This paper will introduce the importance of proper sampling when assessing odours. Generally, when complaints occur in a region, the first step is to investigate any given complaints. Some of the grievances may not be valid due to factors such as wind direction or other meteorological conditions.

   How does one determine which complaints are valid? How do you prove that the odour emanating from the “in question facility” is actually from that facility and not a neighbouring facility? How do you determine the “true” odour concentration at the complaint areas?

Anna Bokowa ¹

¹Principal, Environmental Odour Consulting – Toronto, Ontario, Canada. bokowa.anna@environmentalodourconsulting.com

Competing interests: The author has declared that no competing interests exist.

Academic editor: Carlos N Díaz.

Content quality: This paper has been peer reviewed by at least two reviewers. See scientific committee here

Citation: Bokowa A., Determining the Importance of Proper Sampling when Assessing Odour for Complaint Purposes, Ist International Seminar of Odours in the Environment, 2014, Santiago, Chile, www.olores.org

Copyright: 2015 olores.org. Open Content Creative Commons license., It is allowed to download, reuse, reprint, modify, distribute, and/or copy articles in olores.org website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.

Keyword: Odour Sampling, Dilution, Condensation, Odour Panel Evaluations, Dynamic Dilution Olfactometry, Odour Standards.

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Abstract

   This paper will introduce the importance of proper sampling when assessing odours. Generally, when complaints occur in a region, the first step is to investigate any given complaints. Some of the grievances may not be valid due to factors such as wind direction or other meteorological conditions. How does one determine which complaints are valid? How do you prove that the odour emanating from the “in question facility” is actually from that facility and not a neighbouring facility? How do you determine the “true” odour concentration at the complaint areas?

   There are various different methods for validating complaints^1,2,3, such as; odour observations, community odour surveys and ambient sampling/monitoring. However, these approaches are just one time “snap shots” of the conditions present and are usually performed when complaints occur. At times, it is very difficult to be prompt when complaints occur. By the time the consultant is able to perform observations, the odour may dissipate. Therefore, the most common approach to validate odour complaints and to determine the odour concentration at the complaint areas is to; investigate each potential odour source at the “in question facility,” rank the odour sources by collecting odour samples (meaning odour sampling at each potential odour source), evaluate the collected samples and use the model to predict off site odour concentrations at each complaint area. This approach is commonly used for proper investigation of odour complaints, which predict the odour concentrations at the complaint areas.

  Nevertheless, it is questionable if the predicted by model concentrations represent true and accurate values. How can they if the sampling was not done accurately? How would it influence the results? All developed standards for odour (such as the Australian/New Zealand Standard, 2001, or European EN213725: 2003) emphasize odour evaluations on already collected samples rather than actual sampling and its techniques. How valid are the results if the samples were not collected properly? Why even bother to introduce the same odour sample twice during odour evaluations (as required by some standards) if there was an error during the collection of that sample?

   Most standards require the dilution of samples during their collection above the point when condensation will not occur. Yet there are other factors that are not accounted for that need to be taken into consideration. For example, consider other compounds other than water.

   This paper is based on the study of different dilutions used for the same sample in order to demonstrate that other factor need to be considered other than just to be above the water condensation level.

   The results obtained from this study are based on the collection of samples from the same sources at the same time. Evaluations were performed by the same type of olfactometer and the same group of panellists in order to minimize any deviation caused by other factors.

Introduction

Sampling for Odours: How to Measure Odour at the Source

   Essentially, odour emission tests involve collecting gaseous samples at the source, using specialized sampling procedures, and analyses of these samples to determine the odour detection threshold values. The point source can be a stack or vent, an area source- a lagoon or open piles and tanks, and a fugitive source can be any open doors or trucks waiting to load or unload. At the point source, the volumetric flow-rates are also measured in order to calculate odour emission rates from these sources which are then used as inputs for dispersion modeling.

   Different counties follow different approaches for sampling for odours. An example guideline is The European Standard: EN:13725:2003 “Air Quality-Determination of Odour Concentration by Dynamic Olfactometry” ⁴ or Australian/New Zealand Standard, 2001, “Stationary Source Emissions. Part 3: Determination of Odour Concentration by Dynamic Olfactometry” ⁵. Within these guidelines, there is limited information on how to collect samples for odours especially from hot and humid point sources. This standard puts more emphasis on the analysis of already collected samples using Dynamic Olfactometry rather than the sampling.

