September 2000
Environmental Technology
Verification Report
Opsis Inc. AR-500
Ultraviolet
Open-Path Monitor
Prepared by
Baiteiie
Putting Technology To Work
Battel le
Under a cooperative agreement with
«>EPA U.S. Environmental Protection Agency
ElV ElV ElV

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September 2000
Environmental Technology Verification
Report
ETV Advanced Monitoring Systems Center
Opsis Inc. AR-500
Ultraviolet
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
Brian Canterbury and Paul Webb of Battelle. We also acknowledge the participation of Carl
Kamme and Paul Stenberg of Opsis in this verification test.
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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	4
3.1	Introduction	4
3.2	Test Design 	6
3.3	Experimental Apparatus and Materials	8
3.3.1	Standard Gases 	8
3.3.2	Dilution Gas 	8
3.3.3	Gas Dilution System	8
3.3.4	Gas Cell	8
3.3.5	Temperature Sensor 	8
3.3.6	Ozone Sensor 	8
3.3.7	NO/NH3 Monitor	9
3.3.8	Benzene Measurement 	9
3.4	Test Parameters 	9
3.4.1	Minimum Detection Limit 	9
3.4.2	Linearity 	9
3.4.3	Accuracy	10
3.4.4	Precision	10
3.4.5	Interferences 	10
4.	Quality Assurance/Quality Control 	12
4.1	Data Review and Validation 	12
4.2	Changes from the Test/QA Plan 	12
4.3	Calibration	14
4.3.1	Gas Dilution System 	14
4.3.2	Temperature Sensor	14
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4.3.3	Ozone Sensor	14
4.3.4	NO/NH3 Monitor	14
4.3.5	Benzene Measurement	15
4.4	Data Collection 	15
4.5	Assessments and Audits	16
4.5.1	Technical Systems Audit	16
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	26
6.5	Interferences	28
6.6	Other Factors 	29
6.6.1	Costs	29
6.6.2	Data Completeness	29
7.	Performance Summary	30
8.	References 	31
Appendix A: Data Recording Sheet	 A-l
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Figures
Figure 2-1. Opsis AR-500 Optical Open-Path Monitor	2
Figure 3-1. Test Site at West Jefferson Facility	6
Figure 3-2. Optical Open-Path Monitor Setup	7
Figure 6-1. Source Strength Linearity Plot of the AR-500 	 23
Figure 6-2. Concentration Linearity Plot of the AR-500 Challenged with NO	24
Figure 6-3. Concentration Linearity Plot of the AR-500 Challenged with Benzene	25
Figure 6-4. Concentration Linearity Plot of the AR-500 Challenged with Ammonia	25
Tables
Table 3-1. Target Gases and Concentrations for Testing the AR-500 	4
Table 3-2. Optical Open-Path Monitor Verification: Measurement
Order for Each Target Gas 	5
Table 4-1. Summary of Data Recording Process for the AR-500
Verification Test	15
Table 4-2.	Summary of Performance Evaluation Audit Procedures 	17
Table 6-1.	MDL Data for the AR-500 	 21
Table 6-2.	Minimum Detection Limits of the AR-500 	 22
Table 6-3.	Source Strength Linearity of the AR-500 	 22
Table 6-4.	Concentration Linearity Data for the AR-500 	 24
Table 6-5.	Results of Accuracy Tests for the AR-500 	 26
Table 6-6.	Data from Precision Tests on the AR-500 	 27
Table 6-7.	Results of Precision Tests on the AR-500 	 27
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Table 6-8. Concentration Data from Interference Tests on the AR-500 	 28
Table 6-9. MDL Data from Interference Tests on the AR-500 	 28
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List of Abbreviations
AMS
Advanced Monitoring Systems
CEM
continuous emission monitor
cm
centimeter
CO
carbon monoxide
co2
carbon dioxide
DOAS
differential optical absorption spectroscopy
EPA
U.S. Environmental Protection Agency
ETV
Environmental Technology Verification
GC/FID
gas chromatography/flame ionization detection
GC/MS
gas chromatography/mass spectroscopy
HCHO
formaldehyde
HF
hydrogen fluoride
Hg°
elemental mercury
hno2
nitrous acid
kg
kilogram
lb
pound
m
meter
MDL
minimum detection limit
nh3
ammonia
NIST
National Institute of Standards and Technology
NO
nitric oxide
no2
nitrogen dioxide
NOx
nitrogen oxides (= NO + N02)
o2
oxygen
03
ozone
PPb
parts per billion
ppb*m
parts per billion meters
ppbv
parts per billion by volume
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
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sulfur dioxide
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 provid-
ing 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 Opsis Inc. (Opsis) AR-500 ultraviolet (UV) optical open-path monitor.
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Chapter 2
Technology Description
The objective of the ETV A VIS Center is to verify the performance characteristics of environ-
mental monitoring technologies for air, water, and soil. This verification report provides results
for the verification testing of the AR-500. The following description of the AR-500 is based on
information provided by the vendor.
The AR-500 ultraviolet differential optical absorption spectroscopy (CV DO AS) system uses a
broad-band Xenon light-source that projects a narrow beam of light across a monitoring path
ranging from 1 to 1,000 meters in length. The receiver telescope focuses the light into a quartz
fiber optic cable that connects to the DOAS analyzer.
The AR-500 is a compact, tunable, and fast-scanning spectrometer that measures spectra in the
wavelength regions of interest. The system can provide path-averaged measurements, from the
light source to the receiver, of, e.g., S02, NO, NO-,, NH3, 03, benzene, toluene, p-, m and
o-xylene, styrene, HN02, HCHO,
Hg°, and hydrogen fluoride (HF). The
AR-500 is designated by the U.S. EPA
as an Equivalent Method for
measuring the criteria pollutants S02,
NO,, and 03 in ambient air.
The AR-500 evaluated in this
verification test was bi-static, with
separate emitters and receivers and a
light beam that passed through the gas
volume once.
Figure 2-1. Opsis AR-500 Optical Open-Path Monitor
From the AR-500 monitor, the results
are transferred to a data collection
system for presentation and reporting.
The Opsis EnviMan software suite
(Windows™ 95, 98, NT, 2000),
provides the necessary functions for
data analysis, presentations, and
reporting.
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The AR-500 is designed for continuous operation and is used in a variety of applications,
including ambient air quality measurements; fence-line measurements at industrial plants and
airports; street-level monitoring and tunnel measurements; and industrial continuous emission
monitoring (CEM) and process applications at power plants, incinerators, cement plants, and
aluminum smelters.
The AR-500 uses the Opsis ER-150 emitter/receiver unit for the monitoring path. Two tempera-
ture signals are logged through the signal unit: the temperature of the calibration cell and the
ambient air temperature. The temperature values are used to normalize data, which are stored in
the analyzer and can be extracted directly from the analyzer in ASCII format. Data also are
available on a separate computer that connects to the system.
The AR-500 measures 60 x 44 x 26.6 cm (23.6 x 17.3 x 10.5 inches). It weighs (including the
case) approximately 50 kg (110 lb).
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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) The test was designed to challenge the AR-500 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 AR-500 are shown in Table 3-1. The verification was conducted by
measuring the gases in a fixed sequence over three days. The sequence of activities for testing the
monitor for a single gas is shown in Table 3-2.
Table 3-1. Target Gases and Concentrations for Testing the AR-500

