The legal system for the assessment of odours in ambient air is laid down in the Guideline on Odour in Ambient Air - GOAA. In several studies, the connection between the odour pollution in residential areas expressed as odour frequencies per year and the associated degree of annoyance of residents was investigated. The GOAA provides the legal framework in licensing and monitoring procedures for all types of installations.
This legal framework is linked with the measurement methods for odour emissions at the source (olfactometry) and for odours in the ambient air (field inspection with grid measurements) as well as with a dispersion model for calculating recognisable odours in ambient air. In the GOAA, a scientifically based exposure-impact relationship is translated into limit values for odours in ambient air that also take into account differences in the annoyance potential of different odours types. In this paper, a brief overview of the results of the various investigations is given.
Dr. Ralf Both*, Kathrin Kwiatkowski
North Rhine Westphalian State Agency for Nature, Environment and Consumer Protection, Leibnizstr. 10, 45610 Recklinghausen, Germany. *
Competing interests: The author has declared that no competing interests exist.
Academic editor: Carlos N. Diaz
Content quality: This paper has been peer-reviewed by at least two reviewers. See scientific committee here.
Citation: Dr. Ralf Both, Kathrin Kwiatkowski. Limit values for odour in ambient air – A legal system applied all over Germany. 9th IWA Odour& VOC/Air Emission Conference, Bilbao, Spain, www.olores.org.
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Keyword: odour measurement, odour assessment, .annoyance, nuisance, odour regulation.
The legal system for the assessment of odours in ambient air is laid down in the Guideline on Odour in Ambient Air - GOAA. In several studies, the connection between the odour pollution in residential areas expressed as odour frequencies per year and the associated degree of annoyance of residents was investigated. The GOAA provides the legal framework in licensing and monitoring procedures for all types of installations. This legal framework is linked with the measurement methods for odour emissions at the source (olfactometry) and for odours in the ambient air (field inspection with grid measurements) as well as with a dispersion model for calculating recognisable odours in ambient air. In the GOAA, a scientifically based exposure-impact relationship is translated into limit values for odours in ambient air that also take into account differences in the annoyance potential of different odours types. In this paper, a brief overview of the results of the various investigations is given. One focus is on the way limit values are derived. The practical application of the GOAA is shown on the basis of some individual cases.
North-Rhine Westphalia (NRW) is a very industrialised and crowded part of Germany. Nowadays, more than 17 Million people living here on 34000 km2. Industrial and residential areas are very close. Because of a government decree in NRW in the eighties, the responsible authorities had to deal with odours caused by plants. Nevertheless, the regulation given in the government decree in NRW did not guarantee a consistent and comparable assessment. The limit values consisted of a free combination of different mean hourly odour concentrations and different odour exposure levels given as an odour frequency per year. The possible combinations to generate a limit value in an individual case was great and consequently, the equal treatment of plant operators during permitting or of complaints of the neighbourhood was not ensured. Furthermore, the regulation was not based on scientific investigations but more or less on the experience and the opinion of the people involved in drafting the decree.
One of the first expert reports on odour exposure was in the surrounding of a refinery causing many complaints. Because of many fugitive sources and their not quantifiable emissions, it was obvious that only doing dispersion modelling was not sufficient. There was a strong need to investigate the actual odour exposure in the residential areas to have a substantiated basis for odour assessment. This was the starting point of the development of a more sophisticated odour regulation system.
2. Objectives of regulation
In the Federal Immission Control Act (Bundes-Immisionsschutzgesetz, BImSchG) odours are treated as an air pollution (immission), which is liable to cause a considerable nuisance (Article 3 BImSchG). It is the obligation of operators of installations subject to licensing to avoid considerable nuisances (Article 5 BImSchG). Against this background, the most important question in legal terms is: What makes a nuisance a considerable nuisance?
The scientific challenge was to find a sound exposure-impact relationship, which could be the basis for a substantiated regulatory system. There was an urgent need to establish methods, on the one hand, for the standardised and reproducible measurement of odour exposure and, on the other hand, for measuring and assessing odour nuisance to residents, even if this method is only used to develop an exposure-impact relationship.
3. Development of methods
In Germany in the eighties, olfactometry was already established. However, the results measured by different laboratories were not comparable even if they applied VDI 3881 Part 1:1986, which was withdrawn in 2003. EN 13725 solves this problem in 2003.
In Germany, a new method was developed to measure odour exposure directly in residential areas focusing on the odour frequency of recognisable odours. In investigations were undertaken to find out (among others)
- how long a measuring interval (10 up to 60 minutes) should last,
- how odour should be registered (continuously or clocked),
- how often odour should be measured during half or a whole year and
- what criteria should be taken for the existence of odour (real time or odour hour).
In 1993 VDI 3940 “Determination of Odorants in Ambient Air by Field Inspections” was published and revised in 2006 (VDI 3940 Part 1 “Field inspection with grid measurements”). VDI 3940 Part 1 is nowadays available on European level as EN 16841 Part 1:2016.
