June 17, 2021

expert reaction to research looking at air quality levels compared to pre-pandemic levels

A new study looks at air quality levels in UK cities compared to pre-pandemic levels.

Prof Anna Hansell, Professor of Environmental Epidemiology, Director Centre for Environmental Health and Sustainability, University of Leicester, said:

“We were provided with a pdf of a presentation that presumably is taken from the report, rather than the report itself.  The presentation provided a description of changes in air quality using monitoring station data.  The authors compare measurements with a ‘business as usual’ statistical model that provides information on what the air pollution levels would be expected to be without the lockdown.  These type of statistical models use information on factors such as season of year, monitor measurements in previous years and weather to provide an estimate of concentration levels in the absence of an intervention (here the lockdowns).  We used a similar approach in our evaluation of changes in air pollution during the first UK lockdown in 2020 https://pubmed.ncbi.nlm.nih.gov/33386205/

“The results from this and similar analyses provide important information for policies to reduce air pollution.  Results clearly show that road traffic is an important source of some types of air pollution, but that multiple sources need to be considered.  We will need a range of strategies, including reductions in traffic and/or traffic emissions, to reduce exposure to harmful levels of air pollution.

“We did not have full details of the survey provided.  For any questionnaire, it’s important to know how participants were selected and what the response rate was – it may be that more people who are concerned about air pollution responded.”

Prof John Gulliver, Professor of Environmental and Exposure Sciences, Deputy Director, Centre for Environmental Health and Sustainability, University of Leicester, said:

“Results are not surprising.  In the first lockdown, in our paper (https://pubmed.ncbi.nlm.nih.gov/33386205/) we reported reductions in air pollution for NO2 at (monitored) traffic sites which directly reflected reductions in road transport, other transport, and some other sectors.

“The general expectation is for better air quality during lockdowns (as reported in spring 2020 by some media), but it depends on the pollutant and where you live.  NO2 concentrations were lower at roadside but ozone was higher close to major roads (as expected, but there are very few roadside sites measuring ozone).  Changes in PM2.5 during the pandemic were much smaller – this is largely a secondary pollutant and influenced by trans-national emissions and meteorology e.g. in the spring of 2020, despite reductions in local transport, the meteorological conditions promoted higher levels of PM2.5 especially in the south and south-east of England.”

Prof Alastair Lewis, National Centre for Atmospheric Science, University of York, said:

“This is not peer-reviewed and having looked at the slides, the data doesn’t show quite what is claimed in the headline of the press release.  (Slide 8 is the most informative).  That indicates that NO2 is still lower than business as usual at every site they examine, other than Sheffield, which is fractionally higher than business as usual.  (That could well be to do with some local factors, like a change in traffic routing etc and care is needed not to over interpret data from one location).  So NO2 pollution has not returned to normal, it is still below normal virtually everywhere in the UK.

“The analysis of PM2.5 does not correct for meteorology because it is a longer-lived pollutant; the data shows that PM2.5 is only marginally affected by lockdowns, and is more significantly influenced by the weather.  Their data shows that in May 2021 PM2.5 was lower than the equivalent month in previous years at virtually every site they analyse.”

‘UK air quality study for Nuaire Haven Terminal product launch’ will be published at 00:01 UK time on Thursday 17 June 2021.

Declared interests

Prof Anna Hansell and Prof John Gulliver: “Neither Prof Anna Hansell nor Prof John Gulliver have conflicts of interest to report.

“Anna Hansell is Chair of the Committee on the Medical Effects of Air Pollution (COMEAP), but her comments here are in a personal capacity as Professor in Environmental Epidemiology at the University of Leicester.”

Prof Alastair Lewis: “Employed University of York and National Centre for Atmospheric Science.  Various grants and research contracts from UKRI.  Comments made in a personal capacity, not on behalf of the of Air Quality Expert Group.”