In the eyes of the law, odour is air pollution
Act No. 201/2012 Coll., on Air Protection also treats a substance that causes odour nuisance as a pollutant.
Odour is therefore not merely a neighbourhood or subjective problem.
When permitting stationary sources, air protection authorities must take the risk of odour nuisance into account, and the permit for a specific operation may set technical and operating conditions aimed precisely at limiting it.
Typical examples include covering the technology, extraction, a biofilter, an air scrubber, filtration equipment, cooling of raw materials, closed handling or organisational measures.
Is there a general limit for odour?
Current Czech legislation does not set a single universal ambient (immission) limit of the type:
"no more than X odour units may be exceeded at a residential building".
This matters because odour is not assessed as simply as, for example, the concentration of certain pollutants that have an ambient limit.
The assessment therefore works with a combination of data on the source, the character of the odour, the operating mode, the distance from nearby buildings, meteorological conditions, technical measures and, where appropriate, measurement or modelling.
In practice: Even a very unpleasant odour does not automatically mean that a specific numerical limit has been breached. For the operator, however, it is essential to demonstrate that the source is operated in accordance with the permit and that the stipulated or technically appropriate measures to limit odour are in use.
The old rule "at least 20 people must complain" no longer applies
In practice, one still hears that an authority will only start dealing with odour once more than 20 people complain.
This rule originated in the old Decree No. 362/2006 Coll.
The current legal framework for air protection is not based on any such number of complainants.
A single specific and well-described complaint can therefore be a reason for an authority or the inspectorate to start looking into the situation.
The operator should not argue that "only one neighbour is complaining".
What to do first when a complaint arrives
First, find out as precisely as possible when and under what conditions the odour occurred.
It is useful to know the date, the time, the approximate duration, where the complaint came from and the character of the odour.
This information then needs to be compared with the actual operation.
Was production running at the time? Was the technology being cleaned? Was waste being removed? Was a storage tank being opened? Was loading under way? Was the biofilter or the extraction switched off? Had a raw material been changed?
Meteorological conditions are also very important, above all wind direction and speed.
A simple log of complaints and operating events can be surprisingly effective. After several events it often becomes clear that the odour is linked to one specific operation.
Look for the source of the odour inside the facility first
Odour does not necessarily leave only through the main stack.
It often arises as fugitive emissions from places that were originally not considered a significant source at all.
Typical problem areas include open containers, storage of raw materials or waste, sumps, drains, loading, process baths, open doors, an insufficiently extracted part of a line or leaking pipework.
At some facilities the main vent is well treated, but odour escapes through the hall via doors or roof lights.
It therefore makes sense, before any measurement, to walk through the technology from the incoming raw materials to the waste and to identify the places where odorous substances may arise and escape.
Check the operating permit and the operating rules
If the source is a listed stationary source, one of the first documents to consult should be the valid operating permit.
The regional authority may set in the permit, for example, technical operating conditions, operating parameters or an obligation to use specific equipment for reducing emissions.
For some sources, conditions are also set directly by Decree No. 415/2012 Coll..
For example, for selected food-processing plants, leather processing, paper mills, packaging plants and other technologies, measures to prevent or reduce emissions of odour-nuisance substances are expressly required.
When a complaint arrives, it is therefore necessary to verify not only whether the equipment is running, but whether it is running in a way that corresponds to the permit and the operating rules.
When it makes sense to measure odorous substances
The concentration of odorous substances can be determined by dynamic olfactometry in accordance with ČSN EN 13725.
With this method, a sample of waste gas is taken and the concentration of odorous substances is then determined using an olfactometer and a panel of assessors.
The result is expressed in European odour units ouE/m³.
Such measurement can be very useful, for example, for:
- determining the emissions of a specific vent,
- comparing the situation before and after the installation of a biofilter or other equipment,
- establishing the effectiveness of the technology in limiting odour,
- obtaining input data for further expert assessment.
The measurement must, however, be carried out under representative operating conditions. There is no point in measuring while the source is running at minimum output if the complaints occur at maximum production or during a specific technological operation.
Measurement at the stack alone may not resolve a neighbour's complaint
This is one of the most important points.
