Grosvenor Place, which runs alongside the Queen's London residence, had the highest level of the toxic gas nitrogen dioxide in 2012.
Researchers found 152 milligrams of the gas per cubic metre of air, with a main contributor being diesel engine fumes. The EU legal limit is 40.
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Four men have been arrested after a 21-year-old man was murdered in Lewisham
London is the second least affordable city in the UK, while commuter hotspot St Albans has seen the biggest prices rises
Scotland Yard said the male youths will appear in custody at Westminster Magistrates' Court on Saturday.