Air Quality

Introduction

This chapter describes the methodology followed and potential impacts identified for the air quality assessment of the A75 Springholm and Crocketford Improvements (hereafter referred to as “the proposed scheme”). This assessment has been undertaken with reference to Design Manual for Roads and Bridges (DMRB) LA 105 - Air quality (revision 0.1.0) (hereafter referred to as “DMRB LA 105”) and other relevant standards and guidance set out within this chapter.

Legislative and Policy Framework

This section provides a summary of the legislation and policy that are relevant to this air quality assessment.

Legislation

The following legislation is relevant to this air quality assessment.

Environment Protection Act (1990) amended by the Pollution Prevention and Control Act (1999)

Part III of the Environment Protection Act (1990) amended by the Pollution Prevention and Control Act (1999) provides statutory nuisance provisions for dust, which would be generated during construction.

Environment Act 1995, Part IV

The Environment Act 1995, Part IV introduced a system of Local Air Quality Management (LAQM) in the UK. This requires local authorities to review and assess air quality within their boundaries regularly and systematically against Air Quality Objectives (AQOs), appraise development and transport plans against these assessments and make plans to meet the AQOs where these are exceeded.

The Air Quality (Scotland) Regulations 2000, and The Air Quality (Scotland) Amendment Regulations 2002

Legislates for the AQOs for pollutants set out in the 2000 Air Quality Strategy, which was revised in 2007. AQOs exist for a variety of pollutants including oxides of nitrogen (NO X ), nitrogen dioxide (NO 2 ), particulate matter (PM 10 and PM 2.5 ). These are established for both the protection of human health and the protection of vegetation and ecosystems.

The Air Quality Strategy for England, Scotland, Wales and Northern Ireland (Volume 1)

The Air Quality Strategy for England, Scotland, Wales and Northern Ireland ( Volume 1) updates the 2000 Air Quality Strategy, and sets out how local air quality is managed, through the application of AQOs based on the above Air Quality (Scotland) Regulations 2000 and 2002 Amendments.

Directive 2008/50/EC on ambient air quality and cleaner air for Europe

The Directive 2008/50/EC on ambient air quality and cleaner air for Europe consolidates previous European Directives on ambient air quality. These Directives form the basis for UK air quality legislation and were transposed into UK law via The Air Quality Standards (Scotland) Regulations 2010. Although published in 2007, the Air Quality Strategy (AQS) is consistent with The Air Quality Standards (Scotland) Regulations 2010.

The Air Quality Standards (Scotland) Regulations 2010

The Air Quality Standards (Scotland) Regulations 2010 transposes the formalised Limit Values (LVs) set out in the European Union (EU) Ambient Air Quality Directive 2008/50/EC to Scottish law.

Cleaner Air for Scotland: The Road to a Healthier Future

Cleaner air for Scotland: the road to a healthier future is a national strategy setting out the Scottish Government’s proposals for delivering further improvements to air quality for compliance with EU air quality legislation. Commits to aligning the AQOs in relation to PM with the World Health Organisation (WHO) recommendations.

The Air Quality (Scotland) Amendment Regulations 2016

Updates the annual mean PM 2.5 AQOs from the Air Quality (Scotland) Regulations 2000.

The Environment Strategy for Scotland: Vision and Outcomes

The Environment Strategy for Scotland: vision and outcomes provides the framework and policy priorities for Scotland.

Cleaner Air for Scotland 2 - Towards a Better Place for Everyone

Cleaner Air for Scotland 2 - Towards a Better Place for Everyone (CAFS2) supersedes CAFS and sets out actions to improve air quality and how these will be delivered based upon the 2020 Environment Strategy for Scotland.

EU Directive 2008/50/EC Ambient Air Quality and Cleaner Air for Europe was published to consolidate previous European Directives on ambient air quality. These European Directives form the basis for UK air quality legislation and were transposed to UK law via The Air Quality Standards (Scotland) Regulations 2010. Although published in 2007, the Air Quality Strategy (AQS) is consistent with The Air Quality Standards (Scotland) Regulations 2010.

