London's Oxford Street is world's most polluted
NO2 levels have peaked at 135 micrograms per cubic metre (mcg/m3) of air three times this year, hugely exceeding the EU limit of 40mcg.
The problem is largely because of the large amount of buses and taxis that Oxford Street sees on a daily basis, whose diesel engines produce large amounts of the toxic gas.
London's mayor, Boris Johnson, is now facing calls for urgent action from Oxford Street workers, who want a reduction in the "wall of buses" continually present on the thoroughfare, the London Evening Standard reports.
The problem is particularly serious, as NO2 has been linked to triggering asthma and heart attacks in those who are regularly exposed to it. The figures recorded by the monitoring station is an average, which includes night-time levels when traffic is lower – meaning the true NO2 levels experienced by shoppers and workers during the day is likely to be much higher.
In March, NO2 levels on Oxford Street peaked at a record 463mcg, representing higher air toxicity than in industrial Indian and Chinese cities – countries with established poor air quality records.
However, these areas have higher levels of particulate matter in the air, which is created by unburnt fuel and which can leave thick smog over affected areas.
Speaking to the Sunday Times, David Carslaw of King's College London said: "To my knowledge this [level] is the highest in the world in terms of both hourly and annual mean. NO2 concentrations [in Oxford Street] are as high as they ever have been in the long history of air pollution."