PM10

Clusters of small particles, such as carbon particles, in the air that come mostly from vehicle exhausts. There is a link between increase in PM10 levels and a rise in death rate, increased hospital admissions, and asthma incidence. The elderly and those with chronic heart or lung disease are most at risk.

The smaller the particulates the more dangerous they are: those below 2.5 μm across travel deep into the lungs and lodge there. The particulates themselves may be harmless but they may carry damaging chemicals, such as acids, into the lungs.

A European Commission draft directive released in November 1997 laid down guidelines for acceptable PM10 levels, aiming at maximum concentrations of 50 μg/m3 of air over each 24-hour period by 2005. The directive stipulated a buffer of 25 days in which this may be exceeded (amended in 1999 to 35 days), to be reduced to seven days by 2010.

The US safety limit for PM10 levels is 150 μg/m3. US studies suggest that there is no safe limit and an increase of 10 μg/m3 causes a 1% rise in death rate. The Environmental Protection Agency estimates 60,000 deaths are caused annually by particulates.