In 2016, Scotland became the first country in Europe to adopt the 2005 WHO recommended annual mean guideline value of 10µg/m 3 for Particulate Matter at 2.5 microns or less (PM 2.5 ). Currently, the Scottish Air Quality Objectives (AQOs) for Particulate Matter at 10 microns or less (PM 10 ) are 18µg/m 3 and 10µg/m 3 for PM 2.5 .

Prior to Brexit, the UK Government was responsible to the European Commission (EC) for ensuring that it complied with the provisions of the EU Directive. Although this is no longer the case, the Air Quality Standards (Scotland) Regulations 2010 remain in force and compliance with the Limit Values (LVs) within these regulations is still required.

The AQOs applicable to Local Air Quality Management (LAQM) in Scotland are set out in The Air Quality (Scotland) Regulations 2000 and its associated amendments, whilst LVs are set out in The Air Quality Standards (Scotland) Regulations 2010. AQOs are health-based standards set at a level to provide protection to the whole population. The pollutants relevant to this assessment are NO X , NO 2 , PM 10 and PM 2.5 , which are most likely to be impacted by road traffic at either human health or ecological receptors. The relevant AQOs / LVs for these pollutants are presented in Table 5-1. The AQS also provides a non-statutory objective for NO X , for the protection of vegetation. This is currently not assessed by Scottish local authorities.

To note, NO x has been set as the objective for the protection of vegetation and ecosystem. This standard does not apply to human health.

Table 5-1: Relevant Air Quality Limit Values and Air Quality Objectives
Pollutant Threshold Averaging Period

NO X

30µg/m3

Annual mean

NO 2

40µg/m3 to 200µg/m 3 (not to be exceeded more than 18 times/yr)

Annual and 1-hour mean

PM 10

18µg/m 3 to 50µg/m 3 (not to be exceeded more than 7 times/yr)

Annual and 24-hour mean

PM 2.5

10µg/m3

Annual mean

There are no assessment methods available that can produce robust predictions of short-term air pollutant concentrations associated with road traffic emissions. Therefore, compliance with the short-term AQOs/LVs is assessed by following the guidance presented in Local Air Quality Management Technical Guidance (TG22) (hereafter referred to as “LAQM TG(22)”), which provides relationships between the annual mean concentration and the number of periods per year where short-term air quality standards are potentially exceeded. These relationships have been derived from examination of monitoring data across the UK.

The responsibilities of local authorities with respect to meeting AQOs are not the same as the responsibilities of the UK Government for meeting legally binding air quality LVs. Local authorities do have statutory duties for LAQM; however, they are not obliged to ensure AQOs are met, but rather that they are worked towards. Under Part IV of the Environment Act 1995, the UK Government introduced LAQM, which placed duties on local authorities to undertake periodic reviews of air quality in their areas to assess present and likely future air quality against the AQOs. Where these AQOs are not likely to be met, the local authority must designate an Air Quality Management Area (AQMA) and produce an action plan for improvement in air quality.

It is important to recognise the difference between the LVs (for which compliance is determined at a national level by government) and AQOs (for which compliance is determined at a local level by local authorities under the LAQM regime). Whilst the LVs and AQOs for a pollutant may be set at the same concentration value (for example 40µg/m 3 , as an NO 2 annual mean) the means of determining compliance are fundamentally different, and they must be considered separately.

Compliance with air quality LVs is determined initially via the national monitoring network and national model (the Pollution Climate Mapping (PCM) model). There are important differences between this, and the monitoring/modelling carried out by local authorities to determine compliance with AQOs. Because of these differences, there are many locations across the UK where the national assessment of compliance with LVs, and local assessments of compliance with AQOs, are not in agreement. They are treated separately in this assessment, which is consistent with the advice in the relevant Planning Advice Note (PAN) 51: Planning, Environmental Protection and Regulation (hereafter referred to as “PAN 51”), discussed below, produced by the Scottish Government (which provide further guidance on specific topics) and with DMRB LA 105.