Concentration
Target Gas Concentration
Gas Cell Concentration3
Gas
Level
(ppm*m)
(PPm)

cl
3
60
Ammonia
c2
6
120

c3
10
200

c4
20
400

cl
2
40
NO
c2
5
100

c3
10
200

c4
15
300

cl
2
40
Benzene
c2
3
60

c3
5
100

c4
10
200
aLength of gas cell = 4.98 cm
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Table 3-2. Optical Open-Path Monitor Verification: Measurement Order for Each Target Gas
Times (min.)
Meas. Gas Cell	# of 	 Path Length	Verification Parameter
#
Cone.
Activity
Measurements
Integrate
Equilibrate
(m)
Calculated

n2
Change gas & stabilize


10
100

1
n2°
Collect spectra
25
1

100
Accuracy, Concentration linearity, MDL

cl
Change gas & stabilize


10
100

2
cl
Collect spectra
5
1

100
Accuracy, Concentration linearity
3
cl
Collect spectra - ND 1
5
1

100
Source strength linearity
4
cl
Collect spectra - ND 2
5
1

100
Source strength linearity
5
cl
Collect spectra - ND 3
5
1

100
Source strength linearity

n2
Change gas & stabilize


10
100

6
n2
Collect spectra
5
1

100
Accuracy, Concentration linearity

c2
Change gas & stabilize


10
100

7
c2
Collect spectra
5
1

100
Accuracy, Concentration linearity, Interference effect (Int.)

n2
Change gas & stabilize


10
100

8
n2
Collect spectra
5
1

100
Accuracy, Concentration linearity

c3
Change gas & stabilize


10
100

9
c3
Collect spectra
5
1

100
Accuracy, Concentration linearity
10
c3
Collect spectra - ND 1
5
1

100
Source strength linearity
11
c3
Collect spectra - ND 2
5
1

100
Source strength linearity
12
c3
Collect spectra - ND 3
5
1

100
Source strength linearity

n2
Change gas & stabilize


10
100

13
n2
Collect spectra
5
1

100
Accuracy, Concentration linearity

c4
Change gas & stabilize


10
100

14
c4
Collect spectra
25
1

100
Accuracy, Concentration linearity, Precision
14b
n2
Collect spectra
5


100
Accuracy, Concentration linearity

n2
Change gas & stabilize


10
100

15
n2
Collect spectra
25
5

100
Concentration linearity, MDL


Change to Path length 2


20
250

16
n2
Collect spectra
5
5

250
Int.

c2
Change gas & stabilize


10
250

17
c2
Collect spectra
5
5

250
Int., Accuracy, Concentration linearity

n2
Change gas & stabilize


10
250

18
n2
Collect spectra
5
5

250
Int., Accuracy, Concentration linearity


Change to Path length 3


20
optimumb

19
n2
Collect spectra
5
1

optimum
Int., Accuracy, Concentration linearity

c2
Change gas & stabilize


10
optimum

20
c2
Collect spectra
5
1

optimum
Int., Accuracy, Concentration linearity

n2
Change gas & stabilize


10
optimum

21
N,
Collect spectra
25
1

optimum
Int., MDL
a See Table 3-1 for values of cl-c4 for the three target gases.
b Vendor optimum of 250 meters was selected.

