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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The mayor went on a walkabout at a farmers market in Bedford and signed copies of his new book in a local book store.
People are being encouraged to post pictures of themselves sleeping in "weird" places in a bid to raise money to tackle homelessness.
The actor received the award at Guildhall in recognition of his work for gay rights.