National Policy

The National Planning Framework 4 was adopted in February 2023. The Framework outlines the Scottish Ministers’ policies and proposals for development and land-use in Scotland and details the long-term spatial strategy, spatial principles, priority actions and National Developments up to 2045. The following policy is related to air quality in the context of the proposed scheme:

  • Health and Safety - Policy 23d ‘Development proposals that are likely to have significant adverse effects on air quality will not be supported. Development proposals will consider opportunities to improve air quality and reduce exposure to poor air quality. An air quality assessment may be required where the nature of the proposal or the air quality in the location suggest significant effects are likely’.
  • PAN 51 summarises the statutory responsibilities of the environmental protection bodies. The purpose of PAN 51 is to support the existing policy on the role of the planning system in relation to the environmental protection regimes.

Local Policy and Plans

Air quality within Dumfries and Galloway is generally very good as presented in Dumfries and Galloway 2021 Air Quality Annual Progress Report . Therefore, there are no specific local policies or plans related to air quality.

Assessment Methodology

The following section describes the methodology for the assessment that has been undertaken at DMRB Stage 1. The assessment of the improvement strategies on air quality has been completed with reference to the assessment methodology set out in DMRB LA 105 and Defra’s LAQM TG (22), where applicable.

For the purposes of this DMRB Stage 1 EAR, the assumed opening year for the proposed scheme is 2035, therefore, for the air quality assessment, an opening year of 2035 has been used. There are six improvement strategies, described in full in The Proposed Scheme Chapter of this EAR. The improvement strategies generally run along or in parallel to the existing A75 between Allanton Roundabout in the west and Drummore roundabout at the start of the existing dualled section in the east.

Paragraph 2.10.1 of DMRB LA 105 states ‘the level of assessment is determined by the level of risk and the assessment stage for the project, and at the options selection and preliminary design stage, a simple assessment should be sufficient’. Expected reductions in road traffic exhaust emissions over time, together with the low levels of air pollutants in the area (see the Assumptions and Limitations section of this chapter) all suggest it is very unlikely there will be exceedances of either the AQOs or LVs within the air quality study area in the proposed scheme opening year. Therefore, to provide a proportionate level of assessment at this early stage of the design, the DMRB Stage 1 air quality assessment has followed a limited, qualitative assessment approach, using readily accessible data from the data sources listed below to inform the assessment.

Data Sources

Assumptions and Limitations

Assumptions

The local authority data on AQMAs and monitoring data used to inform this assessment have been obtained from the most recent publicly available documents and resources.

There was no traffic data for the respective improvement strategies to inform this assessment. Therefore, the study area has been based on a 2km buffer of the outer limit of the improvement strategies (hereafter referred to as the “DMRB Stage 1 Assessment Corridor”), which is a buffer being used by other environmental factors at DMRB Stage 1.

All monitoring data used has been reproduced from third party sources and therefore were assumed to be accurate.

Limitations

Paragraph 2.10.1 of DMRB LA 105 states that ‘The level of assessment is determined by the level of risk and the assessment stage for the Project, and at the options selection and preliminary design stage, a simple assessment should be sufficient’. Expected reductions in road traffic exhaust emissions over time, together with projected trends in background pollutant concentrations (see the Baseline Conditions section of this chapter) suggest it is unlikely there will be exceedances of either AQOs or LVs within the air quality study area in the opening year (2035). In addition, traffic data and design information (other than broad outline of improvement strategies) were not available at the time of this assessment. As such, and to provide a proportionate level of assessment at this early stage of the design, this assessment has followed a limited, qualitative assessment approach. Therefore, absolute air pollutant concentrations and the magnitude of potential impacts have not been quantified for this DMRB Stage 1 assessment.

