Stratospheric aerosol perturbation by tropospheric biomass burning and deep convection

The stratosphere is generally considered to be stable, with minimal vertical mixing. However, deep convection can transport low-altitude material above the tropopause. Here we use in situ single-particle measurements from the Dynamics and Chemistry of the Summer Stratosphere mission to show that carbonaceous-sulfate particles from the troposphere account for up to 90% of the stratospheric particles with physical diameter from 0.1 to 1.5 µm in a 4-km layer above the tropopause during an active fire season in 2022. We find that ~43% of the stratospheric carbonaceous-sulfate particles originate from biomass burning. These particles, which are chemically complex and organic-rich, do not remain unchanged once injected into the stratosphere, but form mixtures containing both tropospheric and stratospheric components, indicating perturbation of the stratospheric aerosol layer. We suggest that the increasing frequency and intensity of wildfires combined with increasing deep convection as the climate warms may enhance the delivery of biomass burning products to the lower stratosphere, with implications for ozone chemistry and radiative forcing.