London's Oxford Street has worst NO2 levels world-wide
Kings College researchers report on survey results
British government taken to task in European Court of Justice for high levels of air pollution
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Heavy bus traffic on London's Oxford Street
David Carslaw's paper at the June conference on "Frontiers in Air Quality Science" reports high levels of NO2 levels in Oxford Street (in 2013) with an annual mean of 134 μg m-3, 1568 hours > 200 μg m-3 and a maximum of 489 μg m-3. The EU standard based on WHO guidelines is an annual mean of no more than 40 μg m-3 and maximum of 200 μg m-3 for no more than 18 hours per year. Carslaw reports these may be the highest recorded annual mean concentration and most hourly NO2 exceedances in the World. For WHO guidelines seehttp://whqlibdoc.who.int/hq/2006/WHO_SDE_PHE_OEH_06.02_eng.pdf
Traffic in Oxford Street is mainly taxis and buses, and the cause is that Transport for London has restricted them to diesel engines, in an effort to reduce particulates, however, a side effect is the high level of NO2 in what is a canyon of high buildings.
Buses have been fitted with diesel oxidation catalysts and particle filters. To burn off the black soot from diesel vehicle exhaust requires temperatures in excess of 500oC, which is a much higher temperature than the exhaust gases reach. However, NO2 is a very powerful oxidant and it can be used to help burn off these sooty particles at much lower temperatures (around 200 oC). These emission control systems therefore deliberately produce increased emissions of NO2 to help burn off the sooty particles.
The European Court of Justice is hearing evidence in a case against UK's consistent breaches of EU air standards, see http://www.bbc.co.uk/news/science-environment-28255246
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