Journal Article

On the stratospheric chemistry of midlatitude wildfire smoke

Portmann, Robert, Solomon, Susan, Zawada, Daniel, Rosenlof, Karen H., Yu, Pengfei, Toon, Owen B., Bardeen, Charles G., Dube, Kimberlee, Strahan, Susan E., Stone, Kane, Kinnison, Doug, Boone, Chris, Randel, William, Davis, Sean, Bernath, Peter, Degenstein, Doug, Bourassa, Adam

2022

Overview

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/H₂O particles (specifically the hydrolysis of N₂O₅ to form HNO₃). 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 N₂O₅ 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.

• Publisher: National Academy of Sciences
• Subject: Altitude / Atmospheric chemistry / Australia / Chemical equilibrium / Chemistry / Chlorine / Climate change / Earth, Atmospheric, and Planetary Sciences / Endangered & extinct species / Extinction / Hydrolysis / Latitude / Montreal Protocol / Nitrogen / Ozone / Ozone depletion / Ozone layer / Ozonosphere / Particulate Matter - chemistry / Perturbation / Physical Sciences / Reactive nitrogen species / Recovery / Smoke / Smoke - analysis / Southern Hemisphere / Species extinction / Stratosphere / Stratospheric Ozone - chemistry / Sulfates / Sulfuric acid / Wildfires