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AQC helps to define Decision-Making Thresholds for air pollution impacts on designated nature conservation sites

23-12-2021

AQC has helped to define Decision-Making Thresholds for air pollution impacts on designated nature conservation sites on behalf of the Joint Nature Conservation Committee (JNCC).  AQC worked alongside DTA Ecology and Ecological Planning and Research (EPR) to define Decision-Making Thresholds and Site-Relevant Thresholds. 

AQC has helped to define Decision-Making Thresholds for air pollution impacts on designated nature conservation sites on behalf of the Joint Nature Conservation Committee (JNCC). 

Assessing air quality impacts on designated nature conservation sites has, for many years, been made more difficult by the requirement in both the Habitats Regulations and National Planning Policy Framework (NPPF) for consideration of impacts ‘in-combination’ with those of other projects and plans.  Air quality assessments carried out to support planning applications or environmental permits have thus very often had to predict future changes caused by other committed or expected schemes as well as those of the scheme seeking permission.  This was made more challenging because emissions to air have no physical boundary, meaning that even sources which are a considerable distance away could not be immediately excluded from in-combination modelling. 

Court judgements have been interpreted to mean that plans and projects may only be exempted from assessment (i.e. ‘screened out’) if a suitable ‘assessment in advance’ has already been carried out.  AQC has worked alongside DTA Ecology and Ecological Planning and Research (EPR) to provide this ‘assessment in advance’ for all plans and projects across the UK up to 2030.  This has considered the combined effect of all forecast plans and projects on area-averaged concentrations and deposition fluxes.  It has also provided a probability-based analysis of local in-combination increments.  Together, these analyses have allowed the definition of Thresholds below which significant in-combination effects can safely be discounted.

The Decision-Making Thresholds and Site-Relevant Thresholds relate to changes to concentrations, deposition fluxes, or traffic flows which may be allowed for each individual development without needing to also assess impacts in-combination with other projects and plans

The work involved extensive consultation, including with ecology specialists, regulators, nature conservation advisors, and JNCC’s legal advisors.  It is expected that using these Thresholds will simplify the assessment process for air quality impacts on nature conservation sites.  By targeting effort, for both assessment and mitigation, on those projects and plans where it can have the greatest benefit, the new Thresholds may significantly aid the protection of UK biodiversity.

AQC’s Technical Report, which explains the Thresholds and their derivation, is available here.

The Main Report, which outlines the assessment approach and its legal justification, is available here.



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