AIR pollution in two-fifths of UK schools exceeds the acceptability standards set by the World Health Organization (WHO), a new study has found.

Although the improvement of air quality during lockdown was well documented, levels of dangerous nitrogen dioxide rose again last autumn when children returned to school and more adults travelled to work again.

Despite the rise, however, some improvement in air-quality levels has been maintained. The number of schools where pollution exceeded acceptable levels has fallen from 49 per cent pre-pandemic to 41 per cent.

The figures are published in a study from Airly this month, which provides air-pollution data for governments and cities.

Nitrogen dioxide exacerbates asthma in children and reduces lung function. Children are more vulnerable, as their airways are smaller and still developing. Road traffic and heavy industry are the main sources of nitrogen dioxide.

The study found that schools in deprived areas were more likely to suffer from poor air quality, owing to denser housing, older cars, lack of green space, and, in some areas, the legacy of the Industrial Revolution. London has the highest levels in the UK.

City Hall, in London, said that, this August, its own analysis showed that almost every school in London was in an area that exceeded the WHO’s limits. In 2020, it named 34 schools where pollution exceeded legal limits in the UK, including six Church of England primary schools, one secondary school, and St Paul’s Cathedral School.

St Paul’s C of E Primary School, Hammersmith, was named four years ago as the second most polluted school in London. Situated on the M4 corridor, close by the Hammersmith flyover, the ranking still came as a shock, the head teacher, Claire Fletcher, said.

The school set up a campaign to raise funds to improve air quality. It teamed up with the organisation Trees for Life, and began to replace part of the school’s playground with a planting scheme, including trees, shrubs, herbs, and flowers.

Ivy screening has also been added around the woodland area. Pollution levels are now measured regularly. Ms Fletcher said that the impact on air pollution had started to show after just a few months.

“We started seeing the levels dropping after a few months. The change to a green space has also affected how the children behave: it is much calmer out in the playground. The air tastes different.”

For some of the pupils at the school, which is in a district with high levels of deprivation, the new green playground is their only access to green space.

The latest data from St Paul’s School show that the measurement of nitrogen dioxide has dropped from about 29 micrograms per cubic metre in 2018 to 24 micrograms per cubic metre in 2021.

The Church of England does not collect data on air pollution around its schools.