Particulates

These are small fine particles from the exhaust, invisible to the naked eye and not to be confused with black smoke. They contain a mixture of unburnt and partially burnt fuel as well as lubricating oil and compounds which are regarded as carcinogenic (or cancer forming).

The ones of most concern are referred to as PM10.These are particulates of less than 10 microns which remain suspended in the air and can be inhaled into the lungs.