Parts of the UK face soaring levels of air pollution on Friday, prompting heath warnings for vulnerable people.
High levels of pollution are expected in some areas of south east England, as warming conditions create a build-up of local pollutants from sources such as traffic fumes, combined with pollution from the continent and Saharan dust from the south.
Much of the south east and eastern England will see see high levels of pollution, although the problem is expected to be short-lived with Atlantic winds dispersing the polluted air on Saturday.
In areas experiencing very high levels of air pollution, adults and children with lung problems, adults with heart problems and older people are advised to avoid strenuous activity.
People are also advised to reduce physical exertion, particularly outside, and asthma sufferers may need to use their reliever inhaler more often. Where pollution levels are high, adults with heart or lung problems and children with lung problems should reduce strenuous physical activity, older people should reduce physical exertion and anyone suffering from sore eyes, a cough or sore throat should cut down on activity, particularly outdoors.
Similar conditions were experienced last April when a dust cloud of Saharan dust covered the south east of England, raising pollution levels to their highest in London.
A Defra spokeswoman said: "Locally generated air pollution, combined with pollution from the continent and Saharan dust, could cause high or very high levels on Friday.
"This is expected to clear on Saturday and pollution levels will return to low throughout the morning."