Decision details

Bath Clean Air Plan Annual Report 2021

Decision Maker: Cabinet

Decision status: Approved

Is Key decision?: Yes

Is subject to call in?: Yes


To provide a summary of the performance of the Bath CAZ (Clean Air Zone) in 2021 and consideration of future options.


(1)  To note the Annual report and the ongoing progress which has been made towards achieving reductions in nitrogen dioxide levels both within and on the boundary of the CAZ, which has been realised by the scheme increasing the proportion of compliant, less polluting vehicles driving in and around the city.

(2)  To note the continued performance of the CAZ against the scheme’s financial model, ensuring it covers its costs of operation and avoids placing an additional burden on the Council and local taxpayers. In addition, note that surplus revenue is now being targeted towards sustainable transport projects as laid out in the full business case for the scheme.

(3)  To note the statement from the Joint Air Quality Unit (JAQU) on their assessment of the scheme towards achieving success with the Ministerial Directions which have been served upon the council.

(4)  In line with recommendation 3 of E3322 and Minute 1.5 of E3326, to note that further work to develop and implement a local nitrogen dioxide objective level will be continued.

(5)  To recommend that officers explore options for enhancing the capability to monitor particulate matter pollution within Bath and North East Somerset.


Reasons for the decision:

NO2 levels in Bath have decreased since the CAZ was implemented. Taking into account COVID restrictions and the Cleveland Bridge closure, alongside an analysis of air quality in comparable locations, the suggestion is that the observed improved air quality can be partially attributed to the CAZ introduction.

Evidence suggests that the CAZ has been successful in encouraging the enhancement of vehicle compliance. While COVID is the main driver for the observed fluctuations in the volume of traffic in the CAZ area in Bath, an analysis of the composition of the fleet driving into the CAZ area highlights a clear move toward compliant vehicles across all vehicle types.

A comparison between air quality data in the B&NES CAZ and that in control sites in Reading, Oxford and Worthing suggests that improvements in air quality in Bath may be causally related to the B&NES CAZ. However, a longer time series of quality assured measurements is needed to improve the confidence and certainty of this conclusion.

During the development of the Full Business Case, traffic modelling did suggest that there could be both increases and decreases in traffic flows on some roads because of the CAZ being introduced. However, it could not anticipate the changes in national and local traffic patterns because of the pandemic.  The pandemic has greatly affected working habits and travel patterns since the winter of 2019/2020 with greater visibility of delivery vehicles on the road network. Appendix (b) 2 of the Annual report provides updated information on how concerns about the potential displacement of traffic and pollution have been investigated since the launch of the scheme, which has involved the deployment of temporary ANPR cameras to better understand the proportion of non-compliant traffic in areas of concern. 

  Of the 17 initial investigations, 7 locations have been determined as having no displacement impacts, 2 locations will be reviewed following the full re-opening of Cleveland Bridge, 2 locations have further monitoring in progress and 6 locations require ongoing monitoring at this stage.

To date, this monitoring suggests that there are no ongoing significant displacement impacts due to the introduction of the scheme, however monitoring will continue.  This will include monitoring on key roads such as the A37, where results to date demonstrate that there appears to be no increase in HGV volumes due to the implementation of the CAZ.

There is no clear evidence of a safe level of exposure to NO2 or particulate matter or below which there is no risk of adverse health effects so any further reduction of these pollutant concentrations below air quality standards is likely to bring additional health benefits1. To date, efforts have been directed at achieving compliance with the Ministerial Directions which focus on reducing concentrations of NO2.  The council wants to be ambitious in building upon the progress which has been made by the CAZ in improving air quality throughout the city and its environs and has a will to go further. 

Whilst the aim has been to achieve compliance with the annual average objective level for of 40 µgm3, the council is fully aware of World Health Organisation (WHO) guidelines published in 2021 which propose more ambitious targets for both NO2 and particulate matter in recognition of the serious health risk pollution can have upon global health.  It is ambitious to create its own reducing target to adhere to these guidelines in future years, reinforcing the aspiration that reducing pollution should be an aim in all decision-making.

By introducing a local NO2 objective level for example, where all monitoring locations would aim to achieve an annual average level of at, or below, 36 µgm3 by 2025, it demonstrates a will to be aspirational in further protecting public health. This local target would align with the wider package of measures detailed in the Journey to Net Zero to achieve decarbonisation, including consideration of the introduction of a work-place parking levy and additional residents parking zones. 

Whilst current objective levels for particulate matter are not being breached in Bath and North East Somerset, the council would like to increase the monitoring capacity of this pollutant using surplus funding from the CAZ.  Unlike NO2, particulate matter is a pollutant which can be significantly impacted by regional factors, i.e. sources outside of the local authority and the council aspires to provide the public with wider coverage of actual monitoring data to raise greater awareness of this important pollutant.


Alternative options considered:

None. This is a report providing an annual update on the performance of the Clean Air Zone in Bath.

Report author: Cathryn Brown

Publication date: 15/07/2022

Date of decision: 14/07/2022

Decided at meeting: 14/07/2022 - Cabinet

Effective from: 23/07/2022

Accompanying Documents: