By Kate Kelland
LONDON, Sept 23 (Reuters) - Volkswagen's admission that it rigged car emission tests has prompted environmental and health experts to ask whether such deception is to blame for a lack of progress in reducing death and disease from air pollution.
Air choked with tiny particles, ozone and other pollutants kills some 3.7 million people a year, the World Health Organization (WHO) says -- a toll predicted to double by 2050 if big polluters do not clean up their act.
Volkswagen's chief executive, Martin Winterkorn, was facing the German carmaker's board on Wednesday to explain the falsification of the emission test data from diesel cars in the United States.
While car makers argue that diesel vehicles account for only a fraction of the pollutants in the air, experts retort that the health risks are far greater because cities are where most cars are to be found and where most people live and breathe.
Specialists estimate that the bogus test results may mean as much as 900,000 tonnes of extra nitrogen oxide (NOx) a year could have been pumped out by VW cars alone -- almost equal to the combined emissions for all Britain's power stations, industry, agriculture and vehicles.
And although the main focus is on the United States, VW says 11 million cars worldwide may be affected and experts note that diesel-fueled cars account for just 3 percent of passenger vehicles in America, compared with some 50 percent in Europe.
"In key cities, which is where most people live, cars are a very significant source of the pollution people breathe in, so any failure in emissions controls is very significant for health," said Alastair Lewis, a professor of atmospheric chemistry at Britain's York University.
Air pollution increases the risk of lung and cardiovascular diseases in the population and has its most severe impacts
on people already suffering with conditions such as heart disease, asthma and other respiratory diseases.
Children, old people and the poor are more susceptible.
In 2012, the WHO's specialist cancer research agency reclassified diesel engine fumes as carcinogenic, saying they can cause lung cancer and belong in the same potentially deadly category as asbestos, arsenic and mustard gas.
The WHO also cites epidemiological studies that show symptoms of bronchitis in asthmatic children increase with long-term exposure to NOx and nitrogen dioxide (NO2).
Reduced lung function is also linked to NO2 at the concentrations currently measured in cities of Europe and North America, it said.
PUBLIC HEALTH "PUT AT RISK"
Environmental scientists said they have observed for some time that "real world driving conditions" do not appear to deliver the scale of emissions reductions shown in the lab.
A study published in the Environmental Science and Technology journal earlier this year found that in London, NOx emissions in total from road transport are almost two times higher than those estimated based on laboratory data.
James Longhurst, a professor of environmental science and director of the Air Quality Management Resource Center at the University of Western England (UWE), says concentrations of NOx have not fallen as much as expected in developed countries, despite the introduction of new technology on vehicles.
"If the deliberate bypassing of emission control systems is more widespread than just VW diesel sales in the U.S., then it may help explain what has been observed in measurements of air pollution in cities," he said.
"At this point we don't know the exact size of the problem, but it will, without doubt, have added to the health burden. Public health has been deliberately put at risk."
Jo Barnes, also from UWE's Air Quality Management Resource Center, said she hoped the scandal would focus minds on holding car makers to account on environmental and health matters.
"Perhaps it is not surprising that profit margins take precedence over public health," she said.
"But with transport emissions the main contributor to urban air pollution, resulting in nearly 10,000 early deaths a year in London alone ... the public should be utterly outraged."
(Editing by Gareth Jones)