Ozone pollution reached potentially harmful levels in two UK towns or cities every day in 2018 on average, according to data from Britain’s national weather service.
An analysis by the FT of the latest available data compiled by the Met Office found that there were 965 so-called “moderate pollution days” across 61 urban centres in 2018 — the latest available data. Almost 85 per cent of these were caused by the concentration of ground-level ozone exceeding the limit recommended by the World Health Organisation.
Aldershot and Cambridge had the greatest number of these days — 32 each — followed by Bournemouth, Reading and Slough, which had 31. The WHO’s recommended exposure limit is 100 micrograms per cubic meter, on average, over eight hours
On moderate pollution days, as defined by the government’s daily air quality index, the UK’s Met Office advises people with lung and heart problems to limit their time outdoors.
Ground-level ozone is produced by a reaction between sunlight, nitrogen oxide emissions and volatile organic compounds (VOCs), such as solvents and chemicals found in cleaning products. As a result, the peak pollution days are in the summer months.
Simon Birkett, head of Clean Air London said ozone was “the most irritant gas for humans as it does really unpleasant things to your lungs”.
The pollutant can cause difficulty breathing, trigger asthma and cause inflammation of the eyes, nose and throat. During the 2003 August “smog” event, high levels of ozone are estimated to have caused up to 593 deaths across the UK, according to a government-commissioned report.
Ozone also damages crops, and is estimated to reduce annual yields of wheat, potato and oilseed rape by 5 per cent in the UK.
The Met Office produces daily air pollution forecasts to warn the public about short-term pollution incidents. The forecasts are calculated using a model that considers weather, emissions and other data, and are checked hourly against readings from 150 real-time pollution monitors around the country.
On days when ozone was not the cause of the Met Office’s pollution warning, the spikes were caused by particulate matter (PM2.5) — which has been linked with a host of cardiovascular and respiratory diseases — the FT analysis of the data found.
In the northern hemisphere, the amount of ground-level ozone has more than doubled over the past century, as emissions from transport, industry and agriculture have increased. Rising global temperatures as a result of climate change is making the problem worse.
Polluted cities such as London do not necessarily have the highest levels of ozone: NOx produced by vehicle exhausts consumes ozone when it is freshly emitted, but begins to create ozone as it drifts further away. As a result, ozone levels are often highest in suburban areas.
In the short term, reducing diesel emissions in congested cities is expected to increase ozone levels.
Since ozone can stay in the atmosphere for several weeks and travel thousands of miles, it is a difficult pollutant to tackle locally. Last year, the UK government said the “most effective way to tackle ozone is through concerted, international action.”
Alastair Lewis, professor of atmospheric chemistry at the University of York, said ozone was “one of the most difficult to reduce,” since it needs only a small amount of NOx to form. The other ingredient, VOCs, come from a wide range of consumer and industrial products that have not been regulated “in any serious way”.
“We don’t look at air pollution in a sufficiently holistic way,” said Dr Gary Fuller, air pollution scientist at King’s College London. The focus on nitrogen oxide pollution and on regulating transport emissions at the expense of other pollutants and of household sources are examples of this, he added.