Air quality objectives and standards in Britain follow those set by the EU (to 31st December 2020), meanwhile the WHO published new Global Air Quality Guidelines in 2021 here.
Repeated court decisions have determined breaches in Britain, and as a consequence DEFRA is obliging local authorities (England) to meet legal deadlines for improved air quality in hot spot areas. This is done via Local Air Quality Management (also an EU legacy).
Clean Air Zones are sometimes the result. In addition to the Low and Ultra Low Emission Zones in London, three Clean Air Zones are established in England. The Greater Manchester Clean Air Zone is delayed.
Information on Clean Air Zones is here. Note, there can be different types of Clean Air Zones.
Information on the London Zones is here. Note, London operates a Congestion Charge Zone, a Low Emission Zone and an Ultra Low Emission Zone.
Scotland is planning Low Emission Zones in 2022 – information is here.