Ozone levels increased significantly and exceeded World Health Organisation recommendations, the researchers found after drawing on a national network of air pollution monitoring sites

Extreme temperatures experienced by the United Kingdom have altered the levels of harmful pollutants in the atmosphere, according to researchers from the National Centre for Atmospheric Science (NCAS).

July heatwave has added dangerously high levels of ozone and Particulate matter to the atmosphere. The UK experienced temperatures above 40°C in mid-July for the first time in its recorded history.

The country’s Met Office had issued a ‘red warning’ for central, northern, eastern and southeastern England from July 18 to July 19, 2022.

Researchers at NCAS analysed air pollution data between July 18 and July 19.

The ozone levels increased significantly and exceeded World Health Organisation recommendations, the researchers found after drawing on a national network of air pollution monitoring sites.

The highest levels of ozone were recorded July 19 at observation posts in Sibton, St Osyth and Weybourne.

Unlike many other pollutants, ozone is not frequently released directly by human activity. Instead, it is created as a result of atmospheric reactions. Heatwaves are known to trigger ozone pollution.

Sunlight combines with pollutants already present in the air, such as oxides of nitrogen from car exhausts and volatile organic compounds, to form ground-layer ozone.

During hot spells, slow air movement and rapid evaporation can accumulate pollutants and boost the rate of emissions of volatile organic compounds.Higher ozone concentrations were observed in rural areas compared to urban areas.

“Although both nitrogen dioxide and volatile organic compounds are more common in urban areas, they take a long time to react to form ozone. By the time the reaction takes place, the air has already moven to a different area,” explained Professor Lee from NCAS.

Ground level ozone can worsen asthma attacks and increase our vulnerability to respiratory infections.

“Due to the effects of climate change, we can expect heatwaves more often in the future, leading to a higher frequency of dangerous ozone pollution events across the UK,” said Grant Forster from Weybourne Atmospheric Observatory, the UK.

The scientists also discovered that the bulk of small particulate matter was formed from organic material, which may be more harmful than non-organic ones.

“The small pollution particles we saw were almost all organic material and black carbon, which is surprising,” said James Allan from NCAS.

Allan suspects wildfires and heatwaves to be the reason behind this.

“It’s possible that continental wildfires were contributing burnt materials; the sun’s heat is also likely to have been triggering chemical reactions in the atmosphere, leading to new organic particle formation,” he added.

Weather and air quality are tightly correlated. Hot spells frequently coincide with poor air quality as the heat intensifies the reactivity of airborne chemicals, the researchers concluded.

July heatwave triggers air pollution in UK