Cleaner air for Scotland: the road to a healthier future

A strategy setting out the Scottish Government's proposals for delivering further improvements to air quality.

10. National Modelling Framework

Legislation and policy

A Scotland where all European and Scottish legal requirements relating to air quality are as a minimum complied with.


10.1 The new National Modelling Framework ( NMF) is a key element of the delivery of CAFS. The NMF will provide a significant proportion of the quantitative evidence for the National Low Emission Framework ( NLEF) described in Section 11. The NMF will also support decision making around placemaking and transport planning in relation to air quality management.

We will:

  • Design, develop and implement a two-level modelling system on regional and local scales to provide evidence for appraising and identifying potential transport and planning solutions to local air quality issues

10.2 Through improved data requirements and data analysis, the NMF aims to provide local authorities with the information required to improve urban air quality. The NMF will set out a coordinated approach with respect to:

  • the collection of traffic data;
  • air quality models;
  • related monitoring; and
  • the development of the tools for appraising actions.

10.3 To deliver the NMF, the Scottish Government will work collaboratively with partners to:

Collect appropriate traffic data for relevant cities and towns;

Support the National Traffic Data System (see paragraph 10.15) to store traffic data;

Model the city centre areas and associated adjoining spaces of all four major cities in Scotland by 2018; and

Evaluate the requirements of a regional model and support its development.

Collaboration and partnership

10.4 We recognise that the success of the NMF will rely on the support of many organisations and professions. The Scottish Government, Transport Scotland and SEPA have been working collaboratively to develop the NMF with a range of partners since 2013, learning from the success of early pilot work in Aberdeen (which was being prepared for peer review as CAFS went to press). We will continue to build on this work, and use existing systems, experience, and advice to gather the necessary input data, collate models, and develop new software tools that will provide outputs to support the NLEF and its associated transport and planning decisions, in contributing to the CAFS vision.

10.5 We will continue to work in partnership with each of the Scottish local authorities, RTPs, and other organisations to deliver the NMF. Key to this will be the development of an open access approach to sharing data and models.

A National Approach

10.6 The NMF will provide a standardised approach to modelling air quality at regional and local levels (as shown in Figure 14). This will feed directly into new tools developed to support decisions on potential transport and planning options in order to improve air quality. The NMF will help make sure that the evidence, analysis and decision making is consistent across Scotland, even though transport issues and sources of emissions differ between geographical areas. The issue of emissions from domestic burning will be particularly important in city centre areas, where space heating (listed as ‘other combustion’ in Table 1) contributes significantly to background emission levels.

Figure 14. The NMF approach

Figure 14. The NMF approach

10.7 The regional NMF model will link closely to existing models such as the Transport Scotland Land Use in Transport Integration in Scotland model, and the RTP models. It will introduce a consistent approach, open access to data, and correlation with the local NMF model. The local NMF models will provide the ability to analyse the various parts of the transport fleet contributing to problems with air quality.

10.8 The NMF will be developed using a problem solving approach. We will begin by gathering data which will be analysed to create data visualisation. We will then test for uncertainties to ensure the correct evidence is available to support decision making. The four main steps in this cyclic process are shown in Figure 15.

Figure 15 – NMF Cyclic process

Figure 15 - NMF Cyclic process

Regional NMF model

10.9 Many transport and planning decisions across Scotland affect areas beyond individual local authority boundaries. To assess the impact of these decisions on air quality, we will develop a detailed regional assessment model. The regional model will take cognisance of the approach already successfully adopted in other European countries (such as Belgium and the Netherlands, as shown in case study 13). Initially focus will be on the main agglomerations within the four strategic development planning authority areas (shown in Figure 16):

  • Aberdeen City and Shire.
  • Tay Plan.
  • SES Plan.
  • Glasgow and Clyde Valley.

Figure 16 – Regional NMF areas. 1 = Aberdeen City and Shire, 2 = Tay Plan, 3 = Glasgow and Clyde Valley, 4 = SES Plan

Figure 16 – Regional NMF areas. 1 = Aberdeen City and Shire, 2 = Tay Plan, 3 = Glasgow and Clyde Valley, 4 = SES Plan
Source – Circular 1/2013 Strategic Development Plan Areas [96]

10.10 The regional model will be available to all local authorities and will be developed to allow annual reporting on spatial planning development. The model will be developed collaboratively with SEPA leading on the reporting and model maintenance, and Transport Scotland leading on gathering transport data and storing the data in the National Traffic Database System. The model will be held on a central system made accessible to all local authorities.