By the way, methods have been developed to detect odour intensity and hedonic tone in conjunction with grid measurements (VDI 3940 Part 3), and to detect the annoyance potential (VDI 3940 Part 4). Kwiatkowski presents an example for the use of polarity profiles at this conference.
Using grid measurements, a new problem appears. How could recognisable be calculated by dispersion modelling? The dispersion model AUSTAL2000, which is a Lagrangian particle model (VDI 3945 Part 3; Janicke and Janicke, 2007) solves that problem.
For the measurement of the annoyance degree of resident face-to-face interview according to VDI 3883 Part 1 “Assessment of odour annoyance – Questionnaires” were used. The findings during the investigations led to a revised version of this guideline in 2015.
4. Development of limit values
Since the late eighties, several investigations were carried out in Germany to examine the exposure-impact relationship, the relationship between the odour exposure of residents and the related annoyance degree. The odour exposure was determined as odour frequency in ambient air according to guideline VDI 3940 Part 1:2006, which is the precursor of EN 16841 Part 1:2016. Odour annoyance was assessed according to VDI 3883 Part 1 by face-to-face interviews with residents.
In 1993, the outcome of these results led to the first version of the German Guideline on Odour in Ambient Air - GOAA including limit values for odours in ambient air. In 1998, a project started to assess the effect of hedonic tone on the annoyance potential of odours caused by industrial installations. In 2002, a German wide project on the annoyance potential of odours caused by livestock farming was initiated. The annoyance degree of residents living around animal farms and their odour exposure was assessed with the same methods already used before.
In all these investigations, the results show a statistically significant correlation between odour exposure in terms of odour hour frequencies and odour annoyance. It was possible to clearly distinguish between “not annoyed”, “moderately annoyed” and “seriously annoyed” (Sucker et al, 2008a, Sucker et al. 2008b). For the derivation of limit values, the percentage of seriously annoyed people was correlated with the odour exposure (odour hour frequency per year) for the area (assessment square) where they live (see Figure 1).
Figure 1: Derivation of limit values
In order to generate a limit value, it was decided by convention to allow not more than 10% seriously annoyed residents. From this criterion and in conjunction with the upper confidence level for unpleasant/neutral odours, an odour frequency of approx. 10 % results. This led to a limit value of 0.10 in terms of relative frequencies. Table 1 shows the limit values of the GOAA.
Table 1: Limit values for different area utilization
In Germany, the population's entitlement to odour protection depends on the area utilization in which they live. A village comprises by law dwelling and farms. The same could be the case in commercial and industrial areas. To account for this coexistence, the GOAA defines a higher limit value for odours in these areas.
Figure 2 shows the results for livestock odours in comparison to industrial odours. The results show clearly that with methods given in the GOAA the effect of odours on residents caused by plants can be assessed. It is not necessary to examine the annoyance degree directly by face-to face interviews in every individual case.
Figure 2: Correlation between the percentage of seriously annoyed residents and the odour frequency in their living area for different odours
For industrial odours based on the results found, it is possible to distinguish between unpleasant/neutral odours and pleasant odours (see Figure 2). To decide whether an odour is clearly perceived as pleasant, the method of polarity profiles according to VDI 3940 Part 4 is used, as Kwiatkowski presents at this conference. In 2004 in the GOAA, a bonus factor for definitely pleasant odours (0.5) was incorporated.
For livestock odours, the results show that the annoyance potential of poultry odour is higher in comparison to industrial odours and that the annoyance potential of pig odour is lower and fewest for cattle odour (Sucker et al. 2006). Weighting factors representing the annoyance potential of different animal species are included in the GOAA in 2008 (see Table 2). Based on current studies, it is intended to extend Table 2 by adding weighting factors for goats (0.5), sheep (0.5) (Stoll, 2017, 2019) and pigs in animal welfare housing (0.65) (Kwiatkowski et al. 2021).
Table 2: Weighting factors f for individual types of animals
Animal-dependent odour quality
Weighting factor f
Fattening fowl (turkeys, broilers)
Fattening pigs, sows (up to a capacity of approx. 5000 fattening pigs or for a certain number of sows, respectively, considering the pertinent conversion factors)
Dairy cows, fattening bulls including young cattle (also covering calves, provided their contribution to the ambient odour exposure is negligible)
The concept of using weighting factors has the great advantage that for one area utilization only one limit value exists. If odours with different weighting factors affect the same area, these factors are applied before comparing the measured or calculated odour frequencies with the limit values of the GOAA.
5. Use of German Guideline on Odour in Ambient Air (GOAA) in practice
Responsible authorities apply the GOAA in permit (licensing), in monitoring (surveillance) and in urban land use planning procedures. In all these cases, an expert prepares an expert report that shows an odour frequency in ambient air (odour immission frequency), which is compared with the limit values for evaluation. If the responsible authority has reasonable doubts in connection with the contents of these expert reports, they can send the reports to the North Rhine Westphalian State Agency for Nature, Environment and Consumer Protection (LANUV) with the request to check the plausibility. The LANUV gets 50 to 80 expert opinions to check per year. The following three individual cases are presented as examples to give an impression of the current odour assessment praxis in North Rhine Westphalia, which is comparable to the praxis in Germany.
