Integrated environmental authorisations, odour emissions limits in activities with a history of odour conflicts

When establishing the framework for a potentially odour emitting activity with a prior history of complaints, it is necessary to objectively evaluate both the measures designed to reduce odour emissions and the limits that will be set for an Integrated Environmental Authorisation.

Díaz Jiménez C., Montalbán Núñez F., Estivill Baena G.

Keywords: Integrated environmental authorisation, odour emissions limits, odour complaints, olfactometry.

Acronims: POEA, Potential Odour Emitting Activity; POACA, Potential Odour Annoyance Causing Activity; OACA, Odour Annoyance Causing Activity, EIA, environmental impact assessment.



    When establishing the framework for a potentially odour emitting activity with a prior history of complaints, it is necessary to objectively evaluate both the measures designed to reduce odour emissions and the limits that will be set for an Integrated Environmental Authorisation. In the case of odour emissions, there are different limits set by different regulations. This article will discuss and analyse the need for limits on odour emissions, using several practical examples.



1. Introduction

    The general progress of society implies the management of natural resources to produce goods that generate added value. Society´s growth has been matched by a corresponding increase in industrial odour emissions and their impact on nearby populations.

    In this sense, there isn't any Spanish regulation that addresses the problem of odour emissions in a concrete and explicit fashion.

    At the same time, various regulations have been developed at an industrial level for the regulation of various types of emissions activities, the most important example of this has been the Directive 96/61/EC, now replaced by the D 2010/75/EU.

    The concept of Best Available Techniques (BATs) has meant a change for the orientation of environmental management work.

    Using the Best Available Technology Reference Documents (BREF documents) the value ranges of the emission value limits of these parameters have also been established. All of this work has resulted in a greater array of tools for technicians of environmental agencies who are tasked with regulating an activity that has a history of odour conflicts.

    When working with chemical compounds, the emission of substances can be limited for activities. For example, in Spain hydrogen sulphide (H2S) generally has an emissions limit of 10 mg/Nm3.

    However, when working with odour emissions, setting an emissions limit becomes an even more complicated task. Two basic principles are established in odour management:

1. In the case of chemical substance emissions, the fact that there are no receptors does not mean that emissions are zero. In contrast, odour emissions from an activity are zero if there are no receptors.

2. Even if there are receptors that detect the emissions from a particular activity, if there is no annoyance caused by these emissions, there is no need to limit the odour emissions from thatactivity.

    Therefore, instead of discussing Potential Odour Emitting Activities (POEAs) as one would with Potential Atmospheric Polluting Activities (APCAs based on the acronym in Spanish) of Decree 833/1975, a somewhat different concept must be used. In this case it is preferable to refer to Potential Odour Annoyance Causing Activities (POACAs) and when there have been a confirmed set of complaints we can begin to speak of Odour Annoyance Causing Activities (OACAs).

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Figure 1. Diagram of activity types.

    In these adjustment processes, the OACAs subject to Environmental Impact Assessment (EIA) with a history of odour conflicts and whose resolution includes, among other things, an atmospheric emissions authorisation, should modify their gas treatment facilities for new odour emission values, which did not exist when the activity began.

    This article aims to clarify the framework for both technicians of environmental agencies in Spain and for industrial activities in cases where valid complaints about odours have occurred.


2. Work method

    When odour conflicts occur, it is very important to first identify the problem with precision. In this process that involves the identification of responsibilities, it is essential to establish transparency and dialogue between the different parties to the conflict.


Table 3: Precision in the resolution of conflicts. (Hammerbacher based on Fietkau, WZB, 2000).




Conflict of interests

The conflict is perceived correctly.

Example: bad odours

Solution or compromise

Latent conflict

A pre-existing conflict, which expands.

Ex: historical events


Conflict assigned incorrectly

There is a conflict between the wrong parties.

Ex. Residents and company A instead of company B.


Conflict defined incorrectly

The parties discuss different things.

Ex. Health risks instead of odour emissions


Conflict of perceptions

The conflict depends on circumstances that are not perceived. Ex. Other odour emitters


Apparent conflict

The conflict stems from misunderstandings/ misperceptions. Ex. Prefer odours on the weekend



    Once the conflict is correctly identified, the next step is to reach a solution or compromise which in many cases means greater regulation of odour emissions from the activity.

    If an OACA performs a modelling of emissions, they will have a field of work defined for establishing objectives for a set time period. Any effort that moves the OACA towards the improvement of their emissions will be welcomed by the affected populations, provided that it is not too late.

    In this case, each OACA will have their own unique emissions limit, independent of other activities in the same sector.

    Let us suppose that the problem has been identified and the objectives have been established, and work begins with the activity. Let us also suppose that as a first step, a local extraction of the most problematic processes has been identified for implementation. In this way, we collect the odorous gases of a process in an OACA and send them through the burner of a boiler as combustion air (Figure 2).