The impact of COVID-19 travel restrictions on traffic flows will have affected air quality monitoring data for 2020 and 2021. The use of data in previous years (especially for 2019) are, however, considered likely to have negated the impact of this limitation.

The affected road network is not known at present for this high-level assessment and therefore the extent of the impacts is unknown.

Study Area

In the absence of traffic data, the study area for the air quality assessment has been based on professional judgement and as such is based on a 2km buffer of the DMRB Stage 1 Assessment Corridor, as it is unlikely there will be significant rerouting in the area. The study area included land within the areas administered by Dumfries and Galloway Council as shown in Figure 5-1. The study area is not exhaustive and could be subject to change once the affected road network (ARN) has been defined at DMRB Stage 2. The DMRB Stage 2 ARN will be defined based on the DMRB LA 105 traffic scoping criteria. The DMRB scoping criteria are based on the change in traffic flows in the opening year between the Do Minimum (DM; without the proposed scheme) compared to the Do Something (DS; with the proposed scheme) as follows:

  • Annual Average Daily Traffic (AADT) change greater than or equal to 1,000.
  • HDV (Heavy Duty Vehicle) AADT change great than or equal to 200.
  • A change in speed band (for definition refer to DMRB LA 105 Appendix A, a band of speeds such as 5 – 20kph).
  • A change in carriageway alignment by greater than or equal to 5m.

Baseline Conditions

Local Air Quality Management (LAQM)

All local authorities are expected to regularly undertake air quality monitoring, assessment and reporting in their administrative area in line with their LAQM duties. No AQMAs have been declared within the 2km buffer or within the boundary of Dumfries and Galloway Council.

Air Quality Monitoring

Local air quality monitoring data from the most recent Dumfries and Galloway AQ APR and UK Air Information Resource Annual and Exceedance Statistics have been collated. Further updated progress reports and monitoring data will be obtained (if available) at DMRB Stage 2. There is no monitoring within the study area. The nearest monitoring sites are in the centre of Dumfries, over 4km away from the study area. The highest monitored NO 2 concentration within Dumfries and Galloway, in the most recent 5 years (2016-2020) within the Dumfries and Galloway AQ APR was 31.1µg/m 3 in 2019 measured at the automatic monitoring site in Buccleuch Street, Dumfries, which is significantly below the 40µg/m 3 Air Quality Objective/Limit Value (AQO/LV). More recent data for this automatic monitoring site was available from UK Air Information Resource Background Mapping data for local authorities - 2018 with concentrations ranging from 20-22µg/m 3 for the NO 2 annual average. There have been no exceedances of the short-term 1 hourly NO 2 objective since 2016. Some historic PM monitoring noted in the Dumfries and Galloway AQ APR has been undertaken for both PM 10 and PM 2.5 but was discontinued, due to low levels of both pollutants.

Due to the lack of monitoring data near to the improvement strategies, an NO 2 diffusion tube monitoring survey is being undertaken from May 2025 for six months to support the air quality assessment at DMRB Stage 2.

Mapped Background Concentrations

The LA Data provides empirically derived national background maps, as part of the Scottish Air Quality Database project, which provide estimates of background pollutant concentrations at a 1km x 1km grid square resolution. Data for 2018 (the likely base year for the traffic model) were downloaded in March 2025 using a previously available dataset for NO X , NO 2 and PM 10. For 2035 (the opening year for the proposed scheme) and 2024 (as an interim between 2018 and 2035) NO X , NO 2 , PM 10 and PM 2.5 have been obtained for the Dumfries and Galloway Council area from an updated dataset from LA Data.

Scotland specific maps for PM 2.5 were not available from LA Data for 2018. Therefore, the PM 2.5 data for 2018 were taken from UK Air Information Resource Background Mapping data for local authorities - 2018 using base year mapped background maps for 2018.

The range of pollutant concentrations within the Dumfries and Galloway Council area are presented in Table 5-2, 5-3 and 5-4. To note, NO x has been set as the objective for the protection of vegetation and ecosystem. This standard does not apply to human health.

