Wildfires can damage the ozone layer

As well as endangering habitat, property and lives, wildfires are also putting our atmosphere at risk.

Satellite observations of the ozone layer after widespread fires burned across Australia in 2020 revealed that it was being depleted by chemicals released in the smoke. These chemicals sped up the processes that normally regulate ozone in our atmosphere, reducing the UV protection this layer affords.

Prof Peter Bernarth, the study's lead author, says, 'The Australian fires injected acidic smoke particles into the stratosphere, disrupting the chlorine, hydrogen and nitrogen chemistry that regulate ozone.

'This is the first large measurement of the smoke, which shows it converting these ozone-regulating compounds into more reactive compounds that destroy ozone.'

While the holes patch themselves up over time, more frequent wildfires as a result of climate change will allow more UV to pass through the ozone layer, increasing the risk of a range of health impacts.

The findings of the study were published in the journal Science. 

What is ozone?

Ozone is a form of the gas oxygen. Unlike the more common form of the element which has two oxygen atoms bonded together, ozone is made of three.

It is naturally formed when O₂ is exposed to high energy sources, such as UV radiation and lightning. With three oxygen molecules it becomes unstable and reactive, and breaks down into the more stable two-molecule form of oxygen over time. 

It can also form as a result of human activity, through the reaction of common exhaust pollutants such as nitrogen oxides and hydrocarbons in sunlight. At ground level, it is considered a pollutant in its own right and can harm health through causing lung damage and inflammation.

However, in the atmosphere, ozone is beneficial to life on Earth. When UV enters the atmosphere, much of it is absorbed by ozone and causing it to break down into oxygen molecules and a free atom. These molecules react with more oxygen, ozone and UV to regenerate the initial ozone.

The gas forms a layer of the planet's atmosphere, and without it greater levels of UV exposure would lead to more cases of sunburn, eye and immune system damage and a range of cancers. 

In the 1980s, it was discovered that a hole had formed in the ozone layer over Antarctica. Research suggested that ozone was being broken down by gases known as chlorofluorocarbons (CFCs) which were used in products such as aerosols and refrigerators.

CFCs catalysed the breakdown of ozone, but were not themselves destroyed by the process. This allowed molecules of these compounds to continue to react with further ozone molecules, exacerbating the damage to the atmosphere.

The severity of the issue was quickly recognised, and in 1987 countries around the world agreed to the Montreal Protocol and began to phase out the production of chemicals which deplete the ozone layer, including CFCs. 

It is estimated that the rapid agreement of the protocol saved billions of pounds, thousands of lives, and tonnes of crops. As CFCs also act to trap greenhouse gases, their phasing out is also believed to have prevented around 2.5⁰C of global warming by 2100.

While the ozone hole is recovering, the layer is closely monitored to check for further damage. A team of Canadian researchers have now shown that wildfires are harming its ability to provide UV protection. 

How do wildfires affect the atmosphere?

Using equipment from the Canadian Space Agency's Atmospheric Chemistry Experiment (ACE) satellite, the scientists were able to analyse how levels of different chemicals in the atmosphere changed during wildfires.

'The ACE satellite is a unique mission with over 18 continuous years of data on atmospheric composition,' Peter explains. 'ACE measures a large collection of molecules to give a better, more complete picture of what is happening in our atmosphere.

'Models can't reproduce atmospheric smoke chemistry yet, so our measurements provide a unique perspective on it not seen before.'

Following the beginning of the fires, these compounds in the smoke caused ozone levels above Australia to drop and remain persistently lower than any other year recorded by the satellite. 

It is believed this is due to a cocktail of different compounds in smoke entering the ozone layer. Extreme wildfires do this through the production of pyrocumulonimbus clouds which rapidly move compounds through different layers of the atmosphere.

The chemicals in smoke were then catalysing reactions between various chlorine and nitrogen containing compounds, which then reacted with ozone to break it down. 

While the resulting damage is not as severe as the Antarctic ozone hole, which is not expected to recover until at least the 2050s, the expected increase of wildfires will cause the damage to happen more often.

Though these holes will repair themselves once the smoke has stopped, the increase in UV exposure will likely impact on the health of humans, plants and animals. The paper adds that continuing fires 'have the potential to affect ozone chemistry in unexpected ways.'