in an attempt to reduce air pollution, the European Commission has laid down strict standards not only for pm 10s - particles with a diameter of less than 10 micrometres, but also for pm 2.5s which are less than 2.5 micrometres. It is felt that these rules will halve emissions of microscopic particles that are blamed for tens of thousands of premature deaths from heart and lung disease.

The directive says that by the year 2005, pm 10 concentrations should be kept below an average of 50 micrograms per cubic metre of air over a 24-hour period - although this can be exceeded on 25 days a year. The proposed European standards for pm 2.5s are even tougher than those recently laid down by the Environmental Protection Agency in the us.