   In the Ontario province of Canada, compliance sampling for odours followed the Ontario Ministry of the Environment (MOE) Draft Source Sampling for Odours, Version #2, February 1989⁶. This guideline outlined sample collection protocols and referenced the MOE’s Source Testing Code (November 1980)⁶ for stack gas velocity, volumetric flow-rate and moisture determination procedures. In this guideline there was a need to determine the optimum dilution for sampling. It was required that collection of samples be at four different dilution ratios in order to determine the optimum dilution in order to ensure minimum odour loss during collection of samples. The sample with the highest odour concentration was considered a sample at the optimum dilution for further sampling. Three samples were required to be collected at that chosen optimum dilution.

   However in 2010, a new guideline was issued by the MOE – Ontario Source Testing Code, Method ON-6” Determination of Odour Emissions from Stationary Sources” ⁸

   In this guideline the samples should be collected at a dilution that is calculated based on the gas stack moisture content and the lowest temperature at which the gaseous sample is expected to reach during transport and analysis. If the sample temperature is maintained at a level higher than the sample dew point temperature (the temperature at which the gaseous sample becomes saturated with water vapor), water vapor remains gaseous. If the sample cools to a temperature below the dew point, water vapor will condense. However, there is no mention or consideration of the vapor of other compounds, only water. How these other compounds would affect the results if not considered during sampling?

   On the other hand, in the United States there are no standardized guidelines for odour sampling at point sources. Rather, a simple method is used allowing to collect an undiluted/grab sample from any point source. In this technique samples are collected in a Tedlar or Nalophan gas sample bag by controlling the vacuum in the sampling lung using a leak-free pump. Obviously then, this technique does not allow dilution while sampling. This method is not acceptable in Ontario, Canada, especially for moist, elevated in temperature sources, where there is potential for condensation, chemical reaction or oxidation and therefore a significant loss of odour.

   When it comes to the dilution at the source, it predominantly occurs that emission gases are diluted with odourless nitrogen as the gases are extracted from the emission source. This procedure is designed to minimize the loss of odourants by adsorption, condensation and oxidation. There are several available odour samplers for the collection of samples at the point source. One is based on the eductor /aspirator where the eductor, creates suction and draws the sample into the stream. The nitrogen is used as dilution gas. Another type of odour sampler is based on a dilution probe and in a similar way the nitrogen is used as dilution gas. Different dilution ranges are used for the collection of samples. However, the most common range for dilution for collection of the samples used in Europe is between three times to ten times dilution and it begs the question, is ten times enough for sampling at specific sources? In Canada, higher dilutions has been used in the past, however with the new MOE guideline, when only water vapours are considered there is a trend to use a low dilution at certain sources, which may not be sufficient.

   The entire dilution sampler should be maintained at the temperature of the source. The diluted sample, under positive pressure, is collected in pre-conditioned Tedlar gas sample bags or Nalophan bags. Each sample bag should be purged twice with diluted stack gas and then refilled. Each sample should also be covered immediately after sampling in order to minimize potential photochemical reactions.

   How different would the results be if these two techniques ( dilution versus undilution) are compared and used while sampling at hot or humid sources? What variation in results would occur if the dilution used at a source is too low and does not compensate for the other compounds and only considers water evaporation.

Methodology

   Several studies were performed for this paper. In the first three studies, three samples were collected using a dynamic dilution sampler at the same time as three samples were collected using a lung sampler, where samples were not diluted.

   All other studies were based on the collection of three samples at the sources; three samples collected at one higher dilution and three samples collected at a lower dilution. Two dynamic dilution odour samplers were used for this purpose at the same time.

   All samples were collected over ten minute periods. All sample bags were purged twice with a gas sample before collection of the samples. All samples were transported to the laboratory for odour panel evaluations using dynamic olfactometry and screened panellists. All evaluations were performed according to the Ontario Source Testing Code- “Method ON-6’ Determination of Odour Emissions from Stationary Sources” which requires to follow the European Standard EN 13725:2003 with exceptions that the sample is introduced only once and that eight screened panellists are mandatory for odour evaluations.

Results: Case Studies

Determining Odour Loss: Undiluted Samples versus Diluted Samples

Case Studies 1, 2 and 3

   Presented below are three cases studies comparing and contrasting undiluted sampling versus diluted sampling techniques.

Study 1

   The first study included collection of three samples at 50 times dilution at the same time as three samples collected undiluted. The source was 150 degrees Celsius.

Table 1A presents the results when the dilution technique was applied for the collection of the samples and when the undiluted samples were collected at the same time, at the same source.

Table 1A: ODTV of Samples Collected at 50 Times Dilution versus Undiluted (Hot Source)

• Up to17 times lower ODTV value for undiluted samples

   Based on the results of this study the odour losses when samples collected undiluted are up to 17 times greater compared to the samples collected at 50 times dilution.

Study 2

   During the second study, samples were collected at a stack where the moisture content was high. Concurrently, three samples were collected at 30 times dilution and three samples were collected undiluted.