Table 5-2: Background Pollutant Concentrations for 2018 (µg/m3)
Pollutant AQO/LV (µg/m 3 ) Mapped Background Pollutant Concentration Range (µg/m 3 ) 2018

NO X

30

2.5 - 19.5

NO 2

40 (LV/AQO)

1.8 - 13.5

PM 10

18 (AQO)

6.8 - 12.1

PM 2.5

10 (AQO)

4.5 - 7.2
Table 5-3: Background Pollutant Concentrations for 2024 (µg/m3)

Pollutant

AQO/LV (µg/m 3 )

Mapped Background Pollutant Concentration Range (µg/m 3 ) 2024

NO X

30

1.5 - 10.7

NO 2

40 (LV/AQO)

1.2 – 8.0

PM 10

18 (AQO)

5.3 - 10.5

PM 2.5

10 (AQO)

3.1 – 5.9
Table 5-4: Background Pollutant Concentrations for 2035 (µg/m3)
Pollutant AQO/LV (µg/m 3 ) Mapped Background Pollutant Concentration Range (µg/m 3 ) 2035

NO X

30

1.1 - 12.7

NO 2

40 (LV/AQO)

0.8 - 9.4

PM 10

18 (AQO)

4.9 - 10.1

PM 2.5

10 (AQO)

2.7 - 5.4

As shown in Table 5-2, 5-3 and 5-4, background pollutant concentrations of NO X , NO 2 , PM 10 and PM 2.5 are well within the relevant AQOs/LVs.

Pollution Climate Mapping

The PCM model is run by Ricardo-AEA on behalf of Defra and is designed to assess LV compliance. The PCM model reports on the concentrations of NO 2 and PM in the atmosphere at representative roadside locations that need to be assessed for LV compliance. Modelled PCM concentrations are projected from a base year (2018) and for every year up to 2030, for NO 2 . For PM 10 and PM 2.5 results are available for the base year, 2020, 2025 and 2030 (2025 has been used as representative of 2024). As there are no PCM data after 2030, 2030 has been used in place of 2035 to represent the opening year.

Using UK Air Information Resource 2020 NO2 and PM projections data (2018 reference year) , a review of the most recent PCM NO 2 , PM 10 and PM 2.5 model projection data, which have a base year of 2018, was undertaken as part of this assessment for all PCM links within the study area. There are two PCM links within the study area, both in Castle Douglas, which are part of the A713 as shown in Figure 5-1. The concentrations for NO 2 for the specific assessment years are shown in Table 5-5, 5-6 and 5-7. It should be noted that there were no Defra reported PCM PM concentrations in the study area, with the nearest PCM links with reported PM concentrations being in Dumfries.

Table 5-5: PCM Links Within the Study Area for 2018 (µg/m3)

Pollutant

Census ID

Projected Roadside Annual Mean Concentration (µg/m3) 2018

NO 2

802080313

10.4

NO 2

802080325

8.0
Table 5-6: PCM Links Within the Study Area for 2024 (µg/m3)

Pollutant

Census ID

Projected Roadside Annual Mean Concentration (µg/m3) 2024

NO 2

802080313

7.3

NO 2

802080325

5.6
Table 5-7: PCM Links Within the Study Area for 2030 (µg/m3)

Pollutant

Census ID

Projected Roadside Annual Mean Concentration (µg/m3) 2030

NO 2

802080313

5.4

NO 2

802080325

4.4

Within the study area, there were no PCM links which were predicted to exceed the annual mean NO 2 LV (40µg/m 3 ) in any year and by 2030 concentrations were less than 25% of the LV. It is also assumed that there is no expected danger of PM LV exceedance in the study area, given historic monitored PM data included in the Dumfries and Galloway AQ APR.

