Measurement science issues relating to PM10 and PM2.5 airborne particles.

Airborne Particulate Matter (PM) is associated with major health effects in Britain and elsewhere. It also has a significant role in climate change. Current UK and European legislation sets limit values on health grounds for ambient concentrations of PM10 (total mass per unit volume of air of particles with aerodynamic diameter less than 10 µm) and PM2.5 (the fraction less than 2.5 µm, called the fine fraction). However, it is well known that measurements of these quantities can vary by amounts of the order 50% depending on the method and instrument used, making compliance with legal obligations more problematic than for other important pollutants. Standardisation of manual measurements for EU purposes is being carried out through CEN. There has also been a recent EU-led exercise to define in practical terms how a non-standard method can be determined to be equivalent to the standard method. In a separate but related development, CEN has started work on standardisation of automated methods for measuring PM. Both the standardisation process and the revision of the equivalence procedure are currently ongoing. This short Report aims to summarise: