The Mayor said the level of dangerous particulates in the air has been reduced by 15% because of action on encouraging clean vehicles, walking and cycling. He also said he has introduced a plan to bring in an Ultra Low Emission Zone for vehicles in London by 2020.
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Official readings are recorded three metres in the air but a study found levels of nitrogen dioxide (NO2) were higher at pushchair level.
Tubes, trains, trams, buses, cable cars, river buses, taxis and going by foot - your guide to getting around during the strike.
Union officials rejected a revised offer from Underground managers during a meeting at the conciliation service ACAS this afternoon.