   Table 1B presents the results when the dilution technique was applied for the collection of samples and when the undiluted samples are collected at the same time, at the same source.

Table 1B ODTV of Samples Collected at 30 Times Dilution versus Undiluted (Humid Source)

*Up to 15 times lower ODTV value for undiluted samples

   Based on the results of this study the odour losses when samples are collected undiluted, are up to 15 times greater compared to the samples collected at 30 times dilution.

Study 3

   Three samples were collected at the humid source using dynamic dilution sampler with eighty times dilution. Concurrently, three samples were collected undiluted using the lung technique.

Table 1C presents results for this study.

Table 1 C: ODTV of Samples Collected at 80 Times Dilution versus Undiluted (Humid Source)

• Up to 9 times lower ODTV value for undiluted samples

   Based on the results obtained by these three studies, when samples were collected undiluted at hot or humid sources, the odour loss is anywhere between nine and seventeen times greater compared to diluted samples.

Determining Odour Losses When Different Dilutions Are Used

Case Studies 4, 5 and 6

   In the following case studies, two dynamic dilution odour samplers were concurrently used during the collection of samples at the same source. Three samples were obtained with each sampler at different dilution ratios.

Study 4

   In this study, three samples were collected at two different dilutions. The first set of three samples were collected at 60 times dilution whereas at the same time, a second set of three samples were collected using the same methodology with the exception that samples were collected at 9 times dilution .

  Table 2A presents the results when two different dilutions were used on site for the same source- one 60 times and the second only 9 times dilution.

Table 2A: ODTV of Samples Collected at 60 Times Dilution Versus 9 Times Dilution.

*Up to 8 times lower ODTV value for samples collected at the lower dilution

   Based on the results, when samples were collected using lower dilutions, the odour losses are up to eight times greater, then when compared to the results obtained when a higher dilution of 60 times was used.

Study 5

   During this study, three samples were collected at 50 times dilution concurrently three samples were collected at 20 times dilution. Table 2B shows the results.

Table 2B: ODTV of Samples Collected at 50 Times Dilution versus 20 Times Dilution

*Up to 3 times lower ODTV value for samples collected at the lower dilution

   Based on these results, when the lower dilution of 20 times was used for collection of samples, the odour losses were up to three times greater when compared to the results obtained when a higher dilution of 50 times was used.

Study 6

   During this study, three samples were collected at 200 times dilution while concurrently three samples were collected at 50 times dilution. Table 2C shows the results.

Table 2C: ODTV of Samples Collected at 200 Times Dilution versus 50 Times Dilution

*Up to 5 times lower ODTV value for samples collected at the lower dilution

   Based on the results obtained by these three studies, the odour detection threshold values for the samples collected at higher dilutions are much higher than at the samples collected at lower dilutions. In this particular study, the odour losses were up to five times greater at 50 times dilution, compared to the samples collected at 200 times dilution.

   Odour loss may be attributed to the vapours of other compounds which are not currently considered under guidelines during collection of samples.

Conclusions

   Based on extensive studies and concurrent sampling at different dilutions at the same source, there is significant odour loss when sampling at a lower dilution or sampling without dilution compared to that of sampling at a higher dilution.

   There is a possibility of odour losses due to the fact that vapours of other compounds, apart from water, are not currently considered by recognized guidelines.

   Based on the case studies described, when sampling at humid, hot sources, it is important to dilute samples with nitrogen during sampling to prevent any odour losses, which may be significant. The odour losses may be up to 17 times if dilution is not used.

   Proper sampling methods should be used and emphasized during collection of samples and other important compounds other than water vapours should be considered by authorities approving odour sampling methods.

References

1. Bokowa A. “ Techniques for Odour Assessment”; IWA 2003

2. Bokowa A “Odour Sampling in Ontario”, A&WMA 2003

3. Chemical Engineering Transactions, Volume 23, 2010, International Conference on Environmental Odour Monitoring and Control, NOSE 2010, September 2010, Volume 17 ISBN 978-88-95608-14-3, September 2010; Bokowa A “The Effects on Sampling on the Measured Odour Concentration”

4. The European Standard EN:13725:2003 “Air Quality-Determination of Odour Concentration by Dynamic Olfactometry”

5. Australian/New Zealand Standard, 2001, “Stationary Source Emissions. Part 3: Determination of Odour Concentration by Dynamic Olfactometry”

6. The Ontario Ministry of the Environment (MOE) Draft Source Sampling for Odours, Version #2, February 1989

7. The Ontario Ministry of the Environment“SourceTesting Code”, November 1980

8. Ontario Source Testing Code , Method ON-6” Determination of Odour Emissions from Stationary Sources”, October 2010