By Seibik Bugri, April 6, 2014
A hydrogen fuel cell Taxi Defra’s
report says the nitrogen dioxide emissions generated by the typical
diesel vehicle, such as a London black taxi, have risen steadily over
the past 10-15 years
YEARS of official efforts to encourage motorists to switch to diesel
cars have backfired spectacularly, according to new evidence from
government scientists. They have found that the engines are responsible
for most of the pollution that is causing 29,000 premature deaths a year
in Britain and which has left the country facing legal action by the
The scientists have told ministers in a report that the only solution is a wholesale move back to petrol vehicles.
The report, commissioned by Defra, the environment ministry, says the
nitrogen dioxide (NO2) emissions generated by the typical diesel
vehicle have risen steadily over the past 10-15 years and there is no
prospect of reversing the trend. There are also serious problems with
diesel particulates, the tiny toxic particles that pass through the
lungs to enter every organ of the body. Both pollutants raise the risk
of heart attacks, strokes and asthma attacks, the actual causes of
mortality in most the 29,000 premature deaths.
Separate research into the long-term impacts show that children
exposed to diesel particulates have an elevated risk of developing
autism and schizophrenia, while older adults may experience accelerated
cognitive decline and depression. The Defra report, from scientists
on the government’s air quality expert group, tells ministers that
cleaning up diesels would take so long that it would be better to
promote a wholesale switch to petrol.
“What we are seeing is a complete failure of the emissions regulatory system,” said David Carslaw, of King’s College London, a co-author.
“The policy on cutting pollution over the past two decades has
been based on the idea that technological improvements could cut the
emissions produced by diesel vehicles — but this has not happened.
Nitrogen dioxide emissions per vehicle have actually risen.
“The key failure is that the European testing regime is too lenient
and does not measure how vehicles perform when driven on real roads.
They all pass the test but our research shows that when driven on real
roads they typically emit 4-5 times more than the tests suggest.
“It might be possible to fix this but it would take many years so,
for now, the reality is that switching to petrol is the best idea for
light vehicles like cars, vans and taxis.” Such a move would have huge
policy implications because about a third of Britain’s 29m private cars
are diesel powered, as are about 95% of its 3.3m vans. The proportion is
also rising — in 2012 about half of the 2m new cars registered were
diesel. In London, Birmingham, Manchester and many other cities diesel
engines also power almost all the taxis and buses.
The new report is the third to recommend getting rid of diesels. The
first two ended up in Defra’s archives with no action taken. In the
first report, in 2011, Carslaw and his colleagues said: “We found that
in diesel cars and light goods vehicles emissions of nitrogen dioxide
have not decreased for the past 15–20 years.”
For their second study in 2012 they used smog sensing camera traps,
in which beams of infrared and ultraviolet light were shone across a
busy road to analyze the exhaust plume of passing vehicles,
simultaneously photographing their number plates, to measure emissions.
The system showed that NO2 emissions for almost every type of diesel
vehicle were several times higher than implied by the European Union
test results. The latest study uses the same technology to look at buses
and other large vehicles and is expected to draw similarly powerful
The scale of the failure is illustrated by recent pollution levels in
Oxford Street, central London, one of the capital’s most popular
shopping and tourist areas.
The EU limit for nitrogen dioxide is 40 micrograms per cubic metre of
air averaged over a year. In Oxford Street it seldom fell below this
and sometimes went far above — briefly reaching 800mcg on one occasion
last August and often exceding 400mcg. Last year it was above 200mcg for
1,500 hours; 18 hours is the maximum allowed for that level.
Carslaw said: “That is the highest long-term concentration anywhere
in Europe and could make it the most polluted place in the world, above
even Mexico City or Beijing. ”
Ian Mudway, a respiratory toxicologist at Kings College London, who
recently coauthored a World Health Organisation (WHO) report on European
air pollution, said: “This is not just about vulnerable groups like
asthmatics and people with heart conditions.
“In the long term everyone will have subclinical effects that shorten
their lives. We have no choice what we breathe and if you are exposed
throughout the year then there is a risk of long-term damage to your
lungs and other organs.” The new warnings follow a week in which Britain
has been covered by a layer of smog caused by dust blown north from the
Sahara mixed with diesel particulates and other pollutants, some blown
in from Europe, but much of it generated by domestic traffic.
