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Introduction
1. In 1995 the Panel recommended for the United Kingdom an Air Quality Standard for airborne particulate matter of aerodynamic diameter less than 10 micrometres (PM10) of 50 µg/m3, measured as a running 24-hour average. This recommendation was accepted by the Government and adopted within the National Air Quality Strategy in 1997 as a provisional objective, to be achieved at the 99th percentile by 2005. The objective was subsequently incorporated into regulation. The Panel’s recommendation included a statement that the techniques for monitoring the Standard should be consistent with the PM10 measurements made by the Department of the Environment’s Automatic Urban Network (i.e. TEOM or equivalent measurements).
2. The Government and Devolved Administrations have recently reviewed the 1997 National Air Quality Strategy objectives and, in January 2000, published a new Air Quality Strategy for England, Scotland, Wales and Northern Ireland (DETR 2000). In addition, during 1998 the Airborne Particles Expert Group reviewed the sources and levels of PM10 in the UK (APEG 1999). A PM10 limit value of a 24-hour mean of 50 µg/m3, not to be exceeded on more than 35 days per year, and an annual mean of 40 µg/m3, both based on a gravimetric system of measurement, were set out in the first European Daughter Directive (Council Directive 1999/30/EC). In light of the APEG analysis, the PM10 limit values were adopted in place of the original PM10 objective. This is seen as a staging post on the road to a more stringent objective, rather than the final outcome.
3. Since the EPAQS recommendation on PM10 was made, evidence has emerged that PM10 might not be the measurement most representative of the fraction of the ambient aerosol that is responsible for its harmful effects on health. Evidence has accumulated that this toxicity may lie in a finer fraction of the particles, perhaps below 2.5 µm or smaller. Moreover, it has become apparent that PM10 measurements may include an amount of resuspended dust of probable low toxicity, leading to difficulties in compliance with the Standard in areas where coarse particles, such as wind-blown dust or sea spray, may make an important contribution.
4. In view of this evidence, the Panel has been asked to investigate the possibility of recommending an additional (or perhaps alternative) Standard for particulate matter, taking account of the smaller size range thought to be responsible for toxic effects. We have reviewed the evidence and report our conclusions here, setting out our arguments and making recommendations for further research.
References
APEG. Source apportionment of airborne particulate matter in the United Kingdom. Report of the Airborne Particles Expert Group. London: Department of the Environment, Transport and the Regions, 1999.
DETR. Air Quality Strategy for England, Scotland, Wales and Northern Ireland. London: The Stationery Office, 2000. ISBN 010 145482 1.
Published 17 May 2001
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