September 2000
Environmental Technology
Verification Report
UNISEARCH Associates
LasIR® Tunable Diode Laser
Open-Path Monitor
Prepared by
^11^
Battelle
. . . Putting Technology To Work
Under a cooperative agreement with
SEPA U.S. Environmental Protection Agency
ElV ElV ElV
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September 2000
Environmental Technology Verification
Report
ETV Advanced Monitoring Systems Center
UNISEARCH Associates
LasIR® Tunable Diode Laser
Open-Path Monitor
By
Jeffrey Myers
Thomas Kelly
Charles Lawrie
Karen Riggs
Battelle
Columbus, Ohio 43201
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Notice
The U.S. Environmental Protection Agency (EPA), through its Office of Research and
Development, has financially supported and collaborated in the extramural program described
here. This document has been peer reviewed by the Agency and recommended for public release.
Mention of trade names or commercial products does not constitute endorsement or
recommendation by the EPA for use.
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the
Nation's air, water, and land resources. Under a mandate of national environmental laws, the
Agency strives to formulate and implement actions leading to a compatible balance between
human activities and the ability of natural systems to support and nurture life. To meet this
mandate, the EPA's Office of Research and Development (ORD) provides data and science
support that can be used to solve environmental problems and to build the scientific knowledge
base needed to manage our ecological resources wisely, to understand how pollutants affect our
health, and to prevent or reduce environmental risks.
The Environmental Technology Verification (ETV) Program has been established by the EPA to
verify the performance characteristics of innovative environmental technology across all media
and to report this objective information to permitters, buyers, and users of the technology, thus
substantially accelerating the entrance of new environmental technologies into the marketplace.
Verification Organizations oversee and report verification activities based on testing and Quality
Assurance protocols developed with input from major stakeholders and customer groups
associated with the technology area. At present, there are 12 environmental technology areas
covered by ETV. Information about each of the environmental technology areas covered by ETV
can be found on the Internet at http://www.epa.gov/etv.htm.
Effective verifications of monitoring technologies are needed to assess environmental quality and
to supply cost and performance data to select the most appropriate technology for that assess-
ment. In 1997, through a competitive cooperative agreement, Battelle was awarded EPA funding
and support to plan, coordinate, and conduct such verification tests for "Advanced Monitoring
Systems for Air, Water, and Soil" and report the results to the community at large. Information
concerning this specific environmental technology area can be found on the Internet at
http://www.epa.gov/etv/07/07_main.htm.
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Acknowledgments
The authors wish to acknowledge the support of all those who helped plan and conduct the
verification test, analyze the data, and prepare this report. In particular we would like to thank
Adam Abbgy and Paul Webb of Battelle and Gervase Mackay, Alak Chanda, and Doug Beynon
of UNISEARCH Associates, Inc.
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Contents
Notice ii
Foreword iii
Acknowledgments iv
List of Abbreviations ix
1. Background 1
2. Technology Description 2
3. Test Design and Procedures 3
3.1 Introduction 3
3.2 Test Design 5
3.3 Experimental Apparatus and Materials 7
3.3.1 Standard Gases 7
3.3.2 Dilution Gas 7
3.3.3 Gas Dilution System 7
3.3.4 Gas Cell 7
3.3.5 Temperature Sensor 7
3.3.6 Relative Humidity (RH) Sensor 7
3.3.7 Carbon Dioxide Monitor 8
3.3.8 NO/NH3 Monitor 8
3.3.9 HF Measurement 8
3.3.10 Methane Measurement 8
3.4 Test Parameters 9
3.4.1 Minimum Detection Limit 9
3.4.2 Linearity 9
3.4.3 Accuracy 9
3.4.4 Precision 10
3.4.5 Interferences 10
4. Quality Assurance/Quality Control 11
4.1 Data Review and Validation 11
4.2 Changes from the Test/QA Plan 11
4.3 Calibration 13
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4.3.1 Gas Dilution System 13
4.3.2 Temperature Sensor 13
4.3.3 RH Sensor 14
4.3.4 Carbon Dioxide Monitor 14
4.3.5 NO/NH3 Monitor 14
4.3.6 HF Measurement 14
4.3.7 Methane Measurement 14
4.4 Data Collection 14
4.5 Performance Systems Audits 15
4.5.1 Technical Systems Audit 15
4.5.2 Performance Evaluation Audit 16
4.5.3 Data Quality Audit 17
5. Statistical Methods 18
5.1 Minimum Detection Limit 18
5.2 Linearity 18
5.3 Accuracy 18
5.4 Precision 19
5.5 Interferences 19
6. Test Results 20
6.1 Minimum Detection Limit 20
6.2 Linearity 22
6.2.1 Source Strength Linearity 22
6.2.2 Concentration Linearity 23
6.3 Accuracy 26
6.4 Precision 27
6.5 Interferences 27
6.6 Other Factors 29
6.6.1 Costs 29
6.6.2 Data Completeness 29
7. Performance Summary 30
8. References 30
Appendix A: Data Recording Sheet A-l
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Figures
Figure 2-1. UNISEARCH Associates LasIR TDL Open-Path Monitor,
Controller, Telescope, and Retroreflector 2
Figure 3-1. Test Site at Battelle's West Jefferson Facility 5
Figure 3-2. Optical Open-Path Monitor Setup 6
Figure 6-1. Source Strength Linearity Plot for the LasIR 23
Figure 6-2. Concentration Linearity Plot of the LasIR Challenged with Methane 24
Figure 6-3. Concentration Linearity Plot of the LasIR Challenged with
HF 25
Figure 6-4. Concentration Linearity Plot of the LasIR Challenged with
Ammonia 25
Tables
Table 3-1. Target Gases for Testing the LasIR 3
Table 3-2. Optical Open-Path Monitor Verification: Measurement
Order for Each Target Gas 4
Table 4-1. Summary of Data Recording Process for the LasIR
Verification Test 15
Table 4-2. Summary of Performance Evaluation Audit Procedures 16
Table 6-1. MDL Data for the LasIR 21
Table 6-2. Minimum Detection Limits of the LasIR 22
Table 6-3. Source Strength Linearity of the LasIR 22
Table 6-4. Concentration Linearity Data for the LasIR 24
Table 6-5. Results of Accuracy Tests for the LasIR 26
Table 6-6. Data from Precision Tests on the LasIR 28
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Table 6-7. Results of Precision Tests on the LasIR 28
Table 6-8. Concentration Data from Water Interference Tests on the
LasIR 29
Table 6-9. MDL Data from Water Interference Tests on the
LasIR 29
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List of Abbreviations
AMS Advanced Monitoring Systems
CEM continuous emission monitor
C2H2 acetylene or ethenylidene radical
C2H4 ethylene or polyethylene
CH4 methane
cm centimeter
CO carbon monoxide
C02 carbon dioxide
EPA U.S. Environmental Protection Agency
ETV Environmental Technology Verification
GC/FID gas chromatography/flame ionization detection
HC1 hydrochloric acid
HF hydrogen fluoride
H2 hydrogen
H20 water
m meter
MDL minimum detection limit
NDIR nondispersive infrared
NH3 anhydrous ammonia
NIST National Institute of Standards and Technology
N2 nitrogen
NOx nitrogen oxides (= NO + N02)
N02 nitrogen dioxide
02 oxygen
ppm parts per million
ppm*m parts per million meters
QA quality assurance
QC quality control
QMP Quality Management Plan
RH relative humidity
RSD relative standard deviation
S02 sulfur dioxide
TDL tunable diode laser
TSA technical systems audit
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Chapter 1
Background
The U.S. Environmental Protection Agency (EPA) has created the Environmental Technology
Verification (ETV) Program to facilitate the deployment of innovative environmental tech-
nologies through performance verification and dissemination of information. The goal of the ETV
Program is to further environmental protection by substantially accelerating the acceptance and
use of improved and cost-effective technologies. ETV seeks to achieve this goal by providing high
quality, peer-reviewed data on technology performance to those involved in the design,
distribution, permitting, purchase, and use of environmental technologies.
