Odor Transmission


Melinda Cseh1, Katalin F. Nárai2,
 Endre Barcs3, Dezso Szepesi4







Abstract-ODOR TRANSMISSION is a regulatory model to estimate setback distance on virtual map. It was prepared by interdisciplinary team of experts. The dispersion part is based on the former results published in Development of regulatory transmission modeling in Hungary (Időjárás, 2005), the odor emission part is taken mostly from US results. An estimated setback distance is presented on virtual map. The model is part of the EIONET which is the model catalogue of the European Union.


Key-words: odor, odor unit, transmission modeling, setback distance, exceedance probability


1. Introduction


In the last decades odor nuisance of livestock units has become more frequent and intensive in our environment. The fundamental human right requires the pure, livable environment, which includes the odorless air as well. To find solutions against odor problems, standard regulations must be done. This involves the need of the determination of setback distances around animal production farms, municipal solid waste landfills, wastewater treatment plants and factories that emit odorous gaseous. Most of the existing setback guidelines were determined either by individual judgment and experience or by a combination of neighbor surveys and odor measurements, instead of calculations of dispersion models (Guo et al., 2004). The determination of odor nuisance by olfactometria (the testing and measurement of the sensitivity of the sense of smell) is essential, although it contains many subjective factors. Therefore it is essential to establish a science based model to predict the setback distances more objective, which can become an effective practice for the experiments as well as for the regulatory agencies and decision-makers. The aim of this study is to present the newly developed ODOR-TRANSMISSION model for odor setback distance determination. The model is based on the Transzmisszió 1.1 (in EIONET called HNS-TRANSMISSION) softver and data system, which is used in the Hungarian regulatory system. Both models have been enrolled in the Model Documentation System of EIONET (ODOR-TRANSMISSION: http://pandora.meng.auth.gr/mds/showlong.php?id=179,


2. Estimation of odor source term


2.1. Odor


Odor is the property of a chemical substance or substance mixtures, dependent on the concentration, to activate the sense of smell and thus being able to start an odor sensation (Winneke, 1994). As odor sensitivity is differ in each person, a completely objective and analytical measurement cannot be done, however it is possible to define the annoyance level of the odorant by several methodology.

To measure odor olfactometry methodology is used which based on a panel of human noses as sensors. For the determination of the quantity of odorants odor concentration is used, which dimension is European odor unit per m3 (OUE/m3). The European odor unit by definition is: That amount of odorant(s) that, when evaporated into one cubic meter of neutral gas at standard conditions, elicits a physiological response from a panel (detection threshold) equivalent to that elicited by one European Reference Odor Mass (EROM), evaporated in one cubic meter of neutral gas at standard conditions. (CEN TC264 Draft). Where European Reference Odor Mass (EROM): The accepted reference value for the European odor unit, equal to a defined mass of a certified reference material. One EROM is equivalent to 123mg n-butanol (CAS 71-36-3) evaporated in one cubic meter of neutral gas. This produces a concentration of 0.040 mmol/mol. (CEN TC264 Draft).

The above mentioned olfactometric measurements are needed to determine a reference scale for each odorant. However for the everyday regulation system these processes are too complicated and require plenty of time. Therefore, more effective and straightforward techniques should be used, that can be achieved by building models based on the results of analytical measures. This is the aim of the ODOR-TRANSMISSION program.


2.2. Odorants and its sources


The ODOR-TRANSMISSION program is developed for one component odorants emitted from faculties, livestock operations and municipal waste fills.

The odor that is detected from a livestock operation is a complex mixture of gases. Most often the odor is a result of the uncontrolled anaerobic decomposition of manure. However, feed spoilage can also contribute to the odor. The odor that is detected by the human nose can be a combination of 60 to 150 different compounds. Some of the most important types of odor causing compounds are: volatile fatty acids, mercaptans, esters, carbonyls, aldehydes, alcohols, ammonia, and amines. The odor strength of these compounds does not combine in an additive manner. That is, sometimes mixing several of these compounds can result in reduced odor by dilution of the strongest smelling compounds. In other instances, the mixture is worse than any of the individual compounds. Ammonia can create strong odors near a building, but is not a significant component of odor downwind from an animal production facility because ammonia is highly volatile and moves upward in the atmosphere quickly where it is diluted.