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3.2 Test Design
The verification test was performed near West Jefferson, Ohio, at an outdoor testing area
belonging to Battelle, between April 11 and April 16, 2000. 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
AR-500 receiver was mounted on top of an 8-foot-tall, concrete block column near the edge of a
lightly traveled road and pointed toward the AR- 500 source, which was on top of another
concrete block column located along the road at a distance of 100 meters. Another column was
located at 250 meters from the receiver, and the source was located on top of this second column
for the measurements that required a longer path length. The power supply, the computer, and the
optical bench were located inside a temperature-controlled trailer near the receiver. The open
space in the foreground of Figure 3-1 shows the test site at Battelle's West Jefferson facility. The
testing area was near the edge of several farm fields. It also was located near a set of train tracks,
and periodically trains passing by affected the NO measurements. In those cases, the testing was
suspended until the train passed. Occasionally vehicles traveled along the road next to the test
site. Testing was not suspended when vehicles passed, which may have contributed to
background levels of NO.
Figure 3-1. Test Site at West Jefferson Facility
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The AR-500 was challenged with the target gases shown in Table 3-1 at known concentrations,
and the AR-500 measurement 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.
TARGET
GAS
CELL
GAS CELL
	
OPTICAL
PATH
LIGHT
SOURCE
FIBER
OPTIC
CABLE
I
OPTICAL
BENCH
& PC
GAS
DILUTION
SYSTEM
TO VENT
TARGET GAS
OR GASES
Figure 3-2. Optical Open-Path Monitor Setup
DILUTION GAS
Target gases were measured at different path lengths, integration times, source intensities, and
numbers of replicate measurements to assess
Minimum detection limit (MDL)
Source strength linearity
Concentration linearity
Accuracy
Precision
Sensitivity to atmospheric interferences.
The test procedures shown in Table 3-2 were nested, in that each measurement was used to
evaluate more than one of the above parameters. In Table 3-2, N2 in the gas cell concentration
column denotes a period of cell flushing with high-purity nitrogen. The denotations cl, c2, c3,
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and c4 refer to the concentrations shown in Table 3-1. The last column shows the parameters to
be calculated with the data from that measurement.
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 nitrogen obtained from commercial suppliers.
3.3.3	Gas Dilution System
The dilution system used to generate known concentrations of the target gases was an Environics
2020 (Serial No. 2428). This system had mass flow capabilities with an accuracy of approxi-
mately ±1%. The dilution system accepted a flow of compressed gas standard and could be
diluted with high-purity nitrogen or air. It was capable of performing dilution ratios from 1:1 to
at least 100:1.
3.3.4	Gas Cell
A vendor-provided quartz gas cell 4.98 centimeters in length was integrated into the end of the
receiver. This cell had two 1/4-inch tube fittings that allowed the target gas to flow through.
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
12 months preceding the verification test.
3.3.6	Ozone Sensor
The sensor used to determine ozone in ambient air was a commercial UV absorption monitor
(ThermoEnvironmental Model 49) designated by U.S. EPA as an Equivalent Method for this
measurement. The UV absorption method is preferred for this application over the Reference
Method (which is based on ethylene chemiluminescence) because the UV method is inherently
calibrated and requires no reagent gases or calibration standards. The sensor was operated in
accordance with the manufacturer's instructions.
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3.3.7 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 NO and NH3 concentrations supplied to the
optical cell for verification testing. This monitor sampled gas immediately downstream of the
optical cell to confirm the NO or NH3 concentrations prepared by dilution of high-concentration
NO or ammonia standards. The API monitor was calibrated with a NIST-traceable commercial
standard cylinder of 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%.
3.3.8 Benzene Measurement
Benzene 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 benzene 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.
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 MDL was defined as two times the standard deviation of the calculated
target gas concentrations. The sequence of measurements was conducted at both integration
times, twice at a 100-meter path length and once at a 250-meter path length.
3.4.2	Linearity
Two types of linearity were investigated during this verification: source strength and concentra-
tion. Source strength linearity was investigated by measuring the effects of reducing the source
intensity on the monitor's performance. In the field, light signal levels can be attenuated by mist,
rain, snow, or dirty optical components. As a constant concentration of target gas was introduced
into the gas cell, the light intensity of the source was reduced by placing an aluminum wire mesh
in the path of the light to determine how the monitor's measurements were affected by an
attenuated light source. Three aluminum wire screens of various meshes were placed in the beam
path. These screens were approximately 1 foot square and had a mesh spacing of approximately
Vi, Vi, and 1 inch. At each of these attenuation levels, a measurement was made, and the monitor
analyzed for the target gas. The test was performed at two concentrations (2 ppm*m and
10 ppm*m) using NO.
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Concentration linearity was investigated by challenging the AR-500 with each target gas at the
concentrations shown in Table 3-1, while the path length and integration time were kept constant.
At each concentration, the monitor response was recorded and its linearity evaluated by com-
paring the recorded response with the input target gas concentration.