ETV works in partnership with recognized testing organizations; with stakeholder groups
consisting of regulators, buyers and vendor organizations; and with the full participation of
individual technology developers. The program evaluates the performance of innovative tech-
nologies by developing test plans that are responsive to the needs of stakeholders, conducting field
or laboratory tests (as appropriate), collecting and analyzing data, and preparing peer-reviewed
reports. All evaluations are conducted in accordance with rigorous quality assurance protocols to
ensure that data of known and adequate quality are generated and that the results are defensible.
The EPA's National Exposure Research Laboratory and its verification organization partner,
Battelle, operate the Advanced Monitoring Systems (AMS) Center under ETV. The AMS Center
recently evaluated the performance of optical open-path monitors for use in ambient air or fence
line measurements. This verification report presents the procedures and results of the verification
test for the UNISEARCH Associates LasIR tunable diode laser (TDL) open-path monitor.
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Chapter 2
Technology Description
The objective of the ETV AMS Center is to verify the performance characteristics of
environmental monitoring technologies for air, water, and soil. This verification report provides
results for the verification testing of the LasIR. The following description of the LasIR is based on
information provided by the vendor.
The LasIR uses a TDL to measure concentrations of HF, HC1, CH4, H2, CO, C02, NH3, C2H2,
C2H4, NO, and N02. The LasIR controller houses the laser, its temperature and current control
circuits, a reference cell used to lock the absorption feature to line center, an audit cell into which
a known concentration of the gas being measured may be introduced for calibration purposes, and
a computer to operate the system and process and store the measurement data. The controller can
be placed indoors or outdoors and is connected by a fiber optic cable to the measurement sensors,
which can be located kilometers away. A number of sensors can be operated from the controller
simultaneously. The response of the system for most gases is in the range of a few parts per
million per meter.
The light from the laser, which is mounted, with its focusing optics, in a thermoelectric cooler, is
transferred by a fiber optic cable to a telescope, through the open path, onto a retroreflector, and
back to the telescope. About
10% of the light is split off
before entering the
telescope and directed
through a small internal cell
containing the gas being
measured and then to the
reference detector. This
reference signal is used to
lock the laser to the selected
absorption feature and may
^ also act as a transfer
calibration standard.
r-
V
Figure 2-1. UNISEARCH Associates LasIR TDL Open-Path
Monitor, Controller, Telescope, and Retroreflector
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Chapter 3
Test Design and Procedures
3.1 Introduction
This verification test was conducted according to procedures specified in the Test/QA Plan for
Verification of Optical Open-Path Monitors 1(1) The test was designed to challenge the LasIR in a
manner similar to that which would be experienced in field operations, and was modeled after
Compendium Method TO-16.(2) The monitor was challenged using an optically transparent gas
cell filled with known concentrations of a target gas. The gas cell was inserted into the optical
path of the monitor, during operation under field conditions, simulating a condition where the
target gas would be present in the ambient air. The gas cell was used to challenge the monitor in a
controlled and uniform manner.
The monitor was challenged with three target gases at known concentrations, and the measure-
ment result was compared to the known concentration of the target gas. The gases and concentra-
tions used for testing the LasIR are shown in Table 3-1. The verification was conducted by
measuring each gas in a fixed sequence over three days. The sequence of activities for testing the
monitor for each gas is shown in Table 3-2.
Table 3-1. Target Gases for Testing the LasIR
Concentration
Target Gas Concentration
Gas Cell Concentration
Gas
Level
Path Length (ppm*m)
(ppm)a
cl
4
40
Methane
c2
8
80
c3
40
400
c4
80
800
cl
8.3
67
HF
c2
23.0
165-182
c3
61.8
498
c4
68.0
549
cl
7.5
75
Ammonia
c2
15.0
150
c3
25.0
250
c4
49.4
494
a Length of gas cell = 0.100 m for methane, 0.124 m for HF, and 0.100 m for ammonia.
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3.2 Test Design
The verification test was performed from May 22 to May 26, 2000, near West Jefferson, Ohio, at
an outdoor testing area belonging to Battelle. This location provided sufficient length and a direct
line of sight for each of the two path lengths used during the test, and provided an area that was
away from major chemical sources that might affect the testing. The LasIR telescope was
mounted on a 3-foot-tall tripod near the edge of a lightly traveled road and pointed toward a
retroreflector on another tripod located along the road at a distance of 110 meters. This
arrangement produced a total light path of 220 meters. The tripod was subsequently moved down
the road to a distance of 240 meters, producing a light path of 480 meters. The open space in the
foreground of Figure 3-1 shows the test site at Battelle's West Jefferson facility.
m
Figure 3-1. Test Site at Battelle's West Jefferson Facility
The LasIR was challenged with the target gases shown in Table 3-1 at known concentrations, and
the gas measurement by the monitor was compared to the known concentration of the target gas.
For each target gas, the monitor was set up as if it were operating in the field, except that an
optically transparent gas cell was placed in the light beam's path (see Figure 3-2). National
Institute of Standards and Technology (NIST) traceable or commercially certified standard gases,
a calibrated gas diluter, and a supply of certified high-purity dilution gas were used to supply the
target gases to the gas cell.
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OPTICAL OPEN-PATH
MONITOR
GAS CELL
RETROREFLECTOR
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3.3 Experimental Apparatus and Materials
3.3.1 Standard Gases
The standard gases diluted to produce target gas levels for the verification testing were NIST
traceable gases or commercially certified gases. The gases were obtained in concentrations
appropriate for dilution to the concentrations required for the test.
3.3.2 Dilution Gas
The dilution gas was ultra-high-purity (UHP) nitrogen obtained from commercial suppliers.
3.3.3 Gas Dilution System
The dilution system used to generate known concentrations of ammonia and methane was an
Environics 2020 (Serial No. 2428). This system had mass flow capabilities with an accuracy of
approximately ±1%. The dilution system accepted a flow of compressed gas standard to be
diluted with high-purity nitrogen. It was capable of performing dilution ratios from 1:1 to at least
100:1.
The dilution system for HF consisted of a valved Teflon manifold that added the HF gas to the
dilution gas flow from the Environics diluter downstream of the diluter, to avoid damage to the
Environics from the HF. Because this system did not give the close control of concentrations that
was achieved for the ammonia and methane, each of the HF concentrations delivered to the gas
cell was sampled downstream of the cell as described in Section 3.3.9.
