EPA-340/1-75-009
April 1975
Stationary Source Enforcement Series
APPLICATION OF REMOTE MONITORING
TECHNIQUES IN A!R ENFORCEMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Enforcement
Office of General Enforcement
Washington, D.C. 20460
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SAI-75-638-LJ
(V
I ' , s
N:
APPLICATION OF REMOTE
^ MONITORING TECHNIQUES
x^
IN AIR ENFORCEMENT
by
C. B. Ludwig and M. Griggs
SCIENCE APPLICATIONS, INC.
La Jolla, California 92038
Contract No. EPA 68-03-2137
Project Officers: Dr. F. E. Biros
Office of Enforcement and
General Counsel
Dr. S. H. Melfi
National Environmental
Research Center—Las Vegas
Prepared for:
U. S. Environmental Protection Agency
Washington, D. C. 20460
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EPA REVIEW NOTICE
This repai^Hamb^njseyiewed by the Environmental Protection
publication. Approval does not signify
that* tile conbanteneEiBSiB^^ily reflect the views and policies of the
Agency, nor does, mention: of trade names cm commercial
constitute endorsement or, Recommendation for
11
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FOREWORD
n This report documents the work performed under Contract No.
EPA 68-03-2137 between September 1974 and March 1975. The work
was sponsored by the Environmental Protection Agency, Office of
Enforcement and General Counsel. The object of this program was to
assess the application of remote monitoring techniques to air enforce-
ment programs for stationary source emissions.
The authors wish to thank the many researchers who have pro-
vided valuable information about on-going programs, practical experience
in the field and have given freely their opinions about the role of remote
monitoring techniques. The authors are also indebted to Dr. R. Hildreth
(University of San Diego) for his assistance in legal matters and to their
co-workers at Science Applications, Inc., W. Malkmus, J. Myer,
E. R. Bartle, L. Acton and G. Hall for contributions in the different
topics, and to J. Wang for many calculations. In particular we wish
to thank K. Arnone for her dedication in preparing the manuscript.
111
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IV
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CONTENTS
page
EXECUTIVE SUMMARY 1
1.1 Definitions 1
1. 2 Legal Aspects in Air Enforcement Monitoring 3
1. 3 Present Development and Analysis of 4
Remote Monitoring Techniques
1.4 Advantages and Disadvantages 5
1. 5 Major Conclusion and Recommendations 9
INTRODUCTION 13
2.1 Purpose and Objective of Study 13
2. 2 Background of Air Pollution Regulations 14
2. 3 Modes and Applications of Remote 17
Monitoring Techniques
AIR ENFORCEMENT MONITORING 19
3.1 Overview 19
3.2 Visual Observations of Plumes 22
3.3 Evidence 26
3.4 New Legal Issues 31
3. 5 Performance Specifications and Operating 35
Parameters for the Use of Remote Sensors
3. 5.1 Background and Overview 36
3. 5. 2 Outline of Performance and Test 47
Procedures for the Use of Remote Monitors
PRESENT DEVELOPMENT OF 51
REMOTE MONITORING TECHNIQUES
4.1 Overview 51
4.2 Theory 55
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4.2.1 CW Infrared System 55
4. 2.2 Pulsed Laser Systems 60
4.2.3 Perimeter Monitoring 65
4. 3 Review of Active Systems 66
4.3.1 Differential Absorption 66
4.3.2 Raman Scattering 69
4. 3.3 Resonance Raman 72
4.3.4 Fluorescence 74
4.3.5 Lidar 75
4. 3. 6 Intercomparison of Measurements 79
of Gases
4. 3. 7 Stack Effluent Velocity Measurements 81
4.4 Review of Passive Systems 82
4.4.1 Passive Opacity Techniques 83
4.4.2 Matched-Filter Spectrometer 85
4.4.3 Gas Filter Correlation 88
4.4.4 Medium Resolution Dispersive 92
Spectrometer System
4.4.5 Interferometer-Spectrometer 94
4.4.6 Filter Wheel Sensor 100
4.4. 7 Laser Heterodyne Technique 100
4.4.8 Dispersive Hadamard Transform 106
Spectrometer
4.4.9 Passive Vidicon Instrumentation 108
4. 5 Area Surveys 108
4. 6 On-Going and Planned Research Programs 110
PRACTICAL CONSIDERATIONS 115
5,1 Overview 115
S. 2 Eye Safety Hazards from Laser Systems 116
5. 2.1 The Maximum Permissible Exposure 117
and Minimum Safety Range
5.2.2 Required Modifications 118
5.2. 3 Final System Parameters 119
VI
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5. 3 Error Analysis of Active Systems 121
5.3.1 DAS System 121
5.3.2 Raman Systems 124
5.3.3 Lidar Systems 126
5. 3. 4 Intercomparison of Laser Techniques 128
5.4 Error Analysis of Passive Infrared Systems 136
5.4. 1 Source Strength 136
5. 4. 2 The Measurements of Signal Differences 139
5.4. 3 Perimeter Monitoring Data Analysis (Infrared) 144
6 ADVANTAGES AND DISADVANTAGES OF 145
REMOTE MONITORING TECHNIQUES
6.1 Overview 145
6.2 Cost Effectiveness 146
6.2. 1 Opacity 147
6.2.2 Gas Concentration 148
6. 3 Objectivity in Opacity Measurements 149
6.4 Unannounced and Non-Interfering Monitoring 150
6. 5 Survey of Wide Geographical Areas 150
6. 6 Rapid Response in Pollution Episodes 151
6.7 Limitation under Certain Atmospheric Conditions 153
6. 8 Increased Requirements in Calibration 153
6. 9 Safety Hazard 153
7 CONCLUSIONS AND RECOMMENDATIONS 155
7.1 General Conclusions 155
7.2 Recommendations 160
8 REFERENCES 165
VT.1
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1
EXECUTIVE SUMMARY
1. 1 DEFINITIONS
In EPA's regulatory programs for air pollution, remote monitoring
techniques can generally be applied in the following three areas:
• enforcement programs,
• research and development of regulations, and
• establishment of ambient air quality trends,
The specific purpose of this study is to evaluate the first application
of remote monitoring techniques. In enforcement monitoring, two levels of
"sophistication" are distinguished: (1) evidentiary monitoring for case
development, in which the plant owner is served with a noiice of violation
and court action initiated in the event of non-compliance, and (2) sur-
veillance, in which a large number of stack emissions are screened to
assist in the determination of those stacks in possible non-compliance.
