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One Odour Unit-Precisely how can an Odour Unit be

measured?WEF/A&WMA

Odors and Air Pollutants 2010

Presented by:

Anna H. BokowaORTECH Environmental

Mississauga, OntarioCANADA

Overview• Introduction• Factors influencing off-site odour

concentration determinations• Case studies• Conclusions

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Odour - nuisance in most jurisdictions in Canada, Australia, United States

A nuisance can be demonstrated by verifiable complaints and by odour testing programs

In Ontario, Canada, target 1 ou at the any sensitive receptor (based on predicted odour concentrations using measured odour emission rates and dispersion modelling) or ambient measurements

Introduction

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Introduction (cont’d.) In Queensland, Australia, requirement of

0.5 ou for tall stacks or 2.5 ou for short stacks

How precisely can we measure or predict odour units?

Is it possible to measure or predict 0.5 ou or 1 ou?

1 ou might be 10 ou or greater and will depend on several factors (selection of sources, sampling methodology, analysis, dispersion modelling)

The losses of odour might be significant if proper sampling methodology is not used

1.Careful selection of all potential odour sources in the plant (point, area, fugitive)

2.Sampling methodology 3.Time period between the collection of the

samples and their evaluation4.Selection of the olfactometer used for

odour evaluations5.Panelists selection and their sensitivity6.Dispersion modelling used

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Factors Influencing Off-Site OdourConcentration Determinations

Important to include all sources in the assessment (point sources, area sources, fugitive sources)

Fugitive sources are often omitted Predicted odour concentrations using modelling

are lower than actual or measured ambient levels when sources are omitted

Cases when significant sources were omitted and predicted concentrations were 10 ou as a maximum but measured off site odour was 200 ou

Good practice to combine source testing with ambient sampling

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Factor 1: Selection of all Potential

Odour Sources

Mushroom/Compost Facility- operation carried on as a normal farm practice?

Is it normal to be exposed to 200 ou at a residence

Facility assessed and predicted off-site concentration only 10 ou as the worst case scenario (one consultant)

but measured off site 200 ou (by ambient sampling and odour evaluation by another consultant)

Who is right? Good practice to combine source testing with ambient monitoring

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Factor 1: Example of Missing Sources

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Point Sources In Ontario the methodology is very strict and requires sampling at a dilution when

the minimum odour loss occurs during collection of the samples (optimum dilution)

In the predilution technique, emission gases are diluted with nitrogen in order to minimize the loss of odourant by adsorption, condensation and oxidation

Most European countries use the dilution technique when collecting samples from point sources ( hot, humid)

Factor 2: Sampling Methodology

Factor 2 (cont’d.): Sampling MethodologyPoint Sources

Only in the US, the dilution techniques is not used in most states

Dilution technique is very important especially for hot, humid sources

The loss of the odour might be significant when dilution on site is not used

Therefore the predicted concentration of 1 ou may actually be much higher

1 ou measured might actually be 16 ou

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Factor 2: Effect of Different Techniques used

For Collection of Samples-Point SourcesSamplin

gLocation

SampleNo. Predilutio

n

Raw ODTV(ou)

NetODTV(ou)

Geometric Mean

Net ODTV(ou)

Source 1 1 50 651 32,550

2 50 668 33,400 34,294*

3 50 742 37,100

1 40 636 25,440

1 60 336 20,160

1 1 2130 2,130

2 1 1969 1,969 2,075*

3 1 2130 2,130

* 16X lower value

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Factor 2: Effect of Different Techniques usedFor Collection of Samples- Point Sources

Sampling

Location

SampleNo. Predilutio

n

Raw ODTV(ou)

NetODTV(ou)

Geometric Mean

Net ODTV(ou)

Source 2 1 40 19 760

1 30 50 1,500

2 30 56 1,680 1,588*

3 30 53 1,590

1 20 57 1,140

1 1 123 123

2 1 121 121 124*

3 1 128 128

* 13X lower value

Source PredilutionNet Odour

(ou) Difference

1 50 34,300 16X

None 2,025

2 30 1,600 13X

None 124

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Factor 2: Effect of Dilution-Point Sources

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Different methods: flux chamber method and wind tunnel method

In recent years, several studies in Canada and Europe had shown a significant difference in the results

Wind tunnel technique is a more appropriate method and gives much higher results (up to 11 times higher)

Factor 2: Area Sources

MethodPredilutio

n

Geometric Mean of

OTV Samples

(ou)

Emission Rate

(ou/s/m2)Differenc

e

Wind Tunnel None 760 62 11X

Flux Chamber 20 19,860 5.1

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Factor 2: Study 2 Comparison of Wind Tunnel and Flux Chamber

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In US odour is still regulated based on the ambient levels

Different methods for ambient odour level assessments: collection of ambient samples and evaluation by an odour panel (in Ontario common approach)

Scentometers or Nasal Ranger instruments- mostly in US

Factor 2: Ambient Assessment

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Scentometers-1959 - instrument should not be used any more due to the same deficiency

Results obtained by the Scentometer or Nasal Ranger are based on one person readings and their sensitivity.

