Some of the Black Summer fires were so intense that they injected smoke right up into the stratosphere. Earth observing satellites could see that as the aerosol loading increased (from the smoke intruding into the higher atmosphere) reactive nitrogen molecules decreased. This is an indicator of the ozone depletion chemistry that occurs on the surface of aerosols.

The authors calculated a total ozone loss of one per cent within the month of March 2020. This ozone loss is likely to be repeated during intense fire episodes and these are predicted to increase with climate change in the coming decades. This means that increased wildfire occurrence and intensity may act to slow down the recovery of the ozone layer.

It is important to note that the impact of this is in the mid-latitudes and not over the South Pole (the paper did not model any possible impact on the Antarctic ozone hole). Nevertheless, as a result of huge fire putting smoke into the stratosphere, the long-term overall stratospheric ozone recovery will be slowed by this chemistry. Any slowdown in the recovery of ozone in the mid-latitudes will increase the overall exposure to UV-radiation for Australians and hence may impact the occurrence of skin cancers in future.

Research has confirmed an idea that arose after the 2020 bushfires in Australia, that smoke particles from the fires that rose into the stratosphere, could provide platforms for destruction of ozone molecules. The chemistry is extremely complex, with chemical reactions taking place not in the gas phase, but on the surfaces of particles. The 'predator chemicals' are nitrogen oxides that we are already familiar with as pollutants in the air we breathe. Now they have taken on a whole new role.

Shortly before the discovery in 1974 that the ozone layer was being damaged by chemical fragments from chlorofluorocarbons (CFCs), there was concern that smoke from supersonic aircraft could damage the ozone layer, and nitrogen oxides were in the gun then, too. The Australian Academy of Science investigated this and concluded that there would be no adverse effects from the number of supersonic aircraft expected to be flying by 1985. Other countries came to similar conclusions but not everybody believed it. Fortunately, perhaps, there were only 14 Concorde, they never brought passengers to Australia, and their reign was brief.

Just a reminder of what's going on up there. The concentration of ozone in the stratosphere is maintained by natural processes. Ozone molecules are formed and destroyed, and the two processes are in balance. Adding extra chemical substances to the mix can upset the balance and reduce the ozone concentration.  Laboratory experiments suggest that many different chemical substances can upset this balance by reacting with ozone molecules, but fortunately most of these 'chemical predators'  never get up into the stratosphere.

The impacts of the bushfire smoke are smaller than those the world experienced from the chlorofluorocarbons (CFCs) that were used in spray cans and refrigeration. These chemicals can survive destruction in the lower atmosphere and rise to the stratosphere where they break down. The resulting chlorine fragments can bring about destruction by reacting with ozone molecules on the surface of ice crystals. Restraints to the use of the CFCs, under the Montreal Protocol to the Vienna Convention on protection of the ozone layer, have helped to reduce these impacts and assist the ozone layer to recover.