Stack Sampling for Odour Emissions
Odour emissions can impact nearby communities when they are not effectively dispersed or controlled at source. Industrial processes often manage this risk using stacks, which provide a controlled release point for treated or untreated air.
What Is A Stack?
A stack is a vertical structure that releases air from industrial processes into the atmosphere. Industrial sites use them to manage the dispersion of emissions. By releasing air at height and at a controlled velocity, stacks reduce the likelihood of odours reaching nearby sensitive receptors. For example, homes, workplaces or public spaces.
In simple terms, a stack does not remove odour. It controls how and where the remaining emissions enter the atmosphere.
Key Functions of a Stack:
- Directs odour emissions away from ground level
- Improves dispersion through height and exit velocity
- Supports compliance with environmental permits
- Provides a controlled point for monitoring and sampling
Stack Design & Odour Dispersion
Stacks influence how emissions disperse after leaving an industrial process. Their primary purpose is to reduce the impact of odours on nearby sensitive receptors by promoting dilution in the atmosphere.
To achieve this, stack design must consider both process conditions and the surrounding environment.
| Design Factor | Reason |
|---|---|
| Height & Diameter | Influences how effectively emissions disperse before reaching ground-level receptors. |
| Location | Reduces exposure to nearby sensitive areas such as homes or workplaces. |
| Local Landscape | Nearby buildings, topography and meteorology can all affect dispersion behaviour. |
| Materials | Must withstand process temperatures and chemical characteristics of emissions. |
| Treatment Technologies | Stacks often sit downstream of treatment systems such as scrubbers, biofilters or carbon filters. However, in some cases, they may eliminate the need for treatment technologies altogether. |
Dispersion models can be very helpful tools during the design stage. These mathematical models can predict the behaviour of odour emissions from your proposed stack in different conditions.
Stack Sampling in Emissions Monitoring
Stack sampling is an odour sampling method that measures emissions directly from point sources. For example, stacks, flues and vents. It captures a representative sample and turns it into measurable data for laboratory analysis.
This process provides a direct link between an industrial activity and its emissions. Instead of estimating odour impact, stack sampling measures what actually leaves the system under real operating conditions.
How Stack Sampling Works
Stack sampling follows a structured step-by-step process. This helps ensure emissions data reflects real operating conditions at the time of measurement.
1. Accessing the Stack
Odour specialists access the emission point using safe systems and, where available, pre-installed sampling ports.
The initial stack design directly influences this stage. Well-positioned access points allow consistent, standardised sampling. Poor access design limits measurement capability and reduces data reliability.
For example, low-level stack sampling ports, as seen here, allow safe and efficient access.
2. Measuring Flow Conditions
The sampling team measures key physical parameters inside the stack before sampling, including gas velocity, temperature and moisture content.
These measurements define how emissions behave as they exit the stack.
3. Collecting the Sample
Sample collection follows recognised standards to ensure results remain suitable for laboratory analysis and regulatory use.
| Requirement | Further Reading |
|---|---|
| Odour Sampling Methodology | ↗ How to Collect & Prepare Odour Samples for Laboratory Testing |
| European Odour Standard | ↗ EN 13725:2022 Odour Measurement Standard |
| Stack Sampling Accreditation | ↗ MCERTS Accredited Personnel for Stack Sampling |
| Independent Accreditation | ↗ UKAS-Accreditation for Odour Sampling and Testing |
4. Laboratory Analysis
When samples reach the odour laboratory, they are analysed using dynamic olfactometry. Results typically include odour concentration (ouE/m³) and detection threshold, but can also include chemical analysis, intensity, characterisation and hedonic tone.
How Stack Sampling Data is Used
Stack sampling produces quantitative data that supports regulatory, technical and operational decisions.
| Typical Application | Purpose | Related Guide |
|---|---|---|
| Environmental Permit Compliance | Demonstrate the stack’s efficacy and compliance with emission limits. | ↗ How to Manage Emissions for Compliance |
| Planning Conditions | Support applications for new or expanded operations. | ↗ Odour Impact in Planning & Development |
| Odour Complaints | Validate odour emission sources. | ↗ Odour Complaints & How to Handle Them |
| Routine Odour Monitoring | Track odour emissions over time. | ↗ Odour Monitoring & Site Odour Assessment |
Speak to an Odour Specialist
Reliable stack sampling depends on appropriate stack design, standardised sampling methods and accredited laboratory analysis. Together, these ensure emissions data remains consistent, traceable and suitable for regulatory use.
Stack sampling supports environmental compliance, planning submissions and performance verification across a wide range of industries.
For advice or to arrange stack sampling, contact Silsoe Odours.
Call: 01525 860222
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Published May 2023. Last updated June 2026.