2.2.1. Animal farms


To determine the setback distance around an animal production farm, firstly the odor emission must be predicted. The presented methodology to calculate the odor emission is based on other publicized studies, measurements and experiences. The equation to calculate odor emission is based on the Perdue model, which was developed by Lim et al. (2000) and combines features of Austrian and British setback guidelines (Schauberger and Piringer, 1997; Williams and Thompson, 1985).

The model takes into consideration the following parameters: the type of animals, the amount of animals, the manure removal frequency, the manure dilution factor, the area of the storage building, the wind speed above the ground, and odor abatement.

The method of the estimation of odor emission is based on the Livestock Unit. The Livestock unit (LU) is a unit to compare or aggregate numbers of animals of different species or categories. Equivalences based on the food requirements of the animals are defined (European commission).

While the Perdue model estimates the emission for swine buildings, the currently presented model has developed the methodology for other livestock units as well (Table 1). The presented livestock units are based on the field and laboratory measurements of North Dakota State University, Dickinson Research Extension Center and Minnesota University.

1. Table: Livstock unit of different animals

Animal type



Swine heavier than135 kg


Swine between 25 - 135 kg


Swine under 25 kg



Weaned cow lighter than 360 kg


Young cow between 360 - 405 kg


Cow between 405-495 kg with calf


Cow between 495-585 kg with calf


Cow heavier than 585 kg with calf


Bull lighter than 900 kg


Bull hevier than 900 kg











broiler (liquid manure system)


Chicken heavier than 2,25 kg (dry manure system)


Chicken lighter than 2,5 kg (dry manure system)




Turkey heavier than 2,25 kg


Turkey lighter than 2,5 kg







Concerning the outdoor manure system, an empirical equation is used according to the studies of J. Herber et al. (2002). It considers the area of the storage system and the wind speed above the ground. After calculating the emission for each subsystem of the animal production farm, the results must be summarized for the final quantification.


2.2.2. Municipal solid waste landfills


Odor emission calculation for municipal solid landfills is based on Italian studies (Selena et al., 2005). For the determination of emitted amount of odor the following parameters (Table 2) have to be taken into consideration: (1) the annual waste acceptance, (2) the waste density, (3) the working days in one year, (4) the height of the daily deposited waste layer, (5) the surface of the active parcels and (6) the surface of the restored parcels.


2. Table: Required data and their dimension for odor emission calculation of municipal solid landfills



Annual waste acceptance


Waste density


working days


height of daily deposited waste layer


surface of active parcel


surface of the restored parcels



The result of the emission model in all case (animal production farms, manure storage systems, municipal solid waste landfills) is given in odor unit/second. Odor unit (OU) in this paper is equal to the European Odor Unit (OUE), which was defined above. The OU/s later on must be converted into the measure of kg/h for the further processes in HNS-TRANSMISSION.


3. Atmospheric dispersion


The dispersion part of the model is calculated by HNS-TRANSMISSION (Szepesi et al., 2005), which is well-known and common used softer in the Hungarian air quality protection regulation. The softver considers meteorological parameters (wind direction, atmospheric stability categories) and has database for the whole area of Hungary. In addition, this database can be enlarged if the meteorological data are available from the given territory. Therefore the model can be used not only for Hungary, but for other countries, places as well. With given input data, the program determines the concentration of given pollutants against the distance. Concerning odor nuisance modeling the required data are the following: the coordinates of the livestock sites (EOV coordinates), the odor emission (discussed above), and the outcoming air features (temperature, rate of flow). Based on these parameters, odor concentration against the distance is determinable around the site by the softver.


HSN-TRANSMISSION model applies the Gaussian model of diffusion. It is the most widely used model for plume dispersion. Its most attractive feature is that it fits what we see and experience in the real world for a range of conditions. In addition, the mathematics of the model is fairly straightforward. On the other hand, Gaussian models need significant empirical input to be used for practicable dispersion estimates, making the model results highly dependent on the conditions of the sampling used to derive the empirical values.

Similar to the decision process used to select the appropriate model for regulatory purposes, the selection of the appropriate dispersion model for odor assessment starts with the source type and release scenario. In general, most sources can be categorized as point, area, or volume sources, with continuous or instantaneous releases. The sources responsible for odor complaints are generally continuous sources, such as from stacks, scrubbers, or basins; although routine but instantaneous or very short-term releases (for example, from digester pressure release valves) can also pose problems at nearby receptors. Depending upon the rate of release relative to odor perception's short time frame, intermittent sources can be classified as either continuous sources (release rate on the order of minutes or longer), or instantaneous sources (release rate on the order of seconds).


