‘Uncertainty’ over accuracy of PM2.5 monitoring in UK

There is “serious doubt” over whether the UK is meeting EU reduction targets for particulate matter PM2.5, according to a Defra report, writes Michael Holder

The accuracy and reliability of PM2.5 particulate matter measurements in the UK is “uncertain”, a report published by Department for Environment, Food and Rural Affairs (Defra) has found.

Due to uncertainty and continually evolving measurement methods, the report states, there is “serious doubt” over whether the UK is meeting EU reduction targets for PM2.5.

Chair of Defra's Air Quality Expert Group, Professor Paul S. Monks (Copyright: University of Leicester)

Chair of Defra’s Air Quality Expert Group, Professor Paul S. Monks (Copyright: University of Leicester)

According to the report, there are “significant” challenges associated with accurately measuring particulate matter concentrations, which can make setting future UK air quality policy difficult.

As a result, the report recommends that Defra set up a working group to assess the risks and solutions for improving the accuracy of PM2.5 measurements in the UK.

It also highlights the need to look at ways of reducing non-exhaust particulate matter emissions in future as stricter EU vehicle emissions regulations come into force help to cut emissions from cars.

The report, ‘Fine Particulate Matter (PM2.5) in the UK’, was compiled by the Defra Air Quality Expert Group (AQEG) and looks at the evidence base for PM2.5 in the UK and its robustness for making future policy decisions in the UK.

Chaired by physical chemistry Professor Paul Monks from the University of Leicester, Defra’s AQEG includes a number of air quality experts and academics.

The report states: “The delivery of air quality policy objectives relies upon the ability to measure pollutants in an accurate, reproducible and reliable way. Currently there are significant challenges associated with the reliable and reproducible measurement of PM2.5.”

It continues: “The answer to the question ‘Do we have a robust measure of PM2.5?’ remains substantially uncertain. A major difficulty for assessment of compliance is that PM2.5 measurement methods are still evolving and the reference method is currently being revised. Consequently, measurements made in 2020 may not be directly comparable to those made in the period 2009-2011 (the base period for the EU Air Quality Directive requirement). This sheds serious doubt on our ability to provide evidence that the EU exposure reduction target is being met for PM2.5.”


As part of its recommendations, the report states: “AQEG strongly recommends that a focused working group is put together to make a short-term assessment of the risks of, and solutions and opportunities to mitigate, measurement uncertainties and of the way that uncertainties impact on our ability to deliver air quality policy in the UK.”

As well as setting up a working group, the report recommends that more research needs focus on methods for measuring emissions from dust sources, as there is currently a lack of understanding of these emissions despite the large impact they have on PM2.5 concentrations.

It  states: “Emissions from fugitive dust sources, small-scale wood and waste burning, cooking, agriculture, natural sources and shipping are also poorly understood and difficult to quantify yet can make a significant contribution to PM2.5 concentrations. This needs to be addressed, especially if the benefits of mitigation are to be assessed.”


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