Pollution levels are measured in tiny particles of soot and dirt. The particulate matter, known as PM10s, can cause lung and heart problems when inhaled.
In order to meet the European Commission targets the daily limit for PM10 in the UK must not exceed 50 micrograms per metre squared more than 35 times in a calendar year. London was supposed to meet the target by January 1 2005 but has had to ask for a series of extensions. The latest deadline is September and if London fails again then the UK faces a fine of £300?million.
How, actually, can PM10s be reduced?