Odour Dispersion Modelling

Odour Dispersion Modelling Using ADMS for Quantitative Receptor Predictions

Odour dispersion modelling produces quantitative predictions of odour concentration at receptors in European odour units (ouE/m3) for direct comparison against IAQM benchmarks. Modelling is run in ADMS 6 with building downwash, terrain and the appropriate fluctuations module to capture peak-to-mean behaviour that drives odour annoyance. Source terms are derived from olfactometry-tested ouE/s emission rates or from validated emission factors where direct measurement is not feasible. Outputs include 98th percentile contour plots and discrete receptor tables suitable for permit, planning and abatement design decisions.

Source Term Derivation

• EN 13725 dynamic olfactometry results for stacks, vents and area sources
• Wind tunnel or flux hood measurements for liquid surfaces and lagoons
• Validated emission factors for biofilters, AD, composting and waste transfer where direct sampling is impractical
• Treatment of variable emission rates (operating mode, batch peaks, abatement bypass)

Model Setup

• ADMS 6 with PRIME building downwash and terrain pre-processor where relevant
• Fluctuations module enabled to predict 98th percentile of hourly means
• Three to five years of MIDAS hourly met data from the closest representative station
• Discrete receptors at residential, amenity and ecological locations plus a Cartesian grid for contours

Outputs and Use

Reports present 98th percentile ouE/m3 at each receptor against the relevant IAQM benchmark (1.5, 3.0 or 6.0 ouE/m3 depending on offensiveness). Contour plots show predicted footprint for planning officers and EHOs. Sensitivity runs quantify the benefit of proposed abatement (e.g. % odour removal, scrubber addition) so design decisions are evidence-led rather than assumed.

Related Odour Modelling Services

ADMS odour modelling is the quantitative engine behind our IAQM-compliant odour impact assessment reports, with input data from EN 13725 olfactometry sampling. For multi-pollutant sites we also run broader ADMS air dispersion modelling. Modelling outputs commonly support EA Environmental Permit applications and variations.

Odour Dispersion Modelling for Planning

For planning applications, odour dispersion modelling quantifies whether a proposed odour source — food production, waste transfer, anaerobic digestion, composting, sewage treatment, kitchen extract — will cause odour annoyance at sensitive receptors. The IAQM benchmark of 1.5, 3.0 or 6.0 ouE/m3 (98th percentile of hourly means) is selected based on odour offensiveness, and modelled concentrations at residential, school and amenity receptors determine the significance conclusion. The same modelling supports the IAQM odour impact assessment submitted with the planning application and runs alongside the broader air quality assessment for planning.

Odour Dispersion Modelling for Environmental Permits

For environmental permits, odour modelling supports EA H4 Odour Management Plans and bespoke permit applications. It demonstrates that current or proposed abatement (biofilters, scrubbers, RTOs, activated carbon) reduces receptor-level concentrations below the IAQM benchmark and informs Odour Management Plan content. Modelling is also used in permit variations where capacity changes, new sources or community complaints require updated evidence. Outputs are written to integrate directly into the environmental permit application.

When Modelling Is Needed Alongside an Odour Assessment

A qualitative IAQM odour assessment (FIDOL-based) can be sufficient for low-risk sites with clear separation from receptors. Quantitative modelling becomes necessary when receptors are close, when complaints exist, when permit conditions require it, when abatement options need comparing, or when planning officers request quantitative evidence. A site odour survey often precedes modelling to confirm dominant sources and inform sampling priorities.

Odour Sources, Emission Rates and Receptor Sensitivity

Source types include point sources (stacks, biofilter outlets, scrubber discharges), area sources (lagoons, composting windrows, open tanks) and volume sources (buildings under negative pressure). Emission rates are derived from EN 13725 olfactometry on collected samples, wind tunnel or flux hood measurements for area sources, or validated emission factors at design stage. Receptor sensitivity is graded by land use — residential and schools attract the strictest 1.5 ouE/m3 benchmark for highly offensive odours, while industrial neighbours may use 6.0 ouE/m3. Kitchen extract odour assessments follow a related but separate methodology aligned to DW/172.

Odour Contours, Percentiles and Interpretation

Outputs are presented as 98th percentile ouE/m3 contour plots overlaid on the site and receptor map, plus discrete receptor tables. The 98th percentile of hourly means is used because odour annoyance is driven by short-duration peaks, not annual averages — this is the IAQM-recommended statistic and matches how complaints are generated. Sensitivity runs comparing existing and upgraded abatement quantify the receptor-level benefit of investment, which is often the deciding evidence for permit variations or planning approvals.

What Inputs Are Needed for Odour Modelling

• Site layout with source locations, building footprints and heights
• Source type and operational profile (continuous, batch, seasonal)
• Emission rates: EN 13725 olfactometry results where available, or design parameters
• Abatement details: type, design efficiency, bypass arrangements, maintenance regime
• Receptor list and any complaint history or local authority correspondence
• Met data station preference (we select the closest representative MIDAS station)