What role can planning play in improving urban air quality?

by Claudia Carter

Blog 50 Qhote 1Air pollution has once again become one of the biggest concerns for cities with hard-hitting evidence emerging on the high numbers of premature deaths and the range of health and environmental impacts. While air pollution from industrial processes has been significantly curbed, transport emissions have over the past 40 or so years become the main contributor. Part of the problem has been the sharp rise in diesel cars, traffic congestion (ever increasing numbers of vehicles on the road and stop and start driving) and dirty ‘old-tech’ private and public transport vehicles along with newer less than adequate performing engines (or poor driver skills). Evidence has also emerged on the significant contributions of particulate matter (PM) – and especially particles less than 2.5 micrometres (called PM2.5) that can penetrate deep into the lungs – coming off tyres and breaks even if the engines are relatively clean or emission free (e.g. with the increase in hybrid and electric vehicles) [1] [2] [3].

Poor air quality is an issue in terms of localised high pollution levels – such as toxic corridors along main commuting/transport routes – and also in the form of heightened background levels of pollutants including nitrogen dioxide (NO2), carbon monoxide (CO), particulate matter of various very small sizes (e.g. PM10, PM2.5), sulphur dioxide (SO2) hydrocarbons (HCs) and volatile organic compounds (VOCs).

Earlier this year I attended a Continuous Professional Development seminar organised by the Royal Town Planning Institute (RTPI) West Midlands in Birmingham. The presentations by four speakers were coordinated to cover the legislative background, policy context, green infrastructure solutions and a critical appraisal of a range of mitigation measures in practice. Next I summarised the most prominent and thought-provoking points.

  1. Planning courses and planners to learn about air pollution laws

Strikingly, air pollution laws and regulations have not made it to the forefront of planning; Part IV of the Environment Act 1995 or the 1997 UK National Air Quality Strategy largely draw a blank with planning students and many practitioners. Many of the laws and regulations were initially driven by industrial air pollution and by the early-on recognised transport culprits such as NOx (nitrogen oxides) and SO2 (sulphur dioxide) and have been in force for many years.

The ‘bite’ in the legislation, came with the First Daughter Directive in 1999 (1999/30/EC) and the Air Quality Directive (2008/50/EC) and its transposal into English law with the Air Quality Standards Regulations 2010 setting margins of tolerance and limit values for key air pollutants. For example, NO2 is not to exceed a mean concentration of 40mg per calendar month averaged over a year and stay within a maximum of 18 hours in a calendar year of emissions exceeding 200 micrograms (mg) per cubic metre (m3). A deadline of 1 January 2010 was set for achieving those limits with a maximum of 5 years extension allowed based on establishing an Air Quality Plan.

  1. Improving air quality needs cross-departmental government action

Air quality is a cross-departmental issue of concern and debates and reviews have taken place by several parliamentary committees to reform air quality plans, policies and measures. While some of the steps seem rather slow and past Government responses to air pollution breaches have been heavily criticised and deemed unsatisfactory in court action [4], there are also already some examples where development is being refused due to its negative impact on air quality (e.g. the Gladman Developments case in Kent, 2017) [5].

Pressure remains on the Government to produce a more comprehensive and specific Air Quality Plan and provide sufficient guidance and financial support to assists local and combined authorities in their air quality actions. Will voluntary clean air zones work? Should we focus on the worst affected areas or deal with all significantly polluted air spaces? Birmingham has recently finished its consultation on its city-centre based Clean Air Zone (CAZ) being one of the most extensive proposed CAZ schemes in terms of including all – private and public, small and large – polluting vehicles in the scheme [6].

  1. Take note of invisible pollution

Micro-pollutants, even in low concentrations, are very nasty and the smaller the particles the more deeply they can lodge themselves in lungs, arteries and the brain. Most attention in political debates seems currently focused on roadside air pollution; however, it is important to keep all sources of air pollution on the radar in planning and development. For example, the popularity of wood-burners and biofuel are not as ‘green’ as one may think and contribute to air pollution.

  1. Air pollution is not just a matter of environmental regulations

Dealing with air pollutants is not just a matter of environmental regulations but a key issue for the health sector with implications for the business and transport sectors and associated government and planning departments. An Environmental Impact Assessment (EIA) alone will not help guarantee better air quality or effective air pollution mitigation measures. Local and national level policies and new development controls need to be used to address air pollution and make it an important issue to consider right from the beginning and in the design phase of a development, paying attention to cumulative impact rather than relying on a project-by-project appraisal approach.

