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Decision-Making Threshold for Air Pollution

Welcome to the Decision-Making Threshold for Air Pollution homepage. As progress is made, resources resulting from the project will be available from this page and provided on the Resource Hub.


Project aims

Close-up of a Parasol mushroom surrounded by heather at Thetford Heaths (© Natural England / Paul Glendell, 1999)

The Decision-Making Threshold (DMT) project aims to develop an evidence-based approach for determining when a proposal and the emissions it gives rise to are considered “nugatory” in the context of ecological risk assessment.

We will work with the Inter-agency Air Pollution Group to develop the evidence and discuss its potential with stakeholders. This work could inform a range of uses from decision-making about new or existing proposals to broader policy development and focussing effort to address air pollution effects on ecosystems.

Why is this important?

Current screening thresholds are typically based on professional judgment supported by the best available evidence. For example, the “1% of critical level or load” screening threshold is explained in Air Quality Technical Advisory Group note AQTAG 21 as “a matter of professional judgment”.

Recent case law has outlined that whilst necessary, professional judgment alone is insufficient to provide certainty that the proposals being screened out should not require further assessment. This leaves decisions open to challenge, generates extra cost for case specific analyses and can cause significant delays.

A strong evidence base will supplement this professional judgment and address some of the challenge to current approaches. Better evidence also helps practitioners strike a balance between operational applicability and case law compliance.


Project team

The DMT project is being led by DTA Ecology in a consortium with Air Quality Consultants (AQC), Ecological Planning & Research Ltd​ (EPR) and UK Centre for Ecology and Hydrology (UKCEH).


Project objectives

To meet the overall aim of this project, the specific objectives are to:

  • Review current screening thresholds or methods in the UK and other countries.
  • Produce a clear, broadly applicable rationale for when an emission is unlikely to act together with other emissions in a meaningful way that would require further assessment in relation to effects of air pollution on ecosystems.
  • Quantify or provide an indicative range of emission types, sizes and situations where this rationale can be robustly applied.
  • Quantify the uncertainty within the chosen method and when the rationale is not applicable.
  • Provide a non-technical method to apply the recommended approach (e.g. advice note, tool or video).


How can I get involved?

The DMT project will include stakeholder workshops and expert consultation. You can express your interest by signing up to the JNCC Air Pollution Project Stakeholder list.



Air Pollution

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