Cardiff sees NO2 reduction on car-free day

Data taken from air pollution monitors in Central Cardiff has suggested that nitrogen dioxide levels dropped by an average of 69% during a car-free day in the Welsh capital.

Road closures were enforced on Sunday May 13 to allow roads to be used for the HSBC Let’s Ride Cardiff event, organised by British Cycling (see story).

Streets were closed for the HSBC Let’s Ride Cardiff event on May 13

Three AQMesh air quality monitoring units were provided by Air Monitors UK, and used to measure pollutant levels on both Castle Street and Westgate Street which will be compared to the levels of pollutants recorded on a normal Sunday.

The instruments were located on streets impacted by the day’s event, and within two of the Councils Air Quality Management Areas (AQMAs); City Centre & Stephenson Court, Newport Road. The instruments continuously recorded air quality at these locations for 20 days before, during and after the event.


Commenting on the results, a spokesperson for the council’s Shared Regulatory Services department, said: “In comparing the results obtained during the Car Free Day Event with results from the following Sunday (20 May), the monitor on Duke Street showed an 87% reduction in nitrogen dioxide, the monitor in Westgate Street showed an 84% reduction and the third monitor, which was located less centrally from the main road closures, in Stephenson Court, showed a 36% reduction.

Data was taken from AQMesh pods situated close to the roads

“Comparing the car-free datasets with those of the following Sunday (20 May); the daily average nitrogen dioxide levels recorded by two of the monitors situated within the City Centre AQMA exceeded the EU yearly average limit (40 µg/m3), but on the car-free day, these two monitors measured daily average figures of just 5 and 8µg/m3 of nitrogen dioxide, providing clear evidence that air pollution in Cardiff city centre is generated by traffic.”

In order to assure the quality of the monitoring data, the AQMesh pods that were employed during the project were checked against a reference station.

Cardiff city council has recently set out a series of measures it is hoping to approve to encourage low emission transport within the city, as well as announcing that it will be conducting a feasibility study to determine if a Clean Air Zone is needed within the city to bring nitrogen dioxide levels in line with legal limits (see story).

This follows a legal direction from the Welsh Government stating that the council must identify options for delivering compliance with legal limits for nitrogen dioxide in the shortest possible time, by June 30.

Analysis of data from London on the day of the 2018 London Marathon by the behaviour change charity Global Action Plan has suggested that nitrogen dioxide levels in some parts of the capital had fallen ‘significantly’ due to the closure of roads to vehicle traffic (see story).



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