Ammonia Measurement Techniques

Ji-Qin (Jee-Chin) Ni, Ph.D.

Dept. of Agricultural and Biological EngineeringPurdue University

October 21, 2008Albuquerque, New Mexico

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

Where Is Ammonia a Concern

• Animal barns• Open feedlots• Manure storages• Manure treatment plants • Manure application fields• Farm neighboring area

Why Sampling Ammonia

• Very difficult to catch all the air for ammonia determination

• Reduce cost

• Increase efficiency

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.

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

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

Sampling Volume

• Important for wet chemistry, gas tubes, and other methods

• Not for optical open-path sampling

Not always needed

FTIR for ammonia measurement

Sampling Methods

Sampling method

Closed Point Open path

Exposure Extraction

Localized Centralized

Passive, diffusion

Active with pump

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 • …

Single or Multi-Point Sampling

Gas sampling

Gas sampling

Gas sampling probe

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

Open-Path Sampling

Light source

Detector

Open-path

Emission source

Sampling at 1-dimensional pathPath length: 75 – 500 m

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

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.

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

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

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

Wet Chemistry

Sample air

To concentration determination

Flow rate and time control

Exhaust

Acid solution

Flow meter Pump

pH Test Paper

• Add distilled water

• Wave in air

• Compare color

Low cost: $0.05/test

Low accuracy: ±5 ppm

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

Electrochemical Sensor

Drager

GasAlert

Cost: $495

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

Photoacoustic Infrared Monitor

Multi-gas (up to 6)

Cost: >$30k

Innova Multi-gas monitor

Photo-acoustic Infrared

Sensitive (1 ppm)

Cost: ~$5k

Maintenance: low

Measurement range: 0-100 ppm or 0-1000 ppm

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

Chemcassette Detection System

Cost: ~$5000Cassette: ~$50

Exhaust air

Sample air

Photo-optical detector

Cable Chemcassette

Tape

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.

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:

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?

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?

Methodology and Standards

• QAQC• Methodology

- Sampling & measurement devices

- Comparison of devices- …

• Standards- Terminology- Sampling device & procedure- Measurement- Testing procedures - Calibration (gases)

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.