1

Practical Odour assessment

Nigel Gibson

Odour - the problem

The process of concern

Local residents

2

Topics covered

• Complaints• Off-site survey• Odour/odorant sampling• Odour/odorant measurement• Odour assessment

Objectives of odour monitoring

• Establish whether nuisance exists• Enable mitigation program to be defined

3

Complaints

• Sign of problems with a plant or process• Level of complaints may not represent the

true feeling of the community• Complaint level will vary with time

Factors affecting human response

• Physiological factors - age, sex, health...• Social factors - custom, habit, attitude to

source, past experiences...• Meteorological - temperature, humidity...• Local politics

4

Example site - year 1

complants year 1

09/01/98

23/01/98

06/02/98

20/02/98

06/03/98

20/03/98

03/04/98

17/04/98

01/05/98

15/05/98

29/05/98

12/06/98

26/06/98

10/07/98

24/07/98

07/08/98

21/08/98

04/09/98

18/09/98

02/10/98

16/10/98

30/10/98

13/11/98

27/11/98

date

co

mp

lain

t d

ay

s

complants

Example site - year 2

complaints

20/0

1/99

03/0

2/99

17/0

2/99

03/0

3/99

17/0

3/99

31/0

3/99

14/0

4/99

28/0

4/99

12/0

5/99

26/0

5/99

09/0

6/99

23/0

6/99

07/0

7/99

21/0

7/99

04/0

8/99

18/0

8/99

01/0

9/99

15/0

9/99

29/0

9/99

13/1

0/99

27/1

0/99

10/1

1/99

24/1

1/99

08/1

2/99

month

co

mp

lain

t d

ay

complaints

5

Figure 4 odour control parameters v complaints

0

5

10

15

20

25

30

35

40

45

21/05/98 26/05/98 31/05/98 05/06/98 10/06/98 15/06/98 20/06/98 25/06/98 30/06/98

day

be

d te

mp

. (d

eg

C)

0

1

2

3

4

5

6

7

8

9

10

pH

bed temperature

complaints

mex temp

bed pH

acidic pH

Odour Control Parameters v Complaints

Figure1 showing wind speed, direction and complaints in June 1998

0.0

90.0

180.0

270.0

360.0

3600

3624

3648

3670

3694

3718

3742

3766

3790

3814

3838

3862

3886

3910

3934

3958

3982

4006

4030

4054

4078

4102

4126

4150

4174

4198

4222

4246

4270

4294

4318

4342

4366

Hour

Win

d d

ire

cti

on

(d

eg

ree

s f

rom

no

rth

)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

win

ds

pe

ed

(m

/s)

winddirection

complaints

WIND SPEED

Wind Speed Direction and Complaints in June 1998

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Community based techniques

• Diaries:• useful, especially if the event is short-term, and out of

hours• some discretion in assessing usefulness. (Validation

by complaints?)• Care needed to interpret diaries (some exaggeration

possible, Validation by complaints?)

• Community surveys:• Expensive if done well• Ideally large population base require• Can differentiate between sources.

Boundary fence/off-site survey 1

Many authorisations contain:

• general odour condition “ ……..no offensive odour……………. as perceived by the local authority inspector”

• routine boundary monitoring by operator

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Boundary fence/off-site survey 2

Advantages:• cheap• easy (?)Disadvantages:• positive results only under extremes

conditions• discrete test• are the results believed?• observer fatigue

Off-site survey method 1

Method proposed in guidance to WML regulators (EA website) based on assessment of:

Intensity + Extent + Sensitivity of Location

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Off-site survey method 2

Intensity1. No detectable odour2. Faint odour (barely detectable, need to stand still and

inhale facing into the wind)3. Moderate odour (odour easily detected while walking

and breathing normally, possibly offensive)4. Strong odour (bearable, but offensive odour - will my

clothes/hair smell?)5. Very strong odour (this is when you really wish you

were somewhere else)

Off-site survey method 3

Extent (assuming odour detectable, if not then 0)

1. Local and impersistent (only detected during brief periods when wind drops or blows)

2. Impersistent as above, but detected away from site boundary

3. Persistent, but fairly localised4. Persistent and pervasive up to 50 m from site

boundary5. Persistent and widespread (odour detected >50 m

from site boundary)

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Off-site survey method 4

Sensitivity of Location where Odour Detected (assuming detectable, if not then 0)

1. Remote (no housing, commercial/industrial premises or public area within 500 m)

2. Low sensitivity (no housing, etc. within 100 m of area affected by odour)

3. Moderate sensitivity (housing, etc. within 100 m of area affected by odour)

4. High sensitivity (housing, etc. within area affected by odour)

5. Extra sensitive (complaints arising from residents within area affected by odour)

Sampling

• Point sources• Open surfaces - with gas flow• Open surfaces - without gas flow

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Point sources

Open surfaces - with gas flow

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Open surfaces - without gas flow

Open surfaces - without gas flow

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Odour measurement/quanitification

• Compound specific techniques• Complex chemical analysis• Olfactometry

Compound specific techniques

• Specific odorants e.g. NH3, RNH2, H2S, RHS

• Marker compounds H2S, methane etc.