Sensitive Human Receptors

DMRB LA 105 indicates that sensitive human receptors include residential properties, schools, hospitals and care homes. There are a number of residential locations in the study area such as: Castle Douglas, Springholm, Crocketford and Brae, which may be affected by changes in air pollutant concentrations as a result of the proposed scheme. The monitored data and PCM data discussed above are considered to give a reasonable approximation of likely worst-case baseline air pollutant concentrations at human receptors in the study area.

Designated Habitats

Whilst the spatial extent of the ARN is not yet known, there are a number of designated ecological sites within the study area that may need to be taken into consideration as part of the air quality assessments undertaken at DMRB Stage 2 and DMRB Stage 3, including areas of ancient woodland. Designated sites within the study area are discussed further in the Biodiversity Chapter of this EAR and shown in Figure 8-1.

Baseline nitrogen deposition values from APIS within the study area indicate critical loads for some types of woodland have the potential to be exceeded.

Potential Impacts

Construction

DMRB LA 105 indicates that air quality impacts from dust during construction have the potential to occur within 200m of construction activities. Furthermore, DMRB LA 105 indicates an assessment is required of potential construction traffic impacts on air quality where construction activities are programmed to last for more than two years.

There is no information available regarding likely construction phase activities at this stage. Furthermore, the exact duration of the construction programme for the proposed scheme is not known at present. Construction impacts will therefore be reviewed at DMRB Stage 2 and/or DMRB Stage 3 when more details regarding construction phase activities and vehicle movements are known.

Any potential impacts of dust during construction can, however, be reduced and controlled through the implementation of appropriate mitigation, such as those outlined in Guidance on the assessment of dust from demolition and construction . As such, impacts from dust generating activities are not likely to be significant.

Operation

Descriptions of the potential impacts on air quality for each of the improvement strategies are presented below. Each of the improvement strategies are described in The Proposed Scheme Chapter of this EAR.

All improvement strategies have the potential to cause changes in vehicle emissions on roads both in the immediate vicinity of the strategy and on the wider road network, as a result of changes in traffic flow and speeds. There are no AQMAs located near any of the improvement strategies or within the study area.

All improvement strategies go through or are located within 200m of a number of designated ecological sites, including ancient woodland. Therefore, it is likely that this realignment would affect rates of nitrogen deposition within these designated sites, the impact of which should be assessed using modelling at DMRB Stage 2.

The highest NO 2 annual average PCM model concentration within the study area in 2030 (illustrative of the opening year), is predicted to be 5.4µg/m 3 , in Castle Douglas. Therefore, there are unlikely to be any compliance issues with the NO 2 LV.

Road traffic emissions are expected to reduce over time due to improvements in the vehicle fleet (such as improved emissions controls and an increased proportion of electric vehicles), meaning that by the opening year of 2035, potential adverse air quality impacts associated with changes in traffic flows will be reduced compared to now. It is therefore unlikely, given the low concentrations within Dumfries and Galloway, that there will be any exceedances of AQOs at human receptors with the proposed scheme in place.

Design, Mitigation and Enhancement Measures

Mitigation Measures – Construction Phase

DMRB LA 105 indicates that the construction dust risk potential of a project shall be used to inform the measures required to support the proposed mitigation. As such, the Environmental Mitigation Plan (EMP) would include measures to reduce construction dust and emissions from construction plant and vehicles. Any mitigation measures would be identified during the DMRB Stage 3 assessment when more advanced design data are available for a preferred route option.

Mitigation Measures – Operational Phase

Given the existing low air pollution levels in Dumfries and Galloway, it is unlikely that there would be any AQO/LV exceedances by that date, however, there may be increases in rates of nitrogen deposition within designated ecological sites containing features sensitive to air pollution. The potential need for any mitigation measures will be identified during the DMRB Stage 2 and/or DMRB Stage 3 assessment when modelling is undertaken. DMRB LA 105 states that ‘where the air quality assessment concluded that the Project triggered a significant air quality effect and/or affect the UK’s reported ability to comply with the 2008/50/EC in the shortest timescales possible, a Project air quality action plan (PAQAP) shall be included in the air quality assessment’.

