Stratospheric biomass burning aerosols compensate record-breaking ozone depletion over the Arctic in spring 2020

Biomass burning aerosols reaching the stratosphere (SBBA) present an emerging yet understudied threat to Arctic ozone (O 3 ). Previous work focuses primarily on SBBA-induced heterogeneous chemistry, while their dynamical effects–altering temperature and circulation–have received less attention. Here, we assess both the chemical and dynamical impacts of SBBA over the Arctic during 2019–2020, a period marked by unusually high SBBA loading and O 3 depletion. With satellite-constrained modelling, we show that SBBA cause a net increase in Arctic O 3 , compensating for 19% of the observed depletion in spring 2020. Dynamical processes dominate this effect via stratospheric heating and enhanced poleward O 3 transport. We link this SBBA event to a confluence of northward fire activities and an anomalous polar cyclonic system. Given projected increases in boreal fires and their northward extension, our findings highlight the critical need to integrate both chemical and dynamical SBBA effects to accurately assess O 3 budget and its consequences in a changing climate.