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Changes in outdoor air pollution due to COVID-19 lockdowns differ by pollutant: evidence from Scotland
  1. Ruaraidh Dobson,
  2. Sean Semple
  1. Institute of Social Marketing and Health, University of Stirling, Stirling, UK
  1. Correspondence to Dr Ruaraidh Dobson, Institute for Social Marketing and Health, University of Stirling, Stirling FK9 4LA, UK; r.p.dobson{at}


Objectives To examine the impact of COVID-19 lockdown restrictions in March/April 2020 on concentrations of nitrogen dioxide (NO2) and ambient fine particulate matter (PM2.5) air pollution measured at roadside monitors across Scotland by comparing data with previous years.

Methods Publicly available data of PM2.5 concentrations from reference monitoring systems at sites across Scotland were extracted for the 31-day period immediately following the imposition of lockdown rules on 23 March 2020. Similar data for 2017, 2018 and 2019 were gathered for comparison. Mean period values were calculated from the hourly data and logged values compared using pairwise t-tests. Weather effects were corrected using meteorological normalisation.

Results NO2 concentrations were significantly lower in the 2020 lockdown period than in the previous 3 years (p<0.001). Mean outdoor PM2.5 concentrations in 2020 were much lower than during the same period in 2019 (p<0.001). However, despite UK motor vehicle journeys reducing by 65%, concentrations in 2020 were within 1 µg/m3 of those measured in 2017 (p=0.66) and 2018 (p<0.001), suggesting that traffic-related emissions may not explain variability of PM2.5 in outdoor air in Scotland.

Conclusions The impact of reductions in motor vehicle journeys during COVID-19 lockdown restrictions may not have reduced ambient PM2.5 concentrations in some countries. There is also a need for work to better understand how movement restrictions may have impacted personal exposure to air pollutants generated within indoor environments.

  • particulates
  • air pollution
  • indoor air

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  • Contributors Both authors conceived of the idea for the study. Both authors designed the study. RD conducted data analysis and drafted the manuscript, which SS critically reviewed. SS supervised the project.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Data are available in a public, open access repository. Data used in this study are available from the Scottish Government’s air quality repository (