Massive Australian wildfires lofted smoke directly into the stratosphere in the austral summer of 2019/20. The smoke led to increases in optical extinction throughout the midlatitudes of the southern hemisphere that rivalled substantial volcanic perturbations. Previous studies have assumed that the smoke became coated with sulfuric acid and water and would deplete the ozone layer through heterogeneous chemistry on those surfaces, as is routinely observed following volcanic enhancements of the stratospheric sulfate layer. Here, observations of extinction and reactive nitrogen species from multiple independent satellites that sampled the smoke region are compared to one another and to model calculations. The data display a strong decrease in reactive nitrogen concentrations with increased aerosol extinction in the stratosphere, which is a known fingerprint for key heterogeneous chemistry on sulfate/H 2 O particles (specifically the hydrolysis of N 2 O 5 to form HNO 3 ). This chemical shift affects not only reactive nitrogen but also chlorine and reactive hydrogen species and is expected to cause midlatitude ozone layer depletion. Comparison of the model ozone to observations suggests that N 2 O 5 hydrolysis contributed to reduced ozone, but additional chemical and/or dynamical processes are also important. These findings suggest that if wildfire smoke injection into the stratosphere increases sufficiently in frequency and magnitude as the world warms due to climate change, ozone recovery under the Montreal Protocol could be impeded, at least sporadically. Modeled austral midlatitude total ozone loss was about 1% in March 2020, which is significant compared to expected ozone recovery of about 1% per decade.
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Unexpected Repartitioning of Stratospheric Inorganic Chlorine After the 2020 Australian Wildfires
The inorganic chlorine (Cly) and odd nitrogen (NOy) chemical families influence stratospheric O3. 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 Clyand NOywere repartitioned. By May, lower stratospheric HCl columns declined by ∼30% and ClONO2columns increased by 40%–50%. The Clyperturbations began and ended near the equinoxes, increased poleward, and peaked at the winter solstice. NO2decreased from February to April, consistent with sulfate aerosol reactions, but returned to typical values by June ‐ months before the Clyrecovery. Transport tracers show that dynamics not chemistry explains most of the observed O3decrease after April, with no significant transport earlier. Simulations assuming wildfire smoke behaves identically to sulfate aerosols couldn't reproduce observed Clychanges, suggesting they have different composition and chemistry. This undermines our ability to predict ozone in a changing climate.
more » « less- NSF-PAR ID:
- 10370611
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 14
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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