Dynamic olfactometry characterises the emission of odorous substances from the source well, but on its own it may not say how often and how intensely people several hundred metres away will perceive the odour.
Between the stack and the residential building, the height of the vent, the volume of waste gas, the terrain, buildings and, above all, meteorological conditions all come into play.
That is why it is sometimes necessary to combine source measurement with other information or with a modelling assessment.
Conversely, in another case olfactometry may not be the first step at all. If it turns out that the odour escapes through open doors during waste handling, it may be more effective to remove the obvious cause first.
In practice: Do not order odour measurement automatically right after the first complaint. First we need to know what problem the measurement is supposed to solve.
Minimum distances are now also being addressed for some sources
From 2026, Czech legislation also applies the concept of minimum distances to selected sources.
Under Section 12a of the Air Protection Act and Annex No. 20 to Decree No. 415/2012 Coll., minimum distances are used when siting certain new sources in relation to residential and other specified areas.
This applies, for example, to certain landfills, composting plants, wastewater treatment plants, production of composites with styrene, rubber processing, or extraction and refining of oils and fats.
The purpose is to limit future conflicts with residential development before the operation comes into being.
For an existing operation facing an odour complaint, however, distance alone will not solve the problem. It is necessary to look for the actual source and a way of limiting emissions.
Which odour-control measures tend to be effective
The right measure depends on the technology and on the chemical character of the odorous substances.
In some cases enclosing the technology and extraction will help; in others a biofilter, a wet scrubber, adsorption on activated carbon or other equipment.
Simple operating measures can also be very effective: shorter storage time for odorous materials, closed containers, cooling of raw materials, limiting open handling or regular cleaning.
It is important to first establish where the odour actually comes from.
There is no point in installing expensive equipment on the main vent if most of the odour escapes elsewhere.
Beware of the civil-law dimension as well
Odour is not dealt with only under the Air Protection Act.
Section 1013 of the Civil Code classes odour among the so-called immissions.
An owner is to refrain from conduct that causes odour to enter a neighbouring plot to an extent disproportionate to local conditions and substantially restricting its ordinary use.
This means that even compliance with the emission permit is not a reason to automatically ignore a complaint.
It is in the operator's interest to have documented that it has looked into the problem and adopted reasonable technical or organisational measures.
What you can send us for assessment
If you are dealing with an odour complaint, send us the valid operating permit and operating rules, a brief description of the technology, the raw materials used, the vents and the air-cleaning equipment.
Information on when the complaints occur, where they come from and what operating mode was running at the time is also very useful.
On the basis of these documents we can assess the likely sources of odour and propose whether an inspection of the technology, measurement of odorous substances, measurement of specific chemical substances or another expert assessment makes sense.
The aim is not just to obtain a measurement report. The aim is to find the cause of the odour and a way to limit it.
You can find more information on the NATURCHEM services page.
Brief summary
Under the Air Protection Act, odour is relevant pollution, but for the general outdoor environment there is no single universal numerical limit for odorous substances.
When a complaint arrives, the most important thing is to link the time and place of the odour with the actual operation of the technology and with meteorological conditions.
The operating permit, the operating rules, the function of the extraction and the emission-reduction equipment must then be checked.
Dynamic olfactometry can help determine the emission of odorous substances from the source, but it is not automatically the answer to every complaint from neighbours.
The best results are usually achieved by a combination of operating data, an inspection of the technology and targeted measurement.
Factual basis of the article
The fundamental regulation is Act No. 201/2012 Coll., on Air Protection. The Act defines as a pollutant also a substance that causes odour nuisance, and requires air protection authorities to take the risks of odour nuisance into account when permitting sources.
Section 12 of the Act governs the conditions of the operating permit and makes it possible to set technical and operating conditions for the source.
Section 12a governs minimum distances of certain sources from specified areas.
Specific technical conditions for selected sources and, from 2026, also minimum distances are set by Decree No. 415/2012 Coll..
For determining the concentration of odorous substances from stationary sources, ČSN EN 13725 is used – Stationary source emissions – Determination of odour concentration by dynamic olfactometry and odour emission rate from stationary sources.
The protection of neighbours against odour immissions is also governed by Section 1013 of Act No. 89/2012 Coll., the Civil Code.