The data set shows performance stats for the Drive in a Clean Air Zone service - https://www.gov.uk/clean-air-zones
DEFRA and DfT are jointly responsible for the 2017 Roadside NO2 Reduction Plan, which is specifically focused on tackling exceedances of NO2 in various local authorities and cities around the country. Poor air quality poses a significant health risk to UK citizens and Government must achieve improvements in standards. Clean Air Zones in England aim to reduce levels of NO2 emissions and support behaviour change of motorists.
Users of the Drive in a Clean Air Zone service might need to pay a daily charge to drive in a Clean Air Zone if their vehicle does not meet emission standards. Clean Air Zone guidance can be found here - https://www.gov.uk/guidance/driving-in-a-clean-air-zone
Bath launched their Clean Air Zone, March 2021 and Birmingham, June 2021.
More cities will implement Clean Air Zones later in 2021 and 2022.