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

Gialitaki, Anna; Tsekeri, Alexandra; Amiridis, Vassilis; Ceolato, Romain; Paulien, Lucas; Kampouri, Anna; Gkikas, Antonis; Solomos, Stavros; Marinou, Eleni; Haarig, Moritz; Baars, Holger; Ansmann, Albert; Lapyonok, Tatyana; Lopatin, Anton; Dubovik, Оleg; Groß, Silke; Wirth, Martin; Balis, D.

doi:10.5194/acp-2020-22

Cited by 8 publications

(11 citation statements)

References 40 publications

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“…If the smoke particles would have had an ideal spherical shape (consisting of a black carbon core and a thick organic carbon shell), the depolarization ratio would have been close to zero (Haarig et al, 2018), as was observed for the Canadian smoke at heights in the middle troposphere. Slight deviations from the ideal spherical form in combination with the monomodal, narrow smoke size distribution (accumulation mode shifted to larger particles with a mode diameter of 600 to 700 nm, absence of a coarse mode) (Dahlkötter et al, 2014;Haarig et al, 2018) lead to the observed enhanced depolarization values and the distinct wavelength dependence, as recently modeled by Gialitaki et al (2020) and also suggested by other modeling groups (e.g., Yu et al, 2019;Liu and Mishchenko, 2020). According to Yu et al (2019), smoke particles consist of an insoluble black carbon (BC) core that is surrounded by an almost spherical shell of organic material and other atmospheric substances.…”

Section: Lidar Observations Of Smoke Optical Propertiesmentioning

confidence: 63%

“…Lidar ratios and depolarization ratios measured simultaneously at both 355 and 532 nm wavelengths are a prerequisite in efforts to successfully homogenize the overall Aeolus-CALIPSO data set of smoke optical properties later on. Simultaneously measured lidar ratios and depolarization ratios are also important parameters in aerosol typing efforts (see, e.g., Burton et al, 2012Burton et al, , 2015Groß et al, 2013;Nicolae et al, 2018;Papagiannopoulos et al, 2018) with lidars from ground and in space to improve optical models developed to simulate the smoke optical properties as a function of particle shape and size characteristics and composition (e.g., Kahnert, 2017;Mishchenko, 2018, 2020;Luo et al, 2019;Gialitaki et al, 2020). Thus, our Punta Arenas lidar observations in January 2020 can be regarded as an important contribution to the global library of aerosol optical properties.…”

Section: Introductionmentioning

confidence: 99%

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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

et al. 2020

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Abstract. We present particle optical properties of stratospheric smoke layers observed with multiwavelength polarization Raman lidar 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 0.85 at 532 nm in mid-January 2020. The main goal of this rapid communication letter is to provide first stratospheric measurements of smoke extinction-to-backscatter ratios (lidar ratios) and particle linear depolarization ratios at 355 and 532 nm wavelengths. These aerosol parameters are important input parameters in the analysis of spaceborne CALIPSO and Aeolus lidar observations of the Australian smoke spreading over large parts of the Southern Hemisphere in January and February 2020 up to heights of around 30 km. Lidar and depolarization ratios, simultaneously measured at 355 and 532 nm, are of key importance regarding the homogenization of the overall Aeolus (355 nm wavelength) and CALIPSO (532 nm wavelength) lidar data sets documenting the spread of the smoke and the decay of the stratospheric perturbation, which will be observable over the entire year of 2020. 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 to 97 sr (mean 71 sr) and 0.2 to 0.26 (mean 0.23), respectively. At 532 nm, the lidar ratios were higher (75–112 sr, mean 97 sr) and the depolarization ratios were lower with values of 0.14–0.22 (mean 0.18). The determined depolarization ratios for aged Australian smoke are in very good agreement with respective ones for aged Canadian smoke, observed with lidar in stratospheric smoke layers over central Europe in the summer of 2017. The much higher 532 nm lidar ratios, however, indicate stronger absorption by the Australian smoke particles.

