Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires

The inorganic chlorine (Cl-y) and odd nitrogen (NOy) chemical families influence stratospheric O-3. In January 2020 Australian wildfires injected record-breaking amounts of smoke into the southern stratosphere. Within 1-2 months ground-based and satellite observations showed Cl-y and NOy were repartitioned. By May, lower stratospheric HCl columns declined by similar to 30% and ClONO2 columns increased by 40%-50%. The Cl-y perturbations began and ended near the equinoxes, increased poleward, and peaked at the winter solstice. NO2 decreased from February to April, consistent with sulfate aerosol reactions, but returned to typical values by June - months before the Cl-y recovery. Transport tracers show that dynamics not chemistry explains most of the observed O-3 decrease after April, with no significant transport earlier. Simulations assuming wildfire smoke behaves identically to sulfate aerosols couldn't reproduce observed Cl-y changes, suggesting they have different composition and chemistry. This undermines our ability to predict ozone in a changing climate.