3.4.3	Accuracy
Accuracy of the monitor 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 five zero measurements were recorded. The target gas was then intro-
duced into the cell and, after flushing with at least five cell volumes, five measurements of the
target gas were obtained. The cell was again flushed with at least five cell volumes of nitrogen,
and five more zero measurements were recorded. The concentration of the target gas was the
average value with the target gas in the cell, minus the average of the zero measurements.
The accuracy was evaluated at concentrations denoted as cl through c4, using an integration time
of 1 minute. The accuracy was then evaluated at concentration c2 using a longer integration time,
and then again at concentration c2 during the interference measurements (Table 3-2). The percent
relative accuracy for an experimental condition is the absolute value of the difference between
the average monitor response and the reference monitor response, divided by the reference
monitor response, 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 the target gas (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 distance (i.e., the path length) between the source and detector of the monitor. For the
UV measurement of the target gases, the main interferences in ambient air are 02 and 03, and
changing the path length effectively changed the amount of interferants in the light path for the
measurement. The purpose of the interference measurements was to determine the effects that the
ambient atmospheric gases have on the accuracy and MDL of the AR-500. These tests were
performed using two different integration times to determine the effect of integration time on the
monitor's ability to perform measurements with interfering gases in the light path.
To determine the effect of the interferences, the path length was first set to 100 meters. Then, 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
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similarly flushing the cell, five measurements were recorded. Finally, the cell was flushed again
and five more measurements were recorded. Atmospheric concentrations of 02 and 03 were
recorded at the beginning and the end of these measurements.
The path length was then set to 250 meters, which was the length that Opsis chose as optimum
(i.e., the path length that theoretically yields the best signal-to-noise ratio), and the entire
measurement procedure was repeated. The sensitivity of the monitor to the interferant was
calculated by comparing the results at different path lengths (i.e., different ppm*m levels of 02
and 03).
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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® 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 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). Deviations from the test/QA plan were as follows:
¦	The test/QA plan called for a one-over-one data review within two weeks of generating the
data. While the entire data set was reviewed within this two-week period, documentation of
this task was not completed. 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 had not
been calibrated within the previous six months, as specified in the test/QA plan. The
thermocouple 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 calls for a performance evaluation audit of the NO 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.
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¦	An additional measurement was recorded because trains and trucks in the area caused
varying background levels of NO. The additional background measurement was taken to
help overcome this problem of fluctuations in the background NO levels.
¦	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 nitrogen was used.
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 set or removed
inefficiencies in the test, ultimately resulting in a reduced test duration. A brief summary of these
amendments is provided below:
¦	MDL was determined using twice the standard deviation, as described in section 3.4.1. The
test/QA plan inadvertently called for the MDL to be determined by two different methods.
The correct method was chosen and used during the verification test.
¦	The benzene analysis procedure was changed from that specified in the test/QA plan. The
test/QA plan specified using Method 18, which is designed 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 for canister
samples.
¦	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.
¦	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 measure-
ment 14. This additional measurement was added to the test matrix as measurement #14b
(see Table 3-2).
¦	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.
13

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¦	The original test/QA plan specified that the ambient oxygen concentration be monitored by
an oxygen analyzer. Instead, the ambient oxygen concentrations were assumed to be 20.9%.
¦	Although monitoring CO was part of the test/QA plan, it was decided that CO measure-
ments would not add any useful information to the verification. No CO monitoring was
conducted.
¦	The test/QA plan called for determining ammonia converter efficiency by placing two
converters in series with the NO monitor. Instead, conversion efficiency was calculated by
comparing NO and NH3 calibration curves.
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.
4.3.2	Temperature Sensor
The thermocouple was calibrated by comparing it to a certified standard in September 1999. This
instrument has a one-year calibration period, and so was still within its calibration interval.
4.3.3	Ozone Sensor
The UV absorption method of ozone measurement is inherently calibrated, relying as it does on
the accurately determined absorption coefficient of ozone. As a result, routine calibration of the
ozone monitor is not needed. However, the monitor was operated according to the manufac-
turer's directions, with careful attention to the diagnostic indicators that assure proper operation.
4.3.4	NO/NH3 Monitor
The NO/NH3 monitor was calibrated with both NO and NH3 standards. 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
14