    Even if the residence time in the boiler is not very long, the temperature is hot enough to oxidise the organic compounds responsible for the odour (heading IPTS, 2003). In this case it makes sense to limit emissions for both the common parameters (NOx, SO2, CO, etc.), as well as of the odour concentration.

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Figure 2. Process schematic for boiler gas treatment and parameters for gas measurement.

    The following table illustrates a possible example for an Integrated Environmental Authorisation (EIA) of an OACA, where a steam boiler is fuelled by natural gas, and whose combustion air is used to treat odorous gases.




value limit


% O2


Suspended particulate matter (SPM)


mg/Nm 3


On dry basis





CO (carbon monoxide)


Odour concentration


ouE/m 3

Reference flow

On wet basis

6,000 m3/h

    In this case, it is reasonable to limit both the concentration of the odour and the rest of the emissions parameters typical for boilers.

    However, using a parallel example; if the aim is to limit the emissions of a thermal oxidiser which runs on natural gas, it is not necessary to limit parameters such as NOx, if the objective is just to treat odour emissions.

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Figure 3. Process schematic for gas treatment in thermal oxidiser and parameters for gas measurement.

    In fact, the higher the temperature in the thermal oxidiser chamber, the more the volatile organic compounds responsible for the odour will be destroyed, while the NOx emissions will also be greater. If this parameter were limited, one would risk having to lower the temperature in the chamber which would affect the degree of odour treatment.

    In the following table a typical example of how to limit a thermal oxidation in an EIA is illustrated.




value limit


Reference flow


Odour concentration


ouE/m 3

20,000 m3/h

On wet basis

    It is evident that this type of limitation makes things very difficult for companies that manufacture odour treatment elements, as a chemical compound limit is no longer required (not even a compound mixture).

    In any case, the limit values reflected in previous tables limits should be established after the prior analysis of the results produced by a dispersion model.

    Is it possible to limit the concentration of odour in an OACA immission? Let us suppose that a suitable dispersion model calculates that the isopleth of odour concentration of 3uoE/m3 at the 98th percentile of annual hours is outside of a given population. This line usually refers to an average time of the maximum concentration at ground level.

    One might think that it would be necessary to limit the immission of the activity that is subject to EIA, in a way that with a given frequency (for example once every 3 years) the management of odour emissions is established. This reasoning is similar to that which would be carried out, for example, for the management of emissions particles of an activity. Nevertheless, this does not make sense if there are no changes in processes or their emissions, since the baseline data of the dispersion model will not have changed and the result will be exactly the same.

    In addition, it is difficult to measure immision odour concentration in hourly averages.


3. Conclusions

    Management of an odour conflict is not simple and requires constant and fluid communication, and complete transparency between the parties.

    The obligation of the environmental agency is to watch over the state of the environment of its citizens, even when there is no specific legislation on the matter.

    The obligation of a company is its economic growth.

    These two objectives should not be seen as incompatible, but as complementary; therefore a good odour emissions management in the environment is based not only on the achievement of odour emissions values, but also a communications strategy for the OACAs regarding the strategies employed to decrease odour emissions and the estimated time periods for the implementation of corrective measures.


4. References

BOE 157 (2002) . Ley 16/2002 de 1 de julio de Prevención y Control integrados de la Contaminación (IPPC).
BOE 1643 (2011) . Real Decreto 100/2011, de 28 de enero, por el que se actualiza el catálogo de actividades potencialmente contaminadoras de la atmósfera y se establecen las disposiciones básicas para su aplicación.
BOE 1645 (2011) . Real Decreto 102/2011, de 28 de enero, relativo a la mejora de la calidad del aire
Díaz Jiménez, C. (2009) The Fascinating Study of the Peak to Mean Ratio (date consulted: 07/07/2012).
DOCE 1996 . Council Directive 96/61/EC of 24 September 1996 concerning integrated pollution prevention and control
Directive 2008/1/EC of the European Parliament and of the Council of 15 January 2008 concerning integrated pollution prevention and control (Codified version)
Hammerbacher R. (2011):Das Lösungspotenzial von Nachbarschaftsdialogen bei Geruchs-konflikten – am Fallbeispiel eines Industriegebiets mit einer hohen Anzahlvon Geruchsquellen. In: VDI Wissensforum GmbH (Hrsg.): Gerüche in der Umwelt. VDI-Berichte 2141, S. 189–197.
IPTS, IPPC, Reference Document on Best Available Techniques in the Slaughterhouses and Animal By-products Industries. May 2005
IPTS, IPPC, Reference Document on Best Available Techniques in Large Volume Organic Chemical Industry. February 2003
IPTS, IPPC, Reference Document on Best Available Techniques in the Slaughterhouses and Animal By-products Industries. May 2005 



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