan dust based on a multi-wavelength Raman polarization lidar. Four cases, including two Taklamakan dust events (Case 1 and 2) and two polluted dust events (Case 3 and 4) are presented. The lidar ratio in the Taklamakan dust outbreak is found to be 51 ± 8–56 ± 8 sr at 355 nm and 45 ± 7 sr at 532 nm. The particle linear depolarization ratios are about 0.28 ± 0.04–0.32 ± 0.05 at 355 nm, 0.35 ± 0.05 at 532 nm and 0.31 ± 0.05 at 1064 nm. The observed polluted dust is commonly featured with reduced particle linear depolarization ratio and enhanced extinction and backscatter Angstrom exponent. In Case 3, the lidar ratio of polluted dust is about 42 ± 6 sr at 355 nm and 40 ± 6 sr at 532 nm. The particles linear depolarization ratios decrease to about 0.25, with a weak spectral dependence. In Case 4, the variability of lidar ratio and particle linear depolarization ratio is higher than in Case 3, which reflects the complexity of the nature of mixed pollutant and the mixing state. The results provide the first reference for the characteristics of Taklamakan dust measured by Raman lidar. The data could contribute to complementing the dust model and improving the accuracy of climate modeling.

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Observation of Long-Range Dust Transport from Mesopotamia and Arabian Peninsula Toward Tehran, Iran

E3S Web of Conferences ◽

10.1051/e3sconf/20199902006 ◽

2019 ◽

Vol 99 ◽

pp. 02006 ◽

Cited By ~ 1

Author(s):

Hossein Panahifar ◽

Hamid Reza Khalesifard

Keyword(s):

Optical Properties ◽

Particulate Matter ◽

Arabian Peninsula ◽

Urban Pollution ◽

Depolarization Ratio ◽

Dust Transport ◽

Linear Depolarization Ratio ◽

Dust Events ◽

Aerosol Types ◽

532 Nm

Continuous vertically resolved aerosol measurements using lidar were performed in Tehran, Iran. Lidar results has been used in combination with particulate matter monitoring, synoptic meteorology observa- tion as well as satellite-based measurements. The aerosol types are classified by their optical properties. The volume linear depolarization ratio (VLDR) at 532 nm lies mostly between 0:05-0:10. These results show that mostly urban pollution mixed with particles are present in the atmosphere above Tehran. During dust events, the VLDR at 532 nm lies between 0:20-0:35.

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

10.5194/acp-2017-1000 ◽

2017 ◽

Cited By ~ 1

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.

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Wildfire Smoke in the Stratosphere Over Europe–First Measurements of Depolarization and Lidar Ratios at 355, 532, and 1064 nm

EPJ Web of Conferences ◽

10.1051/epjconf/202023702036 ◽

2020 ◽

Vol 237 ◽

pp. 02036

Author(s):

Moritz Haarig ◽

Holger Baars ◽

Albert Ansmann ◽

Ronny Engelmann ◽

Kevin Ohneiser ◽

...

Keyword(s):

Lower Stratosphere ◽

Wavelength Dependence ◽

Depolarization Ratio ◽

Wildfire Smoke ◽

Lidar Measurements ◽

Smoke Layer ◽

Lidar Ratio ◽

Linear Depolarization Ratio ◽

532 Nm

Canadian wildfire smoke was detected in the troposphere and lower stratosphere over Europe in August and September 2017. Lidar measurements from various stations of the European Aerosol Research Lidar Network (EARLINET) observed the stratospheric smoke layer. Triple-wavelength (355, 532, and 1064 nm) lidar measurements of the depolarization and the lidar ratio are reported from Leipzig, Germany. The particle linear depolarization ratio of the wildfire smoke in the stratosphere had an exceptional strong wavelength dependence reaching from 0.22 at 355 nm, to 0.18 at 532 nm, and 0.04 at 1064 nm. The lidar ratio increased with wavelength from 40±16 sr at 355 nm, to 66±12 sr at 532 nm, and 92±27 sr at 1064 nm. The development of the stratospheric smoke plume over several months was studied by long-term lidar measurements in Cyprus. The stratospheric smoke layers increased in altitude up to 24 km height.

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

10.5194/acp-2016-246 ◽

2016 ◽

Cited By ~ 1

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.

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