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Catalytic converters, which are fitted to all cars to reduce harmful emissions, are increasing levels of other toxic gases that can be hazardous to human health, according to scientists.
They say that the benefits of the devices, which clean poisonous gases such as carbon monoxide from exhaust fumes, are being offset by the production of two other potentially dangerous compounds, hydrogen sulphide and carbon disulphide.
Since 1993 EU legislation has made it compulsory for all new vehicles to be fitted with three-way catalytic converters in an attempt to reduce carbon monoxide and nitrogen oxide emissions.
While the converters have achieved this goal, they have also changed the forms in which sulphur in petrol is released into the atmosphere: hydrogen sulphide and carbon disulphide are being generated instead of sulphur dioxide.
Levels of hydrogen sulphide measured in British cities are now up to 100 times higher than they were in preindustrial times, according to research by Simon Watts and Stephen Samuel, of Oxford Brookes University, who believe that catalytic converters are partly responsible.
“The amount of sulphur coming out of individual exhausts is lower than previously. However, it is no longer coming out as sulphur dioxide but these other sulphur compounds,” Dr Watts said. “Add to this the fact that there are now so many more exhaust pipes out there, and you see the problem.”
Hydrogen sulphide, a colourless gas that is responsible for the characteristic foul odour of rotten eggs and stink bombs can shut down several critical systems in the body. Carbon disulphide is a neurotoxin and a carcinogen. It can be dangerous to human health at high doses.
“The increasing levels of hydrogen sulphide in the air potentially pose a serious health concern,” Dr Watts said. According to his research, a typical reading in the 1500s would have been 70-100 parts-per-trillion. Recent measurements in Elephant & Castle, South London, found up to 7,000 parts-per-trillion.
Professor Ken Reid, head of the immunochemistry unit at the University of Oxford, said that long-term exposure to hydrogen sulphide could raise the risk of respiratory diseases and lung cancer.
“Hydrogen sulphide can modify antibodies in the lung, which compromises immunity and increases the likelihood of infection,” he said. “It’s now well recognised that this kind of repeated insult can set up a cancerous state.”
The gas may also be responsible for increases in asthma among city-dwellers as it can disrupt the way the lungs regulate the respiratory cycle.
Dr Watts added that lean-burn engines might have been a better solution to the problem. “Our alternative in the early Nineties was lean-burn engines, which produce much less hydrogen sulphide,” he said. “But catalytic converters were the easier option for car manufacturers. I think the EU was swayed by economic considerations.”
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I say we should tax volcanoes. After all, each year they emit 1000 (yes 1000) times more CO2 than the entire human race.
JAmes, Ewell, Surrey
7000 parts per trillion of hydrogne sulphide is already above the detection threshold and therefore likely to have some chronic effects, yet still some way away from acute effects.
While nobody is going to be poisoned soon, it's good that someone keeps an eye on the downside of new technologies.
Niel Malan, Bronkhorstspruit, South Africa
Did anyone know that ALL bio-fuels emit NOX. This is a really bad thing. Who cares, it does not fit the dream. Also water vapour,. The earth's surface is covered 70% with water. No-one seems to be worried by the fact that water vapour is the largest gas on the Planet.
Water rusts metal, and combines in all sorts of interestng ways, and one one says a peep.!!
Desmond Taylor, Houston, USA Texas
7,000 parts per trillion ?!?!!?!?! An outrage !!?!?!?!?!? That'll be 7 parts per billion then ? or 0.007 ppm. Is this really of such concern ? You must get the same quantities from eating an Egg sandwich. You can smell the emissions from that. That'll be in the ppm's or ppt's. I am more concerned about the 2% Benzene in fuel. That IS a carcinogen. And there IS an alternative. (MnO4) Anyone heard of a pea souper ? Now that's what I call pollution. Arrest me for eating egg sandwiches if you like. Direct Injection is the future anyway, for lean burn and efficiency.
Lionel Tiger, Birmingham,
Anyone causing a diesel spillage should be 'banged up' for the same length of time as the life-expectancy of the other road users who are killed as a result of their careless selfishness. That means that a good many drivers of diesel-fuelled vehicles would serve compound life sentences.
Perhaps those incarcerated in that way might find clever lawyers who could (justifiably) argue that our politicians should really be held even more culpable for encouraging diesel use.
D. O'Rorke, Farnham, Surrey
The diesel I buy says that it's very low sulphur to start with - so I feel happy that diesel is best all round -
jack Cohen, NEWENT, Glos
Pot? Kettle? Diesel vehicles are equally nasty; just follow a bus or some old van and try to breathe at the same time.
My car runs on LPG and I feel good.
John, London, UK
The proliferation of man made toxins appears to be almost forgotten in all the noise about CO2 and yet perhaps presents more of a threat. In overall resource depletion and environmental terms, catalytic converters were never a logical solution. And more than that, how could they be when they must be hot to catalyse effectively and yet so much running is short journey cold and warm up? Lean burn was the answer - probably remains so. Meanwhile relatively very clean burning LPG does not get the media or political attention it deserves.
GC, Harrogate, UK
Please ensure when reporting on such matter that you report things accurately.
Throughout the article reference was made to "all cars" when this in not in fact true. The research and resultant data only apply to GASOLINE (i.e. Petrol Powered) cars not the the increasingly popular Diesel powered ones.
Although much lower producers of CO2 than petrol engined cars, Diesel cars are almost universally condemned for their higher "other" pollutants and until recently been more heavily taxed as a result, yet these results reveal that truth that petrol is just as bad, if not a worse
producer of toxic emissions.
Whenever diesel is made out to be bad it is made clear that it is just diesel nthat is being talked about, in this case it is just petrol and nowhere does the Times article make that clear.
Stephen Eeley, London, UK
Continued
Whenever diesel is made out to be bad it is made clear that it is just diesel that is being talked about, in this case it is just petrol and nowhere does the Times article make that clear.
I questioned the writers on the matter and this was the reply from Dr Samuel.
"Currently we are investigating real-world emission species from gasoline engines. We do not have sufficient data to comment on real-world emissions from Diesel engines at the moment"
Stephen Eeley, London, UK
Please ensure when reporting on such matter that you report things accurately.
Throughout the article reference was made to "all cars" when this in not in fact true. The research and resultant data only apply to GASOLINE (i.e. Petrol Powered) cars not the the increasingly popular Diesel powered ones.
Although much lower producers of CO2 than petrol engined cars, Diesel cars are almost universally condemned for their higher "other" pollutants and until recently been more heavily taxed as a result, yet these results reveal that truth that petrol is just as bad, if not a worse producer of toxic emissions.
Whenever diesel is made out to be bad it is made clear that it is just diesel that is being talked about, in this case it is just petrol and nowhere does the Times article make that clear.
I questioned the writers on the matter and this was the reply from Dr Samuel.
To Follow....................
Stephen Eeley, London, UK