An increasing threat to human health is thriving off of the sunny weather.

The weather turned tropical over the weekend, with headlines jubilantly celebrating that parts of Greater Manchester would be ‘hotter than Spain’ as temperatures soared to above 20°C.

For many, it felt like a well-deserved break from months of miserable and wet weather. But, with the hotter weather a new health threat is emerging.

Indeed, residents of Greater Manchester’s northern boroughs with lung or heart problems were warned they should consider reducing their activity during Friday’s sunny weather.

The reason? Ozone pollution.

The Bolton News: Friday's pollution forecast showed moderate pollution throughout much of the north of Greater ManchesterFriday's pollution forecast showed moderate pollution throughout much of the north of Greater Manchester (Image: GM Clean Air/Google)

Sign up to our newsletters to get the latest stories sent straight to your inbox.

Unlike pollutants such as nitrogen dioxide, which is emitted from human sources such as car exhausts, ozone is formed and removed naturally, and can be found at the ground-level and high up in the stratosphere.

High-up in the stratosphere, ozone protects us harmful UVC rays which can cause cancer.

At ground level, however, it can cause problems – and government data shows a long-term increase in urban ozone levels.

The pollutant forms when sunlight triggers a complex series of chemical reactions between other pollutants, including nitrogen dioxide, and volatile organic compounds – human made chemicals found in products including paints, cleaning supplies, and office equipment.

An emerging threat

Professor Hugh Coe is the director of the Manchester Environmental Research Institute at the University of Manchester’s Department of Earth and Environmental Science.

Now, he’s warning of the ‘emerging threat’ of ozone pollution.

Speaking with The Bolton News, Prof Coe said: “Ozone pollution is slightly different to other pollution sources – it’s produced in the atmosphere, so it’s not something that we emit, like particles or nitrogen oxides from motor vehicle exhausts, so you can’t drive less or burn less: you yourself are not emitting that material directly into the atmosphere.

“When we have high incidences of sunlight and you have relatively poorly mixed air – an unusually nice day with a big high pressure so the air doesn’t mix upwards into the atmosphere very much, the atmosphere can make ozone.

“It does that by reacting the oxides of nitrogen that we emit from factories, car exhausts, and from home heating with background organic compounds – things that may be emitted by petrol or diesel, but more commonly these days are emitted from a whole range of other sources.

“When you smell air freshener, when you use screen wash on your car to wash those bugs off, that smell of an organic vapour is what’s being emitted into the atmosphere, and that mixes with vapour being emitted by trees.

“The combination of those two, reacting together in sunlight, forms ozone.”

The Bolton News: Professor Hugh Coe has warned of the 'emerging threat' of ozone pollutionProfessor Hugh Coe has warned of the 'emerging threat' of ozone pollution (Image: Hugh Coe)

Follow The Bolton News on Facebook, Instagram, X (Twitter), and TikTok.

According to Prof Coe, ozone can affect more than just human health.

He said: “Ozone can be quite toxic. It reacts itself with paints and plastics, it’s the sort of thing that makes rubber bands age with time and crack.

“It has the same effect on plants and animals, including humans, so it reacts with our cells and harms them. That gives rise to us suffering from health problems associated largely with breathing – that causes us to cough and splutter.”

Climate change could exacerbate problem

Ozone pollution is difficult to challenge, as there is not just one source. However, climate change could exacerbate the issue.

One potential compounding factor is that nitrogen oxide – not dioxide – also emitted by combustion cars, is an ozone-reducing greenhouse gas.

Prof Coe continued: “I don’t think we’ve had to be too concerned about ozone pollution in the UK, we’ve had one or two incidences over some periods. The issue is what happens next.

“If we reduce nitrous oxide because we want to reduce nitrous oxide pollution, that’s good, and we want to plant trees across the urban space from the perspective of net zero and reaching climate change targets, and also because trees are lovely in a city, then you want to make sure that you’re not going to lead to a higher incidence of ozone events.

“Particularly when you have climate change that’s leading to increased warming and potentially leading to periods when you’ve got very strong heat, like we saw last summer and the summer before.

“It’s under those conditions that there’s potentially this emerging threat of ozone pollution – and the first thing to make sure is that the public are aware of that potentially emerging threat, particularly if you have an underlying health condition where you don’t want to expose yourself to pollution that’s going to irritate your lung function and your breathing.”

Campaign groups calls for more understanding

Sarah Rowe of the Clean Cities Campaign said: “Unfortunately, until we really tackle the root causes of air pollution in our cities – the burning of fossil fuels particularly for road transport - then we will continue to see episodes of high pollution which are particularly dangerous for people with existing health conditions.

“Because of the way that different pollutants react with each other, there is evidence that these episodes will worsen as temperatures rise, so action to reduce both air pollution and tackle climate change are needed to stop the problem getting worse. 

“The good news is that we have plenty of the solutions we need.

“We need action at a national and international level too, but with transport causing a huge proportion of our carbon emissions and toxic air, we know we can improve things at a city region level with policies to make it easier for people to choose walking or cycling and public transport over driving.

“There’s also more we need to do to help people understand air pollution and its impacts so that people can act to protect themselves and their communities.”

If you have a story, I cover the whole borough of Bolton. Please get in touch at