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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).
4.3.5 Benzene Measurement
The GC/FID measurement for benzene was calibrated using two standard gases. One was an
EPA Protocol Gas of 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 primarily by Battelle and the vendor. Table 4-1 summarizes the
type of data recorded (see also Appendix A); where, how often, and by whom the recording was
made; and the disposition or subsequent processing of the data. Test records were then converted
to Excel spreadsheet files.
Table 4-1. Summary of Data Recording Process for the AR-500 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 changed
spreadsheet as necessary
Test Parameters
Battelle
Data Sheet
Every hour during
Transferred to
(temp., 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
Battelle
Data Sheet
At specified time
Transferred to
Monitor Readings


during each test
spreadsheet
15

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4.5 Assessments and Audits
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 AMS 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 the results
were assessed.
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 Center 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 the external TSA, which
was documented in a report to the Battelle Center Manager for review. A response and corrective
action were prepared and returned to EPA. The finding 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 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.
Each of the required procedures for the performance evaluation audit was conducted during the
testing period in accordance with the direction specified in the test/QA plan, except for the
deviation concerning the NO performance evaluation, listed in Section 4.2. The results from the
performance evaluation are shown in Table 4-2. The temperature measurement agreed to within
0.4 °C and the ozone to within 3 ppb. The monitor used for NO/NH3 determination agreed with
the performance evaluation standard within 4%, at a concentration of 75 ppm.
16

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Table 4-2. Summary of Performance Evaluation Audit Procedures
Measurement
Audited
Audit Procedure
Expected
Actual
Difference
Temperature
Compare to independent temperature
measurement (Hg thermometer)
10°C
9.6°C
0.4°C
Ozone
Compare to independent ozone
measurement
16.2 ppb
19 ppb
17.3%
NO/NH3
Compare using another NO standard
from the same supplier
75 ppm
72 ppm
-4.0%
Benzene
Compare to results of gas
chromatographic analysis of canister
sample
0 ppm
40 ppm
60 ppm
200 ppm
0 ppm
37 ppm
56 ppm
168 ppm
0%
-7.5%
-6.7%
-16.0%
The benzene concentrations were audited by independent analysis of the test gas mixture
supplied to the optical cell during verification testing. The results of the performance audit for
the benzene concentrations were within 10% (except one canister, which was within 16%) of the
expected concentrations, which met the test/QA plan criterion.
4.5.3 Data Quality Audit
Battelle's Quality Manager audited at least 10% of the verification data acquired in the verifi-
cation 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 (g0)
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
A= - x 100
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
n -1
1(T„-T)
k= 1
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 cyclohexane in air with an interference concentration of
100 ppm of C02 indicates 30 ppm of cyclohexane when the C02 concentration is changed to
200 ppm. This would result in an interference effect of (30 ppm - 26 ppm)cyclohexane/(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 AR-500 are presented in this section, based upon the
statistical methods described in Chapter 5. The monitor was challenged with nitric oxide (NO),
benzene, and ammonia over path lengths of 100 to 250 meters. These gases were chosen because
they are typical gases that this monitor would be used to detect in the field. Test parameters
included MDL, 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 AR-500's open-path measurement to the
actual gas cell concentration. In addition, where appropriate, the path-average concentrations are
noted. The AR-500 reports concentration averages over the entire path length being monitored.
In this report, a measured concentration of 1.5 ppb means that the path average concentration is
1.5 ppb over the entire 100 or 250 meters, depending upon the stated path length. The path-
average concentration is determined by multiplying the gas cell concentration by the gas cell
length and then dividing by the path length used during the given measurement.
While the measurements conducted during this verification test were done in as controlled a way
as possible, several uncontrollable factors should be pointed out before the results are presented.
There may have been sources of the target gases near the test site that could have affected the
monitor's response during these measurements such as trains, highway traffic, and local vehicular
traffic. Attempts were made to suspend testing during obvious periods of source activity;
however, not all potential sources of the target gases could be eliminated.
6.1 Minimum Detection Limit
The MDL was calculated from measurements in which there were no target gases in the gas cell,
but the monitor analyzed the absorption spectra for the presence of a target gas. 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, in terms of both the path-average MDL value in ppb and the integrated MDL
value in ppb*m over the total path.
The results in Table 6-2 show that the AR-500 has an MDL of between 0.9 and 1.4 ppb for NO,
0.4 and 1.5 ppb for benzene, and 2.8 and 5.8 ppb for ammonia, at the path lengths and integration
times tested. Changing the path lengths between 100 and 250 meters and changing the integration
20

