Children鈥檚 health can benefit from congestion charging schemes that limit city-centre traffic and the airborne pollution it generates. But a comparison of the congestion charges in London and Stockholm suggests the schemes only achieve this if they drive down the amount of nitrogen dioxide belched into city air by vehicles.
of Johns Hopkins University in Baltimore, Maryland and her colleagues tracked air pollution levels in Stockholm, Sweden from 2004 to 2010. In 2007 the city introduced a . Levels of nitrogen dioxide fell by 5-7.5 per cent.
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Nitrogen dioxide is the most harmful pollutant from vehicle exhausts. It aggravates asthma and other respiratory ailments.
The reduction in nitrogen dioxide in Stockholm appeared to benefit children. Before the congestion charge, 18.7 children in 10,000 were admitted to hospital with asthma attacks. Afterwards the number halved to 8.7 per 10,000 ().
London鈥檚 dirty air
However, in London nitrogen dioxide levels rose by around 10 per cent in the four years after a similar congestion charge was introduced in the city centre in 2003, according to . Levels of other pollutants did fall: airborne concentrations of carbon monoxide, nitrous oxide and 鈥淧M10鈥� particulate matter fell respectively by 6, 24 and 30 per cent.
Nitrogen dioxide levels rose because commuters switched from their cars to diesel-powered buses and taxis, says lead author of the Norwegian University of Science and Technology in Trondheim, Norway. 鈥淥ur estimate is an increase of 18 million kilometres per year for taxis and buses together, as a result of the congestion charge.鈥� That is a 20 per cent increase.
It鈥檚 unclear why this didn鈥檛 happen in Stockholm, where most buses were also diesel-powered at the time of the study, although all are now biofuel-powered.
Green鈥檚 study didn鈥檛 explore impacts on childhood asthma, but he says London鈥檚 rise in nitrogen dioxide may well have harmed people鈥檚 health.
Low emissions zones
In 2008 London also introduced a , which spans a larger area than the congestion charge. The owners of polluting diesel vehicles must pay to enter the zone. Green says this may have had a more positive effect than the congestion charge.
鈥淏ut continued exemptions for [black cab] taxis appear to be an issue,鈥� he says. 鈥淚nitiatives or incentives to change the fuel mix of tax-exempt vehicles may be important to get diesel pollution down.鈥�
Matters may improve after 8 April 2019, when the current congestion charge zone will become an . Almost all vehicles that don鈥檛 meet strict exhaust emission standards will be charged to enter the zone.