A paper mill has planned to extend their production. The odour emissions of the existing point sources were measured by olfactometry. The expert estimated the odour emissions in the future. The odour frequencies were calculated by AUSTAL2000, a Lagrangian particle model, in percent per year. The size of the assessment squares is 50 m x 50 m. Figure 3 shows the result of the dispersion modelling based on a representative local wind distribution. White hexagons mark the location of the sources.
Figure 3: Odour immission frequencies [%] calculated by dispersion modelling (green >2.4 – 5%, turquoise >5.4 – 10%, blue >10.4 – 20%, yellow >20)
According to the Technical Instructions on Air Quality Control (TA Luft), which is legally binding, and the GOAA, relevant for the odour assessment, the total (odour) exposure must comply with the limit values (see Table 1). The total exposure consists of the existing and the additional odour exposure. In the case of that paper mill, the total odour exposure in the residential reached a maximum odour frequency of 7 %. The higher values in Figure 3 are located on the plant area itself.
Sewage composting plant
A big wastewater treatment plant wanted to build a new sewage composting plant. Because of other industrial plants especially some with many fugitive sources, the responsible authority insisted on a gird measurement to measure the existing odour exposure, according to EN 16841 Part 1:2016. The assessment squares (100 m x 100 m) represent the areas with dwellings. The results of odour frequencies in percent per year are shown bold black on big, red boxes in Figure 4.
The odour emissions of the existing point sources of the wastewater treatment plant were measured by olfactometry. The future odour emissions were negligible because of the decision of the plant operator to install an odour abatement system (biofilter) for the sewage composting plant and the distance to next relevant dwelling. The odour frequencies caused by the plant were calculated by AUSTAL2000. The size of the assessment squares is 50 m x 50 m. Figure 4 shows the result of the dispersion modelling based on a representative local wind distribution in a grid.
The odour frequencies calculated by dispersion modelling are only caused by the existing and investigated sources and could therefore be compared with the results of the grid measurement. If the results of grid measurements are measured under representative conditions, they reflect the real odour exposure. Because there are differences between the predicted and measured results, it was the task of the expert in an iterative process to adapt the odour emissions as long as the calculated odour frequencies fit to the results of the grid measurement.
Figure 4: Odour immission frequencie s [%] calculated by dispersion modelling (little squares, green >2.4 – 10%, yellow >10.4 – 15%, red >15.4%) and measured by a grid measurement (big red squares with big numbers)
The number of livestock farms in Germany is significantly higher than any other type of facility, the majority of which are facilities that do not require a permit. The number of expert reports submitted for plausibility checks also exceeds that of other facilities.
Depending on the animal species, the weighting factors according to Table 2 are to be considered for the calculation of the odour frequencies.
Farmer H1 had two stables with 2000 fattening pigs and wanted to build a third one with 1000 fattening pigs and required a permit for 3000 pigs. Farmer H2 had 2000 fattening pigs in one stable. Because it is a village, the limit value to be applied is 0.15 (=15%) (see Table 1). Figure 5 shows the calculation of odour frequencies for two pig farms without a weighting factor in the left figure. By applying the weighting factor for fattening pigs of 0.75 (see right figure) on the results of the dispersion modelling (see left figure), the odour exposure is transferred to a so-called “annoyance-relevant” odour exposure. The annoyance relevant odour exposure, which has to comply with the limit values, reached a maximum odour frequency of 18 % per year in the residential area.
Figure 5: Odour immission frequencies [%] calculated by dispersion modelling for two pig farms without (left) and with a weighting factor of 0.75
6. Conclusion and further developments
Since 1993, the GOAA has provided the methodological and regulatory framework in permit and monitoring procedures for all kind of installations. In the GOAA, a scientifically sound exposure-impact relationship is translated into limit values, which also takes into account the different annoyance potentials of different odours by applying weighting factors into account.
In addition, the GOAA is also recognised for the odour assessment in court cases all over Germany, although it is so far only an administrative regulation of the German federal states, not a law.
In the meantime, there is a wide range of experience with the determination and assessment of odours, including
- different types of sources (point, active, fugitive),
- different meteorological conditions (e.g. valley locations, cold air drainage),
- combinations of different methods (dispersion modelling versus measurement of odour in ambient air by using field inspections with grid measurement),
- different kinds of area utilization and
- the application of different of limits values.
In 2021, after more than 25 years of experience, the GOAA will become part of the TA Luft (First General Administrative Regulation Pertaining the Federal Immission Control Act (Technical Instructions on Air Quality Control – TA Luft)), which is legally binding.
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