Air quality has been hitting the headlines recently with Defra forced to publish its draft Air Quality Plan earlier in May. But what is meant by ‘air quality’ and how is it affecting you?

Marked with a grey plaque, Brixton Road breached its annual air pollution limit for peak levels just days into 2017. (credit @londonschoking)

Marked with a grey plaque, Brixton Road breached its annual air pollution limit for peak levels just days into 2017. (credit @londonschoking)

Measures of air quality can include different types of pollutants including particulate matter (PM) and ozone but nitrogen dioxide (NO2) is often used as an overall indicator.

Limits for NO2 levels are set by the EU (Directive 2008/50/EC) in accordance with World Health Organisation’s recommendations and have been in place since 2010.

Limits are for both average levels (measured annually) and peak levels (measured per hour) with a limited number of exceedances permitted per year.

The UK breached the number of exceedances allowed for peak NO2 just five days into 2017 and has failed to reach annual targets for the last 6 years. The UK is not alone however, along with 12 other member states who have faced legal action from the EU and in the UK by ClientEarth who brought the case to the High Court, to force the Government to publish its plans to tackle high NO2.

The public health risks from poor air quality are considered similar to those from obesity in the UK, yet raising public awareness of this invisible problem has been tough. Nobody has ‘death by air pollution’ recorded on their death certificate making it difficult to predict the number of deaths per year attributable to NO2. A report by the Royal College of Physicians suggests there could be as many as 40,000, an estimate subject to large margins of error discussed in more detail by Royal Society Fellow Sir David Spiegelhalter in his blog. Calculating an exact number isn’t essential with these extreme cases likely to be the tip of the iceberg in terms of health impacts and vulnerable groups such as children or asthmatics being at higher risk.

Effects of long-term exposure to poor air quality is notoriously difficult to prove and the impacts of cumulative exposure or the co-exposure to multiple air pollutants are largely unknown. Quantifying harm based on measurements of exposure could be problematic, with further complications due to varying exposures between regions, and even individuals within the same street. However, a workshop held at the Royal Society hosted experts in the air quality field where the consensus supported that despite uncertainty, existing evidence was sufficient to take action to reduce the negative effects of poor air quality.

So why is improving air quality, and reducing NO2 levels in particular, causing so much of a headache?


Protesters in London after publication of the Draft Air Quality Plan on 5th May 2017 (credit BBC news)

At the request of the Royal Society, Fellow David Fowler led a discussion on the barriers to addressing air quality which highlighted challenges in communicating uncertainty in evidence to the public, the difficulties of measuring pollutants or harm, and a lack of ownership of the problem owing to slow policy changes.

Combustion engines and diesel vehicles are often blamed as the worst contributors of NO2 in urban areas, but with people previously encouraged to invest in diesel for its green credentials, targeting these polluters could be morally complicated. In other cities around the world there are proposals to be car-free in the next two decades encouraging individual lifestyle changes with more active travel and public transport use. In Copenhagen, infrastructure improvements for cycling have resulting in nearly half of all commuters getting to work by bike. The improvement of engines to create zero-emission vehicles is also well underway, but particulate pollution created by brakes and tyres will still remain a concern alongside other sources of air pollution such as home central heating or wood burning stoves. It may seem straightforward – reduce car use to improve air quality – but it is worth considering any adverse impacts this could have, for example in more isolated rural communities.

The government’s new draft air quality plan (published May 5) emphasises a localised approach to improving NO2 levels, placing the responsibility mostly with local authorities. While the plan suffered some criticism for lacking detailed proposals, guidance for Local Authorities has been offered through the publication of the Clean Air Zone Framework. Interventions from this framework include encouraging use of ultra-low emission vehicles, retrofitting technologies for existing vehicles and infrastructure change to improve traffic flow. The establishment of Ultra Low Emission Zones is also proposed, with London leading the way with its toxicity ‘T-Charge’ for the worst polluting vehicles to be introduced later this year. London Mayor Sadiq Khan has also proposed improving air quality through greener buses and zero-emission black cabs alongside improved infrastructure for pedestrians and cyclists in the city.


To truly reduce the negative impacts of poor air quality, solutions really need to consider more than just reducing NO2 levels to meet existing legal limits. It’s likely that Defra will need to collaborate closely with other Government departments, including the Department of Health, the Department of Transport and the Department of Business, Energy and Industrial Strategy to come up with cross-sector solutions which truly reduce harm from poor air quality long-term. Defra’s initial draft of the Air Quality plan is open for consultation until 15 June with results expected at the end of July.


For more on this subject, see David Fowler’s blog post from our joint science conference with Defra.