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Air pollution has long been an issue of significant health concern in the United Kingdom. Monitored UK air quality levels are regularly found to exceed legal limits set by the government, which has led to numerous successful lawsuits being brought against the government for exceeding these targets, particularly for nitrogen dioxide (NO2).1 Air pollution is the United Kingdom’s biggest environmental health threat, with outdoor pollutants estimated to contribute towards 40,000 excess premature deaths per year, costing the UK economy upwards of £20 billion (US $25 billion) annually. 2 This excludes the amount of deaths caused by indoor air pollution, which can be generated from sources such as cigarette smoke, incense, wood or coal burners for heating or energy, cleaning products, and cooking. The health impacts of air pollution in the United Kingdom are linked to a range of diseases and health conditions such as asthma, heart disease, lung cancer, and stroke.
Within the areas of the United Kingdom found to exceed the government’s legal limits for NO2, the highest levels were found within the Greater London area, with the next highest levels of NO2 pollution in South Wales, the West Midlands area, and Glasgow.1 Fine particulate matter (PM2.5) also presents a significant health hazard in the UK. In IQAir’s 2019 World Air Quality Report, the UK’s most polluted city was Chatham in England, with an annual average PM2.5 concentration of 15.2 µg/m3.3 The next most polluted cities include Stockton (13.1 µg/m3), Belfast (12.9 µg/m3), Christchurch (12.8 µg/m3), and Sheffield (12.7 µg/m3), all of which exceed the World Health Organisation’s recommended annual exposure limit of 10 µg/m3 by more than 25%. The UK as a whole was also found to exceed the WHO’s recommended limit during 2019 when calculated weighted by population, scoring an average national exposure of 10.5 µg/m3.
In one well-known episode of the UK’s battle against air pollution, the country’s capital London experienced what is known today as the Great Smog of 1952. During a 4-day period starting on 5 December, a heavy smog settled on the capital, caused by a combination of increased coal burning to heat buildings during the winter, and a cold temperature inversion which trapped the resulting smoke. 4,000 people were estimated to have died as a consequence of London air pollution during the Great Smog.4 Since then, the UK has worked to decrease its reliance on coal as an energy source.
In international comparison, the UK in 2019 was ranked 21st out of global countries with the lowest levels of PM2.5 nationally on IQAir’s World’s Most Polluted Countries 2019 report, with an annual average concentration of 10.5 µg/m3. This compares to 10.8 µg/m3 in 2018, which ranked the UK 13th among countries with lowest PM2.5 levels globally. In comparison with other European countries, the UK ranked 27th out of 37 countries with highest PM2.5 levels during 2019, with less PM2.5 nationally than France, Germany and Switzerland, but higher PM2.5 than Spain, Norway and Finland among others.
In urban areas, the main cause of United Kingdom air pollution is transport. Diesel and petrol vehicles both emit pollutants including nitrogen dioxide and particulate matter, while diesel vehicles emit slightly more of both of these than petrol vehicles. Diesel vehicles are a more problematic contributor to air pollution in European countries than in other regions such as North America, since both the European Union and UK government promoted diesel over petrol for environmental reasons in the early 2000’s, on the basis that diesel emits less carbon dioxide per mile, therefore having less climate impact.5,6 As a legacy of this “dash for diesel” policy, currently half the vehicles on the UK’s roads are estimated to be still powered by diesel fuel. 7 However, this policy came with the tradeoff that diesel also produces more air pollution at ground-level than petrol, posing a higher hazard to human health. This provides one example of how policies to combat air pollution and climate change may not always have mutually beneficial outcomes. Regardless of fuel type, another significant source of particulate matter from vehicles comes from the friction of braking and tyres on the road.
The significant role of transport in raising higher levels of air pollution in the UK was reflected in how air quality was affected during covid-19 in 2020. During the early days of the country’s ‘lockdown’, air pollution was found to decrease significantly compared to the previous year, coinciding with greatly decreased levels of road traffic, as reported in IQAir’s Covid-19 Air Quality Report.
Aside from transport in towns and cities, other major sources of air pollution in the UK include:
According to IQAir’s 2019 and 2018 World Air Quality Reports, the cleanest air quality in the United Kingdom can be found predominantly in Scottish cities, for levels of particulate matter. While the majority of the UK’s state governments follow the European Union’s minimum air quality targets, which for PM2.5 levels is <25 µg/m3 annual exposure, air quality in Scotland is held against the much lower limit of <10 µg/m3, which matches the WHO standard.9
During 2018, 6 out of the 10 cleanest UK cities with available data were in Scotland, with Scottish cities Leadburn (1st with 5.1 µg/m3), Greenock, Edinburgh (joint 2nd with 6.2 µg/m3) and Aberdeen (4th with 6.9 µg/m3) ranking as the 4 cleanest cities in the UK, while Borehamwood, Barnstaple (joint 5th with 7.1 µg/m3) and Gateshead (7th with 7.3 µg/m3) ranked with the cleanest England air quality. Welsh cities Swansea and Cardiff ranked 8th and 38th most polluted out of 81 UK cities, with average of 12.8 µg/m3 and 10.3 µg/m3 respectively, while Northern Irish cities Belfast and Catlereagh ranked 5th and 6th most polluted in the UK during 2018, with average PM2.5 levels of 13 µg/m3 and 12.9 µg/m3 respectively.
During 2019, all Scottish cities were found to report an average PM2.5 level within the WHO’s stringent guideline of <10 µg/m3, except one. The cleanest places in the UK during 2019 for PM2.5 levels were English city Harmondsworth (1st, 4.3 µg/m3), Scottish cities Stirling (2nd, 4.9 µg/m3), Midlothian (3rd, 5.1 µg/m3), and Enniskillen in Northern Ireland (4th, 5.2 µg/m3).
