Cardiff pollution halves, as people stay home

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Three weeks into the UK’s shutdown, levels of Nitrogen Dioxide in Cardiff have almost halved compared to a year ago. The city’s two stations for measuring air quality – on the central pedestrianised Queen St, and on the busy Newport Road – both show that levels last week were close to half what they were for the same week last year.

The Telegraph reported a few days ago that there had been a similar drop in Hafodyrynys, outside Caerphilly. The Welsh village is infamous for one of the worst levels of Nitrogen Dioxide, or NO2, in the UK.

NO2 is produced by road traffic and is one of the principal air pollutants in the UK.

This graph shows the average NO2 level in Cardiff last week for each of the daily 24-hour readings. The data is supplied by the UK Department for the Environment (DEFRA) and older data shows much higher levels at almost every point in the day, whether you compare to the same week in April the year previously or to the average hourly figures for the 12 months to April 2020.

pollution measure in central Cardiff

Air pollution is blamed for 2,000 deaths a year in Wales and the Welsh government has just closed a period of public consultations on the Clean Air Plan for Wales it proposed late last year. Cardiff Council meanwhile is considering a congestion charge (for a capital city that has a population of only about 350,000 people).

The NO2 figures were also down on the edge of Cardiff city last week, at times almost a third of what they were the same time last year.

pollution measure on the Newport Road

Similar findings are being reported around the world, as improved air quality becomes an unexpected consequence of the lockdown.

Not, of course, that people get much chance to go out and enjoy it.

The github repository with the data files and python notebook is here.