The main air pollutant of concern in Bath - nitrogen dioxide - has reduced since the introduction of the Covid-19 restrictions in late March 2020 and the graph below shows data from our continuous air quality analyser sites around the city to the end of May 2020.  To suppliment these continuous analysers, we also have over 200 nitrogen dioxide tubes around the district.  Monitoring using these tubes has recently recommenced following a short break due to the lab closing because of the Covid-19 crisis.

Air pollution is affected by a number of factors including meteorological conditions (weather), road layout (eg. how close buildings are to the road), traffic levels and the composition of traffic (how many of the vehicles are cars / vans / buses / lorries etc).  2020 has already had exceptional weather with a very windy February (that disperses pollution) and the lockdown also coincided with the start of spring and finer weather.  This makes a comparison with 2020 troublesome in terms of assessing the impact of reduced traffic or altered fleet compositions.  

The following graph shows the most recent provisional monthly average data to the end of June.  The graph should not be interpreted without consideration for the text below it:

Monthly average nitrogen dioxide levels at automatic sites

[Click on image for clearer PDF version]

  • The graph shows monthly averages of nitrogen dioxide levels since 2018 up to the end of June 2020 at our continuous AQ analyser locations in Bath at the Guildhall, A4 London Road (outside Dominos Pizza), Snow Hill (by Chelsea House) and Windsor Bridge Road.  For comparison there is also data from continuous AQ analysers in Bristol and Swindon.
  • Data since 2018 has been included to enable the trends in the levels to be shown; these indicate the reductions and peaks which are typically experienced during both the summer and winter months and how the reduction we are now seeing as a result of the Covid-19 restrictions compares to this.
  • You will notice that there is a gap in the data collection for the A4 Roadside analyser;  this is because the equipment was relocated from the Old Bank Antiques Centre (due to the sale of this property) to a new location outside Dominos Pizza on the opposite side of the road in 2019.  

Our estimation is that the average levels have reduced by approximately 20% initially on where we would normally expect to see them at this time of year.  However, there are some important caveats to this conclusion:

  • The data is provisional and has not been verified as part of the Council’s Annual Status Report.  This will not be carried out until later in the year.
  • There are many factors which could affect nitrogen dioxide levels other than the Covid-19 restrictions; these include meteorological conditions - which have been exceptional this year due to a very windy start (February - pre-lockdown); prevalent easterly winds and a prolonged sunny period since lockdown commenced; variations in fleet composition over the time period; changes in the location of the analysers and the impact of changes such as the Cleveland Bridge 18T weight limit. 
  • It is not advisable to compare average monthly concentrations in 2020 with the same period in 2019, due to differences in meteorological conditions.  A higher level of confidence in the impact of the restrictions can be gained by comparing with the average over a number of years to account for variations in weather conditions.
  • The effects of weather and seasonality removed will be published later in the year.

Therefore, this graph should be viewed as indicate of how levels have recently changed but does demonstrate how the reduction of traffic can have a beneficial impact in reducing levels of nitrogen dioxide.

We will endeavour to update this webpage monthly with the latest data.  Locally, we are seeing about a 20-30% reduction in nitrogen dioxide levels allied to a reduction in traffic of greater than 60% since the Covid-19 restrictions were introduced.  This is broadly in line with the national picture. 

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