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

• Published in: Atmospheric chemistry and physics 2019-12, Vol.19 (23), p.15183-15198
• Main Authors: Baars, Holger, Ansmann, Albert, Ohneiser, Kevin, Haarig, Moritz, Engelmann, Ronny, Althausen, Dietrich, Hanssen, Ingrid, Gausa, Michael, Pietruczuk, Aleksander, Szkop, Artur, Stachlewska, Iwona S, Wang, Dongxiang, Reichardt, Jens, Skupin, Annett, Mattis, Ina, Trickl, Thomas, Vogelmann, Hannes, Navas-Guzmán, Francisco, Haefele, Alexander, Acheson, Karen, Ruth, Albert A, Tatarov, Boyan, Müller, Detlef, Hu, Qiaoyun, Podvin, Thierry, Goloub, Philippe, Veselovskii, Igor, Pietras, Christophe, Haeffelin, Martial, Fréville, Patrick, Sicard, Michaël, Comerón, Adolfo, Fernández García, Alfonso Javier, Molero Menéndez, Francisco, Córdoba-Jabonero, Carmen, Guerrero-Rascado, Juan Luis, Alados-Arboledas, Lucas, Bortoli, Daniele, Costa, Maria João, Dionisi, Davide, Liberti, Gian Luigi, Wang, Xuan, Sannino, Alessia, Papagiannopoulos, Nikolaos, Boselli, Antonella, Mona, Lucia, D'Amico, Giuseppe, Romano, Salvatore, Perrone, Maria Rita, Belegante, Livio, Nicolae, Doina, Grigorov, Ivan, Gialitaki, Anna, Amiridis, Vassilis, Soupiona, Ourania, Papayannis, Alexandros, Mamouri, Rodanthi-Elisaveth, Nisantzi, Argyro, Heese, Birgit, Hofer, Julian, Schechner, Yoav Y, Wandinger, Ulla, Pappalardo, Gelsomina
• Format: Article
• Language: English
• Subjects: Aerosol observations; Aerosol properties; Aerosol research; Aerosols; Aerosols atmosfèrics; Ageing; Aging; Analysis; Atmospheric aerosols; Atmospheric chemistry; Black carbon; Coefficients; Contaminació atmosfèrica; Decay; Degradació ambiental; Depolarization; Desenvolupament humà i sostenible; Electromagnetic absorption; Enginyeria de la telecomunicació; Fire plumes; Fires; Lidar; Lower stratosphere; Middle atmosphere; Northern Hemisphere; Optical properties; Optical radar; Optical thickness; Ozone; Particle mass; Perturbation; Physics; Plumes; Profiles; Properties; Radiocomunicació i exploració electromagnètica; Remote sensing; Sciences of the Universe; Smoke; Smoke particles; Soot; Soot particles; Stations; Stratosphere; Supersaturation; Teledetecció; Thin films; Thunderstorms; Tropopause; Troposphere; Upper troposphere; Wildfires; Àrees temàtiques de la UPC
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-19-15183-2019

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 wildfire smoke is reported and discussed in terms of geometrical, optical, and microphysical aerosol properties. Enormous amounts of smoke 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 fire 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 at heights between 15 and 20 km since September 2017 (about 2 weeks after entering the stratosphere). Thin layers of smoke were detected at heights of up to 22–23 km. The stratospheric aerosol optical thickness at 532 nm decreased from values > 0.25 on 21–23 August 2017 to 0.005–0.03 until 5–10 September and was mainly 0.003–0.004 from October to December 2017 and thus was still significantly above the stratospheric background (0.001–0.002). Stratospheric particle extinction coefficients (532 nm) were as high as 50–200 Mm−1 until the beginning of September and on the order of 1 Mm−1 (0.5–5 Mm−1) from October 2017 until the end of January 2018. The corresponding layer mean particle mass concentration was on the order of 0.05–0.5 µg m−3 over these months. Soot particles (light-absorbing carbonaceous particles) are efficient ice-nucleating particles (INPs) at upper tropospheric (cirrus) temperatures and available to influence cirrus formation when entering the tropopause from above. We estimated INP concentrations of 50–500 L−1 until the first days in September and afterwards 5–50 L−1 until the end of the year 2017 in the lower stratosphere for typical cirrus formation temperatures of −55 ∘C and an ice supersaturation level of 1.15. The measured profiles of the particle linear depolarization ratio indicated a predominance of nonspherical smoke particles. The 532 nm depolarization ratio decreased slowly with time in the main smoke layer from values of 0.15–0.25 (August–September) to values of 0.05–0.10 (October–November) and