PARTICULATE DANGER You report that Esso and Shell are making
Page 26
If you've noticed an error in this article please click here to report it so we can fix it.
ultra-low-sulphur (ULS) diesel standard at most of their sites ( CM11-17 Feb). The report says reduced particulate emissions and visible smoke are the main benefits of ULS fuel.
That a reduction in fuel sulphur brings down the mass (weight) of particulates in the exhaust is beyond doubt; and it is mass that is measured in emissions legislation certification tests.
But it is the size (and number) of particles rather than their total mass which is now widely regarded as a more realistic health hazard indicator. Three or four years ago the PM10 and later PM2.5 scares highlighted this concern.
However, at an Institution of Mechanical Engineers seminar on diesel particulate control last December, it became clear that medical opinion has swung
to the view that "the smaller they are the more potentially harmful they are". The key concern is the extent to which they can penetrate the alveoli (the narrow respiratory tracts in the lungs).
Now here is the crunch. According to some speakers at the ImechE seminar, cutting fuel sulphur content can have the effect of reducing exhaust particle size, implying a detrimental rather than a beneficial health effect for those with breathing difficulties.
It is known that EU environment ministers would have liked to include a particle size/number clause in the Euro 4.5 requirements they announced on 21 December. But they are hampered by the difficulty of translating its inevitable technical complexity into legal terms, and the likelihood of no practical (or accurate) means of measuring particle size becoming available until at least 2010.
Alan Bunting, Harpenden, Herts.