Investigating the vertical extent of the 2023 summer Canadian wildfire impacts with satellite observations

Abstract. Pyrocumulonimbus clouds (pyroCbs) generated by intense wildfires can serve as a direct pathway for the injection of aerosols and gaseous pollutants into the lower stratosphere, resulting in significant chemical, radiative, and dynamical changes. Canada experienced an extremely severe wildfire season in 2023, with a total area burned that substantially exceeded those of previous events known to have impacted the stratosphere (such as the 2020 Australian fires). This season also had record-high pyroCb activity, which raises the question of whether the 2023 Canadian event resulted in significant stratospheric perturbations. Here, we investigate this anomalous wildfire season using retrievals from two satellite instruments, ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) and OMPS LP (Ozone Mapping and Profile Suite Limb Profiler), to determine the vertical extents of the wildfire smoke along with chemical signatures of biomass burning. These data show that smoke primarily reached the upper troposphere but only a nominal amount managed to penetrate the tropopause. Only one ACE-FTS occultation captured elevated concentrations of biomass burning products in the lower stratosphere on July 30^th, and back and forward trajectories place the source fire in the Yukon. However, OMPS LP aerosol measurements indicate that any smoke that made it past the tropopause did not last long enough to significantly perturb stratospheric composition. While this work focuses on Canadian wildfires given the extensive burned area, pyroCbs at other longitudes (e.g. Siberia) are also captured in the compositional analysis. These results highlight that despite the formation of many pyroCbs in major wildfires, those capable of penetrating the tropopause are extremely rare; this in turn means that even a massive area burned is not necessarily an indicator of stratospheric effects.