  1. Don’t underestimate the connections between urban form and air pollution

There is a clear link between urban form and air quality and this is particularly important to bear in mind when designing nature-based solutions, such as using green infrastructure (GI; especially green walls, hedges and trees) along busy roads. The fact is that GI mitigates and contributes to air pollution depending on how and where exactly it is implemented. Attention has to be paid to the vegetation types and sizes, site characteristics, building heights, local air movement patterns etc. to ensure that air pollution mitigation works effectively through processes such as interception, filtering, ventilation and dilution. Figures 1 and 2 show some good and bad examples of using street trees and the effect of urban form on trapping air pollution.

Figures 1 and 2: Trees can help reduce (top pictures) and increase (bottom pictures) the impacts of air pollution on human health (source: Ferranti et al., 2017 [8])

Figures 1 and 2: Trees can help reduce (top pictures) and increase (bottom pictures) the impacts of air pollution on human health (source: Ferranti et al., 2017 [8])

There is no need to throw the baby out with the bathwater. Differentiated scientific information and practical advice is available to help planners and landscape architects wisen up to what good urban design has to factor in and could look like [8].

  1. Development planning practice needs to look beyond transport flow and behaviour

So what can we learn from existing air quality mitigation practices in development planning? To date transport assessment and research has largely focused on traffic flow and behavioural aspects rather than measuring the impact on air quality and human health. Real-time and open source data, however, is quickly becoming a huge field so that the challenge lies less in data per se, but the processing and ‘cleaning’ of data and their meaningful interpretation. Monitoring the performance of different mitigation actions/mechanisms and calculating the associated benefits will be key. More attention needs to shift towards actively planning to improve air quality in addition to mitigating any negative impacts from new developments. This then requires developers / development partnerships which have a more holistic approach and concern about the impacts and benefits of (re)development – implementing rather than just ‘talking sustainability’.

So what?

In a nutshell, we need to upskill planning students and planning practitioners on the importance, available knowledge and legislation relating to air quality management. The crux is not only to have up to date regulation that facilitates human wellbeing but how awareness, application and enforcement is carried out in spatial planning and in the decision-making of individuals, communities, the nation and across the different professions from architect, to banker, to developer, to entrepreneur, to industrialist, to planner … Visiting cities with advanced GI solutions and low emission zones and other air quality related initiatives may help inspire future pro-active air-quality planning and transport solutions.


[1] Grigoratos, T. and Martini, G. (2014) ‘Non-exhaust traffic related emissions, Break and tyre wear PM’. JRC Science and Policy Reports. Ispra: European Commission, Joint Research Centre. http://publications.jrc.ec.europa.eu/repository/bitstream/JRC89231/jrc89231-online%20final%20version%202.pdf [accessed 31 August 2018]

[2] https://www.autoexpress.co.uk/car-news/101677/government-to-target-particulate-pollution-from-brakes-and-tyres

[3] See, for example, the report published in 2010 by the Committee on the Medical Effects of Air pollutants: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/304641/COMEAP_mortality_effects_of_long_term_exposure.pdf  [22 May 2018]

[4] See e.g. https://www.theguardian.com/environment/2018/feb/21/high-court-rules-uk-air-pollution-plans-unlawful [accessed 9 September 2018]

[5] See e.g. https://www.airqualitynews.com/2017/11/14/planning-decision-upheld-after-air-quality-ruling/ [accessed 9 September 2018]

[6] https://www.birmingham.gov.uk/caz

[7] Ferranti, E.J.S., MacKenzie, A.R., Ashworth K., and Hewitt C.N. (2017) First Steps in Urban Air Quality. A Trees and Design Action Group (TDAG) Guidance Document. UK: London. Available from: http://epapers.bham.ac.uk/3069/

[8] See for example the following: http://www.tdag.org.uk/trees-in-the-townscape.html (2012) and http://epapers.bham.ac.uk/3069/ (2018)


Editor’s Note: A longer report on the CPD event can be found in Tripwire (Magazine of the RTPI West Midlands) Issue 98 (Summer 2018): 19-22. https://www.rtpi.org.uk/the-rtpi-near-you/rtpi-west-midlands/newsletters/

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