Antarctic ozone hole increased by 10% due to Australian megafires

Wildfires can propel smoke into the stratosphere, where the particles linger for more than a year. These particles, while stuck there, can cause chemical processes that erode the Earth's protective ozone layer, according to a new MIT study published in Nature on March 8.

The study, partly funded by NASA, focused on the smoke from the "Black Summer" megafire in eastern Australia, which burnt from December 2019 until January 2020. 

Tens of millions of acres were scorched during this incident; the fires are considered to be the most destructive in American history. Additionally, more than 1 million tons of smoke were emitted into the atmosphere.

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.