Wildfire smoke destroys stratospheric ozone

The inorganic chlorine (Cly) and odd nitrogen (NOy) chemical families influence stratospheric O3. In January 2020 Australian wildfires injected record‐breaking amounts of smoke into the southern stratosphere. Within 1–2 months ground‐based and satellite observations showed Cly and NOy were repartitioned. By May, lower stratospheric HCl columns declined by ∼30% and ClONO2 columns increased by 40%–50%. The Cly perturbations began and ended near the equinoxes, increased poleward, and peaked at the winter solstice. NO2 decreased from February to April, consistent with sulfate aerosol reactions, but returned to typical values by June ‐ months before the Cly recovery. Transport tracers show that dynamics not chemistry explains most of the observed O3 decrease after April, with no significant transport earlier. Simulations assuming wildfire smoke behaves identically to sulfate aerosols couldn't reproduce observed Cly changes, suggesting they have different composition and chemistry. This undermines our ability to predict ozone in a changing climate.

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“…By October Cl y partitioning is within the range of previous years. Similar findings reported by Santee et al (2022) and Bernath et al (2022).…”

Section: Observations Of Aerosol Extinction Chlorine and Nitrogen Spe...supporting

confidence: 92%

“…Bernath et al. (2022) reported spectral signatures of oxygenated hydrocarbons and adsorbed water in the ANY smoke particles. Murphy et al.…”

Section: Introductionmentioning

confidence: 99%

Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires

Strahan

Smale

Solomon

et al. 2022

Geophysical Research Letters

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“…These plumes had significant impacts on the stratospheric composition, including stratospheric ozone (e.g. Yu et al, 2021;Bernath et al, 2022;Ohneiser et al, 2022;Solomon et al, 2022) and the stratospheric aerosol layer at the hemispheric scale (Khaykin et al, 2020). A stratospheric injection of smoke aerosols ranging from 0.4 ± 0.2 Tg (Khaykin et al, 2020) to 2.1 Tg (Hirsch and Koren, 2021) was estimated; this is 2 to 3 orders of magnitude larger than typical pyroCb activity (Peterson et al, 2021).…”

Section: Introductionmentioning

confidence: 95%

Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing

Sellitto

Belhadji

Kloss³

et al. 2022

Atmos. Chem. Phys.

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Abstract. As a consequence of extreme heat and drought, record-breaking wildfires developed and ravaged south-eastern Australia during the fire season 2019–2020. The fire strength reached its paroxysmal phase at the turn of the year 2019–2020. During this phase, pyrocumulonimbus clouds (pyroCb) developed and injected biomass burning aerosols and gases into the upper troposphere and lower stratosphere (UTLS). The UTLS aerosol layer was massively perturbed by these fires, with aerosol extinction increased by a factor of 3 in the visible spectral range in the Southern Hemisphere, with respect to a background atmosphere, and stratospheric aerosol optical depth reaching values as large as 0.015 in February 2020. Using the best available description of this event by observations, we estimate the radiative forcing (RF) of such perturbations of the Southern Hemispheric aerosol layer. We use offline radiative transfer modelling driven by observed information of the aerosol extinction perturbation and its spectral variability obtained from limb satellite measurements. Based on hypotheses on the absorptivity and the angular scattering properties of the aerosol layer, the regional (at three latitude bands in the Southern Hemisphere) clear-sky TOA (top-of-atmosphere) RF is found varying from small positive values to relatively large negative values (up to −2.0 W m−2), and the regional clear-sky surface RF is found to be consistently negative and reaching large values (up to −4.5 W m−2). We argue that clear-sky positive values are unlikely for this event, if the ageing/mixing of the biomass burning plume is mirrored by the evolution of its optical properties. Our best estimate for the area-weighted global-equivalent clear-sky RF is -0.35±0.21 (TOA RF) and -0.94±0.26 W m−2 (surface RF), thus the strongest documented for a fire event and of comparable magnitude with the strongest volcanic eruptions of the post-Pinatubo era. The surplus of RF at the surface, with respect to TOA, is due to absorption within the plume that has contributed to the generation of ascending smoke vortices in the stratosphere. Highly reflective underlying surfaces, like clouds, can nevertheless swap negative to positive TOA RF, with global average RF as high as +1.0 W m−2 assuming highly absorbing particles.

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“…The latter observations are horizontally spaced by 25 km (at the nadir), so that they allow the observation of the 3D distribution of coarse particles having a strong radiative signature in the thermal infrared (such as desert dust). This may also be found for fine particles in some specific cases, due to the presence of significant absorption bands in the thermal infrared, as seen for sulfuric acid and ammonium sulfate [30], or for highly abundant aerosols emitted by large-scale outbreaks, e.g., [31]. However, this is not the case for most fine particles such as those originating from fires and most urban pollution, e.g.…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Distribution of Biomass Burning Aerosols from Australian Wildfires Observed by TROPOMI Satellite Observations

et al. 2022

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We present a novel passive satellite remote sensing approach for observing the three-dimensional distribution of aerosols emitted from wildfires. This method, called AEROS5P, retrieves vertical profiles of aerosol extinction from cloud-free measurements of the TROPOMI satellite sensor onboard the Sentinel 5 Precursor mission. It uses a Tikhonov–Phillips regularization, which iteratively fits near-infrared and visible selected reflectances to simultaneously adjust the vertical distribution and abundance of aerosols. The information on the altitude of the aerosol layers is provided by TROPOMI measurements of the reflectance spectra at the oxygen A-band near 760 nm. In the present paper, we use this new approach for observing the daily evolution of the three-dimensional distribution of biomass burning aerosols emitted by Australian wildfires on 20–24 December 2019. Aerosol optical depths (AOD) derived by vertical integration of the aerosol extinction profiles retrieved by AEROS5P are compared with MODIS, VIIRS and AERONET coincident observations. They show a good agreement in the horizontal distribution of biomass burning aerosols, with a correlation coefficient of 0.87 and a mean absolute error of 0.2 with respect to VIIRS. Moderately lower correlations (0.63) were found between AODs from AEROS5P and MODIS, while the range of values for this comparison was less than half of that with respect to VIIRS. A fair agreement was found between coincident transects of vertical profiles of biomass burning aerosols derived from AEROS5P and from the CALIOP spaceborne lidar. The mean altitudes of these aerosols derived from these two measurements showed a good agreement, with a small mean bias (185 m) and a correlation coefficient of 0.83. Moreover, AEROS5P observations reveal the height of injection of the biomass burning aerosols in 3D. The highest injection heights during the period of analysis were coincident with the largest fire radiative power derived from MODIS. Consistency was also found with respect to the vertical stability of the atmosphere. The AEROS5P approach provides retrievals for cloud-free scenes over several regions, although currently limited to situations with a dominating presence of smoke particles. Future developments will also aim at observing other aerosol species.

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Wildfire smoke destroys stratospheric ozone

Cited by 55 publications

References 23 publications

Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires

Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires

Radiative impacts of the Australian bushfires 2019–2020 – Part 1: Large-scale radiative forcing

Three-Dimensional Distribution of Biomass Burning Aerosols from Australian Wildfires Observed by TROPOMI Satellite Observations

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