A new study, published in Nature Geoscience, examines the proportion of nitrogen dioxide in European roadside nitrogen oxides emissions.
Prof. Paul Monks, Professor of Atmospheric Chemistry and Earth Observation, University of Leicester, said:
“Seems to be a great example of needing to evaluate the real-term performance of vehicles over a longer period of time and as a whole. As a car ages the fraction of primary emissions of NO2 decreases and this has not been accounted for in emission inventories that ‘predict’ the future. It is one of the things that looks like pure luck in terms of the emissions, but is positive in terms of the way it impacts air pollution. A question for the future from this work is around the impact of the reduced emissions on particles.”
Prof. Nick Hewitt, Professor of Atmospheric Chemistry, Lancaster University, said:
“This impressive analysis of roadside concentrations of ozone and the oxides of nitrogen from sites across Europe clearly shows that the ratio of nitrogen dioxide (NO2) to NOx (NOx = NO + NO2, NO being nitric oxide) rose substantially across Europe in the period 1995 – 2009, but since then has decreased. This is positive news for urban air quality, as NO2 is a regulated air pollutant, being toxic to humans. However, what the analysis doesn’t show is the inability of current atmospheric emissions inventories to correctly predict the amount of NOx emitted into the atmosphere, especially from motor vehicles. Our own airborne measurements of the fluxes of NOx over London show that the UK’s national emissions inventory significantly underestimates the emission rates of NOx in London (see Vaughan et al, Faraday Discussions, 2016).”
Prof. Martin Williams, Professor of Air Quality, King’s College London, said:
“This important research describes a novel approach to the problem of roadside NO2 concentrations in Europe and provides an attack on the problem complementary to the measurement of real-world emissions. In order to ensure the best evidence is provided to the policy process it is vital that we continue this type of research as well as that involving real world emission measurements. Moreover it is clear that the European regulatory process has missed a trick in not setting some form of limit on primary NO2 emissions from road vehicles.”
Prof. Ian Colbeck, Professor of Environmental Science, University of Essex, said:
“Air pollution hasn’t got any better; thousands of people a year as still dying because of it. To forecast the impact of road traffic on air quality one has to make assumptions such as future fleet composition, traffic activity as well as the NO2:NOx ratio for all vehicles. This paper has used atmospheric measurements to calculate this important ratio whilst the UK Government uses modelled values. Grange and co-workers conclude that the NO2:NOx ratio is roughly 50% lower than the value used in air quality models suggesting that model predictions may be too pessimistic. If Grange is correct then air quality standards should be realised much sooner than predicted.”
Prof. Anthony Frew, Professor of Allergy & Respiratory Medicine, Royal Sussex County Hospital, said:
“This is encouraging data; for drivers of diesel cars, this news will come as some relief from the recent demonization of diesel.
“UK NOx levels fell by 68% from 1970 to 2015 and have been falling gradually in the past decade, partly as a result of initiatives to reduce tailpipe emissions but mainly due to controls on power generation.
“This study seems well done, and focuses on projections of NOx emissions into the future. It’s good to see that the fall in NOx from diesel cars may actually be coming down faster than was previously predicted.
“About 35% of all UK NOx emissions are from transport, with about one quarter of that from diesel cars. So while this reduction in projected tailpipe emissions is welcome, additional measures targeting other sources will be needed to reduce the overall burden of NOx and meet our emissions targets.”
* ‘Lower vehicular primary emissions of NO2 in Europe than assumed in policy projections’ by Stuart K. Grange et al. will be published in Nature Geoscience on Monday 27 November 2017.
Declared interests
Prof. Paul Monks: “I do chair the government science advisory committee on air quality (AQEG).”
Prof. Nick Hewitt: “I have no conflicts of interest to declare.”
Prof. Ian Colbeck: “Funding from NERC, EU. Fellow of the Institute of Physics.”
Prof. Anthony Frew: “No interests to declare.”
None others received.