Odour Monitoring: How To Measure Smell

Odour may sound difficult to quantify; after all, it’s invisible, subjective and often influenced by environmental conditions. However, in certain industries such as waste management, food processing and agriculture, knowing how to monitor and measure smells is essential. Monitoring and removing odour using methods like odour neutralising can help prevent nuisance complaints, stay compliant with regulations and maintain public trust.

This guide covers the basics of odour thresholds, the science behind smells and the tools used to monitor and control odours effectively.

What is the odour threshold?

Put simply, the odour threshold is the lowest concentration of an odorous substance that the average person can detect. It’s measured in European odour units per cubic metre of air (ouE m³) which represents how many times a sample of the odour is diluted with odourless air before it’s no longer detectable by a panel of trained observers.

The odour threshold varies depending on the substance. Some substances such as hydrogen sulphide (rotten egg smell) have a very low odour threshold, meaning it can be detected even in tiny amounts, whereas others need a higher concentration to be smelled. Odour thresholds will also differ from person to person depending on their age, gender and health so having a diverse panel of observers is important for accurate measurement.

What are odour molecules and how do they affect perception?

Odour molecules are tiny, airborne chemical compounds that are released from substances like waste, chemicals, food or biological materials. These molecules travel through the air and are detected by the olfactory receptors in the human nose. When they bind to these receptors, the brain interprets the signal as a specific smell.

Different molecules trigger different sensory responses. Some are perceived as pleasant (like citrus or vanilla) while others, such as those from sewage or rotting waste, are unpleasant or even offensive. Perception is subjective; what smells mild to one person might be overpowering to another, which is why managing industrial and environmental odours can be so complex.

How to measure odour in industrial and environmental settings

Measuring odour is a vital part of environmental compliance and quality control in industrial operations. There are two key methods used to assess odour emissions:

• Dynamic olfactometry – Dynamic olfactometry measures odour concentration using the human sense of smell. Odorous air is collected in sealed bags at the emissions source and in a lab, those samples are diluted with neutral air and presented to a panel via an olfactometer. Panellists sniff the air and press a button when they detect an odour. The point at which the odour is first noticed determines the odour concentration.
• Chemical analysis with GC-MS – This method identifies and quantifies the specific chemical compounds responsible for odours using instrumental analysis. Odorous air samples are analysed using Gas Chromatography – Mass Spectrometry (GC-MS). GC separates compounds by their properties and MS then identifies them by generating a mass spectrum. The result is a chromatogram, showing peaks for each substance.

What is odour measurement equipment?

To accurately sample and measure odour, you’ll need specific measurement equipment, such as:

• Olfactometers – instrument used to detect and measure odour concentration.
• Odour sampling bags – Used to capture air samples on-site for later analysis.
• Electronic noses – Use sensors to detect the chemical composition of specific substances and gases.
• Sniffing sticks – Used to examine the panel’s ability to recognise certain scents.
• Flux chambers – Enclosures placed over a surface to capture emissions from soil, compost, or other materials.

How to monitor odours and track changes over time

If you carry out odorous activities, such as waste management or sludge treatment, you will need to produce an Odour Management Plan (OMP). This is a document which outlines how an organisation will monitor, manage and reduce odour emissions and is a requirement for many sites with environmental permits. You can refer to the Government’s official guidance for exact details of what your plan must include.

A key part of your OMP is how you will monitor odour emissions, so you can check how effective your control measures are. There are a number of ways to track changes in odour, such as:

• Sniff testing.
• Meteorological monitoring.
• Odour diaries and community surveys.
• Complaints monitoring.
• Surrogate chemicals.
• Process parameters.
• Emissions monitoring.

It’s important to consistently monitor odour emissions and maintain logs and records. Your OMP should include details of your methods and should be reviewed regularly and updated if there are any changes to your processes.

How to remove odour

Removing odour effectively starts with understanding its source, whether it’s a processing activity, a waste issue or something environmental. Once identified, odour can be addressed in several ways:

• Manage ventilation appropriately.
• Contain the odour by covering equipment and sealing ducts.
• Regularly clean equipment to prevent the build-up of odour-causing residue.
• Install an effective extraction system.
• Use an odour neutraliser or eliminator.

At Probe Industries, we offer industry-leading odour neutralisers, such as AiroPure® and AiroNaut™. These work by altering the molecular structure of the odour, completely eliminating the smell rather than simply masking it. Suitable for a wide range of industrial and commercial settings, our solutions help you stay compliant with regulations and maintain a more pleasant environment for both workers and nearby communities.