For nitrogen dioxide levels, only 7 out of 43 zones of the UK were found to comply with the national annual target concentration of <40 µg/m3 in 20191. The two zones with the cleanest air quality in terms of NO2 concentrations are also found in Scotland (the Scottish Borders and Highlands), along with three zones in England (Preston Urban area, Blackpool urban area, and Brighton/Worthing/Littlehampton), and Northern Ireland.
At a national level, in order to tackle the key urban emission source of transport, the UK government has committed to phasing out diesel and petrol vehicles by 2040, although some critics suggest that this timeline is not ambitious enough.7 Additionally, the UK is also working to phase out coal from its energy mix, which has historically contributed harmful emissions to the UK’s air, as for example during the infamous Great Smog of 1952. Shortly following this event, in 1956 the UK implemented its first Clean Air Act, and in 1961 established the world’s first national air quality monitoring network, known as the National Survey.10 These actions laid the foundations for the UK’s modern air quality management system.
The UK’s modern approach to air quality management has been strongly influenced by the European Union’s environmental regulations. The UK’s target limits for PM2.5, the most hazardous pollutant to human health, are aligned with the EU target which is an annual mean of <25 µg/m3 – with the exception of Scotland, which has its own more stringent target of <10 µg/m3. The UK and European Union’s limit significantly exceeds the World Health Organization’s guideline of <10 µg/m3, while Scotland’s lower target matches the WHO. Similarly, the UK target for annual mean PM10 levels is <50 µg/m3, which far exceeds the WHO’s guideline of <20 µg/m3.
The UK’s air quality management policy is largely devolved to local authorities, who are responsible to monitor and track local air quality, to check that national air quality targets are achieved. If it looks as though an area’s air pollution may miss the national target, the local authority sets up an Air Quality Management Area (AQMA) to target the problem and develops a Local Air Quality Action Plan. There are approximately 700 AQMA’s in the UK, 600 of which are in England.11 Most of these AQMA’s have been set up to manage areas that are likely to exceed national nitrogen dioxide limits, which the UK frequently exceeds.
Accordingly, much of the country’s work to mitigate the UK’s air pollution, is carried out at the city level. Many initiatives by UK local authorities to tackle local air pollution focus on the country’s leading urban cause of air pollution: transport. These initiatives can include improving public transport options like buses and trams; incentivizing electric vehicles by providing more charging points around the city; encouraging walking and cycling by developing improved pedestrian areas and cycle paths; and discouraging polluting vehicles in key city areas through financial measures, such as charging a fee for higher-emitting vehicles to drive through certain areas at various times.
One strategy for improving air quality in key areas of a city within the UK, is to implement a Clean Air Zone (CAZ). A CAZ is a designated part of a city, where polluting vehicles are charged a fee to drive through, while low-emission vehicles meeting certain criteria can continue to drive in the zone. This is designed to discourage and therefore lower the number of polluting vehicles creating emissions in the zone. Clean Air Zones are due to be rolled out in Bath, Birmingham and Leeds in early 2021, while other cities such as Sheffield and Bristol are also considering the idea. London’s existing Ultra Low Emission Zone is also scheduled to be expanded further during 2021.
The UK’s capital, London, has taken numerous actions to improve London air quality, most recently under the guidance of Mayor of London Sadiq Khan, who took office in 2016. A self-professed asthmatic, Khan has promoted numerous policies within the city to tackle air pollution levels. London’s air quality policies are governed centrally by the Mayor of London’s office, which co-ordinates London’s 32 boroughs. After having hosted a Low-Emission Zone (LEZ) since 2008, London introduced the world’s first Ultra Low Emissions Zone (ULEZ) in 2019, which is credited with achieving a 35% drop in particulate matter levels since its implementation in April 2019.12 London has been cited by air quality experts as being a leader in expertise on ultra-low emission zones.13
There are numerous different monitoring networks who monitor United Kingdom air quality. Primarily, the government’s Environment Agency co-ordinates the UK’s national monitoring stations, on behalf of the UK government’s Department for Environment, Food and Rural Affairs (DEFRA) and devolved administrations, which include the Scottish and Welsh Parliaments, Northern Ireland assembly and London assembly. IQAir reports real-time data from government, educational institutions and private contributors. Government sources include DEFRA, the Welsh, Scottish and Northern Irish governments. Within London, the London Air Quality Network (LAQN) group also contributes a substantial network of automatic monitoring stations at fixed sites around the city, in collaboration with local authorities. Previously co-ordinated by King’s College London, this group is now based out of Imperial College London.
The UK’s network of governmental sensors typically monitors a range of up to six main pollutants. These include fine particulate matter (PM2.5), coarse particulate matter (PM10), nitrogen dioxide (NO2), sulphur dioxide (SO2), carbon monoxide (CO) and ozone (O3). DEFRA reports air quality levels combining these different pollutants using a specific UK air quality index, called the ‘Daily Air Quality Index’ (DAQI). The DAQI bands air quality levels along a scale of 1-10, which corresponds to different health hazard warning related to air pollution levels, where 1-3 is ‘Low’, 4-6 is ‘Moderate’, 7-9 is ‘High’, and 10 is ‘Very high’.14
The UK is also home to numerous low-cost sensors which are operated by a range of private individuals and non-governmental organisations. A full list of the contributors to the United Kingdom air quality monitoring network is displayed on IQAir’s UK air quality map, together with a UK air quality forecast which is developed using machine learning, weather data and air quality data from all the UK’s sensor contributors.
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