3.3.4. Gas Cell
Acrylic or Pyrex gas cells 0.100 in length for methane, 0.124 meter for HF, and 0.100 meter for
ammonia were integrated into the monitor.
3.3.5 Temperature Sensor
A thermocouple with a commercial digital temperature readout was used to monitor ambient air
and test cell temperatures. This sensor was operated in accordance with the manufacturer's
instructions and was calibrated against a certified temperature measurement standard within the
six months preceding the verification test.
3.3.6 Relative Humidity (RH) Sensor
The RH sensor used to determine the ambient air humidity was a commercial RH/Dew Point
monitor that used the chilled mirror principle. This sensor was operated in accordance with the
manufacturer's instructions, which called for cleaning the mirror and rebalancing the optical path
when necessary, as indicated by the diagnostic display of the monitor. The manufacturer's
accuracy specification of this monitor was ±5% RH.
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3.3.7 Carbon Dioxide Monitor
A commercial nondispersive infrared (NDIR) monitor (Gastech Model RI-411 infrared C02
monitor, Serial No. 9350211) was used to monitor the level of C02 in ambient air during
interference measurements. This monitor was operated in accordance with the manufacturer's
instructions and was calibrated with a commercially prepared cylinder standard of C02 in air.
The limit of resolution of this monitor was 25 ppm.
3.3.8 NO/NH3 Monitor
A chemiluminescent nitrogen oxides monitor [Advanced Pollution Instrumentation (API) Model
200, Serial No. 142] was used with a high-temperature ammonia converter (API Model 1000,
Serial No. 100-233-120F-120H) to monitor the NH3 concentrations supplied to the optical cell
for verification testing. This monitor sampled gas immediately downstream of the optical cell to
confirm the NH3 concentrations prepared by dilution of a high-concentration ammonia standard.
The API monitor was calibrated with a NIST-traceable commercial standard cylinder of nitric
oxide (NO) in nitrogen. The conversion efficiency for NH3 was checked by comparing the
calibration slope for NO with that found in calibrations with NH3. All NH3 measurements were
corrected for the NH3 conversion efficiency, which was generally greater than 95%.
3.3.9 HF Measurement
The test/QA plan(1) specified that impinger sampling and ion chromatographic analysis would be
used as a performance evaluation method in selected tests, to confirm the HF concentrations
supplied to the optical cell. However, the difficulty of delivering known HF concentrations to
the optical cell made it necessary to apply this HF measurement in all tests, rather than as a PE
method.
HF was measured by drawing a measured flow of about 2 1/min of gas, from a "T" fitting at the
outlet of the optical cell, through a series of two impingers containing a total of 100 ml of
deionized water. Sampling durations were 5 to 25 minutes, depending on the HF concentration
provided to the cell. The impinger solutions were then analyzed for fluoride ion by ion
chromatography, and the HF concentrations in the optical cell were calculated from the measured
F" concentrations, sampling durations, and sample flow rates.
3.3.10 Methane Measurement
Methane concentrations provided to the optical cell were checked by collecting a sample at the
exit of the cell using pre-cleaned Summa® stainless steel air sampling canisters. The collected
sample was then analyzed for methane by gas chromatography with flame ionization detection
(GC-FID), according to a method based on EPA Method 18. This method used certified
commercial standards of propane in air for calibration.
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3.4 Test Parameters
3.4.1 Minimum Detection Limit
The MDL was calculated for each target gas by supplying pure nitrogen to the test cell in the
optical path of the monitor and taking a series of 25 measurements using integration times of
1 and 5 minutes. The resulting measurements were then analyzed for the target gas. The MDL
was defined as two times the standard deviation of the calculated concentrations.
3.4.2 Linearity
Two types of linearity were investigated during this verification: source strength and con-
centration. Reduction in light intensity is a common occurrence in the field. Rain, fog, snow, and
dirty optics are some of the reasons that the light intensity would change. The source strength
linearity was investigated by measuring the effects of reducing the source intensity on the
monitor's performance. With a constant concentration of methane in the gas cell, and a constant
total path length of 220 meters, the light intensity of the source was reduced by placing an
aluminum wire mesh in the path of the light. These screens were approximately 1 foot square and
had mesh spacings of approximately lA, 'A and 1 inch, respectively. By placing different mesh
sizes in the path, attenuation of the source intensity by as much as 72% was achieved. At each of
these attenuation levels, a measurement was made, and the monitor analyzed for methane.
Concentration linearity was determined by challenging the LasIR with each target gas at cell
concentrations between 40 and 800 ppm, while the path length and integration time were kept
constant. At each concentration, the monitor response was recorded and used to infer the cell gas
concentration. Linearity was evaluated by comparing the inferred cell gas concentration from the
open-path measurement to the input target gas concentration.
3.4.3 Accuracy
Accuracy of the LasIR relative to the gas standards was verified by introducing known
concentrations of the target gas into the cell. The gas cell was first flushed with at least five cell
volumes of nitrogen, and a measurement was recorded. The target gas was then introduced into
the cell and, after flushing with at least five cell volumes, a measurement of the target gas was
obtained. The cell was again flushed with at least five cell volumes of nitrogen, and a third
measurement was recorded. The three measurements were analyzed for the target gas, using the
background selected by the vendor. The concentration of the target gas was calculated as the
second measurement minus the average of the first and third (flushed cell) measurements.
The accuracy was evaluated at concentrations cl through c4 for each of the three target gases
(Table 3-1). Using an integration time of 1 minute and a path length of 220 meters, ammonia
and HF were evaluated. The accuracy was then evaluated at concentration c2 with the same path
length, but using a 5-minute integration time, and then again at concentration c2 during the
interference measurements (Table 3-2), with 5-minute integration and a 480-meter path. The
accuracy was evaluated for methane using an integration time of 1 min and a path length of
9
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1.5 meters. The path length was then changed to 220 meters and the integration time changed to
5 minutes, and the accuracy was evaluated again. The open path measurements of the LasIR were
used to infer the cell gas concentration. The percent accuracy is the difference between the
average value of all the resulting measurements at the same conditions and the concentration in
the gas cell divided by the concentration of the gas in the gas cell, times 100 (see Section 5.3).
3.4.4 Precision
The procedure for determining precision was very similar to the procedure for determining
accuracy. The gas cell was flushed with at least five cell volumes of nitrogen. The target gas was
then introduced into the cell and, after flushing with at least five cell volumes, 25 measurements
of the target gas were obtained. The relative standard deviation (RSD) of this set of measure-
ments was the precision at the target gas concentration. Precision was evaluated by this
procedure at one concentration of each of the target gases (see Table 3-2).
3.4.5 Interferences
The effects of interfering gases were established by supplying the gas cell with a target gas and
varying the path length between the source and detector of the monitor. The purpose of the
interference measurements was to determine the effects of the ambient atmospheric gases on
accuracy and MDL of the LasIR. Using two different integration times, these tests were also
conducted to determine the effect of integration time on the measurements with interfering gases
in the light path.
To determine the effect of the interferences, the gas cell was supplied with nitrogen; and, after
flushing with at least five cell volumes, five measurements were recorded. Next, the target gas
was introduced into the cell and, after similarly flushing the cell, five measurements were
recorded. Finally, nitrogen was again introduced into the cell, and five measurements were
recorded. As in other tests, the cell gas concentration was calculated from the LasIR's open-path
measurements and compared to the input cell gas concentrations.
