Originally published by Scimex

The chemicals in bushfire smoke can enhance the activation of molecules that destroy ozone, according to Australian research which warns that the findings increase concern that more frequent and intense bushfires could delay the ozone hole recovery in a warming world. Previous research has shown that the smoke from the 2019-2020 Black Summer bushfires changed the chemical composition of the upper atmosphere, including a decline in the levels of ozone, but this new research looks at how this might be happening. They found that the smoke enhances the activation of chlorine radicals — molecules that can destroy ozone.

Journal/conference: Nature

Link to research (DOI): 10.1038/s41586-022-05683-0

Organisation/s: Massachusetts Institute of Technology, USA

Funder: S.S. and K.S. are partly supported by NSF 1848863. D.K. was financed in part by NASA grant 80NSSC19K0952. P.Y. is supported by the National Natural Science Foundation of China (42175089, 42121004). D.M.M. is supported by NOAA base and climate funding. The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy. We gratefully acknowledge high-performance computing support from Cheyenne (https://doi.org/10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by the National Science Foundation.

Media release

From: Springer Nature

Climate: How wildfires deplete the ozone layer (N&V) 

The composition of wildfire smoke promotes chemical reactions that contribute to the destruction of stratospheric ozone, a paper in Nature suggests. These findings increase concerns that more frequent and intense wildfires could delay ozone recovery as the climate warms.

The Australian wildfires of 2019–2020 sent plumes of smoke high into the atmosphere, where it was transported around the world. The smoke was associated with changes in chemical composition of the upper atmosphere, including a decline in stratospheric levels of ozone. However, the mechanism of how wildfire smoke might contribute to ozone depletion has remained uncertain.

Susan Solomon and colleagues propose that the mixture of chemicals in wildfire smoke enhances the activation of chlorine radicals — molecules that can destroy ozone. The authors test their hypothesis by comparing atmospheric observations to model simulations, which reproduce the observed ozone depletion during the Australian wildfires. Their findings indicate that wildfire aerosol chemistry has the potential to contribute to ozone depletion.

The authors note that other reactions beyond those studied here may also be important and recommend further investigation of the effects of different aerosols in the stratosphere. This point is reiterated by V. Faye McNeill and Joel Thornton in an accompanying News & Views: “Solomon and colleagues’ findings emphasize the need for atmospheric chemists to better understand the properties and reactivity of common, but complex, atmospheric particle types, such as those produced from biomass burning, in the cold and dry upper atmosphere”.

Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr Roger Dargaville is Director of Sustainability in the Faculty of Engineering at Monash University. He has conducted research on stratospheric ozone depletion.

“The health of the stratospheric ozone layer is critical for life on this planet – without it, damaging high energy ultra-violet radiation would make the surface of the Earth unhabitable.

Ozone destruction due to CFCs has begun to be reversed through prolonged international negotiations (starting with the Montreal Protocol, first signed in 1987 just two years after its discovery).  Every nation has ratified the protocol and its revision, making it the most successful international agreement in history.

Had the Montreal Protocol not been negotiated and CFC production continued unabated, the Antarctic and (rarely occurring) Arctic Ozone holes would likely have expanded over highly populated areas causing untold damage to people, animals and crops.

The Solomon et al. paper shows that smoke from extreme bushfires entering the stratosphere increases the potency of the chlorine in the atmosphere, risking the progress made through the Montreal Protocol to date.  This highlights the complex nature of interactions in the Earth System, and the potential for dangerous and unanticipated outcomes from human induced global warming.”

Last updated: 07 Mar 2023 1:26pm

Name:Roger Dargaville
Mobile:+61 416 528 437
Email: roger.dargaville@monash.edu

Declared conflicts of interest:

None declared.

Dr Olaf Morgenstern is Programme Leader of the Measuring and Modelling Atmospheric Composition programme and Group Manager of the Lauder Atmospheric Processes group

“Large bushfires are set to become more common as dry seasons become drier and hotter and summers lengthen under global warming. The largest of these events can inject huge quantities of smoke into the stratosphere; the 2019/2020 Australian bushfires are a prominent example. A new study in Nature shows that this aerosol plays a role in atmospheric chemistry.

The Antarctic ozone hole forms because in the stratosphere on the surfaces of cloud particles chlorine is “activated” to form compounds that then deplete ozone. This new study finds that smoke aerosol can activate chlorine too, just like polar stratospheric clouds but at higher, more ubiquitous temperatures and also away from the poles. The authors (led by atmospheric chemist Susan Solomon who in the 1980s also famously explained the ozone hole) highlight a hitherto ignored mechanism of ozone depletion, and one that might become more important as more such bushfire events occur. More research is needed into the chemical properties of such complex bushfire aerosol though.

The paper describes the coming-together of two dimensions of human interference in the climate system that had previously been considered separate.”