We will:

  • Evaluate the requirements of a regional model and then support its development during the first two years of implementing CAFS
  • Develop guidance and promote a support network for all practitioners involved in reviewing and assessing local impacts on air quality resulting from regional decision making

Local NMF model

10.11 The local element of the NMF will focus on gathering, analysing and presenting evidence in a consistent manner to support the NLEF option appraisal stages, whilst also helping to inform planning decisions.

10.12 An effective local NMF model will rely on accurate, high-quality, local fleet composition data (especially in densely populated city centres) and up-to-date emission factors. To achieve this we will follow a two-phased approach. The first phase will ensure that data is collected over a sufficiently large area to inform the model build. The second phase will involve collecting more detailed traffic categorisation data, including Automatic Number Plate Recognition and tailpipe monitoring at specific locations of particular concern. This will ensure that local models – for city centres and surrounding areas of all four major cities in Scotland – are produced at a resolution that offers accurate, insightful information. We will also include future prediction modelling to:

evaluate the impact of planned improvements to the fleet; and

develop a national cost/benefit analysis process for assessing actions related to potential scenarios.

We will:

  • Undertake detailed modelling of all four major cities and associated adjoining spaces in Scotland, covering areas associated with highest levels of poor air quality
  • Identify requirements and undertake data collection for additional urban areas within three years of implementing CAFS

Feedback between the NMF model and NLEF process

10.13 The local model will support a standard approach to providing quantitative evidence for the NLEF appraisal, as outlined in Section 11. The NMF and NLEF must work as a feedback loop (Figure 17). This approach will ensure that NLEF assessments have a robust evidence base to be used in the appraisal of various assess controls, such as Low Emission Zones or Clean Air Zones (as outlined in the NLEF).

Figure 17. Interlinkages between NMF and NLEF

Figure 17. Interlinkages between NMF and NLEF

10.14 Evidence generated by the NLEF appraisal process (outlined in Section 11) whilst relevant to the local geographical areas, will also be integrated into the regional NMF model for future analysis.

Data repositories

10.15 The NMF will be supported by the following linked national databases:

Air quality modelling database – developed from the Scottish Urban Air Quality Database, this will hold all air quality data collected for the NMF;

National Traffic Data System – developed by Transport Scotland as a national database, this will hold the traffic data from the NMF;

Air quality management database – developed by SEPA and accessible through the air quality in Scotland website, this will hold all modelling undertaken as part of CAFS, including the NLEF appraisal and the scenario testing tools.

We will:

  • Implement the national databases for traffic data collection and local modelling outputs associated with CAFS

Case study 13

Nationally consistent modelling – Government of the Netherlands

During the 2000s the Dutch Government noted that a range of disconnected air quality models were used, by a wide range of organisations, to evaluate air quality problems. Recognising the need to improve air quality, and meet air pollution limit values quickly, while allowing for new spatial development projects, in November 2006 the Government introduced a new law on air quality, including a National Air Quality Co-operation Plan. From this plan, a national consistent modelling approach and a new software analysis tool (Saneringstool) were developed to allow stakeholders to calculate the causes of poor air quality and agree appropriate mitigation measures. This new process was designed to deliver the following benefits:

  • Reduced workload of municipal authorities.
  • Central government and local authorities adopting a joint approach
    to improving air quality.
  • PM 10 emission exceedances to largely disappear as a result of national and international policies, however NO 2 emission exceedances may be more challenging.

The software tool assists users in resolving NO 2 and PM 10 exceedences along roads by implementing generic regional and location-specific policy measures. The Clean Air Policy Tool maps the air quality situation along the entire Dutch road network and distinguishes between the secondary road network (132,000 km) and the main road network (2,400 km). It enables users to analyse the air quality situation at different levels of scale, and evaluate the effectiveness of two types of action, generic regional policy measures, and location-specific measures.


Back to top