Is NO₂ as bad as we thought?

Pollution-themed balloons in Germany. Image: Getty.

Air pollution has been found to cause hundreds of thousands of deaths every year around the world. As a result, there has been growing public concern about the health impacts of roadside air pollution – especially in the wake of the 2016 Volkswagen scandal, when investigations found that almost a million tonnes of excess pollution had been pumped into the atmosphere in the US alone.

Governments came under increasing pressure to act – and many drew up plans to reduce harmful pollutants below legal limits. In late July, the UK government published its own national plan for bringing down roadside nitrogen dioxide (NO₂) concentrations. The plan was met by considerable criticism, on the basis that it lacked urgency and effectively dumped the problem on the worst affected local authorities, which would be required to implement Clean Air Zones (CAZ).

But what was perhaps even more remarkable about the publication was that it revised the estimated value of minimising the damage to public health through these measures downward by 80 per cent.

On the final page of the 155-page technical report which accompanied the plan, new estimates of the economic benefits from reducing damage to health through measures to reduce NO₂ were very substantially below those that had been published in a previous report. The previous estimated health benefit of a further 21 CAZs was costed at £3.6bn, but is now £620m – an 80 per cent reduction.

This huge reduction was attributed to new advice from the independent experts of the Committee on the Medical Effects of Air Pollution (COMEAP), which had found it difficult to disentangle the impacts of specific pollutants – in this case NO₂ – from that of the whole mix of traffic-related pollutants. Previously COMEAP had advised that for every 10ug/m3 increase in NO₂ concentration, the increase in mortality risk would be 2.5 per cent.

It now recommends that when measures are primarily targeting NO₂ emissions, this coefficient should be adjusted to account for possible overlap between the direct impacts of small particulates and NO₂. This puts the increase in mortality risk at 0.92 per cent.

My enquiries of the government’s Joint Air Quality Unit (JAQU) confirmed that overall the updated damage costs of NO₂ for road transport are approximately 80 per cent lower than those used during the consultation prior to publication of the new air quality plan. This splits into roughly 60 per cent to 65 per cent resulting from the revised COMEAP advice, with the remaining 15 per cent to 20 per cent resulting from the other updates, such as new dispersion modelling and population data.

The JAQU confirmed that the reduction in the road transport NO₂ damage cost primarily reflects a reduction in the estimated mortality impact associated with NO₂ alone.

Change is in the air

It is not yet clear what this means for the government’s policy on air pollution. Current legislation stems from a European Union directive, which imposes a statutory limit for NO₂ concentration across all regions. In this context, the scale of health benefits from remedial measures is not relevant.

But with Britain on course to leave the EU, future regulation of air quality could be based on UK targets, set to reflect the balance of benefits in relation to costs. In this case, the downgrading of health benefits of policies such as Clean Air Zones would then be relevant, particularly given the expected reductions in pollutants from improved vehicle technology and the introduction of electric propulsion.

The ConversationBut ultimately, future regulation may depend on the outcome of the Brexit negotiations where the politics of air pollution may yet play a key role.

David Metz is honorary professor of transport studies at UCL.

This article was originally published on The Conversation. Read the original article.


CityMetric is now City Monitor! Come see us at our new home

City Monitor is now live in beta at

CityMetric is now City Monitor, a name that reflects both a ramping up of our ambitions as well as our membership in a network of like-minded publications from New Statesman Media Group. Our new site is now live in beta, so please visit us there going forward. Here’s what CityMetric readers should know about this exciting transition.  

Regular CityMetric readers may have already noticed a few changes around here since the spring. CityMetric’s beloved founding editor, Jonn Elledge, has moved on to some new adventures, and a new team has formed to take the site into the future. It’s led by yours truly – I’m Sommer Mathis, the editor-in-chief of City Monitor. Hello!

My background includes having served as the founding editor of CityLab, editor-in-chief of Atlas Obscura, and editor-in-chief of DCist, a local news publication in the District of Columbia. I’ve been reporting on and writing about cities in one way or another for the past 15 years. To me, there is no more important story in the world right now than how cities are changing and adapting to an increasingly challenging global landscape. The majority of the world’s population lives in cities, and if we’re ever going to be able to tackle the most pressing issues currently facing our planet – the climate emergency, rising inequality, the Covid-19 pandemic ­­­– cities are going to have to lead the way.

That’s why City Monitor is now a global publication dedicated to the future of cities everywhere – not just in the UK (nor for that matter just in the US, where I live). Our mission is to help our readers, many of whom are in leadership positions around the globe, navigate how cities are changing and discover what’s next in the world of urban policy. We’ll do that through original reporting, expert opinion and most crucially, a data-driven approach that emphasises evidence and rigorous analysis. We want to arm local decision-makers and those they work in concert with – whether that’s elected officials, bureaucratic leaders, policy advocates, neighbourhood activists, academics and researchers, entrepreneurs, or plain-old engaged citizens – with real insights and potential answers to tough problems. Subjects we cover include transportation, infrastructure, housing, urban design, public safety, the environment, the economy, and much more.

The City Monitor team is made up of some of the most experienced urban policy journalists in the world. Our managing editor is Adam Sneed, also a CityLab alum where he served as a senior associate editor. Before that he was a technology reporter at Politico. Allison Arieff is City Monitor’s senior editor. She was previously editorial director of the urban planning and policy think tank SPUR, as well as a contributing columnist for The New York Times. Staff writer Jake Blumgart most recently covered development, housing and politics for WHYY, the local public radio station in Philadelphia. And our data reporter is Alexandra Kanik, whose previous roles include data reporting for Louisville Public Media in Kentucky and PublicSource in Pittsburgh, Pennsylvania.

Our team will continue to grow in the coming weeks, and we’ll also be collaborating closely with our editorial colleagues across New Statesman Media Group. In fact, we’re launching a whole network of new publications, covering topics such as the clean energy transition, foreign direct investment, technology, banks and more. Many of these sectors will frequently overlap with our cities coverage, and a key part of our plan is make the most of the expertise that all of these newsrooms combined will bring to bear on our journalism.

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As for CityMetric, some of its archives have already been moved over to the new website, and the rest will follow not long after. If you’re looking for a favourite piece from CityMetric’s past, for a time you’ll still be able to find it here, but before long the whole archive will move over to City Monitor.

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I want to thank and congratulate Jonn Elledge on a brilliant run. Everything we do from here on out will be building on the legacy of his work, and the community that he built here at CityMetric. Cheers, Jonn!

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Sommer Mathis is editor-in-chief of City Monitor.