Air pollution falls but high ozone pollution rises

Asthma + Lung UK describes rise in ozone levels as “alarming”, urging government to legally commit to air quality targets aligned with WHO guidelines

Air pollution across the UK fell in the decade 2015-24, but dangerous levels of ozone remain a concern, according to research published in Environmental Science: Atmospheres. 

Scientists from the University of Reading studied pollution at more than 500 monitoring sites, discovering that two types of pollution improved. Nitrogen dioxide (NO₂), produced mainly by traffic, fell by 35% on average at monitoring sites, and PM_2.5, fine particles that are small enough to get deep into lungs, dropped by 30%.

However, incidents of high ozone pollution (O₃) increased from seven to 14 days per year over the same period. This presents a ‘complex challenge’ as its formation depends on the balance of certain gases in the atmosphere and their interaction with sunlight and temperature. 

Dr James Weber, Lead Author said, “The volatile organic compounds (VOCs) that lead to ozone pollution come from human sources such as traffic and industry, plus certain types of vegetation like oak trees. Over the decade, human-driven VOC emissions declined by only 1%.”

He added that UK air quality analysis is often done at city level, given the responsibility of local authorities to improve air quality. “There is less focus on national trends. Pollution from traffic is getting better, but we need both local action and international cooperation to improve all types of air pollution. 

“Local and national policies that cut traffic emissions by incentivising the replacement of older cars with newer, cleaner vehicles, retrofitting buses and restricting entry of the most polluting vehicles into towns and cities will probably reduce nitrogen dioxide further. 

“…unless [reduced traffic emissions] is accompanied by reductions to VOC emissions, both locally and internationally, ozone will continue to rise…”

“But, unless this is accompanied by reductions to VOC emissions, both locally and internationally, ozone will continue to rise, especially with more frequent hot weather.”

Professor Roy Harrison, School of Geography, Earth and Environmental Sciences. University of Birmingham, said that the decline in NO₂ was consistent with a fall in road traffic emissions of nitrogen oxides, “most notable since the introduction of the Euro 6 emission standards and the imposition of real driving emission tests to stop cheating by the motor manufacturers”.

He added: “Ozone is an increasing problem which the UK can do little to influence, as incoming air from the North Atlantic is our main ozone source, which is actually reduced by reactions with locally emitted pollutants, which is why we see increases in urban ozone as traffic emissions decline.”

Chloe Owen, Clean Air Policy Manager at Asthma + Lung UK, said: “It’s promising to see a fall in levels of some air pollutants that can harm people’s lungs, but there’s still a way to go. The rise in ozone levels, for example, is alarming. 

“For people with lung conditions, exposure to ozone can cause coughing, shortness of breath and can trigger symptoms of asthma and other lung conditions. 

‘At Asthma + Lung UK, we are calling on the government to commit to legally binding air quality targets, aligned with the latest World Health Organisation (WHO) guidelines.”