Stratospheric aerosol perturbation by tropospheric biomass burning and deep convection

The stratosphere is often considered to be dynamically stable with limited vertical exchange; however, episodic deep convection can even transport tropospheric air masses into the upper troposphere (UT) and even across the tropopause into lower stratosphere (LS). We deployed a newly developed airborne single particle mass spectrometer, Particle Analysis by Laser Mass Spectrometry – Next Generation (PALMS-NG), aboard a NASA ER-2 stratospheric aircraft to characterize aerosol particles in the UTLS during the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) mission. Here, we present observations revealing substantial perturbations of the stratospheric aerosol layer during an active convection and wildfire season in 2022.We show that carbonaceous–sulfate particles of tropospheric origin account for up to 90% of stratospheric particles with physical diameters between 0.1 and 1.5 µm within an approximately 4 km layer above the tropopause. Approximately 43% of these stratospheric carbonaceous–sulfate particles are directly attributed to biomass burning. The injected particles are chemically complex and organic-rich, and some exhibit internally mixed signatures containing both tropospheric and stratospheric components.Our observations further demonstrate that biomass-burning-related aerosols do not remain chemically unchanged following injections into the stratosphere. Instead, they undergo chemical mixing with stratospheric components, indicating a pronounced perturbation of the stratospheric aerosol layer driven by convective transport.These results highlight the coupling between dynamics and chemistry in modulating UTLS aerosol populations. As wildfire frequency and intensity increase alongside enhanced deep convection in a warming climate, convective delivery of biomass-burning products to the stratosphere may become increasingly important, with implications for ozone chemistry and radiative forcing.