For HF, this procedure was conducted with path lengths of both 220 and 480 meters, the latter
being the length that UNISEARCH chose as optimum, given that 480 meters was the maximum
length available at the test site. Atmospheric concentrations of H20 and C02 were recorded at the
beginning and end of these measurements. The monitor's sensitivity to the interferant was
calculated by comparing the results at different path lengths (i.e., different ppm*m levels of H20
and C02). For methane, measurements were made with a 1.5-meter path length (i.e., the gas cell
only) to avoid the effect of the ambient methane background concentration. Interference tests
were not conducted for ammonia because the TDL light source used for that target gas did not
allow variation of the path length beyond 220 meters.
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Chapter 4
Quality Assurance/Quality Control
Quality assurance/quality control (QA/QC) procedures were performed in accordance with the
quality management plan (QMP) for the AMS Center(3) and the test/QA plan(1) for this
verification test.
4.1 Data Review and Validation
Test data were reviewed by the Verification Testing Coordinator and disclosed to the
Verification Testing Leader. The Verification Testing Coordinator reviewed the raw data and the
data sheets that were generated each day. Laboratory record notebook entries also were reviewed,
signed, and dated.
4.2 Changes from the Test/QA Plan
Two types of changes from the test/QA plan could occur: planned changes to improve the test
procedures for a specific vendor (amendments) and changes that occurred unexpectedly
(deviations). The deviations from the test/QA plan were as follows:
¦ The test/QA plan calls for a on-over-one data review within two weeks of generating the data.
While the entire data set was reviewed within this two-week period, no documentation of this
task was generated. Although this task was documented after the two-week period, no
reduction in the quality of the data occurred.
¦ The thermocouple used in the verification test to monitor ambient air temperatures was not
calibrated within the previous six months, as specified in the test/QA plan. The thermocouple
used had been calibrated within one year, however, and was still within its calibration
certification period. In addition, the thermocouple temperature measurement agreed with the
mercury bulb thermometer temperature measurement during the performance audit.
¦ The test/QA plan called for acid rain CEM zero nitrogen to be used to flush the cell and as
dilution gas. Instead, ultra-high-purity N2 was used.
¦ The gas concentrations used in the verification test of the LasIR differ from the original
concentrations stated in the test/QA plan. The concentrations stated in the test/QA plan were
11
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based upon the best knowledge of the monitors to be tested at the time the test plan was
written. In actuality, the monitor provided required a different gas concentration range.
¦ No independent performance evaluation was conducted for HF. The method planned for the
performance evaluation (impinger sampling) was adopted for all HF measurements as a
means of establishing the gas cell concentration.
¦ The C02 monitor performance evaluation audit was conducted in April, 2000, and not during
the Unisearch test in May, 2000.
¦ The test/QA plan called for a performance evaluation audit of the NO/NH3 measurement
using a calibration standard obtained from an independent supplier. Instead, a separate NO
standard obtained from the same manufacturer was used for the PE audit.
¦ The test/QA plan stated that the C02 measurement would undergo a performance evaluation
audit using a calibration standard obtained from an independent supplier. Instead, a separate
C02 standard obtained from the same manufacturer was used for the audit.
Deviation reports have been filed for each deviation.
Before the verification test began, several planned amendments were made to the original
test/QA plan to improve the quality or efficiency of the test. These procedural changes were
implemented and, in each case, either increased the quality of the collected data or removed
inefficiencies in the test, ultimately resulting in a reduced test duration. A brief summary of these
variations is provided below:
¦ Although monitoring CO was part of the test/QA plan, it was decided that CO measurements
would not add any useful information to the verification. No CO monitoring was conducted.
¦ The Summa® canister analysis procedure was changed from that specified in the test/QA
plan. The test/QA plan specified using Method 18 to determine the hydrocarbon emissions
from combustion or other source facilities. This method broadly describes an analysis
procedure, but does not specify how the analysis is to be done and calls for the use of Tedlar
bags rather than Summa® canisters. Instead of as described in the test/QA plan, the analysis
was done according to Battelle's GC/FID/MS analysis procedure.
¦ The long and the short path lengths in the test/QA plan, which were specified as 100 and 400
meters, were changed to meet the specific technology requirements of the monitor tested.
¦ The order of testing in the test/QA plan was changed. The test order was originally
developed to maximize the efficiency of the test procedure. Several improvements were made
to the test matrix to further improve its efficiency. For example, instead of conducting all of
the measurements for one gas then changing to the next gas, all of the short path
measurements were conducted before moving to the long path. This was done because
changing the path length was more time consuming than changing the target gas.
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¦ One additional test was added to complete the data set collected. Originally, the test/QA plan
lacked a nitrogen flush after measurement 14, under the same conditions as measurement 14.
This additional measurement was added to the test matrix as measurement #14b (see Table 3-
2).
¦ The schedule of steps in testing (as indicated in Table 3-2 of the test/QA plan) was modified
for this test because of the need to use a 1.5 meter path length in some tests to avoid
atmospheric methane background. Additional tests were performed, to obtain the needed test
data at both short and long paths.
¦ The test/QA plan for verification of optical open-path monitors (Revision 1, dated 10/28/99)
contains a contradiction. Sections 5.3.2, 5.4.2, and 5.5.2 all correctly indicate that the
minimum detection limit (MDL) will be calculated as twice the standard deviation of a series
of measurements taken at zero target gas concentration. However, Section 9.2.1 states an
incorrect equation to calculate the MDL. This revision changes Section 9.2.1 to eliminate the
contradiction.
¦ The test/QA plan specified that source strength linearity would be tested for each of the
gases. The original intent was to conduct this test for one gas only. The source strength
linearity test thus was conducted only for a single gas.
Amendments required the approval of Battelle's Verification Testing Leader and Center
Manager. A planned deviation form was used for documentation and approval of all
amendments.
Neither the deviations nor the amendments had a significant impact on the test results used to
verify the performance of the optical open-path monitors.
4.3 Calibration
4.3.1 Gas Dilution System
Mass flow controllers in the Environics gas dilution system were calibrated prior to the start of
the verification test by means of a soap bubble flow meter. Corrections were applied to the
bubble meter data for pressure, temperature, and water vapor content, when necessary.
4.3.2 Temperature Sensor
The thermocouple was calibrated by comparing it to a certified standard within the six months
preceding the test.
4.3.3 RH Sensor
The RH sensor used the manufacturer's calibration.
13
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4.3.4 Carbon Dioxide Monitor
The NDIR C02 monitor was calibrated before testing using a commercially prepared, certified
standard of C02 in air.
4.3.5 NO/NH3 Monitor
The NO/NH3 monitor was calibrated with both NO and NH3 standards before verification testing
of each open-path monitor. The NO standard was a Certified Master Class Calibration Standard
of 6,960 ppm NO in nitrogen, of ±1% analytical uncertainty (Scott Specialty Gases, Cylinder No.
K026227). The NH3 standard was also a Certified Master Class Calibration Standard, of 494 ppm
NH3 in air, of ± 2% analytical uncertainty (Scott, Cylinder No. ALM 005256). The ratio of the
slopes of the NH3 and NO calibration curves established the NH3 conversion efficiency.