Not necessarily a direct correlation with odour

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Marker compounds- landfill

Marker compounds- STW

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Marker compounds- brickworks

Figure 1 Odour and H2S concentrations throughout one kiln cycle

0.E+00

5.E+05

1.E+06

2.E+06

2.E+06

3.E+06

3.E+06

4.E+06

4.E+06

5.E+06

5.E+06

6:18

7:20

8:15

9:14

10:1

3

11:1

3

12:1

4

13:1

4

14:1

6

15:1

6

16:1

5

17:1

7

18:1

6

19:1

5

20:1

7

21:1

5

time

Od

ou

r c

on

ce

ntr

ati

on

(o

u/m

3)

0

0.5

1

1.5

2

2.5

3

3.5

time

H2

S c

on

ce

ntr

ati

on

(p

pm

)

tot odour

tot h2s

Complex chemical analysis

Adsorption followed by GC-FID or GC-MS‘Electronic nose’

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Chemical analysis - GC

Gas chromatography is a widely used analytical technique for characterising odour emissions

Advantages:• Provides quantitative analysis for a broad

range of chemicals

Chemical analysis - GC

Disadvantages

• Does not detect inorganic species, e.g. ammonia & hydrogen sulphide

• Poor detection of highly reactive species• Time resolution of passive sampling is poor

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Chemical analysis - GC

Chemical Analysis (3)

• Does not take into account additive effects, e.g.

Compensation IabIa+Ib

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Electronic nose 1

Electronic sensors work in 1 of 2 ways:

Chemical reaction:- responds to the products (or starting materials) of reaction

Micro-environmentally sensitive:- functions by reaction changes occurring in electrical properties. Mixture not substance specific

Electronic nose 2

In the future the electronic nose may offer a practical solution for objectively assessing odours.

Unlike gas chromatography the electronic nose measures all components in a mixture at any one time.

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Electronic nose 3

Olfactometry 1

It involves the step-wise dilution of a sample of odour-free air and subsequent presentation to a panel of observers in order to determine the number of dilutions required for odour to be perceived by 50% of the members of the panel.

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Olfactometry 2

1 odour unit =

The amount of odorant(s) that, when evaporated into 1 cubic metre of odourless gas at STP, causes a physiological response from a panel (detection threshold) equivalent to that elicited by 40ppb (0.123mg/m3) of n-butanol

Source: CEN TC264/WG2

Olfactometry 3

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Olfactometry 4

Olfactometry 5

% Negative response50%10 000

100 000

2

4

3

56789

45 000

Log

10(D

ilutio

n)

Log10 (Dilution) Vs % Negative response

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Impact assessment overview

Screening or detailed modelling?

• Screening èemission factor data, e.g. for pig farming:weaners 6 ou/animal/sdry sow 19.1 ou/animal/sboar 22.6 ou/animal/sèsimple model (dmax)

• Detailed - full measurement (olfactometry) and modelling study (ADMS, AERMOD)

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Odour assessment criteria

• Two components:èa concentration component, and èa percentage compliance component.

E.g.Odour concentration shall not exceed X OU/m 3 , corrected for the appropriate peak to mean ratio, for more than Z% of the meteorological conditions.

Criteria used in UK

5 ou/m3 as a 98th%ile of 1 hour averages

• set using pre-1995 Dutch data• Dutch correction factor: 1 ouE/m3 =2 GE/m3

therefore criteria should now read:2.5 ou/m3 as a 98th%ile of 1 hour averages

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Dutch criteria (NER 2000)

Process Target98th%ile

Limit98th%ile

Bakeries 5Breweries 1.5Slaughterhouse 0.55 1.5Meat processing 0.95 2.5Grass drying 2.5Coffee roaster 3.5Animal feed plant 1composting 0.5 1.5wwtw 0.5-3.5

Example output as a 98th%ile

348000.00 348400.00 348800.00 349200.00 349600.00 350000.00461000.00

461200.00

461400.00

461600.00

461800.00

462000.00

462200.00

462400.00

462600.00

462800.00

463000.00

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Summary

complaints Off-siteassessment

Monitoring Impactassessment

Nuisanceassessment

Yes Yes Possibly Yes

Mitigationprogram

Possibly Possibly Yes Yes