In the present study remote monitoring is defined ss sensing, by an
electro-optical technique, specific chemical and/or physical parameters
of the environment where the monitoring instrument and the parameter
under investigation are separated by a distance. Presently, EPA, NASA,
NOAA, DOT and other federal agencies are sponsoring the development of
instruments and/or techniques to remotely monitor the environment.
These instruments and/or techniques utilize active or passive systems.
Active systems consist of two basic units: a transmitter and a receiver,
while passive systems consist only of a receiver. The transmitter in an
active system emits a beam of energy, which interacts with the plume/atmo-
sphere by scattering, absorption and/or stimulated emission, which is
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subsequently observed by the receiver. In the passive system, the receive!
merely observes the radiation from the plume/atmosphere, which may be
emitted by thermal radiation, or scattered solar radiation.
lir enforcement monitoring, several modes can be distinguished
(see Figure "_-!): Direct observation of the plume by passive or active
monitors, perimeter monitoring by uplooking from van-based platforms
or down-looking from airborne platforms, and horizontally by active long-
path systems, although the latter application is limited to cases where
the horizontal long-path is representative of a given situation (Section 4. 5).
In addition, area monitoring using an aircraft, can be used in surveillance.
These surveys of wider geographical areas can also assist in the deter- «
mlnation of environmental quality degradation, plant site selection, the
design of contact monitoring networks, and the tracking of plumes to study
atmospheric dispersion, diffusion and fate of pollutants.
Figure 1-1.
Modes of active and passive remote techniques in
enforcement monitoring: Direct observation of
stack plume, perimeter monitoring (ground and
airborne) and area monitoring.
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1. 2 LEGAL ASPECTS IN AIR ENFORCEMENT MONITORING
A review is given of the legal aspects of air enforcement monitoring,
the specific requirements in case development, and the existing proposed
and promulgated rules for performance specifications of sources and mea-
surement methods. A literature search revealed a lack of legal cases in
which analytical instruments were used in environmental enforcement pro-
ceedings. However, a number of cases involved the visual observations
of plume emissions, which were either accepted as admissible evidence,
or rejected as too subjective to be admissible. Based on tie available
material, we believe that visual observations will be more and more
questioned by the courts as admissible evidence in light of the avail-
ability of instruments, even though EPA has revised and strengthened
the Reference Method 9 (Visual Determination of Opacity) in response
to court rulings (Section 3. 2).
Based upon established practices for introducing admissible evidence
into a court of law, it appears that evidence obtained through the application
of remote techniques (other than visual observations) could be introduced into
court proceedings the same way as evidence has been presented in previous
(non-environmental) cases. In this procedure, the field enforcement officer
convinces himself that the remote sensor is producing reliable data, and
accumulates a "preponderance of evidence". The common sense questions
the courts would likely ask in deciding whether to accept that evidence are
expected to be: Is the scientific principle underlying the instrument's operation
valid? Does the instrument successfully embody and apply this underlying
principle? Was the instrument in proper working order and properly cali-
brated at the time of the test ? Was the person conducting the test qualified
to do so? Did the person conducting the test use the proper procedures?
If different from the person conducting the test, is the pere-.on interpreting
the test's results qualified to do so? It is believed, however, that a great
percentage of cases will not even lead to court action. Once evidence of
non-compliance is obtained, past experience indicates that the plant owner/
operator will probably take steps to comply (Section 3. 3).
In enforcement monitoring, the accuracy of the reirote instrument
must be known, but does not need to be of a given absolute value. Recent
court decisions indicate that the measured departure from :he standards
must merely be beyond the boundaries of probable measurement error.
Thus, there is no requirement of an absolute lower limit on the instrument
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sensitivity and-accuracy, as long as it is better than the departure
from the standard to be measured. However, remote instruments
used imreseareh and development must have specified limits in ac-
curacy/rand sensitivity, like other instruments used in scientific re-
search.
In recent years, new legal issues have been raised after par-
ticular measurement methods were challeneged. Questions about the
equivalency of measurement methods used in setting the standards and
in. establishing non-compliance in enforcement proceedings are involved.
Thus, test methods and technical support for standards must be care-^
fully established and logical quantitative relationships between standards
and tests used for compliance must be developed (Section 3. 4). As a
consequence, we believe that performance specifications and test pro-
cedures must be developed to establish the acceptability of remote
monitoring instruments. Particular attention must be directed toward
the requirements of specifying the effects of atmospheric and back-
ground interi'erences (Section 3. 5). The right of conducting passive
remote measurements by enforcement personnel without notice was
recently affirmed by the Supreme Court in the case of Colorado Air
Pollution Variance Board vs. Western Alfalfa Corp. (1974), where
visual observations were involved. (Cases involving "invisible pol-
lution" and the probing with active techniques must yet be tested in
court.) Legal opinions by environmental lawyers representing industry
stress that the Fourth;Amendment is being violated by the unannounced
monitoring o* sources and by entry of premises without search warrants
(Section 3.4),
1. 3 PRESENT-DEVELOPMENT AND ANALYSIS OF
REMOTE MONITORING TECHNIQUES.
