On health risks of ambient PM in the Netherlands. Executive summary.

Particulate Matter (PM) in the ambient air can lead to health effects and even to premature mortality. This result has been found in a score of epidemiological studies, but its cause is not yet clear. It is certain, however, that these effects are so serious and so extensive that further action is warranted. In the scientific literature ambient aerosols are known as PM, short for Particulate Matter. Depending on the diameter or size of the particles, they are termed PM₁₀ (for particles with diameters of up to approximately 10 micrometres) or PM_2.5 (for those less than 2.5 micrometres in diameter). One micrometre is a thousandth of a millimetre. Humans inhale particles smaller than 10 micrometres, which end up deep in our airways.