Air pollution reaches high levels in parts of England
3 April 2014 Last updated at 01:51 BST
Air pollution in parts of England has reached high levels in the past 24 hours, Defra has said.
People with health problems have been warned to take particular care because of the pollution - a mix of local emissions and dust from the Sahara.
Greater London, rural areas of south-east England and East Anglia's towns and cities experienced the high levels.
David Shukman reports.