Emissions of fine particles from traffic and chemical plants should be halved by 2010 according to recommendations published on Monday by the British government. Experts welcomed the targets, but said a greater understanding of how particulates damage health is needed if industry is to make effective cuts.
鈥淩ight now, we know the effect they have, but we don鈥檛 know what makes them toxic,鈥� says Stephen Holgate, who chairs the government-appointed Committee on the Medical Effects of Air Pollution (COMEAP).
A COMEAP study of 1996 data found that particulates caused the early death of 8100 鈥渧ulnerable鈥� people and lead to 10,500 hospital admissions for respiratory diseases associated with particles.
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鈥淔rom a single set of particles, you could find 150 different major chemicals on their surfaces,鈥� says Holgate. Finding out whether these chemicals are toxic and whether different sizes of particles are responsible for health problems is vital if industry is to find the best way to improve fuels and engines, Holgate says. 鈥淚f they knew the toxic fraction, they could do it,鈥� he says.
Filtering effect
A common source of particulates is diesel engines, says Tony Burgess of the Combustion Research Group at University College, London. Particles measuring tens of micrometres and less are formed when combustion of the diesel is incomplete and the fuel does not have enough oxygen to burn efficiently.
Filters could be used to restrict emissions, but Holgate points out these do not always have the desired effect. Some filters designed to strip out carbon monoxide, nitrogen oxides and sulphur compounds have been found to increase the number of fine particles produced.
In May, a second COMEAP study found that cutting levels of fine particles by five per cent could increase life expectancy by between three and 6.5 months for a million people vulnerable to their effects.
The proposed cuts will limit the average daily level of particulates to no more than 20 micrograms per cubic metre over a year, with average daily levels not exceeding 50 micrograms per cubic metre for more than one week a year.