A performance evaluation audit was also conducted once during the test, in which the API
monitor's response was tested with a different NO standard. For that audit, the comparison
standard used was a NIST-traceable EPA Protocol Gas of 3,925 ppm NO in nitrogen, with ±1%
analytical uncertainty (Scott, Cylinder No. ALM 057210).
4.3.6 HF Measurement
Calibration for HF was performed by preparing solutions of known fluoride content by serial
dilution, using deionized water and ACS reagent grade sodium fluoride. These standards were
analyzed with each batch of impinger samples, along with blank samples collected at the
verification test site.
4.3.7 Methane Measurement
The GC/MI ) measurement for methane was calibrated using two standard gases. One was an
EPA Protocol Gas of 32.73 ppm propane in air, with analytical uncertainty of ± 2% (Cylinder
No. AAL 20803, Scott Specialty Gases). The other was a Certified Working Class Calibration
Standard of 340 ppm propane in air, with ± 5% analytical uncertainty (Cylinder No. ALM
025084, also from Scott).
4.4 Data Collection
Data acquisition was performed both by Battelle and the vendor during the test. Table 4-1
summarizes the type of data recorded (see also Appendix A); where, how often, and by whom the
recording is made; and the disposition or subsequent processing of the data. Data recorded by the
vendor were turned over to Battelle staff immediately upon completion of the test procedure.
Test records were then converted to Excel spreadsheet files.
4.5 Performance Systems Audits
14
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4.5.1 Technical Systems Audit
A technical systems audit (TSA) was conducted on April 13 and 14, for the open-path monitor
verification test conducted in early 2000. The TSA was performed by Battelle's Quality Manager
as specified in the AMS Center QMP. The TSA ensures that the verification test is conducted
according to the test/QA plan(1) and that all activities associated with the test are in compliance
with the ETV Center QMP.(3) Specifically, the calibration sources and methods used were
reviewed and compared with test procedures in the test/QA plan. Equipment calibration records
and gas certificates of analysis were reviewed. The conduct of the testing was observed and
compared to the test/QA plan. The performance evaluation audit conducted by the staff was
observed, and the results were assessed.
Table 4-1. Summary of Data Recording Process for the LasIR Verification Test
Recorded
Where
Data Recorded
By
Recorded
When Recorded
Disposition of Data
Dates, Times, Test
Battelle
Data Sheet
Start of each test,
Used to compile result,
Events
whenever testing
manually entered into
conditions
spreadsheet as necessary
changed
Test Parameters (temp.,
Battelle
Data Sheet
Every hour during
Transferred to
RH, etc.)
testing
spreadsheet
Interference Gas
Battelle
Data Sheet
Before and after
Transferred to
Concentrations
each measurement
spreadsheet
of target gas
Target Gas
Battelle
Data Sheet
At specified time
Transferred to
Concentrations
during each test
spreadsheet
Optical Open-Path
Vendor
Data Sheet
At specified time
Transferred to
Monitor Readings
during each test
spreadsheet
All findings noted during the TSA on the above dates were documented and submitted to the
Verification Testing Coordinator for correction. The corrections were documented by the
Verification Testing Coordinator and reviewed by Battelle's Quality Manager, Verification
Testing Leader, and Pilot Manager. None of the findings adversely affected the quality or
outcome of this verification test, and all were resolved to the satisfaction of the Battelle Quality
Manager. The records concerning the TSA are permanently stored with the Battelle Quality
Manager.
In addition to the internal TSA performed by Battelle's Quality Manager, an external TSA was
conducted by EPA on April 14, 2000. The TSA conducted by EPA included all the components
listed in the first paragraph of this section. A single finding was noted in this external TSA,
which was documented in a report to the Battelle Center Manager for review. A response and
15
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corrective actions were prepared and returned to EPA. The findings did not adversely affect the
quality or outcome of this verification test.
4.5.2 Performance Evaluation Audit
A performance evaluation audit was conducted to assess the quality of the measurements made in
the verification test. This audit addressed only those measurements made by Battelle in con-
ducting the verification test. The performance audit procedures (Table 4-2) were performed by
the Battelle technical staff responsible for the measurements. Battelle's Quality Manager was
present to assess the results. The performance evaluation audit was conducted by comparing test
measurements to independent measurements or standards.
The results from the performance evaluation audit are shown in Table 4-2. The temperature
measurement agreed to within 0.5 °C and the relative humidity agreed to within 0.1% RH. The
carbon dioxide monitor was calibrated before the test and agreed to within 25 ppm (i.e., within
the resolution of the monitor) at 600 ppm.
Table 4-2. Summary of Performance Evaluation Audit Procedures
Measurement
Expected
Actual
Audited
Audit Procedure
Reading
Reading
Difference
Temperature
Compare to independent temperature
measurement (Hg thermometer)
9.6°C
10.1°C
0.5°C
co2
Compare measurement using an
independent carbon dioxide standard
600 ppm
625 ppm
4.2%
RH
Compare to independent RH measurement
(wet/dry bulb device)
70% RH
70.1% RH
0.14%
Methane
Compare to results of gas chromatographic
analysis of canister samples
80 ppm
88 ppm
10%
NO/NH3
Compare to measurement using an
independent NO standard
150 ppm
152 ppm
1.3%
The methane concentrations were audited by independent analysis of the test gas mixture
supplied to the gas cell during verification testing. The results of the performance audit for the
target gas concentrations were within 10% of the expected concentrations, which met the test/QA
plan criterion.
The performance evaluation of the NO/NH3 monitor was based on analysis of a different NO
standard than that ordinarily used for calibration. As Table 4-2 shows, the agreement of the
performance evaluation standard with the calibration of the monitor was within 2 ppm at
150 ppm NO.
No performance evaluation audit was conducted for HF, because the impinger sampling
procedure planned for use as a PE method was instead used routinely to determine HF con-
centrations in all verification tests with that gas. This change in procedure was necessitated by
16
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the difficulty of supplying accurately known HF concentrations to the test cell, using dilution of a
commercial HF standard.
4.5.3 Data Quality Audit
Battelle's Quality Manager audited at least 10% of the verification data acquired in the verifica-
tion test. The Quality Manager traced the data from initial acquisition, through reduction and
statistical comparisons, to final reporting. All calculations performed on the data undergoing
audit were checked.
17
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Chapter 5
Statistical Methods
The following statistical methods were used to reduce and generate results for the performance
factors.
5.1 Minimum Detection Limit
The MDL is defined as the smallest concentration at which the monitor's expected response
exceeds the calibration curve at the background reading by two times the standard deviation (c0)
of the monitor's background reading.
MDL = 2a
O
5.2 Linearity
Both concentration and source strength linearity were assessed by linear regression with the
certified gas concentration as independent variable and the monitor's response as dependent
variable. Linearity was assessed in terms of the slope, intercept, and correlation coefficient of the
linear regression.
y = mx + b
where _y is the response of the monitor to a target gas, x is the concentration of the target gas in
the optical cell, m is the slope of the linear regression curve, and b is the zero offset.
5.3 Accuracy
The relative accuracy (A) of the monitor with respect to the target gas was assessed by
R-T
=—x 100
A
R
where the bars indicate the mean of the reference (R) values and monitor (T) results.
