Screening vs Detailed Air Quality Assessment
Not every planning application needs a full detailed dispersion modelling study. A clear, proportionate screening assessment is often all that is required. Here is a plain-English guide to which you need, when and why.
Choosing the Right Level of Assessment
UK air quality assessments fall broadly into two tiers: a screening assessment (sometimes called a Stage 1 or Tier 1 assessment) and a detailed assessment (Stage 2 or Tier 2). Both are defined in the IAQM/EPUK 2017 guidance Land-Use Planning and Development Control: Planning for Air Quality, which is the de facto standard for planning-related air quality work in the UK and is referenced in NPPF paragraph 192 and the supporting Planning Practice Guidance.
A screening assessment is a proportionate, evidence-led check that applies the IAQM/EPUK criteria to your scheme: traffic generation thresholds (typically more than 100 two-way HGV trips/day or 500 LDV trips/day on roads within or near an AQMA), proximity to a busy road (the 10m and 200m receptor thresholds), the presence of new sensitive receptors, and any combustion plant on site. If all the criteria are clearly below the screening thresholds, a short narrative report concluding "not significant" is sufficient. If even one criterion is exceeded — or is borderline — a detailed assessment is needed.
A detailed assessment quantifies pollutant concentrations at specific receptors using dispersion modelling (ADMS-Roads is the UK industry standard for traffic), supported by background concentration data from DEFRA's PCM model, baseline monitoring where relevant, and a full IAQM 2017 significance evaluation. It is more involved and costs more, but it provides the robust, defensible evidence base that planning officers and environmental health teams will accept when the issue is real.
Malcolm Pounder CEnv MIAQM personally reviews every assessment we issue. We do not over-engineer screening jobs, and we do not under-deliver detailed ones — the level of work is matched to what the planning authority actually needs.
Screening vs Detailed — Side by Side
The short version. Both follow the same IAQM/EPUK 2017 framework; what differs is the depth of analysis.
| Screening Assessment | Detailed Assessment | |
|---|---|---|
| When needed | Small to medium schemes; traffic generation below IAQM thresholds; no on-site combustion; not within an AQMA. | Schemes exceeding any IAQM trip-generation threshold; within or close to an AQMA; CHP/biomass/gas plant on site; LPA specifically requests detailed work. |
| Cost | Lower — a fraction of a detailed assessment. Fixed-fee, often single-figure days of work. | Higher — reflects dispersion modelling, traffic data processing, receptor identification and full significance evaluation. |
| Timescale | Typically 3–5 working days from instruction. | Typically 2–4 weeks; longer if baseline monitoring or EIA-scale work is involved. |
| Methodology | Application of IAQM/EPUK 2017 screening criteria, DEFRA background mapping check, AQMA proximity review, sensitive-receptor identification. | ADMS-Roads or AERMOD dispersion modelling, baseline NO2 diffusion-tube monitoring (where required), full receptor network, IAQM 2017 significance criteria, mitigation appraisal. |
| Deliverable | Concise screening report (typically 10–20 pages) with conclusion that effects are "not significant". | Full detailed assessment report (typically 40–80 pages) with figures, modelled contours, receptor tables, significance evaluation and mitigation. |
| Status with LPA | Normally accepted where IAQM thresholds clearly not exceeded; may be challenged in borderline cases. | The robust technical evidence base; expected for major applications, EIA developments, and any scheme within an AQMA. |
Both Tiers, Done Properly
We are happy to start with screening and only scale up to detailed if the criteria actually require it.
IAQM/EPUK Screening Assessment
A clear, concise report applying the IAQM/EPUK 2017 criteria to your scheme, including AADT and HGV trip generation, AQMA proximity, dwelling counts within the 10m and 200m road thresholds, and background concentration check. Designed to be accepted by the LPA without further work where the criteria are clearly met.
Detailed Dispersion Modelling
Full ADMS-Roads (or AERMOD for industrial sources) dispersion modelling, calibrated against local monitoring data, with predicted NO2, PM10 and PM2.5 concentrations at all sensitive receptors and a full IAQM 2017 significance evaluation. Suitable for major and EIA-scale schemes.
Pre-Application Triage
If you genuinely don't know which level of assessment your scheme needs, send us the basic details and we'll triage it for free. A 15-minute phone call often saves a developer from commissioning a detailed assessment that wasn't required — or, conversely, from submitting a screening report that the LPA will reject.
Screening-to-Detailed Upgrade
Where a screening exercise reveals that one or more thresholds is exceeded, we scale up to a detailed assessment using the data and site understanding already gathered. The screening fee is credited towards the detailed fee, so clients are never paying twice for the same work.
When Each Tier Typically Applies
These are common scheme types and what level of assessment usually applies. Every project is different and we will confirm in writing.
The IAQM/EPUK thresholds are the starting point, but local validation lists and AQAP/Air Quality Action Plan areas can add to the requirement.
- 5–10 dwellings, rural road — Screening
- 20–50 dwellings, suburban — Screening
- 50+ dwellings near AQMA — Detailed
- Major housing scheme — Detailed
- Logistics/warehouse with HGVs — Detailed
- Small office, non-AQMA — Screening
- Care home/school near road — Detailed
- EIA-screening required — Detailed
Frequently Asked Questions
What is a screening air quality assessment?
A screening air quality assessment is a proportionate, evidence-led check carried out using the IAQM/EPUK 2017 criteria to determine whether a development is likely to have a significant air quality effect. It looks at the scale of traffic generation, proximity to AQMAs, distance to busy roads (typically the 10m/200m thresholds), and the number of new residential dwellings or sensitive receptors. If all criteria are clearly below the screening thresholds, a short report concluding "not significant" is usually sufficient for planning.
When is a detailed air quality assessment needed?
A detailed assessment is required when screening criteria are exceeded — for example: the development generates more than 100 two-way HGV trips/day or 500 LDV trips/day on a road within an AQMA; the development sits within or close to an existing AQMA; the site includes more than around 10 dwellings within 10m, or larger numbers within 200m, of a busy road; or the LPA specifically requests detailed modelling. In these cases dispersion modelling (typically ADMS-Roads) and significance assessment against IAQM 2017 criteria are needed.
What is the cost difference between screening and detailed?
A screening assessment is typically a fraction of the cost of a detailed assessment because it does not involve dispersion modelling, baseline monitoring or a wide receptor network. Detailed assessments cost more because they require ADMS-Roads or AERMOD modelling, traffic data processing, background concentration mapping, receptor identification and a full IAQM significance evaluation. We provide fixed-fee quotes for both — get in touch for figures specific to your project.
Can I upgrade from a screening to a detailed assessment?
Yes. We often start with a screening exercise and, if the criteria are exceeded or the LPA requests further work, we scale up to a detailed assessment using the data already gathered. Starting with screening avoids paying for a detailed report you may not need, and we credit the screening work towards the detailed fee where it is the same project.
Who decides whether screening or detailed is required?
Ultimately the local planning authority (usually via the environmental health officer) decides whether the air quality evidence is acceptable. However the IAQM/EPUK 2017 guidance sets out objective thresholds that we apply, and a robust screening assessment that clearly demonstrates the criteria are not exceeded is normally accepted without challenge. Where the LPA has bespoke local validation requirements, we tailor the assessment to suit.