Antarctic ozone hole increased by 10% due to Australian megafires

The MIT researchers discovered a formerly unrecognized chemical process via which smoke particles from the Australian wildfires exacerbated ozone depletion. 

The southern hemisphere's mid-latitudes, including the areas surrounding Australia, New Zealand, and some sections of Africa and South America, experienced a 3-5 percent reduction in total ozone due to this fire-triggered reaction.

Furthermore, the fires appear to have impacted the polar areas, eating away at the edges of the ozone hole above Antarctica, according to the researchers' model. By the end of 2020, smoke from the Australian wildfires had increased the size of the Antarctic ozone hole by 2.5 million square kilometers, or 10 percent more than the previous year.

That said, it remains to be seen what kind of long-term impact wildfires will have on ozone recovery.

How are wildfires destroying the Ozone?

Building on a previous study by the team, they uncovered that chlorine-containing compounds, originally emitted by factories as chlorofluorocarbons (CFCs), could react with the surface of fire aerosols. This interaction created a chemical cascade that produced chlorine monoxide — the ultimate ozone-depleting molecule. 

"But that didn't explain all the changes that were observed in the stratosphere," Solomon said. "There was a whole bunch of chlorine-related chemistry that was totally out of whack."

The current study found that chlorine monoxide concentrations increased while hydrochloric acid concentrations decreased noticeably in the atmosphere months after the wildfires. Still,  Chlorine cannot destroy ozone while it is bonded to other elements such as HCl.

Chlorine can, however, combine with oxygen to generate chlorine monoxide, which depletes the ozone layer, if HCl disintegrates. The group discovered that aged smoke particles were breaking up HCL.

Although this reaction with HCl is likely the primary route by which wildfires reduce ozone, Solomon hypothesizes that other chlorine-containing molecules may be drifting in the stratosphere that wildfires could unleash.

The United Nations recently stated that the ozone hole and ozone depletion around the world are on a recovery track thanks to a multinational effort to phase out ozone-depleting chemicals.

However, "The effect of wildfires was not previously accounted for in [projections of] ozone recovery. And I think that effect may depend on whether fires become more frequent and intense as the planet warms,” Solomon asserted.