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Ammonia Measurement Techniques
Ji-Qin (Jee-Chin) Ni, Ph.D.
Dept. of Agricultural and Biological EngineeringPurdue University
October 21, 2008Albuquerque, New Mexico
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Why Measuring Ammonia
• Risk assessment
• Scientific research
• Pollution abatement
• Policy-making
Feed and grazing
Bedding material
Manure
Meat, milk, and eggs to market
Gases, dust, and odor to atmosphere
Organic N and NH4+
to soil and water
Gases, dust, and odor to atmosphere
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Where Is Ammonia a Concern
• Animal barns• Open feedlots• Manure storages• Manure treatment plants • Manure application fields• Farm neighboring area
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Why Sampling Ammonia
• Very difficult to catch all the air for ammonia determination
• Reduce cost
• Increase efficiency
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What Is Ammonia Sampling
• The technique or procedure that determines the location where the air sample is taken, controls the time (when, how long, how frequent) of measurement, and regulates the mass (volume) of air sample to be measured.
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Sampling Location
• Animal & worker exposure: breathing zone
• Emission rate: background & exhausts
• Dispersion modeling: upwind, source, & downwind
Dealing with spatial variations and depending on objective of measurement
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Sampling Time
• Diel (diurnal) variations• Seasonal variations• Variations caused by ventilation or wind
Dealing with temporal variations
0
4
8
12
16
0 3 6 9 12 15 18 21 24
Time, hour of day
Co
nce
ntr
atio
n, m
g/m
3
0
50
100
150
200
250
Ven
tilat
ion
, 100
0 m
3 /h Wall fans
Ventilation
Headspace
Pit fans Example: NH3
variations in a swine barn
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Sampling Volume
• Important for wet chemistry, gas tubes, and other methods
• Not for optical open-path sampling
Not always needed
FTIR for ammonia measurement
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Sampling Methods
Sampling method
Closed Point Open path
Exposure Extraction
Localized Centralized
Passive, diffusion
Active with pump
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Closed: Sampling Chamber
Flow controller Stirring fan
In-situ analysis
Zero-air
Inlet air Outlet air
Ammonia release surface
Lab analysis
Ambient air
Filtered air
Other names:• Lindvall box• Dynamic chamber• Convective flux chamber• Wind tunnel• Measuring chamber • …
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Single or Multi-Point Sampling
Gas sampling
Gas sampling
Gas sampling probe
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Multi-Point Extraction Sampling
`
Loc#1
2
3
4
5 0 10 20 30 40 50 60 70 min
A single set of equipment shared by different sampling locations
1
2
3
4
5
1
2
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Open-Path Sampling
Light source
Detector
Open-path
Emission source
Sampling at 1-dimensional pathPath length: 75 – 500 m
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Selection of Sampling Methods (1)
Closed sampling
Point sampling Open-path sampling
Cost Equipment Low Very low for exposure method.
Medium for localized extraction method. High for centralized extraction method.
Medium to very high
Setup Medium Very low to high for exposure and localized extraction methods. Very high for centralized extraction method.
Low to medium
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Selection of Sampling Methods (2)
Closed sampling Point sampling Open-path sampling
Study objectiveTreatment comparison and surface release.
Animal and human exposure, baseline emission, treatment comparison, and dispersion modeling.
Human ambient exposure, baseline emission, treatment comparison, and dispersion modeling.