A review of the recent development of remote monitors sponsored
by Federal and other agencies, as well as by private industry, both in the
UTSiiAii.and other countries, revealed that several active and passive tech-
nique&?were worthy of further analysis. The active techniques included
the pulsed laser systems that involve differential absorption, Raman,
resonance Raman, fluorescence, and Lidar, as well as the continuous wav<
(CW) systems that involve laser, dispersive and non-dispersive component
(Section 4. 3). The passive techniques include dispersive and non-dispersiT
correlation systems, spectrometers, interferometer-spectrometers,
radfomBters, heterodyne radiometers, photography and vidicons
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(Section 4.4). An overview of these techniques and their main char-
acteristics are presented in Tables 1-1 and 1-2.
The air pollutants (previously identified as important to monitor)
that are judged to be amenable to remote monitoring in th>3 immediate
and near-term time frame include particles/opacity, SOo, NO2, CO, light
hydrocarbons, HC1, HF, NHg, NO , tUS, HNO«, O3 andvinyr chloride;
and in the long-term time frame include heavy nydrocarbons, oxides of
sulfur, certain specific trace elements, and chlorinated hydrocarbons.
In addition, many newly identified pollutants of interest can probably be
monitored by remote monitors, after their spectral characteristics are
identified.
Our general conclusion is that the applicability in (erms of range
in plume temperature and pollutant concentration is greater for the active
than for the passive systems. In addition, the passive systems are also
more influenced by interfering parameters, such as backg round radiation.
On the other hand, passive systems are cheaper than the active systems
and can be made into cost-effective tools for enforcement monitoring, as
long as the measured deviation from the standard in pollu:ant concentration
is larger than the error limits (Section 4. 2).
1.4 ADVANTAGES AND DISADVANTAGES
Based upon the review of the remote monitoring techniques, we
have identified the following advantages which apply in varying degrees
to the two modes, case development and surveillance.
• Cost Effectiveness
Although the initial capital costs are higher for re.note inscruments
than for point samplers, the operational costs are less because of
their mobility allowing rapid coverage of more sources and areas.
Our estimate is that for some remote monitoring applications the
operational costs are less by as much as about a factor of 10.
Remote techniques provide also a cost-effective method to monitor
and survey wide geographical areas for the purpose of assisting in
the determination of environmental quality degradation, plant site
selection, design of contact monitoring networks, and in tracking
plumes.
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TABLE 1-1. Overview of Active Systems Under Development
Technique/ SpectrO. Species/
Instrument Region Parameter
Differential Vis/UV SO2, NO2
Absorption
SO,, NO*
O/ 2
IR Many
Gases
Lidar Vis Opacity
Particles
Laser Doppler IR Velocity
Veloclmeter
Mass Flow
Long-Path Vls/UV Many
/IR Gases
Raman Vis/'JV SO2
Many
OisSPH
ItMuMilKtB- • Vln/UV- All (ianoa
KIUIUUI (?)
Fluorescence Vis/UV Many
Gases
FabryPerofc. V.ls/'JV Some
Raman Gases
Mode Application
Stack
Perimeter/
Area
Stack
Perimeter/
Area
Stack
Area
Stack/
Perimeter
Stack
Area
Stack
Slack/
Area
HI ark/
Area
Stack/
Area
Stack/
Area
Evld/Surv
Evld/Surv
Evld/Surv
Evid/Surv
Evld/Surv
Surv
Evid
Evid
Surv
Surv
Surv
Surv.
?
?
Development
Status Remarks
Field Tested
Available
Under
Development
Under
Development
for A/C
Field Tested
Field. Tested
on A/C
Field Tested
Under
Deve'opment
Field Tested
Field Tested
Theoretical
I, >l> Study
Lab Study
Lab Study
Ground-based - Present Instrumentation
as used not eye-safe (Section 4. 3. 1)
Has not been done, but feasible (Section
4. '3), both ground and aircraft based
See Table 4-15
See Table 4-15, at present for ozone
Not eye safe yet, (Section 4. 3. 5) eye-
safe system being developed
Gives- 3-dtmensional mapping of relative
concentrations (Section 4. 5)
Necessary for some emission standards
(Section 4. 3. 7 and Table 3-1)
Relates opacity and mass concentration
(Section 4. 3. 7)
Using remote transmitter ot retro-
reflector; can be laser, dispersive or
non-dispersiv* systems (Table 3-16);
useful mainly for ambient air monitoring
Limited in range, especially during day
(Sections 4.3.2 and 5.3.2)
l!s»fulne»rn limited 'S^ctirrfi 4 3. 2 an*?
1 3 2)
Nc nils tti her clon"/tio»< al oil \t, !)»!.),
pi ja ol bio Interference duirlo fluor unctiiKe
by gasfltt and utlier Mpeoles (fieoliun 4. 3. 3)
Looks doubtful in terms of sensitivity
aral specificity; (Section 4. 3.4)
Provides Increased sensitivity over
vibrational Raman; still limited In range, -
especially during day (SeCtibn 4. 3. 2)
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TABLE 1-2. Overview of Passive Systems Under Development
Technique/ Spectral
Instrument Region
Matched Filter UV/Vis
Correlation
Gas Filter IR
Correlation
Photography Vis
Vidicon UV
Species/
Parameter
S02, N02
SO,
CO
so2
Opacity
*>*
Mode
Stack/
Perimeter
Stack
Perimeter
Perimeter
Stack
Stack
Application
Surv.
