Ozone layer punctured again by the Black Summer bushfires

The ozone layer is a rare environmental success story – but increased bushfires from climate change could be reversing the gains made over the past decade.

A study published in Nature has shown how the smoke from the 2019-2020 Black Summer Bushfires caused a decline in the ozone layer.

It was already known that there was a decline in ozone during the Black Summer. These researchers, based at Massachusetts Institute of Technology, US, demonstrated that the smoke from these fires increased the amount of chlorine radicals in the stratosphere, where they deplete the ozone layer.

They then used modelling to show how this mechanism mirrored the depletion seen during the Black Summer fires: a loss of 3-5% of the southern mid-latitude ozone.

The climate change-fuelled Black Summer fires burned more than 24 million hectares of land in eastern and southern Australia, killed 33 people directly, and 450 more from smoke inhalation.

The further depletion of the ozone layer is new research.

“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,” explains Dr Olaf Morgenstern, a researcher at New Zealand’s National Institute of Water Research, who wasn’t involved in the study.

“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.”

Professor Ian Rae, a former advisor to the United Nations Environment Programme on chemicals in the environment and former President of the Royal Australian Chemical Institute, also not involved in the research, agrees.

“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,” says Rae.

“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.”