No assurance that the operators nose has re-established its peak level of sensitivity, therefore the readings would be lower than results obtained by collecting ambient samples and analysis

1 ou measured might actually be up to 13 ou

Factor 2 (cont’d.): Ambient Assessment

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Study 3Effect of Techniques used for Ambient

AssessmentsLocation Sample Number Odour Concentration Nasal Ranger Ratio Nasal Ranger

determined by on site Odour Concentration in the bag

olfactometer in the Bag ou D/T to Nasal Ranger D/T

Site 1Location 1 Sample 1 48 7 6.9 4

Sample 2 87 7 12.4 4Sample 3 73 7 10.4 4

Location 2 Sample 1 91 15 6.1 7

Sample 2 86 15 5.7 7Sample 3 60 7 8.6 4

Site 2Location 1 Sample 1 26 4 6.5 2

Sample 2 34 4 8.5 2Sample 3 48 4 12.0 NM*

Location 2 Sample 1 38 4 9.5 2

Sample 2 52 4 13.0 2Sample 3 122 NM* ND** 7

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Study 3Effect of Techniques used for Ambient Assessments

Location Sample Odour Concentration Nasal Ranger Ratio Nasal Ranger Readings

Number determined by Readings Odour Concentration in the Bag

olfactometer on site in the Bag ou D/T to Nasal Ranger D/T

Location 1 Sample 1 164 60 2.7 30Sample 2 128 60 2.1 15Sample 3 178 60 3.0 15

Location 2 Sample 1 262 100 2.6 30

Sample 2 186 60 3.1 15Sample 3 207 60 3.5 30

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Losses of odour might be significant, when compounds are not stable (H2S)

Analysis should be done within few hours

ORTECH performs analysis within 6 hours (preferably) but not exceeding 12 hours

Factor 3: Time between the samplingand odour evaluation

Factor 4: Types of Olfactometers Different types of olfactometers: one station

and multiple station Multiple station-evaluation of samples at the

same time by 6 or 8 panelists (ORTECH has 8) One station-evaluation done by one panelist at

a time (greater error in the results due to several factors such as uncertainty in using the same dilution for all panelists, short mixing time, possible contamination of the system with so many dilution changes for each panelist)

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European Standard EN 13725:2003 requires panelists with an average sensitivity of 20 ppb to 80 ppb for n- butanol

One laboratory uses panelists with average sensitivity of 20-30 ppb and second with 70-80 ppb

Difference in the results by a factor of about 3-4 times

1 ou measured might actually be 3 ou or 4 ou just by selecting the panelists

Factor 5: Panelist Selection

Compliance with odour regulations such as 1 ou or 0.5 ou is difficult to demonstrate unless a proper sampling methodology is developed, approved and followed by all consultants

1ou might be very easily 10 ou or greater and will depend on factors such as:

• Methodology used for the collection of the samples, their evaluation, time elapsed between sampling and analysis, omitting significant odour sources at the plant, ambient techniques for assessing ambient odours

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Conclusions

When assessing odours at the facility it is important to include all sources in the plant (point, area, fugitive)

Proper sampling methodology is required especially when sampling at hot, humid sources (dilution technique) to avoid any odour losses during sampling

Undilution technique should not be used for collection of samples from hot , humid sources

Limit the time between sampling and evaluations

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Conclusions (cont’d.)

When sampling at area sources a wind tunnel technique is the preferred technique under conditions where the wind might have some influence on emissions

When assessing ambient levels the technique with collection of ambient samples and evaluation by a dynamic olfactometry is the preferred method

Scentometers should be not used due to their deficiencies

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Conclusions (cont’d.)

Final CommentRegulation of 1 ou or 0.5 ou is unrealistic unless step by step sampling and analysis methodologies are followed

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Contact Information

Anna H. Bokowa, M.Sc.Manager, Odour

Assessment

ORTECH Environmental804 Southdown RoadMississauga, Ontario

L5J 2Y41-877-774-6560, Ext. 669

abokowa@ortech.ca