Evid/Surv
Evid/Surv
Evid/Surv
Evid/Surv
Surv
Development
Status Remarks
Field Tested
Field Tested
Field Tested
Under
Development
Field Tested
Ground &
Aircraft
Field Tested
Quantitative interpretation difficult due
to varying aerosols (Section 4. 4. 2 and
4.5)
Limited m concentration and tempera-
ture range (Section 4. 4. 3), but tem-
perature effect reduced
No quantitative data reported as yet
(Section 4. 5)
See Table 4-14
Needs firther development for quantita-
tive analysis; nighttime observations
feasible with image intensifier (Section
4.4.1)
Quantita ive interpretation difficult due
to varying aerosols; has potential as a
velocimeter (Section 4. 4. 9)
Heterodyne
Radiometer
IR SO,
IR
Dispersive IR
Spectrometer
Many'
Gases
Many
Gases
Stack
Stack/
Perimeter/
Area
Stack
Surv Planned Indepenc-ent knowledge of piume tempera- i
ture required for quantitative analysis; j
has potential as a veiocimeter (Section j
4.4.9) j
j
!
Evid(?)/ Lab Study Achieve"; high specificity; has yet to be |
Surv demonstrated in field (Section 4.4,7) j
Surv Field Tested includes scanning spectrometer and in-
ter feror'.eter-spectrometer; requires
;,:gh spectral resolution for specificity
und requires knowledge of plume tem-
peraturt (Section 4. 4. 4 and 4. 4, 5)
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Objectivity in Opacity Measurements
Opacity measurements taken with instruments are objective, in
contrast to the subjective visual observations. The Appellate
Court in Washington, as well as several State regulations, favor
opacity measurements taken by instruments,.
Unannounced and Non-Interfering Monitoring
The remote technique provides a most effective tool to mdnitor
suspected violators, even at night, without requiring entry on
the facility premises. In addition, remote monitoring does not
interfere with the normal plant operations.
Rapid Response
In cas 9S of air pollution episodes, the highly mobile and flexible
remote monitors can be used to assess the extent, trend, and
required response to counteractions more rapidly than the stationary
in-situ sensors.
The following disadvantages have been identified:
Possible High Initial Capital Costs
At the present time, the purchase price of all remote instruments
are more expensive than the extractive or in-situ devices. The
active systems are more so than the passive systems. However,
as more and more instruments are built, one can assume that the
purchase price will come down.
Limited Applications Under Certain Conditions
Adverse weather conditions such as fog, heavy rain or extremely
high psirticulate content in the atmosphere can affect the measure-
ment capability of the remote techniques.
Calibration Procedures More Complicated
Indications are that the remote techniques will be more difficult
to calibrate than the extractive or in-situ devices because of the '
atmospheric influence. It is anticipated that—similar to the cali-
brated smokestack used in smoke schools—a test range with a remote
stack source must be provided in which several atmospheric con-
ditions can be reliably simulated.
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Possible Eye Safety Hazard
Caution must be exercised in using lasers so that they comply
with the Federal Regulations. Thus, some of the laser applications
which demand an increase in emitted power in order to meet the
sensitivity and range requirements, had to be eliminated from the
list of useful systems.
1. 5 MAJOR CONCLUSION AND RECOMMENDATIONS
Based upon our review and analysis of the remote techniques being
developed, our major conclusion is that remote monitoring" can play a signi-
ficant role in EPA's enforcement activities, commencing v/ith a few opera-
tional programs in the very near future, and expanding to larger involvement
in the long term. However, not all techniques/instruments presently deve-
loped are equally well suited for enforcement monitoring of smokestacks.
For direct observation of hot plumes and indirect observation of
complex sources through perimeter monitoring, the less expensive passive
systems will suffice, while the direct observation of cool plumes will require
the application of the more expensive active laser systems. The laser systems
that are most promising for near-term operational use are differential ab-
sorption, Lidar and laser Doppler velocimeter. The most promising passive
systems are correlation instruments, vidicons and aircraft photographic tech-
niques. For area surveys, both active and passive systems (ground-based
and airborne) have application.
Based upon the above conclusion, we make the following recommenda-
tions:
• Formulate training programs for the field use of remote monitoring
techniques and initiate the training of field enforcement officers;
• Place existing remote monitors in the hands of trained field enforce-
ment officers for use in surveillance and case development monitoring
of smokestacks;
• Introduce evidence obtained by remote monitors into a court of law
in strong non-compliance cases, i. e., cases for which the common
sense questions listed above can be answered in the affirmative;
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• Adapt.existing performance specifications of continuous monitors
tar emote monitoring application and initiate the formulation of
adfliticnaLtest.procedures required in the application of remote
monitors;
• Consider the establishment of one or more test ranges, in which
remote monitors:can be calibrated;
'• .Goiitinue^and^oirparticipate in the development of remote techniques
ior: enforcement: monitor ing. In particular, the following tasks are
judged to^be, of about equal priority:
--maka the-;most promising active systems (differential absorption,
Lidar and laser Doppier~velocimeter) operational for van-based
and airborne applications for the gaseous pollutants SC>2 and NC>2
and ^articulate pollutants,
--maka the most promising passive systems (correlation instrtimentr
vidicons and aircraft photographic techniques) operational for
smokestack monitoring for the gaseous pollutants SC»2 and NO2,
--extend the active differential absorption techniques to other species
utili:2ing:lhe UV and IR spectra,
--extend the/passive correlation instruments to other species,
^-continued-passive perinreter monitoring;
• Continue ajid^/oirparticipate in the development of remote techniques
for researtJhxsndi development of regulations and for anibient air
trendtinonitDring. IIE particular, continue the development of long-
pathrlaser systems and long-path correlation instruments;
• -Continue—witfr.somewhat less priority than the above—the developmei
-of techniques wnose practical applications have yet to be demonstrate
in particular, resonance Raman and heterodyne radiometry.
The implementation of the above recommendations is believed to be
possible mtne time frame as shown in Figure 1-2.