18
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5.4 Precision
Precision was reported in terms of the percent RSD of a group of similar measurements. For a set
of measurements given by T\, T2,Tn, the standard deviation (a) of these measurements is
O =
1/2
where T is the average of the monitor's readings. The RSD is calculated from
RSD =
x 100
and is a measure of the measurement uncertainty relative to the absolute value of the
measurement. This parameter was determined at one concentration per gas.
5.5 Interferences
The extent to which interferences affected MDL and accuracy was calculated in terms of
sensitivity of the monitor to the interferant species, relative to its sensitivity to the target gas, at a
fixed path length and integration time. The relative sensitivity is calculated as the ratio of the
observed response of the monitor to the actual concentration of the interferant. For example, a
monitor that indicates 26 ppm of methane in air with an interference concentration of 100 ppm of
C02 indicates 30 ppm of methane when the C02 concentration is changed to 200 ppm. This
would result in an interference effect of (30 ppm - 26 ppm)methane/(200 ppm - 100 ppm)C02 = 0.04,
or 4% relative sensitivity.
19
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Chapter 6
Test Results
The results of the verification test of the LasIR are presented in this section, based upon the
statistical methods shown in Chapter 5. The monitor was challenged with methane, HF, and
ammonia over path lengths of 1.5, 220, and 480 meters, which cover typical path lengths for this
monitor. These gases were chosen because they are targeted in key market areas for the vendor.
Test parameters include minimum detection limit, linearity, accuracy, precision, and the effects
of atmospheric interferants on concentration measurements. In many cases, verification results
are based on comparing the test cell concentration of target gas calculated from the LasIR's open-
path measurement to the actual gas cell concentration. In addition, where appropriate, the path-
average concentrations are noted. The path-average concentration is determined by multiplying
the gas cell concentration by the gas cell length and then dividing by the total path length used
during the given measurement.
6.1 Minimum Detection Limit
The MDL was calculated from the variability of measurements in which there were no target
gases in the gas cell, but in which the monitor analyzed the absorption data for the presence of a
target gas. In the case of methane, it is not possible to eliminate the methane from the atmo-
spheric measurement path, so scatter would result in the data from variation in the ambient
methane. Therefore, the MDL measurements for methane were performed at a path length of
1.5 meters, i.e., by excluding atmospheric methane entirely. The data used to determine the MDL
were obtained under several experimental conditions, including different path lengths and
integration times, as shown in Table 6-1.
Table 6-2 shows the results of the MDL calculations. As is common practice, units of ppm*m are
shown in Table 6-2. This is the path length of the measurement times the path-average
concentration for that measurement.
Table 6.2 summarizes the LasIR MDL measurements. Based on measurements made with path
lengths of 1.5 m (methane), 220 m (ammonia and HF), and 480 m (HF) and integration times of
1 minute and 5 minutes, the LasIR has an MDL between 0.09 and 1.21 ppm*m for methane,
between 0.13 and 0.23 ppm*m for HF, and between 1.05 and 13.7 ppm*m for ammonia. The
MDL tests for methane were not conducted under the same experimental conditions as those for
HF and ammonia because the background concentration of methane in the air is typically around
1.7 ppm, and removing the effect of the variation in atmospheric methane could only be
20
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Table 6-1. MDL Data for the LasIR
Methane
HF
Ammonia
Path Length
(m)
Path Length (m)
Path Length (m)
1.5
1.5
220
220
480
220
220
220
Integration
Time (min)
Integration Time (min)
Integration Time (min)
Measurement
Number
1
5
1
5
1
1
5
1
Concentration
ppm
ppm
PPb
PPb
PPb
PPb
PPb
PPb
1
1.67
1.91
0.64
-1.30
-0.38
-3.60
-15.5
5.70
2
1.70
2.09
0.38
-1.40
-0.42
-1.60
-9.11
1.90
3
1.71
1.95
0.08
-1.30
-0.34
1.90
-7.37
1.90
4
1.72
1.63
-0.58
-0.90
-0.30
-3.40
-2.77
4.10
5
1.72
1.30
-0.76
-0.70
-0.30
3.20
-3.37
-0.60
6
1.71
1.14
0.23
-0.50
-0.23
2.40
8.05
-2.30
7
1.76
1.21
0.66
-0.30
-0.25
1.90
8.82
-3.70
8
1.77
1.47
0.38
-0.30
-0.21
3.90
11.2
-7.80
9
1.75
1.78
0.13
-0.20
-0.21
1.40
9.75
-10.5
10
1.74
2.08
0.52
-0.10
-0.15
3.90
9.36
-20.6
11
1.76
2..28
0.27
0.00
-0.28
5.40
2.72
-77.8
12
1.75
2.35
-0.19
0.00
-0.27
5.30
-4.49
-77.8
13
1.75
2.31
0.02
-0.10
-0.27
3.20
5.55
-71.0
14
1.74
2.15
0.30
-0.50
-0.34
3.50
3.90
-57.0
15
1.73
1.89
0.26
-0.50
-0.39
4.50
1.57
-47.0
16
1.73
1.63
-0.31
-0.70
-0.49
3.30
-4.55
-47.5
17
1.73
1.37
-0.14
-0.60
-0.43
0.20
-12.4
-41.0
18
1.73
1.18
0.22
-1.00
-0.49
1.80
-12.0
-29.0
19
1.70
1.10
-0.05
-1.10
-0.53
2.70
-15.0
-27.0
20
1.66
1.10
-0.32
-1.10
-0.56
-0.20
-11.2
-21.0
21
1.70
1.15
-0.35
-1.20
-0.59
1.60
-6.20
-8.00
22
1.69
1.25
-0.36
-1.50
-0.60
2.60
-3.41
2.90
23
1.66
1.38
-0.57
-1.50
-0.65
4.00
0.69
11.80
24
1.69
1.55
-0.62
-1.40
-0.66
1.70
-9.05
26.00
25
1.68
1.74
-1.07
-0.78
-0.40
-0.50
-19.4
38.00
21
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Table 6-2. Minimum Detection Limits of the LasIR
Path Length
Integration
MDL
MDL
Target Gas
(m)
Time (min)
(ppm)
(ppm*m)
Methane
1.5
1
0.063
0.09
Methane
1.5
5
0.095
1.21
HF
220
1
0.00091
0.20
HF
220
5
0.0010
0.23
HF
480
1
0.00030
0.13
Ammonia
220
1
0.0048
1.05
Ammonia
220
5
0.018
3.90
Ammonia
220
1
0.062
13.7
accomplished by placing the retroreflector near the target gas cell. Therefore, for this target gas,
only the integration time was varied, with the shorter integration time giving the better detection
limit. The MDL tests for ammonia were conducted at a single path length of 220 meters because a
480-meter path length was too long for the laser diode being used (the only laser available to the
vendor at the time of the testing was of very low power). At the 220-meter path length and the
one-minute integration time, the MDL varied between 1.05 and 13.7 ppm*m. During these
measurements, it began raining and approximately half of the data obtained was collected during
that period. During the rain, the power was significantly reduced due to scattering of the laser
beam, which resulted in a significant increase in the relative noise of the system. This is reflected
in the greater MDL for this species. Stable readings and low MDLs were seen during the HF
measurements, with the lowest MDL occurring at the 480-meter path length.
