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Big fall in NO2 concentrations recorded across Gtr London

Andrew Forster
06 March 2020

A big reduction in nitrogen dioxide concentrations has been recorded at monitoring stations across London in the last four years, according to the Greater London Authority. 

A new report evaluates data from air quality sites across the capital between 2016 to 2020, during which time the central London ultra-low emission zone (ULEZ) and 12 low emission bus zones have been implemented. 

The EU has two limit values for nitrogen dioxide: a short-term limit for an hourly average of 200μg/m3 not to be exceeded more than 18 times in a year, and an annual average of 40μg/m3.

Data for 25 sites that exceeded the 18 hourly breaches in 2016 shows that the number of hours in excess of the hourly average fell from over 4,000 hours in 2016 to just over 100 in 2019.

Only one of the sites, on the Strand in Westminster, exceeded the 18 hours breach in 2019. It recorded 20 hours in total. 

Putney High Street, where the first low emission bus zone was introduced in 2017, recorded  1,279 hours in excess of 200μg/m3 in 2016 but just 11 in 2019.

Another low emission bus zone, Brixton Road in Lambeth, had 530 hours above the legal limit in 2016. Technical difficulties meant this monitoring site was offline in the first quarter of the 2019 but the monitor did not record a single hour over the threshold limit in the last three quarters of the year, nor have any been recorded this year. 

On Oxford Street in Westminster, NO2 exceeded legal limits for 168 hours in 2016. In 2019  no single hour was recorded above the legal limit. 

Oxford Street does, however, continue to fail to meet the annual average 40μgm3 limit.  

A comparison of data from 86 sites with enough data in both 2016 and 2019 shows that 36 still exceeded the average annual limit in 2019. This compares with 56  in 2016.

Every one of the 86 sites  recorded a reduction and the annual average across all sites dropped from 50μg/m3 in 2016 to 39μg/m3 in 2019.

A number of locations still have levels far above the 40μg/m3. The worst were the Strand (Westminster) 74; Walbrook Wharf (City of London) 71; Putney High Street (Wandsworth) 69; Euston Road (Camden) 69; Brent – IKEA 63; Marylebone Road (Westminster) 63; and Beech Street (City of London) 60. 

On fine particulates, the report says: “More action is needed to tackle PM2.5, as over 80 per cent of monitoring sites in 2019 still recorded levels of PM2.5 above the World Health Organisation recommended limit.

“In London more action is needed particularly to address non-transport sources such as construction and wood burning, currently sources the mayor does not have the powers to abate.” 

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