10
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CALENDAR YEAR
Initiate Training Programs
Establish Test flange
Particle - Opacity
Available
Initial court cases
Particles - Mass Flow
Available
SO2/NO2
Available
Initial court ease*
Other Gases
Available
1975
A
A
A
A
M
1976
•M^
>BMMB«M»
1977
A____
A
1978
±
A- -,
A----
1979
A
A
1980
£,
1981
;
;
I
S
.
i
A
:
1982
j
i
Figure 1-2. Overall time schedule of introducing remot2
techniques to enforcement monitoring.
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12
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2
INTRODUCTION
2. 1 PURPOSE AND OBJECTIVE OF STUDY
Presently, EPA, NASA, NOAA and other federal agencies are
sponsoring the development of remote monitoring instruirents for sensing
air quality. Remote monitoring, for the purpose of this cocument, is
defined as sensing a specific chemical and/or physical parameter of ihe
environment where the monitoring instrument and the parameter under
investigation are separated by a distance. Some of these instruments
have been developed to the point where they are presently useful to EPA
in its monitoring program. Other instruments have not been developed
to this stage.
The purpose of the present study is to evaluate how remote moni-
toring instruments and techniques may aid the agency in tne enforcement
monitoring area. In particular, the specific technical problems are re-
viewed that are associated with enforcement and case development moni-
toring in respect to stationary source emissions and, where appropriate,
ambient air quality determination; the precision, accurac/, and nature
of the information and data required for enforcement purposes are dis-
cussed, including related source process and environmental parameters
that are presently monitored as a result of requirements of existing
regulations and are projected to be monitored as a result of proposed
and/or otherwise anticipated legal regulations or standards; remote
monitoring techniques are reviewed, including those presently available,
those that are being evaluated and those that may be available in the next
few years, assuming continued or increased research effort; completed
and on-going studies of EPA and other agencies are summarized that
involve the development of remote monitoring instruments and their
comparison with conventional manual techniques; the advantages and
13
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disadvantages of remote monitoring techniques are discussed; and,
finally, conclusions and recommendations as to future applicability
and R/D requirements are given.
2. 2 BACKGROUND OF AIR POLLUTION REGULATIONS
The Clean Air Act (42 U. S. C. 1857} of 1963 encouraged state,
regional and local regulatory control programs by providing matching
funds for research and technical assistance, and at the same time,
gave authority to the Federal Government to intervene in enforcing the
abatement of air pollution in interstate problem areas. The specific
abatement procedures included—a) conference with the cognizant
official agencies, b) public hearing, and c) court action. These pro-
cedures could take up several years, involving complex procedures
to prove non-compliance. There were ten cases (Ross 1972) which
were pursued under the 1963 Clean Air Act by Federal abatement
authorities. In some of these cases, extensive measurement programs
were undertaken to establish the effect of reduction in source emission
on the ambient air. For example, the case of the New York-New Jersey
Metropolitan areas, begun in January 1967, resulted in state actions to
limit the sulfur content in fuel oil and coal (1 percent by May 1968 and
0. 2 percent by October 1971). In another case, involving interstate
particulate and sulfur oxide air pollution in the area of Parkersburg,
West Virginia, and Marietta, Ohio, it was found after extensive mea-
surements that the combustion of coal accounted for two-thirds of the
total emissions of particulate matter in the area and that undesirable
atmospheric reactions between chlorine and various chemicals took
place. In other cases, the cause for action was determined not by
direct measurement, but by indirect indicators. The fluoride emissions
froih a plant near Garrison, Montana, which processes phosphate rock
to produce an animal food supplement increased the fluoride content of
grasses in the area above the state standard for forage fed to livestock.
The Clean Air Act as amended in 1967 established "air quality
control regions" for the purpose of setting ambient air quality standards,
based upon "air quality criteria" which reflect the latest scientific and
medical knowledge of effects of air contaminants on health and welfare.
It also callec: for the development and issuance of information on re-
commended pollution control techniques, and the initiation of joint
government-industry research to develop and demonstrate improved
14
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emission control technology to the degree required to prevent and abate
air pollution. It is clear that monitoring devices had to be available
for control assist.
The Clean Air Act as amended in 1970 extended the geographical
coverage of the Federal program for the prevention, control and abate-
ment of air pollution from both stationary and moving sources. In par-
ticular, emission regulations for environmental control was established.
It was established that research and development for measurement tech-
niques of the following air pollutants should be conducted as listed in
Table 2-1.
TABLE 2-1. Pollutants to be Monitored (Ellison 1974)
1.
a.
a.
4.
S.
(.
7.
«.
9.
10.
11.
a.
it.
14.
15.
16.
17.
18.
Oxides at sulfur
(SOj. 80,, Hj804)
Oxides o£ nKrogtn
(NOj, NO, NOj, HNO,)
Participate m.UUr (atae distribution
chemical composition)
Asbestos
Mercury
Beryllium
Carbon mono- id;
Nonmetlune hydrocarbon*
Certain specific hydrocarbons
Polychlorinated blphenyls
Poljrnuclaar organic matter
Reactive hydrocarbons
Hydrogen chloride
Manganese
Selenium
Arsenic
Phosphoric acid
Chlorine
19.
10.
91.
«.
U.
M.
as.
ae.
n.
as.
18.
90.
31.
aa.
aa.
M.
as.
ae.
Hydrogen fluoride
Hydrogen eulfide
Mercaptans
Ammonia and amines
Organic acids
Aldehydes
Odor
|
Photochemical oxidanU .
1
Copper
Zinc
Boron
Tin
Lithium
Chromium
Vanadium
Cadmium
Lead
Aeroallerfena
Basically, two regulatory parameters for each of these pollutants
must be established: an emission standard and a measurement method.