6.2 Linearity
6.2.1 Source Strength Linearity
Table 6-3 shows the results from this evaluation of source strength linearity. Figure 6-1 shows a
plot of the effect that the light signal level has on the monitor's measurements of methane in the
gas cell. The average power determined from the background measurement, and the subsequent
measurement with added methane for each pair of measurements at a particular power attenuation
is used in the figure. The relative signal power is the measure of light attenuation during that
measurement. For example, a relative signal power of 0.60 means that the light level for the test is
60% of the light level during normal operating conditions. The methane concentration is the path-
average concentration at 220 meters during the measurement, and the monitor response is the
resulting reading from the LasIR. The LasIR showed a maximum departure from the known added
methane concentration of 0.019 ppm (4%) of the path-average concentration of 0.454 ppm over
220 meters. The linear regression results in Figure 6-1 indicate a near-zero correlation (r2=0.09)
22
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and minimal slope (-0.01). These results show that, over the attenuation range tested, the LasIR
measurements are independent of source strength.
Table 6-3. Source Strength Linearity of the LasIR
Path-Average
Path Average
Monitor
Path-Average Methane
Monitor
Monitor Response
Response
Relative
Concentration from
Response with
with Methane in
Difference
Signal Power Added Methane (ppm)
Empty Cell (ppm)
Cell (ppm)
(ppm)
1.00
0.454
1.65
2.09
0.445
0.67
0.454
1.62
2.08
0.458
0.56
0.454
1.58
2.05
0.473
0.32
0.454
1.49
1.94
0.449
6.2.2 Concentration Linearity
Table 6-4 and Figures 6-2 through 6-4 show the results of the concentration linearity tests. The
linear regression results are shown on the individual figures.
The concentration linearity results show that the LasIR responds linearly to all three target gases.
This performance is especially noteworthy for HF and ammonia because of the nature of these
gases, which introduces uncertainty in the preparation and delivery of known concentrations in the
gas cell.
~ Path Average Concentration from Added Methane (ppm)
¦ Monitor Response Difference (ppm)
Linear (Monitor Response Difference (ppm))
y = -0.01x + 0.^
r = 0.09
0.60 0.6
Relative signal strength
Figure 6-1. Source Strength Linearity Plot for the LasIR
23
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Table 6-4. Concentration Linearity Data for the LasIR
Target Gas
Gas Cell
Concentration (ppm)
Monitor Response3
(ppm)
Methane
40
44.9
Methane
80
72.4
Methane
400
399
Methane
800
800
HF
67
79.8
HF
165
188
HF
182
173
HF
182
170
HF
498
355
HF
549
469
Ammonia
75
60.2
Ammonia
250
286
Ammonia
150
145
Ammonia
250
243.
Ammonia
250
261
Ammonia
494
551
aTest cell concentration calculated from open path readings of the LasIR.
"Determined from dilution of standard cylinder gas with nitrogen. In the case of HF, the concentration was
determined from impinger samplers taken downstream of the gas cell. Errors associated with the dilution and
impinger methods contribute to differences between the monitor response and the target gas cell concentration.
Concentration Linearity - Methane
-g- 1000.00 -|
g- 800.00 -
2 ~ 600.00 -
§ « 400.00 -
2 g_ 200.00 -
2 0.00 -
Figure 6-2. Concentration Linearity Plot of the LasIR Challenged
with Methane
Input Concentration (ppm)
24
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Concentration Linearity - HF
E
Q.
0 -S300.00
~
-------
6.3 Accuracy
The relative accuracy of the LasIR was evaluated at each target gas concentration introduced into
the cell. These concentrations were introduced at the path lengths and integration times shown in
Table 6-5. The accuracy results compare cell gas concentration inferred from the open-path
monitor response with the target gas concentration as delivered by the Environics 2020 diluter for
methane and ammonia, and with impinger sample results for HF.
It should be noted that the relative accuracy includes the uncertainty in the delivery and
determination of the target gas. This is particularly true for ammonia and HF, which are both
sticky gases and difficult to dilute accurately.
Table 6-5. Results of Accuracy Tests for the LasIR
Gas Cell
Monitor
Relative
Concentration
Path Length
Integration
Response
Accuracy
Target Gas
(ppm)
(m)
Time (min)
(ppm)
(%)
Methane
40
1.5
1
44.9
12.3
Methane
80
1.5
1
72.4
9.60
Methane
400
1.5
1
399
0.38
Methane
800
1.5
1
800
0.02
HF
67
220
1
79.8
19.1
HF
165
480
1
188
13.7
HF
182
220
1
173
5.15
HF
182
480
170
6.54
HF
498
220
1
355
28.7
HF
549
220
1
469
14.6
Ammonia
75
220
1
60.2
19.7
Ammonia
250
220
1
286
14.2
Ammonia
150
220
1
145
3.66
Ammonia
250
220
243
3.64
Ammonia
250
220
1
261
4.23
Ammonia
494
220
1
551
11.5
aNo assessment of the accuracy associated with the determination of the standard gas concentration has been
included.
The percent relative accuracy for methane ranges between 0.02 and 12.3%, with the lower value
occurring at a gas cell concentration of 800 ppm.
The HF percent relative accuracy ranged between 5.2 and 28.7%, relative to the results of
impinger sampling, at gas cell concentrations of 67 to 549 ppm. Overall, the LasIR achieved very
good results considering the difficulties encountered when attempting to deliver known
concentrations of HF gas.
26
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The percent relative accuracy for ammonia ranged between 3.64 and 19.7% at the 220-meter path
length, with gas cell concentrations of 75 to 494 ppm.
6.4 Precision
Precision data were collected during measurement #14 (see Table 3-2) using an integration time
of 1 minute and a path length of 220 meters (except methane, for which data were collected at 1.5
meters). The target gas was introduced into the gas cell, and 25 successive analyses were made for
the target gas. The input concentrations delivered during these tests were 800 ppm for methane,
549 ppm for HF, and 494 ppm for ammonia (i.e., path-average concentrations of 309 ppb for HF
and 225 ppb for ammonia). The data from these measurements are found in Table 6-6, and the
results are shown in Table 6-7. These results show that the LasIR had an RSD of 0.63% for
methane, of 1.19% for HF, and of 1.84% for ammonia.
6.5 Interferences
Interference tests of the LasIR evaluated the effect that the common atmospheric interferants,
water and carbon dioxide, have on the monitor's ability to determine the concentration of the
target gases and on the MDL for the target gases. Both water and carbon dioxide have absorption
features in the same infrared region that the monitor uses to analyze for the target compounds.
Because the concentration of these two potential interferants is usually much greater than the
concentration of the compounds of interest, the presence of water and carbon dioxide can make
analyzing for target compounds difficult. The monitor uses various methods to deal with these
interferants, and this test evaluated the effectiveness of these methods. Tables 6-8 and 6-9 show
the data used to determine the interference effect of water vapor and carbon dioxide on the
concentration and MDL determination.
These results did not permit calculation of relative sensitivity, as described in Section 5.5. Instead,
a comparison of the measured concentrations was made to the input concentrations.
