PM10 is produced by exhaust fumes as well as tyre and brake wear and can cause asthma, cardiovascular problems, lung cancer and premature death.

BBC: Boris Johnson sticks by gluing pollution to roads

The report also says that the congestion charge has caused reductions in the two most concerning pollutants to London, by 8% for nitrogen oxides and 7% for particulate matter that is fine enough to penetrate the lungs and cause health problems (referred to as PM10).

FORBES: Paul Maidment

The combined effect of charging and improved vehicle technology, notably cleaner-burning diesel engines that are being used in more buses and taxis, has led to an overall reduction of 13% in nitrogen oxides and 12% in PM10 via vehicle tailpipe emissions in the charging zone.

FORBES: Paul Maidment