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Evaluation of Caerphilly roadside NO2 improvements

Evaluation of Caerphilly roadside NO2 improvements

Ricardo's RapidAir model, together with a remote-sensing-based emissions model and microscale flow model, was used for Caerphilly County Borough Council to evaluate the feasibility of air pollution mitigation measures and identify a preferred option to achieve nitrogen dioxide (NO2) compliance objectives in the Welsh village of Hafodyrynys.

"The combination of RapidAir’s modelling capability, coupled with remote-sensing technology and the team’s technical expertise, meant we were able to identify a preferred option, in addition to completing the study within the timeframe set by the Welsh Government." Maria Godfrey, Caerphilly County Borough Council Persistent air pollution exceedances in Welsh town, Hafodyrynys


In March 2018, the Welsh Government placed a legal duty on Caerphilly County Borough Council, through a formal direction, to undertake a feasibility study in accordance with the HM Treasury’s Green Book approach. The purpose of the study was to identify the option that would deliver compliance with legal limits for NO2 in Hafodyrynys, a small village community with persistent air pollution exceedances. This required the council to submit initial scoping proposals by 31 March 2018 that set out its proposed approach to the feasibility study including a scope of work, governance, resourcing, procurement approach, indicative costs and timings.

A further requirement of the formal direction was to submit an initial plan that set out the case for change. This included identifying, exploring, analysing and developing options for measures that the local authority would implement to deliver compliance in the shortest possible time.

Ricardo supported the council in addressing the requirements, including collating primary data, and delivering a modelling and assessment work programme.

The legal obligations placed on Caerphilly County Borough Council involved complex scenario testing and consultation, combined with a strict delivery timetable. This represented significant challenges to the successful delivery of the project. Ricardo’s consultants’ extensive experience and reputation for the successful completion of similar work, combined with the unique capabilities of RapidAir, were key factors in Ricardo being contracted to undertake the project.


The dispersion situation at Hafodyrynys Road, a main road running through Hafodyrynys village, is complicated by regional and local topography, and traffic flows (especially at peak times).

Ricardo supported Caerphilly County Borough Council in undertaking detailed air quality dispersion modelling of the baseline situation. Once established, further analyses were then undertaken to identify scenarios that would enable the council to meet the limit values in the shortest time. The approach taken enabled Ricardo to test a wide range of options involving emission mitigation (such as HGV rerouting and traffic signal optimisation) and modifying the physical environment to improve air flow through the area (such as modelling impacts of tree removal and building demolition to understand the impact on local ambient concentrations).

The application of the RapidAir modelling system, coupled with Ricardo’s unique air quality capabilities in remote sensing and microscale flow, enabled the council to:

  • Undertake the legally required evaluation of scenarios to improve air quality within the area.
  • Identify the preferred solution and complementary measures.
  • Identify the associated wider impacts, to ensure that compliance could be achieved in the shortest time possible.

"Ricardo’s RapidAir model was integral to the successful completion of Ricardo’s investigation of potential solutions to an air quality problem at Hafodyrynys Road. The feasibility work for Hafodyrynys has been a long process over a period of 2 years or more – that has thrown many obstacles our way, which Ricardo has found solutions to each time." Maria Godfrey, Caerphilly County Borough Council


Ricardo’s unique expertise in air quality modelling and management, and the innovative capability of RapidAir supported Caerphilly County Borough Council in successfully completing the air quality requirements of the Welsh Government with respect to Hafodyrynys within the required timeframe.

Ricardo’s ability to apply remote-sensing, microscale flow models and RapidAir to support the complex air quality modelling at Hafodyrynys was particularly beneficial to the council. Doing this enabled a large number of complex scenarios to be tested and evaluated in detail within a relatively short period. This provided the council and the Welsh Government with confidence in the results and the certainty that all feasible scenarios had been evaluated, enabling the selection of the most effective option. This capacity, combined with the unique skills and expertise held by Ricardo’s consultants, provided a comprehensive offering to the council and delivered the most detailed evaluation possible within the timeframe available.

To find out more about Ricardo's RapidAir dispersion model, visit


Caerphilly County Borough Council

Start and end dates

04/2018 - 06/2020


14 months


Wales, Caerphilly

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