The severe air pollution saw a surge in 999 calls from people
suffering asthma, heart attacks and strokes — all of which increase when
pollution rises. But the new research suggests the danger comes not
just from peaks in pollution but also from long-term exposure,
especially to the young. Britain has some of the highest levels of such
pollutants in Europe.
There is also strong emerging evidence that diesel emissions,
especially particulates, can damage the brains of children living near
busy roads, altering the way they develop and raising the risk of
developing schizophrenia, autism and other diseases.
Scientists in America have found that long-term exposure to the tiny
particulates alters the way children’s brains grow, potentially altering
their thought processes and behaviour all through life.
Some scientists have likened the impact of diesel particulates to
those emitted by lead in petrol. This was banned in 1999 after
scientists found that the lead additives caused brain damage in exposed
children — reducing their IQ and increasing their propensity to violent
and criminal behaviour. The emerging threat from particulates is summed
up in a report on European air pollution by the WHO. It said: “Emerging
evidence suggests possible links between long-term PM2.5 exposure [of
particles less than 2.5 micrometres in diameter] and neurodevelopment
and cognitive function … including impairment of cognitive functions in
adults and children.”
Mudway said: “This is an emerging field of study but there is already
strong evidence for diesel pollutants having an effect on cognitive
function in kids. “Some of that research came from California, where the
proportion of diesel vehicles is low. We plan to carry out a similar
study in London, where it is far higher, so we expect stronger effects.”
The California research was reported last year in The Journal of the
American Medical Association and involved a study of 525 children, of
whom 279 had autism. It found that the pollution levels experienced by
their mothers in pregnancy and by the children in their first year of
life were strongly correlated with the risk of developing autism. It
concluded: “Exposures to traffic-related air pollution, PM and nitrogen
dioxide were associated with an increased risk of autism.”
Another study led by Jennifer Weuve, professor of internal medicine
at Rush Medical College in Chicago, was based on data from 19,000 women.
It found that older women who had been exposed to high levels of
particulates experienced greater cognitive decline compared with other
women their age.
dy by Melinda Power of the Harvard School of Public Health found
the same effect in older men, with those exposed to high levels of
particulates suffering reduced cognitive performance, equivalent to
ageing by about two years.
Deborah Cory-Slechta, professor of environmental medicine at the
University of Rochester medical centre in New York, said: “Evidence is
growing … that air pollution targets the brain. Several epidemiological
studies report associations of air pollution with autism, two report
associations with schizophrenia. Several others have reported cognitive
deficits and even increased attention deficit hyperactivity disorder.”
Cory-Slechth has also used animals to try to work out how
particulates affect the brain. She found that when mice were exposed to
the smallest of particles soon after birth their brains developed
enlarged ventricles (cavities) and the animals had problems with
learning and memory.
Michelle Block, professor of neurobiology at Virginia Commonwealth
University medical centre, in Richmond, Virginia, has looked even
deeper, studying microglia, the brain’s immune defence cells, to see how
they are affected: “We found that these cells can become reprogrammed,
hijacked by air pollution, so they aberrantly cause central nervous
Although much of the latest research is American, the United States
has far less to be worried about than Britain because diesel is used
mainly in buses and goods vehicles, with most US cars and light vehicles
powered by petrol. Europe, by contrast, has increasingly switched to
diesel in the mistaken belief that it is cleaner and greener.
In Britain in 2012 half of the 2m or so new cars bought were diesel,
compared with just 18% 11 years previously. Of the 3.3m registered vans,
95% were diesel. The number of diesel vehicles is the key reason why
Britain is experiencing so many pollution problems. Last week’s
pollution cloud gained national attention because it was the first to be
publicised under the Met Office’s new pollution prediction system, but
little mention was made of two peaks that preceded it last month. Mudway
said: “Neither the government nor the mayor of London said anything
about those previous episodes even though people with asthma, heart
disease or other conditions would have benefited from knowing.”
Alan Andrews, a lawyer with ClientEarth, an environmental law firm,
is taking action against the government to force it to comply with EU
legislation. He said: “The UK will breach the directive in 16 parts of
the country up to 2020 and in London up to 2025.” A government spokesman
said: “No one type of transport is the sole cause of air pollution and
there is no single magic bullet to tackle it.
“To improve air quality we must take the full range of actions
including increasing the uptake of cycling, supporting the market for
ultra-low emission vehicles and helping to buy low-carbon buses. Since
2011 we have committed £2bn to reduce emissions and improve air quality
around busy roads.”