IAQM Guidance: Why It Doesn’t Always Mean a Good Air Quality Assessment
When reviewing air quality assessments, it’s common to see statements such as:
“The assessment has been undertaken in accordance with IAQM guidance.”
And in many cases, that’s entirely appropriate. However, it’s important to recognise that:
Meeting IAQM guidance doesn’t automatically mean an assessment is good.
And this is where things can quietly go wrong.
What IAQM Guidance is Designed to do
IAQM guidance plays a vital role in the UK planning system. It helps to:
- provide a consistent framework for assessments
- support proportionate decision-making
- ensure a common approach across the industry
It is an essential reference point for consultants, planners and regulators alike. But it was never intended to be used as a rigid checklist.
Compliance is not the same as quality
Two assessments can both be described as “IAQM compliant”…
…and still arrive at very different conclusions.
This is because guidance does not remove the need for professional judgement. The quality of an air quality assessment depends not just on whether guidance has been followed, but how it has been applied.
What this Looks Like in Practice
This is often where the difference becomes clear. In practice, the difference between a compliant assessment and a good one is often subtle — but important. We regularly see examples where an assessment technically follows guidance, but the approach taken doesn’t fully reflect the site-specific context.
For example:
- background concentrations are taken directly from mapped data, despite local monitoring indicating higher levels
- detailed dispersion modelling is undertaken where a proportionate screening approach would have been sufficient
- standard assumptions are applied without considering whether they are representative of the development
In each of these cases, the assessment may be described as “IAQM compliant”, but the outcome is not as robust or representative as it could be.
By contrast, a well-judged assessment will:
- select the most appropriate data sources for the site
- apply guidance proportionately, rather than by default
- and clearly explain the reasoning behind key assumptions
It is this application of professional judgement that ultimately determines whether an assessment is simply compliant — or genuinely useful for decision-making.
What actually defines a good assessment?
A robust air quality assessment goes beyond compliance. It requires:
Proportionate scoping
Understanding what matters for the specific site and avoiding unnecessary complexity.
Realistic assumptions
Ensuring that inputs — such as traffic data, background concentrations, and future scenarios — reflect likely conditions.
Clear interpretation of results
Explaining what the outputs mean in practice, not just presenting them.
Professional judgement
Making informed decisions where guidance allows flexibility, particularly in areas such as:
- model verification
- receptor selection
- significance of effects
Why this matters for planning and design
Air quality assessments are not just technical exercises.
They play an important role in:
- informing design decisions
- identifying risks early
- supporting planning applications
- and ultimately protecting public health
If the assessment is not properly tailored to the site, there is a risk that:
- key issues are overlooked
- opportunities for better design are missed
- or unnecessary mitigation is introduced
Air Quality is More Than Modelling
There can sometimes be a perception that air quality assessment is primarily about running models.
In reality, modelling is just one part of the process.
The real value lies in understanding:
- what the results mean
- how they relate to the development
- and what actions, if any, are needed
A Proportionate, Judgement-led Approach
At Haze Environmental, we apply IAQM guidance as it is intended — as a framework to support proportionate, site-specific assessments.
This means:
- focusing on what is relevant
- applying professional judgement
- and providing clear, practical advice
Rather than simply demonstrating compliance, the aim is always to produce an assessment that is:
- robust
- understandable
- and genuinely useful for decision-making
Final thoughts
IAQM guidance is essential — but it is not a substitute for experience.
Two assessments can follow the same guidance and still lead to very different outcomes.
The difference is not whether the guidance has been followed — but how it has been applied.
And that is where experience, judgement, and a clear understanding of real-world impacts become critical.
Need a second opinion?
If you’re reviewing an air quality assessment or would like a sense check on an approach, we’re always happy to provide clear, independent advice.
About Haze Environmental
Haze Environmental is an independent air quality and odour consultancy, supporting planners, architects and developers across the UK to manage planning risk and deliver healthier places.
Our mission is to make a positive impact — for the clients we work with and for the environment we all share.