The model determines the number of exceedances against distance in each wind direction. The calculation requires the determination of the threshold limit for odorants. In European countries the applied threshold limit is differ from 3 to 10 odor unit/m3 (Table 3). Concerning sensitivity studies the suggestion of air quality consultants for odor threshold limit for Hungary is between 3 and 5 odor unit/m3. The exact value must be determined by local authorities.

Based on the number of exceedances, the setback distance around the virtual emitting point in each wind direction can be calculated. The setback distance represents the area where odor nuisance appears more frequently than it is allowed according to the percentage of the hours of a year. Therefore, for example in the area, where 1% the exceedance probability; odor nuisance appears in 88 hours per year. To develop a standard modeling system this exceedance probability must be determined by the authorities based on further studies. In international aspect the most recently used value is 2%, which means that odor nuisance occurs in 176 hours per year.


3. Table: Odor threshold limit in European countries (Ritvay, Kovács, 2006)


Odor threshold limit (OU/m3)



The Netherlands



3 or 6



Hungary (suggestion)




4. Presentation of setback distance on virtual map


The ODOR-TRANSMISSION model plots the setback distance on G-map with accuracy of plus minus 1 meter. In order to define the setback distance accurately, the units of the animal farm must be evaluated. Based on it, the center which is taken as the virtual emitting point is defined. The longitude and latitude coordinates of this point is the base of the plotting system. The setback distance is measured from this point. Plotting the setback distance in the 16 wind directions the odor impact zone is well given on the map (Figure 1).

1. Figure: Visualization on Google map of the setback distance around an animal farm. The distance is measured from the virtual emitting point in 16 wind directions.


The final visualization is a helpful tool for decision makers as the impact zone is well determined with an accuracy of plus/minus one meter, well visible furthermore the mode of the map can be switch from normal map to satellite and vice versa.


5. Case study


A case study was made to calculate odor emission from a municipal solid waste landfill in Dunakeszi. The parameters of the landfill are given in Table 4.


4. Table: Input and output data for odor emission calculation for municipal solid waste landfill in Dunakeszi.

Input Data


Annual waste acceptance

200000 t/yr

Waste density

0.6 t/m3

working days

300 d/yr

height of daily deposited waste layer

3 m/d

surface of active parcels

3000 m2

surface of the restored parcels

22000 m2

Output Data


Emission from the daily deposited waste layer

21852 OU/s

Emission from active parcels

24000 OU/s

Emission from restored parcels

88000 OU/s

Total odor emission (OU/s)

133852 OU/s

Total odor emission (kg/h)

0.48186 kg/h


The required meteorological parameters for the calculation of dispersion are given in the database of HNS-TRANSMISSION in the file called Vac1.

The output of the emission calculation is presented in Table 4. The total odor emission is determined both in the dimension of OU/s and kg/h. The latter dimension is required as it is the input data for HNS-TRANSMISSION to calculate odor dispersion. Based on the odor emission the frequency of odor exceedances is calculated with this Gaussian dispersion model. From the analysis of the frequency of exceedances against the hours of a year the resulted setback distance is plotted on Google map around the emitting point in the function of distance in the 16 wind directions (Figure 2).

2. Figure: Odor setback distance in 16 wind directions around a municipal solid waste landfill in Dunakeszi.



6. Testing and validation


For the validation the ODOR-TRANSMISSION model was compared to three international odor models (Guo et al., 2004). For the comparison the results of an earlier study called Comparison of five models for setback distance determination from livestock sites (Guo et al., 2004) was used.

In this research odor setback distance calculations were made for 12 American swine farms. The calculations were made by 5 different models: Ontario MDS-II model, W-T Model, Austrian Model, Purdue model, Minnesota OFFSET model. The first four model based on empirical principles, while OFFSET model is calculating with the dispersion model.

The livestock facilities were located in the surroundings of Minnesota. The sizes of the swine farms were different and the type and amount of animals differed as well (Table 5).