EPA is proceeding along these lines and standards and measurement
15
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methods haw been established for some of the above pollutants. A
progress reoort about the status of these developments was recently
writtenbby Ellison (1974). In the same report, a brief statement about
the remote irreastrrement of air pollutants was made. Ellison states
that "... the potential effectiveness of air pollution measurement and
monitoring by means of these techniques justifies a reasonable effort
to investigate their usefulness. "
inDeeemirer 1971, the standards of performance for new sta-
tionary: sources were codified as 40 CFR Part 60, for five industries
together wit,! several reference test methods, applicable to the in-
stack measurements of sample and velocity traverses, gas velocity
and Volumetric flow rate, CO2 and excess air, moisture, particles,
SO2, NOx, sulfuric acid mist and to the remote visual observations of
the opacity of emissions.
Since that time, standards of performance for fourteen more
industries have either been proposed or promulgated, together with
additional reference test methods, applicable to the in-stack measure
ments of CO, H2S, SO2, and total fluorides. In addition, performance
.specifications of'-'continuous in-stack monitors for some gases were
proposed.
In 1971, the/fEmrironmental Protection Agency promulgated the
National PrimaryjandiSecondary Ambient Air Quality Standards as
40 CFR Par", 50. Subsequently, the requirements for the preparation,
adoptionand: submittal:of implementationplans (40 CFR Part 51) and
,tfee approval and promulgation of the implementation plans (40 CFR
Bart 5$) were codified.
In February 1975, the rules for ambient air monitoring were
promulgated and the relationship between "reference methods" and
"equivalent methods" established (40 CFR Part 53).
Except for the visual observations of emissions, no test methods
terrr-emote sensing techniques have yet been proposed for either the
emissions from stationary sources of the ambient, air quality.
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2. 3 MODES AND APPLICATIONS OF
REMOTE MONITORING TECHNIQUES
In EPA's regulatory programs for air pollution, romote moni-
toring techniques can generally be applied in the following three areas:
(i) enforcement programs, (ii) research and development of regulations,
and (iii) establishment of ambient air quality trends.
Remote monitoring in enforcement programs can be conducted
on two levels: (1) Evidentiary monitoring for case development, in
which the plant owner is served with a notice of violation and court
action is initiated in the event of non-compliance, and (2) Surveillance,
in which a large number of stack emissions are screened to assist in
the determination of these stacks in possible non-compliance.
The application of remote monitoring techniques to the develop-
ment of regulations consists of source monitoring to gain an overview
of emission levels for the different types of industries.
In monitoring ambient air quality trends, remote lechniques
can assist in determining significant air quality deterioration. According
to 40 CFR 52, areas in the U. S. were designated as Class I, II or III,
in which the annual mean and 24 hour maximum for particulate matter
and SO2 were prescribed.
An overview of the applications and modes is given in Table 2-2,
where the symbols • and o indicate heavy and limited involvement,
respectively.
In enforcement monitoring, several modes can be distinguished
(see Figure 2-1): Direct observation of the plume by passive or active
monitors, perimeter monitoring by up-looking from van-oased platforms
or down-looking from airborne platforms, and horizontally by active
long-path systems, although the latter application is limited to cases
where the horizontal long-path is representative of a given situation.
In addition, area monitoring using an aircraft can be used in surveillance.
These surveys of wider geographical areas can also assist in the deter-
mination of environmental quality degradation, plant site selection, the
design of contact monitoring networks, and the tracking of plumes to
study atmospheric dispersion, diffusion and fate of pollutants.
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TABLE 2-2. Modes and Applications
^"^---^^^ Modes
Applications "~^~^___^
Enforcemerr:
Cave' Dey*:op4nent
Enforcemcr :
Surveillance
Research ard Derrtopment
of Regulations
Monitoring nf Ambient
Air QuilU- Trends
Direct Observation
of Stack Plume
•
e
•
Perimeter
Monitoring
O
•
• •
Open Path
Monitoring
o
9
9
•
Aria
Surrey
O
o
•
•
Figure 2-1. Modes of active and passive remote techniques in
enforcement monitoring: Direct observation of
stack plume, perimeter monitoring (ground and
airborne) and area monitoring.
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3
AIR ENFORCEMENT MONITORING
S. 1 OVERVIEW
In this section we review some of the legal aspects of air en-
forcement monitoring, the specific requirements in case development,
and the existing proposed and promulgated rules for performance
specifications of sources and measurement methods.
One phase of this review involved the scanning of the legal
publications and the analysis of court cases, in which remote and/or
analytical measurements were used as evidentiary material. Another
phase of this review involved the contact with enforcement personnel
in the field in order to learn about the practical approaches and impli-
cations in evidentiary and surveillance monitoring.
In our scan of the literature (Environmental Law, 1970-1974), we have
found only cases involving the visual observations of pluir.e emissions.
Several interesting court decisions were found, which either accepted
these observations as admissible evidence or rejected them as too sub-
jective to be admissible. Based on the available maierial we have
concluded that visual observations will be more and more questioned
by the courts as admissible evidence, in .view of the fact that instru-
ments become available. The subject of visual observations is dis-
cussed in Section 3.2.
To gain insight into what represents admissible evidence in
environmental cases, we have reviewed and discussed briefly two
documents, one was written by enforcement officers in the field (Peirce
and Quebedeaux 1973), the other one was originated in the General
Counsel of EPA (Rogers 1974). In addition, we have abstracted several
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legal briefs that are concerned with the 'Vnr'f;eler:cy of evidence" in
environmental cases. Since we had found ro :-ir pollution case in which
analytical instrumentation was involved, we Lave included the pre-
sentation of evidence in a breath analyzer cas-;. These subjects are
discussed in Section 3. 3.
Based upon the material presented i Tection 3. 3, it appears
that evidence obtained through the applica,.on of remote techniques
(other than visual observations) can be In.r .sc-.ced Into court proceedings
the same way as evidence has been proaeiv, .x in previous (non-environ-
mental) cases. In this procedure, after to • f eld enforcement officer
convinces himself that the remote sensor . i.-educing reliable data,
he accumulates a "preponderance of evi/jer^p". The common sense
questions the courts would likely :;.-:'•: i'' ?,e: :/.€;'• rig whether to accept that
evidence may be:
(1) Is the scientific principle underlying fie instrument's operation
valid ?
