Introduction

The current lockdown measures in place to control the spread of the Covid-19 pandemic has resulted in a dramatic drop in road traffic within Scotland’s cities. It is well established that road traffic is the main source of oxides of nitrogen (NOx) within these cities and so it is safe to assume that nitrogen dioxide (NO₂) concentrations will have decreased during the lockdown. The current situation provides an opportunity to investigate what improved air quality within Scotland’s cities could look like in the future.

In addition to NO₂, particulate matter (PM₁₀ and PM_2.5) is of great interest. Analysis of PM is more difficult due to the secondary nature where particles are formed through chemical reactions of other pollutants; and transboundary nature, where PM forms and travels over long distances. As a result, both the weather e.g. where the air mass originated from, and emissions from elsewhere (e.g. Europe) can have a much greater impact on local concentrations.

The following summary analysis provides an indication of the extent of the reduction in NO₂ and PM₁₀ concentrations at a the following sites:

• Aberdeen Union Street
• Dundee Lochee Road
• Edinburgh St John’s Road
• Fife Dunfermline
• Glasgow Kerbside
• Glasgow High Street
• Inverness
• Perth Atholl Street
  
  

It is important to note that this type of analysis doesn’t take into account the important influence of weather on ambient pollutant concentrations. More detailed analysis for NOx can be found here.

Note that the 2020 data are provisional at the time of carrying out this analysis and will be subject to further quality control.

Analysis - NO₂

Figures 1 to 7 show NO₂ concentrations measured between 23 March and 29 April in the years 2015 to 2020 at the seven sites. The data indicate that NO₂ concentrations have dropped by between 45% and 82% from previous years.

Analysis - PM₁₀

Figures 8 to 13 show PM₁₀ measured between 23 March and 29 April in the years 2015 and 2020 at six sites accross Scotland. The potential reduction in concentrations is less clear, but it can be seen that average PM₁₀ concentrations during the lockdown have decreased by between 8% and 48% compared to previous years. Note that these figures should be treatred with caution due to the reasons outlined in the introduction. This is especially the case for 2019 where a PM episode was experienced, caused by fires in Europe and Russia at the end of April 2019.

Analysis - PM_2.5

Figures 14 to 19 show PM_2.5 measured between 23 March and 29 April in the years 2015 and 2020 at six sites accross Scotland. The potential reduction in concentrations is not clear - it can be seen that average PM_2.5 concentrations during the lockdown have decreased by between 0% and 56% compared to previous years (excluding 2019), however, there is no clear pattern accross the sites. Note again that these figures should be treated with caution due to the reasons outlined in the introduction. Again, this is especially the case for 2019 where a PM episode was experienced; caused by fires in Europe and Russia at the end of April 2019.