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Table 6-1. MDL Data for the AR-500
NO	Benzene	Ammonia
Path Length (m)	Path Length (m)	Path Length (m)
100 250 100	100 250 100	100 250 100
Measure- Integration Time (min)	Integration Time (min)	Integration Time (min)
ment 1 1 5	1 15	115
Number	Concentration (ppb)
1
1.41
2.50
2.40
2.70
0.30
-0.30
-5.70
1.41
-0.40
2
1.43
1.60
4.28
2.70
0.20
0.30
-2.30
1.50
0.00
3
1.06
1.80
3.01
2.80
0.10
0.30
-6.30
1.00
-0.40
4
1.82
2.50
2.70
2.60
-0.10
0.10
-2.50
2.70
-0.50
5
0.59
1.50
2.35
2.70
0.00
0.30
-1.80
0.20
-0.50
6
1.94
2.00
2.79
2.90
0.30
0.30
1.20
2.80
-1.10
7
1.75
1.70
2.13
2.80
0.40
0.50
-3.50
3.90
2.50
8
1.68
1.00
5.63
2.90
0.60
0.30
-9.70
-0.10
-1.10
9
2.01
1.90
2.68
2.50
0.70
0.00
-1.60
1.30
-2.40
10
1.29
2.30
2.55
3.00
0.00
0.10
-2.90
0.20
-2.00
11
0.98
2.00
2.88
2.60
-0.10
0.00
-0.90
-0.20
0.60
12
1.73
1.80
2.47
2.50
-0.20
0.30
-1.00
0.20
2.60
13
1.39
1.90
2.89
3.40
0.10
0.30
0.40
1.20
-0.20
14
1.78
1.50
3.21
3.00
-0.10
0.30
-1.60
4.20
-0.60
15
1.23
1.30
2.82
-0.70
-0.20
0.50
-4.10
1.60
0.60
16
0.93
1.50
2.56
2.80
0.00
0.60
1.40
0.30
1.40
17
0.16
2.40
3.17
2.60
0.00
0.20
0.90
1.10
0.90
18
1.42
2.40
3.28
3.30
-0.20
0.00
0.00
-0.80
1.70
19
1.71
2.90
2.78
3.00
0.10
0.30
-0.30
-0.90
-1.60
20
0.51
2.50
2.64
2.50
-0.40
0.30
1.20
2.10
-0.80
21
1.07
2.00
2.64
2.10
0.10
0.30
2.60
3.50
-2.60
22
0.87
2.20
2.40
2.50
0.00
-0.10
-0.10
0.40
-2.60
23
1.06
1.60
2.39
2.70
0.00
-0.10
0.70
1.20
-0.30
24
0.43
1.50
2.61
2.40
0.10
0.10
2.50
2.60
1.90
25
0.76
2.10
2.59
3.30
0.20
0.00
-1.20
2.60
0.40
times between 1 and 5 minutes had little consistent effect on the MDL. For two of the three target
gases, the MDL is lowest at the 250-meter path length, which is consistent with the vendor's
claim of a better signal-to-noise ratio at longer path length.
21

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Table 6-2. Minimum Detection Limits of the AR-500

Path Length
Integration
MDL
MDL
Target Gas
(m)
Time (min)
(ppb)
(DDb*m)
NO
100
1
1.01
100
NO
250
1
0.91
225
NO
100

1.42
140
Benzene
100
1
1.51
150
Benzene
250
1
0.50
125
Benzene
100

0.42
42.2
Ammonia
100
1
5.8
580
Ammonia
250
1
2.8
700
Ammonia
100
5
3.1
310
6.2 Linearity
6.2.1 Source Strength Linearity
Table 6-3 shows the results from this evaluation of source strength linearity, and Figure 6-1
shows a plot of the effect that the light signal level has on the monitor's measurements. In
Table 6-3, the relative signal power is the measure of light attenuation during that measurement.
Table 6-3. Source Strength Linearity of the AR-500
Relative
Signal Power
NO Concentration
(PPb)
Monitor
Response (ppb)
1.00
20
19.5
0.81
20
21.1
0.67
20
20.4
0.40
20
19.6
1.00
100
103
0.81
100
106
0.67
100
105
0.40
100
106
22

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X	X X 	 x
y = -3.047k + 107.12
R2 = 0.4938

~ Rath Average NO conc.
(PPb)
¦ Instrument Response (ppb)
Rath Average NO conc.
(PPb)
—X— Instrument Response (ppb)
	Linear (Instrurrent
Response (ppb))
- - - Linear (Instrurrent
Response (ppb))




y = 0.2619x+19.945
R2 = 0.0078
— - ¦ —
¦ ¦ — ¦
0.00	0.20	0.40	0.60	0.80	1.00	1.20
Relative signal strength (Arb. Units)
Figure 6-1. Source Strength Linearity Plot of the AR-500
For example, a relative signal power of 0.81 means that the light level for that test is 81% of
what the light level is during normal operating conditions. The NO concentration is the con-
centration of gas being delivered to the gas cell during the measurement, and the monitor
response is the resulting reading from the AR-500. The source strength results show that there is
little degradation in monitor performance during conditions of declining source strength. The
maximum differences between AR-500 response and the NO concentration were 1.1 ppb at
20 ppb NO and 6 ppb at 100 ppb NO. The data do not indicate any consistent effect of source
strength on NO measurement, with source reductions of up to 60%. In addition, the coefficients
of determination (r2) of 0.0078 and 0.4938, shown in Figure 6-1, indicate that reducing the source
strength had little effect on the monitor's response over the range tested.
6.2.2 Concentration Linearity
Table 6-4 and Figures 6-2 through 6-4 show the path-average results of the evaluation of
concentration linearity. The regression analysis results are shown on the individual figures.
The concentration linearity results show that the AR-500 has a linear response over the
concentration ranges tested. The monitor response as given by the slope of the linear regression
line is 1.02 for NO, with an r2 value of 0.9994; a slope of 0.95 for benzene, with an r2 value of
0.9992; and a slope of 1.11 for ammonia, with an r2 value of 0.9997.
23

