Addressing the Significance of Air Quality at the CIEEM Spring Conference – by Prof. Duncan Laxen


Recent court judgements have focused attention on the assessment of impacts of air quality associated with new plans and projects on sensitive habitats protected under the Habitats Regulations. One of the consequences of the judgements is that many more of these plans and projects are proceeding from the screening stage to the appropriate assessment stage, whereby an assessment of the effect on the integrity of the protected habitat is required, be it a Special Area of Conservation (SAC) or Special Protection Area (SPA). Importantly, it is now emphasised that it is essential to consider the impacts of plans and projects both alone and in-combination with other plans and projects that might affect the habitat. The greater emphasis on in-combination impacts is to ensure that many smaller plans and projects, which alone can be considered insignificant, could add together to create a significant effect on site integrity that would require mitigation measures to be put in place.

It is therefore very timely for CIEEM to devote its Spring Conference to looking at the assessment and mitigation of air quality impacts on biodiversity. The conference will address some of the challenges posed by recent judgements, in particular how we should be carrying out assessments that meet the new requirements. Importantly, these assessments require input from air quality specialists to define the impacts and from ecologists to determine the effects, drawing on more academic expertise for both professions.  (Note that I use the term ‘impact’ to mean change in the exposure, while ‘effect’ is the outcome of this change for the ecosystem, as is conventional for EIA work.)

The focus for air quality specialists is on assessing the impacts arising from emissions of nitrogen oxides and ammonia, both of which may have direct effects on ecosystems and also contribute to additional nitrogen deposition. We know that critical loads and critical levels have been set to protect habitats.  We also know that critical loads are widely exceeded across sensitive habitats and that critical levels can be exceeded close to emission sources.  This raises important questions as to how impacts and effects are assessed, given that to protect sensitive ecosystems the aim should be to drive deposition rates and concentrations down to below the critical loads and levels, but new plans or projects will generally take us in the other direction.  Other important questions are: when can we screen out impacts as being insignificant?  How do we judge when effects are significant?  How do we take account of in-combination impacts and effects?  How do we assess impacts that affect part of a SAC or SPA? How do we take account of site management practices that may affect impacts?  Then, once we identify that the integrity of a site will be adversely affected, how do we mitigate this?

The air quality specialists start the assessment process by modelling the impacts that will arise from the plans and projects both alone and in combination.  The sources range from agricultural activities that emit ammonia, such as intensive poultry farms that have localised impacts, through to emissions of both nitrogen oxides and ammonia from road traffic for which impacts are focused alongside the line of the road. The ecologists then use the information on impacts and determine whether they will significantly affect the integrity of the habitat.

In-combination impacts are proving especially challenging to include in the assessment procedure.  In an ideal world, the in-combination impacts will be addressed in detail during the development of local plans, which will essentially include all projects that might come forward.   These local plans will include measures to mitigate the in-combination impacts, such as is currently happening as part of the Epping Forest Local Plan.  This will mean that when a project comes along it will not need to address in-combination impacts, as this will have been done at the local plan stage.  The challenge is that not many local authorities have carried out detailed in-combination assessments, so it then becomes necessary for the assessment of a new project to also cover the in-combination impacts.

There are clearly many challenges both for air quality specialists and ecologists as we come to grips with the new challenges of assessing and protecting sensitive habitats.  The conference will explore many of these challenges and hopefully take us closer to better and more consistent practice in our assessments, and ultimately to better protection of our sensitive habitats.

Prof. Duncan Laxen

Associate of Air Quality Consultants.

Duncan Laxen is a Professor of Air Quality Management and Assessment and is currently Associate at Air Quality Consultants Ltd. Duncan’s area of expertise is in the assessment of ambient air quality. This includes modelling, monitoring and assessment of a wide range of pollutants and sources, including roads, shipping, railways, aircraft and industry. He has been closely involved in the development of air quality management in the UK.


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