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The UK Air Quality Problem: A Narrative in Numbers

Since the first version of the UK Air Quality Plan was published by the Government in December 2015, which targets the improvement of roadside air quality, a series of legal challenges brought by ClientEarth have led to the latest High Court ruling handed down to the Government. As a result, the Government is required to publish a supplement to the existing Plan by October of this year.


The current version of the Plan focusses on reducing levels of nitrogen dioxide (NO2), which is a key pollutant of concern within urban areas and is emitted primarily from road traffic.

Here, WSP provides the key numbers on the drivers for air quality improvements across the country and the context to an evolving and complex legal saga:

- 23 out of 28 member states of the European Union (EU) include areas where air quality standards are still being exceeded, including the UK.  The EU sets legally binding air quality limits, which have been translated into UK law and should not be exceeded. 

- 40,000 premature deaths each year are estimated to be attributed to poor air quality in UK cities and towns.  Vehicle emissions, particularly from diesel engines, are the key contributor to roadside air pollution.  

- 1.2 million: the number of diesel cars sold in the UK between 2008 and 2015 under the VW, Seat, Audi, and Skoda brands that were fitted with a so-called ‘defeat device’ to be able to pass laboratory emissions testing. This effectively resulted in higher emissions of harmful air pollutants when these cars were driven in the real world. On the back of this, public awareness of poor air quality and the role of diesel vehicle emissions was heightened.

- 40 micrograms per cubic metre (µg/m3) is the annual average legal limit value for NO2 set by the European Union.  The UK Air Quality Plan targets all areas where this limit value is not being achieved.

- 3: the number of successful High Court challenges brought against the Government by ClientEarth in relation to the UK Air Quality Plan.  The latest ruling made by the High Court last week orders the Government to submit a new Air Quality Plan by 5th October of this year.

- 61: the total number of local authorities throughout England that are required to take further action in reducing NO2 in areas that do not comply with the legal limit;

     i) 5 cities in England ordered to implement a Clean Air Zone (CAZ) to achieve compliance by 2020 including Birmingham, Leeds, Nottingham, Derby, and Southampton.  This requirement has remained in place since Plan in 2015.

     ii) 23 local authorities directed to undertake feasibility studies before 2019 to identify measures to reduce NO2 levels in specific areas, as dictated by the current version of the 2017 Plan.

     iii) 33 local authorities are potentially affected following the latest High Court ruling and these will be required to undertake feasibility studies where the legal limit will not be achieved this year.

- £3.5 billion to be invested by the UK Government in improving air quality and reducing harmful emissions.

- 2040: the year by which sales of all new conventional petrol and diesel cars and vans will be banned in the UK.

The delivery of the UK Air Quality Plan and the CAZs is being managed by the government’s Joint Air Quality Unit (JAQU), a cross government body comprising of staff from both the Department for Environment Food and Rural Affairs (Defra) and Department for Transport (DfT).

WSP is working closely with two of the aforementioned cities that have to deliver a Clean Air Zone (CAZ); Leeds City Council and Birmingham City Council. These schemes are currently being assessed for their feasibility and potential impact, with the aim to achieve compliance with the EU legal air quality limit in 2020 or before.  Similarly, we have been assisting the Welsh Government in evaluating the potential impacts of measures to improve NO2 on the strategic road network, with measures ranging from behaviour change (e.g. speed control, modal shift) to junction closures.

The tasks and methodologies being completed by WSP for these local authorities are directly transferable to other areas of the country where air quality is a concern and can be scaled.

The following are being applied by WSP as part of Leeds and/or Birmingham CAZ feasibility studies, but these city-scale tasks are equally transferable to relatively smaller geographic areas where air quality is a concern and requires targeted improvement measures:

- Vehicle fleet distribution and projection analyses;

- Traffic model output analyses;

- Vehicle emissions inventory development;

- Atmospheric dispersion modelling of baseline and future CAZ scenarios;

- Verification of dispersion model outputs using widespread baseline pollutant monitoring data;

- Air quality and transport planning advice with focus on contributing to compliance; and,

- Stakeholder engagement.

For further information on the capabilities WSP can provide in terms of CAZ studies or to discuss the wider air quality services that WSP provide to our clients, please contact Damian Pawson (Associate Director, Air Quality); damian.pawson@wsp.com