5. Table: Parameters of the 12 livestock operation farms (Guo et al., 2004)



Odor source

Building (m2)

Outside manure storage


960 nursery to finishing

4 barns (735)



1720 finishing

2 barns (1637)



2500 nursery/finishing

7 barns (2725)



750 sows

2 barns (1869)

1 lagoon (91*91 m)


600 sows, 2500 nursery/finishing

6 barns (3450)

1 earthen basin (31*38 m)


1300 sows, 4000 nursery

3 barns (4167)

2 earthen basins

(58*58 m, 58*61 m)


2000 nursery, 1000 sows

3 barns (3534)

1 earthen basin (61*61 m)


1300 sows farrowing to weanling

3 barns (3348)

2 earthen basins

(61*48 m, 61*61 m)


1400 sows, 2800 nursery

4 barns (4508)

2 earthen basins

(48*48 m, 48*76 m)


2400 sows farrowing to weanling

3 barns (6882)

1 tank (1116 m2),

1 basin (61*76 m)


4600 sows farrowing to weanling

6 barns (13020)

2 tanks (1116 m2),

1 basin (61*122 m)


3500 nursery, 3500 finisher

5 barns (4185)

2 earthen basins

(61*152 m, 61*203 m)


Based on the given data concerning farm size, animal types, outdoor manure storage and meteorological parameters; odor setback distances were calculated by the newly developed ODOR-TRANSMISSION program as well, and were compared to the given results (Guo et al., 2004). The correlations are shown in Figure 3.

The graphs show that how much is the setback distance, considering the time of nuisance per year. The given percentages stand for the number of hours per year, when odor is annoyance. In each animal farm the maximum setback distance is shown.

Considering the Offset model (Figure 3a), which also uses air dispersion model for the setback distance determination, the 2, 3 and 4% exceedance probabilities show good correlations with ODOR-TRANSMISSION model, while in the case of Purdue model (Figure 2b) it is 3, 4 and 5% of exceedance probabilities, where the results correlate well. In general the best fit can be seen with the W-T model (Figure 3c) in the case of 2% exceedance probability.

3. Figure: Comparison of ODOR-TRANSMISSION (OT) model with a) Offset model, b) Purdue model, c) W-T model. Odor setback distance is plotted for the 12 animal farms considering different exceedances frequencies (the numbers (percentages) refers to the exceedance frequencies against the hours of one year).


Control calculations were made for ODOR-TRANSMISSION model by two Hungarian environmental inspectors Tibor Paksa and Tibor Nagy Ph.D. Both of them find the model satisfactory and suggested for further application in practice.

7. Sensitivity Study


A sensitivity study was made in order to compare the setback distance in the function of the animal type, number of animals and the threshold limit. The study was made for city Kecskemét and the exceedances probability was considered 2%. Firstly calculations were made for chicken, beef and duck. In all case two cases were considered according to the number of animals. The results show (Table 6) that if the number of animals is doubled, the setback distance grows but not in the proportion of the changes of animal number.

Considering different threshold limit (3 OU/m3, 4 OU/m3, 5OU/m3) the setback distance is inversely proportional to the threshold limit.

6. Table: Sensitivity analysis in a livestock production farm in Kecskemét. Odor emission is studied in the functions of animal type and animal number. Setback distance is analyzed in the function of threshold limit.


Number of animals

Odor emission

Setback distance (m) in the function of threshold limit



3 OU/m3

4 OU/m3

5 OU/m3









































The setback distance was also compared for a swine farm containing 10000 swine in the function of the threshold limit. The change of the setback distance was studied for 3, 4 and 5 OU/m3. The figures (Figure 4, 5, 6) show well that if the threshold limit increases, the setback distance decreases. In the case of
3 OU/m3, the maximum setback distance from the emitting point is 1.75 km (Figure 4). This value is 1.5 km if the threshold limit is taken as 4 OU/m3 (Figure 5), while for 5 OU/m3, the setback distance is just 1.3 km (Figure 6).


4. Figure: Setback distance in the 16 wind directions around a swine farm (10000 swine) in the case of 3 OU/m3 threshold limit. The maximum setback distance is 1.75 km.


5. Figure: Setback distance in the 16 wind directions around a swine farm (10000 swine) in the case of 4 OU/m3 threshold limit. The maximum setback distance is 1.50 km.

6. Figure: Setback distance in the 16 wind directions around a swine farm (10000 swine) in the case of 5 OU/m3 threshold limit. The maximum setback distance is 1.30 km.



8. Conclusions


ODOR-TRANSMISSION is an objective method to determine setback distance around odor emission. The use of the program is quite straightforward; it does not require any special skills. If the input data are correctly given, than odor annoyance can be determined quantitatively and in a standardized way. The results of the calculation can help both decision makers and adepts in controlling, planning or decision making as well.



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