Media playback is unsupported on your device

How pollution levels are tested

2 April 2014 Last updated at 18:09 BST

Air pollution has reached "high levels" in parts of rural south-east England, Defra has confirmed.

Government warnings have been issued, with particular reference to those with health problems living in affected areas of England.

David Shukman looks at how the levels of pollution are monitored.

Copyright © 2015 BBC. The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.