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Selection of Sampling Methods (3)
Closed sampling
Point sampling Open-path sampling
Technical aspect Size of sampling area Small release
surfaceFlexible Large
Intrusiveness Intrusive Little intrusive Non-intrusive
Controllability Controllable for airflow at release surface
Controllable for sampling flow
Not controllable
Source isolation Very good Good Poor
Instrument sharing Yes Yes in centralized extraction method
Yes for scanning system
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Concentration and Emission
Measurement objectives Measurement variables
Air pressure
Air exchange rate or air speed
Air temperature
Indispensable Optional
Ammonia concentration
Emission baseline
Dispersion modeling
Human/animal exposure
Comparison study
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Selection of Measurement Devices
W/D Sens Pt/path Readout Sensor Active/passive Response CostWet chemistry Wet 0.01-1mg/L Point Indirect S A h L 5pH paper/test strip Wet ppm Point Direct S P s VLGas tubes Dry ppm Point Direct S A min LPassive gas tubes Dry ppm Point Direct S P h LPassive sampler Dry ppb Point Indirect S P h LElectrochemical Dry ppm Point Direct M A; P HNOx analyzers Dry ppb Point Direct M A 2 min VHFTIR spectroscopy Dry ppb Path Direct M P VHRosemount NDIR Dry ppm Point Direct M A s H-VHPAS 1302 Dry 0.01-1ppm Point Direct M A 35 s VHUV-ODAS Dry ppb Path Direct M P HChemcassette Dry ppm Point Direct S A s HSolid state sensor Dry ppm Point Direct M P s M
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Wet Chemistry
Sample air
To concentration determination
Flow rate and time control
Exhaust
Acid solution
Flow meter Pump
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pH Test Paper
• Add distilled water
• Wave in air
• Compare color
Low cost: $0.05/test
Low accuracy: ±5 ppm
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Gas Detection Tubes
Gas tube
Chain
Hand-pump
Direction of sample airflow and tube color change
Tube connector Concentration scale
• Active tube (need a pump)
• Passive tube (does not need pump
• $5-10 per tube
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Electrochemical Sensor
Drager
GasAlert
Cost: $495
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Chemiluminescence Analyzers
PMT
NO signal [NO]
O3
O3
Exhaust
[NO2] = [NOx] - [NO]
“NOx”
as NO
NO2 NO
NO2 + NO
Sample air
NO2* detection chamber NOx signal
[NO]
Ozone generator
NO2* detection chamber
PMT Converter
NOx detection pathway
NO detection pathway
Sensitive (1 ppb ±0.5ppb)
Cost: ~$20k
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Photoacoustic Infrared Monitor
Multi-gas (up to 6)
Cost: >$30k
Innova Multi-gas monitor
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Photo-acoustic Infrared
Sensitive (1 ppm)
Cost: ~$5k
Maintenance: low
Measurement range: 0-100 ppm or 0-1000 ppm
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Infrared Analyzer
Model Rosemount 880A, Cost: ~$25k
Chopper
Infrared sources
Reference cell Sample cell
Air sample in
Air sample out
Component of interest
Other molecules
Detector
Diaphragm distended Signal
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Chemcassette Detection System
Cost: ~$5000Cassette: ~$50
Exhaust air
Sample air
Photo-optical detector
Cable Chemcassette
Tape
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Importance of Data Quality
• Data quality is critical to any research program.
• Erroneous data are worse than no data because bad data misleads scientific conclusions, regulatory decisions, abatement technique evaluations, and health risk assessments.
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Bias and Precision
*
High bias + low precision = low accuracy Low bias + low precision = low accuracy
High bias + high precision = low accuracy Low bias + high precision = high accuracy
* * * * *
* * *
* *
*
* *
* *
* * * * * * * *
* * * * * * * *
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Quality Assurance
Accuracy
Bias
Precision
Operation
Measurement devices:
Interferences Sensitivity
Data processing
Temporal variationSampling:
Devices & procedureSpatial variation
GasesProcedure
Calibration:
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Errors: Calibration Gases
0
10
2030
40
50
60
53.1 ppm 33.2 ppm 9.33 ppmA
mm
on
ia, p
pm Certified
Reading
Three NH3
cylinders
05
101520253035
29.6 ppm 9.6 ppm
Am
mo
nia
, p
pm
Re-Certified
Reading
Two re-certified NH3 cylinders
How much can we trust?
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Errors: Measurement Devices
Three sensors 1. EC sensors 2. Active gas tubes 3. Passive gas tubes
Example: (Wheeler et al. 2000)
Performances - Lab: Good. - Chambers: Not good. - Layer houses: poor.
• Interferences
• Relative errors
• Absolute errors?
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Methodology and Standards
• QAQC• Methodology
- Sampling & measurement devices
- Comparison of devices- …
• Standards- Terminology- Sampling device & procedure- Measurement- Testing procedures - Calibration (gases)
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Reference cited: Ni, J.-Q. and A. J. Heber. 2008. Sampling and measurement of ammonia at animal facilities. Advances in Agronomy, vol. 98, Chapter 4. pp. 201-269. D.L. Sparks, ed. San Diego: Elsevier Academic Press Inc.