(2) Does the instrument successfully embody and apply this under-
lying principle?
(3) Was the mstrum3-.it in proper v-cr!:., f order and properly cali-
brated at the time of the test'?
(4) Was the person conducting the test rubified to do so?
(5) Did the person conducting the test u;.e the proper procedures?
(6) If different from the person conduct'.P-T the test, is the person
. interpreting the test's results oimli'iei to do so?
It is believed, however, that a grea,, percentage of cases will
not even lead to court action. Once evidenre 3! non-compliance is
obtained, past experience indicates that th^ r'ant owner/operator will
probably taka steps to comply.
In enforcement monitoring, tbe accuracy of the remote instru-
ment must be known, but does not need to te jf a given absolute value.
The Appellate Court in Washington, D. C. (AMOCO OIL vs. EPA 1974),
has declared that the measured departure .'re;m the standards must merely
be beyond the boundaries of probabe measurement error. Thus, there is ,
no requirement of an absolute lower limit c~ .he instrument sensitivity and
accuracy, as long as it is better than the o -p?,rture from the standard to be
measured. However, we believe that remi ;•: Instruments used in research
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and development must have specified limits in accuracy and sensitivity,
like other instruments used in scientific research.
In the early days of the Clean Air Act, the courts have often
taken a pro EPA view, as in Houston Compressed Steel Corporation,
d/b/a Dyer's Barge Terminal vs. The State of Texas (456 S. W. 2d 768,
1971). In this case, the Houston Compressed Steel Corporation con-
tended that the Clean Air Act was vague and that the definition of "air
pollution" given in the Act was inadequate. The Court of Civil Appeals
of Texas stated, that the emphasis of the newer pollution statutes is
on regulatory standards, and that the science of air pollution control
is new and inexact. Thus, the court felt that standards are difficult
to devise, "but if they are to be effective they must be bred. If they
are too precise they will provide easy escape for those who wish to
circumvent the law."
Recently, however, new legal issues were raised after particular
measurement methods were challenged. These are discussed in Section
3.4, and have to do with the "equivalency" of measurement methods
used in setting the standards and in establishing non-compliance in en-
forcement proceedings. Thus, Denney from the General Counsel of EPA
(1974) has stated: "Courts are looking much more closely at the test
methods and technical support for standards than they once did. There-
fore logical quantitative relationships between standards and tests used
for compliance must be developed and clearly articulated in support of
all EPA test methods. Mere reliance on agency "expertise" will no
longer be adequate to withstand legal attacks on EPA standards and test
methods". As a consequence, we believe that performance specifica-
tions for remote sensing techniques must ultimately oe developed,
similar to the performance specifications established for the continuous
monitors that measure ambient air quality and stack emissions.
The right of conducting remote measurements by enforcement
personnel without notice was recently affirmed by the Supreme Court
in the case of Colorado Air Pollution Variance Board vs. Western
Alfalfa Corp. (1974). Here, the Colorado Court of Appeals had ruled
that the company's Fourth Amendment rights against unreasonable
search and seizure was violated. In June 1974, the Supreme Court,
unanimously ruled that Colorado had not deprived Western Alfalfa of
due process, and that such inspections fall within prior court decisions
which decline to extend Fourth Amendment rights to sights seen in
"the open fields. " The field inspector did not enter the plant or offices,
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Justice William O. Douglas wrote for the Court. "He was not in-
specting stacks, boilers, scrubbers, flues, grates or furnaces; nor
was his inspection related to [the company's] :;iles or papers. He had
sighted what anyone in the city who was near tne plant could see in the
sky—plumes of smoke. " Douglas noted that regulations for conducting
opacity tests require that inspectors stand certain distances from the
base of a smokestack, distances which may place him either inside
or outside a company's property line. In this case, Douglas said,
"we aren't acvised that [the inspector] was on premises from which
the public was excluded. "
An interesting point is raised by Zirnpritch (1975), who inves-
tigates the relationship between remote sersiiig technology of stationary
sources and the Fourth Amendment of the Constitution. The premise
of Zimpritch's argument is that the right tc erter any premises with
stationary emission sources vested in enforcement officers by the
Clean Air Act is in conflict with the right, o:~ privacy guaranteed by the
Fourth Amendment. This is so because of :hr severity of the Act's
penalties, which can be imposed through the results of an on-site in-
spection. Thus, the owner of an emission source is impelled "to an
uncomfortable nexus between administrative and criminal law, where
the routine character of an administrative inspection is linked with
extraordinary penalties.' With the developrr.eri of greater sophistication
in air pollution monitoring techniques, it may be possible in the future
to detect violations of air pollution controls by means of external sur-
veillance. The ability of inspectors to detect violations without the
necessity of entering the premises of an emission source, combined
with the criminal nature of the Clean Air Act's enforcement provisions,
arguably means that an inspector would have to prove strict probably
cause as a prerequisite to obtaining the issuance of a search warrant
once such sophisticated monitoring technology is developed.
3. 2 VISUAL OBSERVATIONS OF PLUMES
Visual observation of plumes (including photography) is the only
remote sensing technique being used in litigations at the present time.
There have been several court cases in which the objectivity of visual
observations was challenged. However, there were also a number of
other cases in which visual observations were accepted, even of un-
trained observers. To illustrate the somewhat confusing picture, we
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give in the following a sampling of court rulings, which clearly indicate
that observations based upon instrument readings will be much less
subject to question.
The Air Pollution Commission of Pennsylvania issued an abate-
ment order (JAPCA 23, 328, 1973) directing the North American Coal
Corporation to install control equipment to reduce the emission of
particulate matter from two stacks, about 24 m in height. The chief
witness for the Commission was an air pollution control engineer em-
ployed by the Pennsylvania Department of Health. He testified to making
visual observations of emissions from the two stacks while off the site.