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Section: Lidar Observations Of Smoke Optical Propertiesmentioning

confidence: 63%

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…CC BY 4.0 License. study of the optical properties of the non-spherical smoke particles has been performed (Gialitaki et al, 2019). This study suggest that the smoke particles were compact and almost spherical in shape.…”

Section: Particle Shape and Size Characteristicsmentioning

confidence: 92%

The unprecedented 2017–2018 stratospheric smoke event: Decay phase and aerosol properties observed with EARLINET

Baars¹,

Ansmann²,

Ohneiser³

et al. 2019

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Abstract. Six months of stratospheric aerosol observations with the European Aerosol Research Lidar Network (EARLINET) from August 2017 to January 2018 are presented. The decay phase of an unprecedented, record-breaking stratospheric perturbation caused by wild fire smoke is reported and discussed in terms of geometrical, optical, and microphysical aerosol properties. Enormous amounts of smoke (mainly soot particles) were injected into the upper troposphere and lower stratosphere over fire areas in western Canada on 12 August 2017 during strong thunderstorm-pyrocumulonimbus activity. The stratospheric smoke plumes spread over the entire northern hemisphere in the following weeks and months. Twenty-eight European lidar stations from northern Norway to southern Portugal and the Eastern Mediterranean monitored the strong stratospheric perturbation on a continental scale. The main smoke layer (over central, western, southern, and eastern Europe) was found between 15 and 20&#8201;km height since September 2017 (about two weeks after entering the stratosphere). Thin layers of smoke were detected to ascent to 22&#8211;24 km height. The stratospheric aerosol optical thickness at 532&#8201;nm decreased from values >&#8201;0.25 on 21&#8211;23 August 2017 to 0.005&#8211;0.03 until 5&#8211;10 September, and was mainly 0.003&#8211;0.004 from October to December 2017, and thus still significantly above the stratospheric background (0.001&#8211;0.002). Stratospheric particle extinction coefficients (532&#8201;nm) were as high as 50&#8211;200&#8201;Mm&#8722;1 until the beginning of September and of the order of 1&#8201;Mm&#8722;1 (0.5&#8211;5&#8201;Mm&#8722;1) from October 2017 until the end of January 2018. The corresponding layer mean particle mass concentration was of the order of 0.05&#8211;0.5&#8201;&#956;g&#8201;cm&#8722;3 over the months. Soot is an efficient ice-nucleating particle (INP) at upper tropospheric (cirrus) temperatures and available to influence cirrus formation when entering the tropopause from above. We estimated INP concentrations of 50&#8211;500&#8201;L&#8722;1 until the first days in September and afterwards 5&#8211;50&#8201;L&#8722;1 until the end of the year 2018 in the lower stratosphere for typical cirrus formation temperatures of &#8722;55&#8201;&#176;C and ice supersaturation values of 1.15. The measured profiles of the particle linear depolarization rato indicated the predominance of non-spherical soot particles. The 532&#8201;nm depolarization ratio decreased with time in the main smoke layer from values of 0.15&#8211;0.25 (August&#8211;September) to values of 0.05&#8211;0.10 (October&#8211;November) and <&#8201;0.05 (December&#8211;January). The decrease of the depolarization ratio is consistent with the steady removal of the larger smoke particles by gravitational settling and changes in the particle shape with time towards a spherical form. An ascending layer with a vertical depth of 500&#8211;1000&#8201;m was detected (over the Eastern Mediterranean at 32&#8211;35&#176;&#8201;N) that ascended from about 18&#8211;19&#8201;km to 22&#8211;23&#8201;km height from the beginning of October to the beginning of December 2017 (about 2&#8201;km per month) and may be related to the increasing build up of the winter-hemispheric Brewer&#8211;Dobson circulation system.

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“…They hypothesize that the organic-coated particles were most likely solids because they either froze in the stratosphere or effloresced. Gialitaki et al (2019) modeled the optical properties (PLDR and lidar ratio at 355, 532, and 1064 nm) of the aged nonspherical smoke particles and compared the results with the respective multiwavelength lidar observation presented by Haarig et al (2018). These extensive simulations suggest that the smoke particles with particle effective radii of 550 nm were compact and almost spherical in shape.…”

Section: Particle Shape and Size Characteristicsmentioning

confidence: 95%

The unprecedented 2017–2018 stratospheric smoke event: decay phase and aerosol properties observed with the EARLINET

et al. 2019

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

Cited by 8 publications

References 40 publications

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

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

The unprecedented 2017–2018 stratospheric smoke event: Decay phase and aerosol properties observed with EARLINET

The unprecedented 2017–2018 stratospheric smoke event: decay phase and aerosol properties observed with the EARLINET

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