Millions of vulnerable people, such as asthma sufferers, across the UK have been advised to stay indoors as unusually high levels of pollution sweep across London, southern England, the Midlands, and Wales.
The Wednesday announcement comes just weeks after severe air pollution led to restrictions on vehicle use in Paris and Brussels, and prompted the French government to introduce free public transport in some cities.
The unusually high levels of air pollution are due to powerful dust storms being blown into Britain by strong south-easterly winds from the Sahara in North Africa, coupled with homegrown air pollution.
"The current elevated pollution levels over parts of the UK are caused by light winds allowing the build-up of pollution, plus dust from the Sahara contributing to pollution levels," according to the Department for Environment Food and Rural Affairs (Defra) forecast.
But experts said the levels of pollution are not that unusual for this time of year; the only difference is that the public and press know about it this time because of a new forecasting system just introduced by the Met Office.
On Tuesday, Defra handed over responsibility for reporting air pollution to the Met Office, which provides the UK’s national weather service and is historically good at communicating the weather.
“Two weeks ago, when the air pollution map of the south-east turned red, no one was informed. The BBC ran stories about the pollution in Paris and Milan, but no one thought it worthwhile to inform the British public they were being exposed to dangerous levels of fine particles,” Dr. Ian Mudway, lecturer in respiratory toxicology at King’s College London, told the Guardian.
"I think it has to be a good thing, because the Met Office are good at communicating to the public and it depoliticizes it; it takes away the issue of a minister worrying about looking bad because of putting out a pollution warning," said Alan Andrews from environmental law firm ClientEarth.
Because of the new warning system, adults, children, and elderly people with lung problems and heart defects are being urged to avoid strenuous activity and stay indoors.
Professor Frank Kelly, also of King’s College London, said the tiny particles over British skies can cause problems for individuals suffering from asthma, as well as longer term problems for most people, the Guardian reported.
The smog is expected to travel north on Thursday and affect most areas of the country up to central Scotland, although the southernmost counties of England should feel some respite as cleaner air blows in from the Atlantic.