Australian wildfire smoke in the stratosphere: the decay phase in 2020/21 and impact on ozone depletion

Abstract

Abstract. Record-breaking wildfires raged in southeastern Australia in late December 2019 and early January 2020. Rather strong pyrocumulonimbus (pyroCb) convection developed over the fire areas and lifted enormous amounts of biomass-burning smoke into the tropopause region and caused the strongest wildfire-related stratospheric aerosol perturbation ever observed around the globe. We discuss the geometrical, optical, and microphyscial properties of the stratospheric smoke layers and the decay of this major stratospheric perturbation. A multiwavelength polarization Raman lidar at Punta Arenas (53.2° S, 70.9° W), southern Chile, and an elastic-backscatter Raman lidar at Río Grande (53.8° S, 67.7° W) in southern Argentina were operated to monitor the major record-breaking event until the end of 2021. These lidar measurements can be regarded as representative for mid to high latitudes in the Southern Hemisphere. A unique dynamical feature, an anticyclonic, smoke-filled vortex with 1000 km horizontal width and 5 km vertical extent, which ascended by about 500 m per day, was observed over the full last week of January 2020. The key results of the long-term study are as follows: The smoke layers extended, on average, from 9 to 24 km in height. The smoke partly ascended to more than 30 km height as a result of self-lifting processes. Clear signs of a smoke impact on the record-breaking ozone hole over Antarctica in September–November 2020 were found. A slow decay of the stratospheric perturbation detected by means of the 532 nm aerosol optical thickness (AOT) yielded an e-folding decay time of 19–20 months. The maximum smoke AOT was around 1.0 over Punta Arenas in January 2020 and thus two to three orders of magnitude above the stratospheric aerosol background of 0.005. After two months with strongly varying smoke conditions, the 532 nm AOT decreased to 0.03–0.06 from March–December 2020 and to 0.015–0.03 throughout 2021. The particle extinction coefficients were in the range of 10–75 Mm−1 in January 2020, and later on mostly between 1 and 5 Mm−1. Combined lidar-photometer retrievals revealed typical smoke extinction-to-backscatter ratios of 69 ±19 sr (at 355 nm), 91 ± 17 sr (at 532 nm), and 120 ± 22 sr (at 1064 nm). An ozone reduction of 20–25 % in the 15–22 km height range was observed over Antarctic and New Zealand ozonesonde stations in the smoke-polluted air with particle surface area concentrations of 1–5 μm2 cm−3.

Annual cycle of aerosol properties over the central Arctic during MOSAiC 2019–2020 — light-extinction, CCN, and INP levels from the boundary layer to the tropopause

“…Lidar signals are measured with a near-range and a far-range telescope, covering different height ranges so that backscatter coefficients and depolarization ratios are measurable from about 100 m to 30 km, and extinction coefficients and lidar ratios from about 400 m upward. The main features of the basic MOSAiC aerosol data analysis (including signal correction, Rayleigh backscattering and extinction correction, temporal averaging and vertical smoothing of signal profiles) are described in Ohneiser et al (2020Ohneiser et al ( , 2021Ohneiser et al ( , 2022.…”

“…These lidar ratios indicate continental fine-mode aerosol (Mattis et al, 2004) and are in agreement with the high Arctic Ångström exponents of 1.4-1.6. Lidar ratios for a clean marine environment are around 20-25 sr at 532 nm (Groß et al, 2015(Groß et al, , 2016 and >70 sr for strongly light-absorbing wildfire smoke particles (Haarig et al, 2018;Ohneiser et al, 2020Ohneiser et al, , 2022. The extinction-to-volume conversion factor c v , the extinction-to-surface-area conversion factor c s , and the extinction-to-number conversion factors c rmin for 532 nm are obtained from the analysis of the Arctic AERONET observations regarding the relationship between measured aerosol optical and retrieved microphyscial properties following the procedure described by Ansmann (2016, 2017).…”

Australian Bushfires (2019–2020): Aerosol Optical Properties and Radiative Forcing

“…Smoke aerosols affect the Earth's climate system in both direct and indirect ways, as they can highly absorb the sunlight due to their high content of black carbon (BC), but they can also modify the cloud properties (i.e., cloud life-time, precipitation, and ice formation) [1][2][3][4][5][6]. Freshly emitted soot particles are initially hydrophobic, but become hydrophilic as a result of aging.…”

“…To date, an important number of studies have already investigated the event of the 2019-2020 Australian bushfires in terms of the aerosol optical, chemical, and radiative properties [3][4][5][6][27][28][29][30]. These studies either focus on specific regions/sites [4,30], or they utilize mostly passive remote-sensing techniques, without any information on the vertical distribution of aerosol properties.…”