New air quality research indicates that measuring ultra-fine particles can distinguish between particles generated through human activities, such as combustion, and larger particles, which are more likely to arise from mechanical processes and natural sources.

The smallest air particles are from combustion sources such as vehicles and power plants, and easily enter the body. However, air quality measurements today typically focus on larger particles from mechanical processes, which may be less relevant from a health perspective.

Air quality standards in Europe were developed using PM2.5 and PM10 particle sizes (less than 2.5 and less than 10 micrometers in diameter, respectively). The limitations of the measurement equipment available at the time were at least partly responsible for the choice of these particle sizes. Research using data on over 6000 particle samples from a range of environments explored whether measuring PM1 and PM10 levels would lead to a better distinction between the different types of pollution source.

The research found that PM2.5 data were hard to interpret, because they included particles from both mechanical processes and from combustion. PM1 measurements, however, could be used to distinguish between particles from combustion processes distinct from mechanically generated particles. Data from many environments around the world showed a clear cut off point around the PM1 mark, with particles below this size being derived almost exclusively from combustion.

This suggests that PM1 and PM10 would be more useful measures of air quality than the current system. Switching to PM1 measurements could be made now as the measurement technology is already available. In future it may become increasingly useful to focus on the ultrafine particles vehicles emit in large quantities. These are even smaller than PM1 and very lightweight. Monitoring technologies are now available that can measure these ultrafine particles. Determining the best measure of air quality is important.

Particle size plays a key role in determining exposure to pollutants; it plays a part in both the chemistry of the particle and the likelihood we will breathe it in. The nose, for example, filters out most particles larger than PM10. These include particles from mechanical grinding, plants and dust caught by the wind. Most anthropogenic pollution is combustion-related, and creates particles less than 1 micrometer in diameter (PM1). Additional information: The European Commission's proposal for a directive on ambient air quality and cleaner air for Europe (COM (2005) 447 2005) introduces new air quality objectives and monitoring requirements for PM2.5 (fine particles) in line with WHO recommendations and the most recent scientific evidence.

At the time of the proposal, there was no adequate information to introduce objectives on PM1. A review of the directive, which will enter into force in May 2008, is foreseen in 2013. One purpose of the review is to ensure that the most appropriate metrics based on the latest scientific evidence are used in the particulate matter objectives related to the protection of human health.

The EC's LIFE programme co-finances a number of projects dealing with air pollution. The most relevant and recent ones have been grouped into a LIFE thematic project list: http://ec.europa.eu/environment/life/themes/air/documents/air_pollution.pdf . Additional air-related LIFE information can also be found here: http://ec.europa.eu/environment/life/themes/air/index.htm Source: Morawska, L., Keogh, D.U., Thomas, S.B., and Mengersen, K. (2008). Modality in ambient particle size distributions and its potential as a basis for developing air quality regulation. Atmospheric Environment. 42 (7): 1617-1628. Contact: vollebergh@few.eur.nl