- 1Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, OSUC, Univ Orleans, CNRS, CNES, F-45071 Orleans, France
- 2Laboratoire de Météorologie Dynamique (LMD-IPSL), CNRS, Sorbonne Université, ENS-PSL, École Polytechnique, Paris, France
The increasing severity and duration of forest fire seasons, exemplified by the Canadian fires of 2017 (Pacific Northwest Event) and the Australian fires of 2019-2020 (Australian New Year's event), have highlighted the significant impact of these events on the stratosphere. Through intense pyrocumulonimbus activity, these fires injected large quantities of gases, biomass burning products, and other pollutants into the stratosphere. During both fires, a unique phenomenon was observed, i.e. the formation of vortex structures in the stratosphere.
Theses vortex structures confined the injected mixture of gases and aerosols, transporting them over weeks in the case of the Canadian fires and months for the Australian fires. These vortices caused localized disturbances in stratospheric chemical composition and triggered specific chemical reactions.
This study focuses on the localized impact created by these vortices, particularly their role in ozone depletion. By confining and transporting biomass combustion products, these vortex structures created conditions for unique chemistry. Data from the Microwave Limb Sounder (MLS) and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) revealed substantial increases in water vapor and biomass burning tracers, including CO, CH₃Cl, HCN, and CH₃OH. Simultaneously, significant depletions were observed in critical stratospheric reservoirs such as HNO₃, ClONO₂, and HCl. This was accompanied by a marked decrease in ozone mixing ratios with respect to unperturbed conditions, initially associated with injection of ozone-poor tropospheric air but maintained throughout the course of the vortices, questioning about the occurrence of potential ozone destruction through heterogeneous chemical processes, even if no direct evidence of chlorine activation is observed.
Similarities in the chemical content are clearly highlighted for these two events. While this analysis sheds light on the impact of these vortices on stratospheric chemistry, further investigations are necessary to explore the role of organic compounds in the observed ozone depletion and to better understand the broader implications of increasingly severe wildfire events on atmospheric composition and dynamics.
How to cite: Vieille, L., Jégou, F., Berthet, G., Duchamp, C., and Legras, B.: Observed perturbation of stratospheric chemical composition caused by wildfires smoke vortices, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10043, https://doi.org/10.5194/egusphere-egu25-10043, 2025.