‘High’ ozone warning issued for London

High levels of ozone air pollution are expected for London over the coming 24 hours, according to a forecast from the London Air Quality Network.

In its outlook for Thursday (26 July), published earlier today, the Environmental Research Group at King’s College London, which runs the LAQN, said that weather conditions are likely to lead to widespread ‘Moderate’ ozone, with ‘High’ ozone possible in suburban and outer-London areas.

Soaring temperatures have led to warnings over high levels of ozone

It said: “Thursday is forecast to be very hot with temperatures rising to 33 or 34 degrees and no cloud cover.

“Back trajectories show a southerly and south-westerly air feed which brings the chance of imported pollutants adding to local emissions.

“These emissions and the strong unbroken sunshine provide the conditions for prolonged ground-level ozone generation peaking in the late afternoon/early evening.

“Widespread ‘Moderate’ ozone is likely and ‘High’ ozone is possible in suburban and outer-London areas.”

Other air pollutants are forecast to remain low.


High ozone levels are most common during summer months in Europe due to the warmer temperatures and higher levels of solar radiation.

Ozone is formed in the atmosphere from emissions of pollutants such as nitrogen oxides from vehicles, organic compounds and methane from agriculture, which react with sunlight. Once formed, ozone can remain in the atmosphere for many days.

Ground-level ozone pollution has been associated with risks including lung inflammation, decreased lung function and an increase in asthma attacks.

The forecast has prompted City Hall to issue its own warning to Londoners. Mayor of London, Sadiq Khan, said: “This week has seen London experience extremely high temperatures. The heat, combined with London’s toxic air, a lack of cloud cover and emissions travelling from the continent, means I am triggering a ‘high’ air pollution alert today, for tomorrow, under our comprehensive alert system. This is the second time in six months that we have had to use the ‘high’ alert system and shows just why air pollution is a public health crisis.”


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