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AQC Responds to Defra call for Evidence on Air Quality Changes as a Result of COVID-19 Lockdown


Air Quality Consultants Ltd has updated its analysis of the impacts of the COVID-19 social and travel restrictions on air quality in response to Defra’s call for evidence.  The analysis uses statistical models to remove the effects of weather, which would otherwise obscure trends.  NOx and NO2 concentrations at the roadside have both fallen by about 30% on average as a result of the pandemic.  Roadside ozone concentrations have increased following the lockdown.

Air Quality Consultants Ltd has responded to Defra’s call for evidence on changes to air pollution during the COVID-19 pandemic by updating and refining its previously-published analysis (previous report can be seen here).  Changes in air quality are often obscured, or caused, by changes to the weather.  AQC has applied statistical analyses using Boosted Regression Trees to isolate and remove these effects so as to reveal the underlying changes.

After removing the effects of weather, the analysis shows that NOx and NO2 concentrations have fallen at almost all roadside monitors in the UK.  Most of these reductions lie in the range of 20-40%, with the largest falls at the most polluted sites.  The average improvement at roadside monitors has been about 30% for both NOx and NO2.  NOx and NO2 concentrations at rural sites have, on the other hand, increased slightly since the lockdown, but this is not thought to relate to COVID-19. There is no obvious regional variation in the changes.

NOx emissions contribute to the formation of ground-level ozone at a regional level.  At the same time, fresh NOx reacts with, and thus removes, ozone.  This means that ozone concentrations are usually lower close to roads.  The reduction in roadside NOx concentrations following the lockdown caused an increase in roadside ozone. 

The results are summarised in a note which has been issued to Defra’s Air Quality Expert Group in response to the call for evidence and is also available here.

Much of the analysis has also been presented by Air Quality Consultants Ltd in webinar for the Institute of Air Quality Management, which is available here.

© Air Quality Consultants 2021