Last updated: 07 Mar 2023 1:08pm

Name:Olaf Morgenstern
Phone:04 386 0928

Declared conflicts of interest:

None declared.

Dr Laura Revell is an Associate Professor in Environmental Physics at the University of Canterbury.

“Following the widespread use of chlorofluorocarbons (CFCs) in the 1970s and 1980s, there are still substantial amounts of chlorine in the stratosphere (approximately 10-50 km above Earth’s surface), where the protective ozone layer resides. Stratospheric chlorine causes the Antarctic ozone hole to form each spring, although early signs of Antarctic ozone recovery have been visible since approximately the mid-2010s. In the absence of any major changes, we expect that stratospheric chlorine concentrations will gradually decrease this century and that the ozone hole will get smaller year by year.

This study looks at the massive wildfires that occurred in Australia during the summer of 2019-2020. These fires injected vast amounts of wildfire smoke into the stratosphere – a rare event. The authors find that wildfire aerosols in the stratosphere can “activate” chlorine into a more destructive form and enhance ozone loss. Of concern is that while the ozone hole usually forms over Antarctica because of the cold temperatures there, wildfire aerosols appear to be capable of promoting ozone losses at the relatively warmer temperatures present at mid-latitudes which are heavily populated.

Overall, the authors show that wildfire aerosol chemistry led to a 3-5% depletion of southern mid-latitude stratospheric ozone during 2020, and a larger-than-expected Antarctic ozone hole the same year. Ozone depletion of 3-5% in a single year is not an overwhelming loss, however as the authors note, it is significant given that ozone should be increasing by 1% per decade because of bans on CFCs. Given that wildfires are likely to become more frequent and severe in a warming world, the implications of this study for future ozone recovery are concerning. We cannot afford to be negligent when it comes to protecting the ozone layer.”

Last updated: 07 Mar 2023 1:04pm

Name:Laura Revell

Declared conflicts of interest:

None declared.

Professor Ian Rae is an expert on chemicals in the environment at the School of Chemistry at the University of Melbourne. He was also an advisor to the United Nations Environment Programme on chemicals in the environment and is former President of the Royal Australian Chemical Institute

“Ozone is continuously formed and destroyed in the stratosphere. As a result of these competing processes, there is a steady, albeit small, concentration of ozone up there and because it absorbs ultraviolet light, we gain a measure of protection from this skin-damaging radiation.

Nearly fifty years ago it was observed that stratospheric ozone concentrations over the Antarctic were reduced (the so-called ‘ozone hole’) in early Spring and the blame was sheeted home to chlorofluorocarbons (CFCs). Research showed that it was chemical reactions with chlorine atoms, derived from the CFCs. that destroyed some of the ozone. Under the intergovernmental Montreal Protocol the uses of these and  related substances have ceased and the ‘ozone hole’ is shrinking year by year.

Over the last two years it has become evident that chemical reactions with constituents of bushfire (wildfire) smoke can also destroy ozone molecules. The authors of this latest paper modelled the absorption of hydrogen chloride (HCl, a combustion product) onto the partly-burnt organic matter in smoke particles. This provides a pathway for the transport of a range of chlorinated substances to the stratosphere where they can release their destructive chlorine atoms. The results of the modelling agree well with the experimental results.

The nature of the chemical reactions is not completely nailed down but the overall picture is probably correct. Unlike the way nations dealt with the CFCs, I don’t think there will be another ‘Montreal Protocol’ for bushfires, which the authors warn are likely to become more frequent under climate change that we can already see happening.”

Last updated: 07 Mar 2023 11:37am

Name:Ian Rae
Phone:+61 413 979 174

Declared conflicts of interest:

None declared.

Dr Martin Jucker is a lecturer at the University of New South Wales and Associate Investigator at the ARC Centre of Excellence for Climate Extremes

“The study by Solomon and coauthors studies how the black summer bushfires could have influenced the ozone hole observed the year after in 2020. While previous studies have already made the link between bushfire smoke and stratospheric ozone depletion, this work provides a detailed description of the chemical reactions behind the depletion, and what makes bushfire smoke so special.

Of particular interest for Australia is the extension of the ozone hole further equatorward, which means that the ozone layer can become thinner much closer to where millions of Australians live. An important implication is that as we expect more bushfires in the future, the ozone hole might recover more slowly than expected.

In addition, the study confirms once again that when it comes to climate, all things are connected, and events of which we think we know the effects can in fact have many more far-reaching consequences. The authors also rightly point out that there are still many basic mechanisms we don’t understand, even in a subject like the ozone hole which we thought was a solved problem.”

Last updated: 07 Mar 2023 1:08pm

Name:Martin Jucker
Mobile:+61 481 129 599


Available during usual working hours, except Wed 12-2pm, Thu 1-2pm, Mon 10-12 due to teaching. He might also be difficult to reach Thursday 9 March before 11am, though he should be able to take calls.

Declared conflicts of interest:

None declared.