Changing the total number of water and carbon dioxide molecules in the path length had a small
effect on the LasIR's ability to accurately determine the concentrations of the target gas. The
measured gas concentrations were 72.4 to 103 ppm for methane delivered to the target gas cell at
80 ppm and from 173 to 188 ppm for HF delivered at 165 and 182 ppm, while the water
concentration in the path changed from approximately 2.4 x 104 to 5.2 x 106 ppm*m, and the
carbon dioxide concentration varied from approximately 8.1 x 102 to 1.6 x 105 ppm*m. For
methane, the best accuracy, relative to the gas cell concentrations, occurred at the lower water and
carbon dioxide levels in the light path. Accuracy for HF was within 14% at all water and carbon
dioxide path concentrations.
27
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Table 6-6. Data from Precision Tests on the LasIR
Analysis
Target Gas
Methane (ppm)
HF (ppm)
Ammonia (ppm)
1
818.6
452.1
552.2
2
819.3
447.8
556.6
3
819.3
455.3
558.8
4
819.5
455.1
569.8
5
820.5
458.6
569.8
6
821.0
454.9
569.8
7
822.0
458.1
563.2
8
821.3
456.0
572.0
9
821.1
458.8
569.8
10
822.1
460.9
563.2
11
822.1
460.1
576.4
12
825.3
463.2
567.6
13
829.0
460.8
574.2
14
831.9
460.0
567.6
15
834.4
463.2
567.6
16
834.5
460.1
565.4
17
832.1
463.2
556.6
18
832.3
467.3
554.4
19
831.5
468.0
556.6
20
831.4
466.6
547.8
21
827.5
469.8
536.8
22
826.3
467.0
545.6
23
821.9
467.0
552.2
24
822.3
465.1
550.0
25
826.4
465.4
547.8
Table 6-7. Results of Precision Tests on the LasIR3
Test Cell
LasIR
Standard
Concentration
Average
Deviation
Relative Standard
Target Gas
(ppm)
(ppm)
(ppm)
Deviation (%)
Methaneb
800
826°
4.2
0.63
HF
549
461
5.5
1.19
Ammonia
494
560
10.3
1.84
integration time = 1 minute, path length = 220 meters
bl.5-meter path length
includes contribution from ambient methane
28
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Table 6-8. Concentration Data from Water Interference Tests on the LasIR
Path
Concentration Concentration Input Gas Cell
Calculated
Relative
Target
Length
of C02
of H20
Concentration
Concentration of
Accuracy
Gas
(m)
(ppm*m)
(ppm*m)
(ppm)
Target Gas (ppm)
(%)
Methane
1.5
8.1E+02
2.4E+04
80
72.4
9.6
Methane
220
1.2E+05
1.6E+06
80
103
28.8
HF
480
1.6E+05
5.0E+06
165
188
13.5
HF
220
6.6E+04
1.8E+06
182
173
5.2
HF
480
1.3E+05
5.2E+06
182
170
6.4
Table 6-9. MDL Data from Water Interference Tests on the LasIR
Path Length
Concentration of C02
Concentration of H20
MDL
Target Gas3
(m)
(ppm*m)
(ppm*m)
(ppm*m)
HF
480
1.7E+05
6.3E+06
0.13
HF
220
7.2E+04
2.4E+06
0.20
a MDL tests were conducted with zero concentration of target gas in the test cell.
Increasing the total number of water carbon and dioxide molecules in the path length had no
significant deleterious effect on the monitor's MDL for HF. In fact, as shown in Table 6-9, the
MDL varied from 0.13 to 0.20 ppm for HF, while the water concentration in the path varied from
approximately 2.4 x 106 to 6.3 x 106 ppm*m and the carbon dioxide concentration varied from
approximately 7.2 x 104 to 1.7 x 105 ppm*m. That is, the MDL for HF actually decreased with
greater H20 and C02 in the light path.
6.6 Other Factors
6.6.1 Costs
The total cost of the LasIR, as tested, is approximately $80,000, according to UNISEARCH.
6.6.2 Data Completeness
All portions of the verification test were completed, and all data that were to be recorded were
successfully acquired. Thus, data completeness was 100%.
29
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Chapter 7
Performance Summary
The LasIR exhibited detection limits of 0.09 and 1.21 ppm*m for methane, 0.13 to 0.23 ppm*m
for HF, and 1.05 to 13.7 ppm*m for ammonia. In these field tests, there was no strong trend in
detection limits with either path length or integration time for the target gases.
The tests of the LasIR to determine the effects of source strength showed that there was no
consistent degradation of the monitor's performance with a decrease in source strength of up to
72%. The LasIR showed a maximum deviation of 0.019 ppm at a path-average concentration of
approximately 0.454 ppm over 220 meters, under this range of source reduction.
The concentration linearity results showed that the LasIR had a response slope of 1.00 and an r2
value of 1.00 for methane over a gas cell concentration range of 40 to 800 ppm; a response slope
of 0.71 and an r2 value of 0.96 for HF over a gas cell concentration of 66 to 549 ppm; and a slope
of 1.17 and an r2 value of 0.99 for ammonia over a gas cell concentration of 75 to 494 ppm.
The percent relative accuracy for methane ranged between 0.02 and 12.2%, with the best accuracy
found at a gas cell concentration of 800 ppm. The HF percent relative accuracy ranged between
5.1 and 28.7%, at a path length of 220 meters. The percent relative accuracy for ammonia ranged
between 3.66 and 19.7% at the 220-meter path length. Note that these results are subject to
uncertainties in the delivery and determination of the target gases, especially for NH3 and HF. In
particular, it should be noted that the reference concentration was determined by impinger
sampling downstream of the optical cell, which is subject to potential uncertainty from losses of
HF, adding to uncertainty
Using a path length of 220 meters for HF and ammonia and 1.5 meters for methane, the LasIR
exhibited precision in repetitive measurements of 0.63% RSD for methane, 1.19% RSD for HF,
and 1.84% RSD for ammonia at target gas cell concentrations of 800, 549, and 494 ppm,
respectively.
Analysis of the effects of ambient water vapor and carbon dioxide on the LasIR's measurements
showed no consistent effect of these species on the accuracy of measurement for methane and HF.
The MDL for HF was also not significantly affected with increased levels of H20 and C02 in the
light path.
30
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Chapter 8
References
1. Test/QA Plan for Verification of Optical Open-Path Monitors, Battelle, Columbus, Ohio,
October 28, 1999.
2. Compendium Method TO-16 Long-Path Open-Path Fourier Transform Infrared Monitoring
of Atmospheric Gases, EPA-625/R-96/010b, U.S. Environmental Protection Agency,
Cincinnati, Ohio, January 1997.
3. Quality Management Plan (QMP) for the ETVAdvanced Monitoring Systems Pilot, U.S.
EPA Environmental Technology Verification Program, Battelle, Columbus, Ohio,
September 1998.
31
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Appendix A
Data Recording Sheet
A-l
-------
Operator:
Reviewed by:
Date:
Sample Gas:
Measurement #
s
u
H
"S
U
4mbient 02 Concentrations (ppb)
4mbient C02 Concentrations (ppb)
g
a
s
-1
4mbient 03 Concentrations (ppb)
4mbient Temp (F)
Integration Time
3ath Length
Concentration in Cell
¦9
OJ)
G
D
hJ
U
Time of Measurement
A-2
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