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Table 6-4. Concentration Linearity Data for the AR-500
Target Gas
Target Gas Concentration
(PPb)
Monitor Response
(PPb)
NO
20
19.5
NO
20
22.7
NO
50
51.6
NO
20
23.4
NO
100
103
NO
150
155
Benzene
20
18.9
Benzene
12
10.4
Benzene
30
29.4
Benzene
12
10.4
Benzene
50
48.3
Benzene
100
93.9
Ammonia
30
33.1
Ammonia
24
25.4
Ammonia
60
66.7
Ammonia
24
23.2
Ammonia
100
110
Ammonia
200
221
Concentration Linearity - NO
200
y = 1.02x + 1.28
o. 150
Q.
r2 = 0.9994
a)
g 100
o
a> 50
0£
0
50
100
150
200
Input Concentration (ppb)
Figure 6-2. Concentration Linearity Plot of the AR-500 Challenged with NO
24

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Concentration Linearity - Benzene
100
c
o
y = 0.95x - 0.22
^ 80
r2 = 0.9992
~ 60
0 20 40 60 80
Input Concentration (ppb)
100
120
Figure 6-3. Concentration Linearity Plot of the AR-500 Challenged with
Benzene
Concentration Linearity - Ammonia
Q.
>- s
3 a)
c g
£ o
S Q.
0)
0)
ai
250
200
150
100
50
0
y= 1.11x-1.47
r2 = 0.9997
50
100
150
200
250
Input Concentration (ppb)
Figure 6-4. Concentration Linearity Plot of the AR-500 Challgenged with
Ammonia
25

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6.3 Accuracy
The accuracy of the AR-500 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 the monitor response with the target gas concentration
as delivered by the Environics 2020 diluter. The AR-500's relative accuracy ranges from 2.7 to
17% for NO, from 2.1 to 14% for benzene, and from 3.3 to 11% for ammonia. Integration time
had little effect on accuracy of the AR-500. The longer path length improved accuracy for
ammonia, but had the opposite effect for NO and benzene.
Table 6-5. Results of Accuracy Tests for the AR-500

Expected

Integration
Monitor
Relative

Concentration
Path Length
Time
Response
Accuracy
Target Gas
(PPb)
(m)
(min)
(PPb)
(%)
NO
20
100
1
19.5
2.7
NO
20
250
1
22.7
14
NO
50
100
1
51.6
3.2
NO
20
250

23.4
17
NO
100
100
1
103
3.4
NO
150
100
1
155
3.0
Benzene
20
100
1
18.9
5.8
Benzene
12
250
1
10.4
14
Benzene
30
100
1
29.4
2.1
Benzene
12
250

10.4
14
Benzene
50
100
1
48.3
3.4
Benzene
100
100
1
93.9
6.1
Ammonia
30
100
1
33.1
10
Ammonia
24
250
1
25.4
5.6
Ammonia
60
100
1
66.7
11
Ammonia
24
250

23.2
3.3
Ammonia
100
100
1
110
9.5
Ammonia
200
100
1
221
10
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 100 meters. The target gas was introduced into the gas cell at a
fixed concentration, and 25 successive analyses were made for the target gas. The data from these
measurements are found in Table 6-6, and the results are shown in Table 6-7. In both tables, the
data are shown in terms of the path-average concentration of the target gas. Table 6-7 shows
precision of about 0.5% RSD for NO, 0.6% RSD for benzene, and 1.5% RSD for ammonia.
26

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Table 6-6. Data from Precision Tests on the AR-500
Target Gas

NO
Benzene

Ammonia
Analysis
(PPb)
(PPb)

(PPb)
1
168
96.7

219
2
168
96.9

221
3
166
97.6

220
4
167
97.4

221
5
167
97.2

220
6
167
96.6

214
7
166
95.8

221
8
167
96.1

228
9
168
96.2

220
10
168
96.6

222
11
169
96.8

225
12
167
96.2

220
13
167
97.0

219
14
167
96.4

221
15
168
96.4

223
16
168
96.2

219
17
168
96.2

223
18
169
96.2

227
19
167
95.8

231
20
166
96.2

219
21
168
95.6

219
22
167
97.2

221
23
168
96.8

223
24
168
97.5

224
25
168
97.0

221
Table 6-7. Results of Precision Tests on the AR-500
a


Gas Cell
AR-500



Concentration
Average
Standard
Relative Standard
Target Gas
(PPb)
(PPb)
Deviation (ppb)
Deviation (%)
NO
150
167
0.77
0.46
Benzene
100
96.8
0.55
0.57
Ammonia
200
222
3.40
1.53
integration time = 1 minute, path length = 100 meters.
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6.5 Interferences
Interference tests of the AR-500 evaluated the effects that the common atmospheric interferants
02 and 03 have on the monitor's ability to determine the concentration of the target gases and on
the MDL for the target gases. Tables 6-8 and 6-9 show the data used to determine the inter-
ference effects of ozone and oxygen on the concentration and MDL.
Table 6-8. Concentration Data from Interference Tests on the AR-500