If required, mitigation measures set out in a PAQAP should be viable and be provided with a quantification of the change in concentrations associated with the measure. DMRB LA 105 describes the mitigation measures expected to be assessed (including vertical barriers and speed limit adjustments) alongside any other proposed viable mitigation measure.

Enhancement Measures

None identified at the time of reporting.

Assessment of Likely Significant Effects

Construction Phase

As noted within DMRB LA 105, with the appropriate implementation of good practice dust and air quality mitigation measures, it is unlikely that construction dust would have a significant residual effect in terms of air quality. Similarly, construction traffic data is not yet available, however, given the existing low air pollution levels in Dumfries and Galloway, it is considered unlikely that exceedances of AQOs or LVs would occur at human receptors during the construction period. This is due to the expected improvement in emissions from road vehicles and the existing downward trend in measured concentrations combined with the low existing concentrations. Construction phase impacts are therefore scoped out until detailed design information is available, such as at DMRB Stage 3.

Operational Phase

Based on this qualitative assessment for all improvement strategies and given the existing low air pollution levels in Dumfries and Galloway, it is considered unlikely that exceedances of AQOs or LVs would occur at human receptors during the opening year due to the expected improvement in emissions from road vehicles and the existing downward trend in measured concentrations combined with the low existing concentrations.

The risk of the improvement strategies affecting compliance with AQOs within AQMAs in the opening year is considered to be low based given the existing low air pollution levels in Dumfries and Galloway and as there are no AQMAs in Dumfries and Galloway.

The highest PCM model NO 2 concentration within the study area in 2030 (illustrative of the opening year), is projected to be 5.4µg/m 3 , in Castle Douglas. The risk of affecting compliance with the NO 2 LV in the opening year is, therefore, considered to be low as it is deemed unlikely that exceedances of the NO 2 LV would occur within the study area. The PCM model does not include links within the study area for PM 10 and PM 2.5 as these are unlikely to be exceeded at roadside locations. Therefore, no exceedances of these LVs are anticipated.

Potential increases in traffic associated with the operation of the improvement strategies have the potential to cause increases in rates of nitrogen deposition greater than 1% of the lower critical load at some designated ecological sites within 200m of the ARN where critical loads are currently exceeded. Therefore, there is a risk that the improvement strategies could have significant effects on designated ecological receptors. This would be assessed further at DMRB Stage 2.

Overall, due to expected reductions in vehicle emissions over time, it is assumed that the likelihood of significant operational effects from the improvement strategies on human, AQMA and PCM receptors is low, with the risk being higher at ecological receptors.

At DMRB Stage 2, the assessment will identify the potential risks of significant operational effects of the route options.

Proposed Scope of Future Assessment

A simple DMRB assessment (based on DMRB LA 105) should be undertaken at DMRB Stage 2 to assess the operational opening year impacts at designated sites within 200m of the ARN. A small number of human receptors close to the route options could also be assessed for illustrative purposes using a simple approach. Due to the lack of monitoring data near to the route options, an NO 2 diffusion tube monitoring survey is being undertaken from May 2025 for six months to support the air quality assessment at DMRB Stage 2.

It is proposed to not undertake any construction assessment until DMRB Stage 3.

Summary

It is unlikely there will be exceedances of AQOs/LV for human receptors, however, there may be significant effects at designated sites (for example ancient woodland) within 200m of the ARN. Therefore, a simple DMRB assessment (based on DMRB LA 105) should be undertaken at DMRB Stage 2 to assess the operational opening year impacts at designated sites within 200m of the ARN. A small number of human receptors close to the improvement strategies could also be assessed for illustrative purposes using a simple approach to show that concentrations at human health receptors will be significantly below the AQOs/LVs.

It is proposed that construction assessment is not undertaken until DMRB Stage 3.