Air Quality

Air Quality

Poor air quality caused by pollution can have significant adverse effects upon human health and ecosystems. Pollutants can come in the form of solid particles, liquid droplets, or gases. They may come from natural sources (such as volcanic eruptions) or man-made, such as power generation, transport, and manufacturing processes. In cities around the Severn Estuary, air quality monitoring stations record any changes in pollutants over time. The main pollutants which affect air quality include sulphur dioxides, nitrogen oxides, particulate matter, carbon monoxide and Volatile Organic Compounds (VOCs).

Current air quality in the Estuary

Trends in annual levels of pollutant emissions across the UK have been decreasing since 1970, allowing air quality to increase1. Figure 1 illustrates large decreases in particulate matter (PM10 and PM2.5), nitrogen oxides, ammonia, non-methane volatile organic compounds, and sulphur dioxide since 1970.

Currently, the majority of air quality issues across the Severn Estuary region are largely related to emissions from road transport. In the Estuary, pollutant levels are generally quite low, with some higher concentrations around the cities of Cardiff and Bristol, as shown in Figures 2 and 3. In 2019, average nitrogen dioxide concentrations around the Estuary averaged 9.01 µg m-3 compared to 14.14 µg m-3 in 20102. The concentration of PM2.5 particles in 2019 averaged 7.74 µg m-3 compared to 9.63 µg m-3 in 20102. Most of the other common air pollutants have also been decreasing within the Estuary, ensuring the environmental quality of the Estuary is protected for many generations to come.

Figure 1. Trends in pollutant concentrations compared to 1970 levels in the UK1.

Air Quality Legislation

The 2019 Clean Air Strategy sets out a plan of action for the UK government to tackle air pollution. The UK has set a goal of reducing human harm from air pollution by 50% for 20303.

A large part of the Clean Air Strategy includes the ‘Road to Zero’ legislation which is tackling pollution from transport. The main goal of the Road to Zero is to end the sale of new conventional petrol and diesel engines by 2040, and that almost every vehicle is zero emissions by 20504. This acts to greatly reduce air pollution, especially nitrous oxides and particulates, and includes the promotion of electric vehicles and the monitoring and regulation of car manufacturers4. Consultations on creating all new homes with electric car chargepoints will also be held in the future. In terms of public electric vehicle chargepoints, these locations have increased significantly since 2011 and are readily available in most service stations.

Figure 2. Nitrogen Dioxide annual mean for the Severn Estuary in 20192
Figure 3. Nitrogen Dioxide annual mean for the Severn Estuary in 20192

Another method tackling air pollution from vehicles comes in the establishment of ‘Clean Air Zones’ within cities. A Clean Air Zone is an area identified as needing specific action to improve air quality and promote good health within urban areas5. Only the cleanest vehicles can operate within these zones, reducing local air pollution within these areas. This includes fully electric vehicles, hydrogen fuel cell vehicles and hybrid vehicles (powered by both electricity and conventional fuel) which are ‘geofenced’ to operate only in electric within the zone5. Within the Severn Estuary, certain urban areas are setting up their own versions of Clean Air Zones. In Cardiff, concepts are being developed and put into motion to reduce air pollution from transport6. The city is targeting nitrogen dioxide (NO2) emissions, working to reduce them in the shortest possible time. This includes methods such as establishing non-charging Clean Air Zones, implementation of electric buses and increasing the range of 20 mph limited zones6. In Bristol, plans for a Clean Air Zone covering much of the city centre are also currently under review7. This Clean Air Zone is based on Bristol’s Air Quality Management Area (AQMA) and will involve charges for older and more polluting vehicles.

Air Quality Management Areas

Since 1997, local authority areas within the UK have assessed the air quality within their boundaries. This includes monitoring of current pollution levels and forecasting future pollutant levels8. If problems are identified in meeting target levels for any of the pollutants, the local authority is required to declare an Air Quality Management Area (AQMA) and produce an action plan to tackle the problem. AQMAs within the Severn Estuary include Barton Street (Gloucester), Bristol, Caerleon Road (Newport, Wales), Cardiff City Centre, Ely Bridge (South Wales), George Street (Newport, Wales) Llandaff (South Wales) and Staple Hill (Bristol). The sizes of AQMAs vary considerably, with some covering most of the city centre, such as Bristol, and some only covering specific roads.

Buses in Cardiff City Centre (Photo credit Jeremy Segrott, 2015)

For more information, visit:

  1. Emissions of air pollutants in the UK – Summary (DEFRA, 2021)
  2. UK AIR: Air information resource. UK Ambient AQ Map (DEFRA, 2020)
  3. Policy paper: Clean Air Strategy 2019 executive summary (DEFRA, 2019)
  4. The Road to Zero: Next steps towards cleaner road transport and delivering our Industrial Strategy (Department for Transport, 2018)
  5. Clean Air Zone Framework Principles for setting up Clean Air Zones in England (DEFRA, 2020)
  6. Cardiff Council: Clean Air Cardiff  
  7. Clean Air for Bristol

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