Gas Cell





Path
Concen-
Concentration
Concentration
Concentration Relative
Target
Length
tration
of Oxygen
of Ozone
of Target Gas Accuracy
Gas
(in)
(PPb)
(%*m)
(ppb*m)
(PPb)
(%)
NO
250
20
5225
500
22.7
14
NO
100
20
2090
3440
19.5
2.5
NO
250
20
5225
1075
23.4
17
Benzene
250
12
5225
6725
10.4
13
Benzene
100
30
2090
1270
29.4
2.0
Benzene
250
12
5225
7100
10.4
13
Ammonia
250
30
5225
4575
33.1
10
Ammonia
100
24
2090
1900
25.4
5.8
Ammonia
250
24
5225
4450
23.2
3.3
Table 6-9. MDL Data from Interference Tests on the AR-500

Path
Concentration
Concentration


Target
Length
of Oxygen
of Ozone
MDL

Gas
(111)
(%*m)
(ppb*m)
(PPb)

NO
250

5225
3400
0.91

NO
100

2090
3290
1.01

Benzene
250

5225
7325
0.50

Benzene
100

2090
530
1.51

Ammonia
250

5225
5900
2.81

Ammonia
100

2090
1150
5.75

Both ozone and oxygen have absorption features in the same spectral region that the AR-500
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 these compounds can make analyzing for the target compounds difficult. The AR-
500 uses various methods to deal with these interferants, and this test evaluated the effectiveness
of these methods.
28

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Changing the total number of ozone and oxygen molecules in the path length had little effect on
the monitor's ability to accurately calculate the concentrations of the target gas. The best
accuracy for benzene was found with the lowest 02 and 03 levels, but this was not clearly the
case for the other gases. Overall, no consistent effect on relative accuracy could be inferred.
During these measurements, the ozone concentration in the path changed from 500 to
7100 ppb*m, and the oxygen concentration varied from 2090 to 5225 %*m.
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.
Likewise, changing the total number of ozone and oxygen molecules in the path length had little
effect on the monitor's MDL for the target gas. The MDL varied from 0.91 to 1.01 ppb for NO,
from 0.50 to 1.51 ppb for benzene, and from 2.81 to 5.75 ppb for ammonia; while the ozone
concentration in the path changed from approximately 530 to 7325 ppb*m, and the oxygen
concentration varied from approximately 2090 to 5225%*m.
6.6 Other Factors
6.6.1	Costs
The cost of the AR-500, as tested, was not available from the vendor. Costs for the AR-500
depend on the specific application and are established in discussion with the vendor.
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 AR-500 detection limits ranged between 0.9 and 1.4 ppb for NO, between 0.4 and 1.5 ppb
for benzene, and between 2.8 and 5.8 ppb for ammonia. While the variation in detection limits
could be due to the changes in path length and integration time, there was no consistent trend.
That is, longer integration times did not, in general, lead to lower detection limits, nor did the
longer path lengths.
The tests of the effects of source strength on the measurement capability of the monitor showed
that there was little to no degradation of monitor performance, with reductions in source strength
of up to 60%. Coefficients of determination at two different test concentrations were low,
indicating that reducing the source strength had little effect on the monitor's response over the
range tested. The concentration linearity results showed that the AR-500 had a slope of 1.02 and
an r2 value of 0.9994 for NO over a range of 20 to 150 ppb; a slope of 0.95 and an r2 value of
0.9992 for benzene over a range of 12 to 100 ppb; and a slope of 1.11 and an r2 value of 0.9997
for ammonia over a range of 24 to 200 ppb.
Percent relative accuracy was evaluated over the same ranges of concentration noted above for
concentration linearity testing. Relative accuracy over these ranges was 2.7% to 17% for NO, 2.1
to 14% for benzene, and 3.3 to 11% for ammonia. The monitor performed about equally well at
long and short integration times and at long and short path lengths.
Precision results showed that the AR-500 had an RSD of 0.46% for NO at a concentration of
150 ppb, an RSD of 0.57% for benzene at a concentration of 100 ppb, and an RSD of 1.53% for
ammonia at a concentration of 200 ppb. This RSD was calculated at one experimental condition
using a path length of 100 meters and an integration time of 1 minute.
Analysis of the effects of the interferences of oxygen and ozone on the measurement ability of
the AR-500 showed that neither the accuracy nor the MDLs for the target gases were affected in
a consistent way by the oxygen and ozone in the light path. Variations in MDL and accuracy
were similar to those found during the other measurements made under normal operating
conditions.
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 E TV Advanced 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

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Sample Gas:
Date:
Operator:


Reviewed bv:

Measurement #












Dell Temp (F)












\mbient 02 Concentrations (ppb)












\mbient C02 Concentrations (ppb)












\mbient RH (%)












\mbient 03 Concentrations (ppb)












\mbient Temp (F)












Integration Time












r'ath Length












Concentration in Cell












Dell Length












Time of Measurement













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