The coal company appealed. The Commonwealth Court of Pennsylvania
declared: "... it is not reasonable, nor does it follow the well estab-
lished principles of fairness, in our system of jurisprudence, to permit
such a witness to declare a citizen of this Commonwealth to be in vio-
lation of the Commission's regulations based solely upon visual tests,
when more reliable scientific tests are available.. .we hold that the
Commission did not meet its burden of proof in this case. "
In another case, a Dallas jury (Air/Water Pollution Report,
May 27, 1974) has returned a $63, 150 verdict against Frv Roofing Co.
for failing to comply with requirements for the installation of stack gas
measuring equipment, because on 25 separate days, company had per-
mitted particulate emissions in excess of state standards. Since no
measuring equipment had been installed, inspections were made visually.
Company said particulate emissions were within limits, adding most of
the emission was steam. In the verdict, jury fined company $43, 400 for
failure to install testing facilities and $19, 750 for excess emissions over
the 25 days as claimed by the state. Appeal is expected.
In the case of Bortz Coal Co. vs. Dep. Env. Resources (7 ?a.
Commonwealth 362, 1973)? the court commended the caso back to the
Department of Environmental Resources (DER) because the alleged
violation was not proven by substantial evidence. The experts had
merely made visual observations of the smoke plumes coming from
the ovens, while the record indicated that there were acceptable and
well-recognized scientific tests available. The court, held that where
there are available established instrumental methods for determining
violations, those methods must be used. In the appeal case, the court
found that the Department of Environmental Resources had presented
on remand "substantial evidence of air pollution caused by the emis-
sions from Bortz's coke ovens, as measured and determined by the
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use of a recognized scientific testing device known as a Ringelmann
Chart. The Commonwealth experts not only used the Ringelmann
Smoke Chart, they also used an MSA Smokescope and a Plibrico
Smoke Chart in their determination that the smoke plumes from the
Bortz coke ovens were in violation. Unlike the evidence produced at
the original hearing, DER has now more than adequately proven its
case."
The major points in the case of Western Alfalfa vs. Colorado
Air Pollution Variance Board (3 ERG 1399, 1974) were made by the
court in favor of the petitioner Western Alfalfa: The Board should
have shown by preponderance of evidence that the manufacturer was
in non-compliance, and not have required manufacturer to carry
burden of proof. Further, the Colorado Department of Health's re-
fusal to permit attendance of training school and certify visual obser-
vers who are not public employees is invalid since it precludes manu-
facturers from presenting testimony. The court further found that the
Ringelmann Chart is too inaccurate when the emission is largely mixe;d
with non-pollutant and that unrelented testimony of approximately 10
minutes observation by one witness is not considered "support by sub-
stantial evidence, "
In the case of State of Oregon vs. Lloyd A. Fry Roofing Company
(51 ALR 3rd 1007, 1972), the smoke reader's evidence'was considered
sufficient. The constitutionality of an administrative rule prohibiting
air pollution was upheld, since the court's interpretation of "equivalent
opacity" as reduction of transmitted light and obscuration of background,
applicable to white smoke which obscures more than 40 percent of the
background and to black or gray smoke as dark or darker than that de-
signated as No. 2 on the Ringelmann Chart, was not so vague and ar-
bitrary as to violate constitutional standards controlling the validity of
criminal legislation. The court also held the state's evidence in the
form of testimony and records of smoke readers, certified as such just
prior to making the readings in question, was admissible, and such evi-
dence was sufficient to sustain the convictions. This case contains also
an Annotation about evidence as to Ringelmann Chart observations
(Bockrath 1972). The author concludes that the statutes and ordinances
based upon Ringelmann Chart standards have repeatedly withstood con-
stitutional challenge, and their validity seems well settled. In each
case in which the evidentiary aspects of Ringelmann Chart observations
have been discussed, and where the competency of witnesses regarding
the observations has been at issue, the witness has been held qualified
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to give testimony. Ringelmann Chart observations, being rather un-
scientific in nature, apparently need not, to be admissible, be made
by one qualified as an expert. If there is doubt as to a witness' quali-
fications, it may reflect on the weight to be given to his testimony,
but has no effect on its admissibility. Since most ordinances and
statutes which incorporate Ringelmann standards forbid the discharge
of contaminants as dark as, or darker than, No. 2 on the Ringelmann
Smoke Chart, the question arises as to whether it is necessary that
the observer have a chart in his presence at the time the observation
is made. Although one court has held that an observer must be equipped
with the chart, other cases have held that the chart itself is no longer
necessary after the observer has become experience at making the
readings. "As is the case in other criminal prosecutions, each es-
sential fact of the charges must be proved beyond reasonable doubt.
This may include not only the degree of obscuration, but also the fact
that the emission is a pollutant, not merely steam. " It has also been
held that the Ringelmann Chart by itself is insufficient to sustain a
conviction for air pollution, particularly where more precise scientific
tests are available. Thus, Ringelmann Smoke Chart observations have
been held both sufficient and insufficient to sustain conviction.
In contrast to these conclusions, engineers and environmental
lawyers (Henz 1970; Haythorne and Rankin 1974) have repeatedly
argued that "eyeball judgments" are inaccurate at present levels and
that, more basically, opacity is not a reliable measure of the amount
of pollution in the plume. The most recent status of thess issues in
given in the case of Portland Cement Association vs. Ruckelshv-L
(1973), where the Appellate Court in Washington, D. C. made a ruling
pertaining to visual observations. The main trust of the petitioners
comments was that the visual opacity test is arbitrary, and that in-
spectors will be unable within any reasonable degree of accuracy to
determine whether permitted opacity is 10%. The c,-urt found tlii;
there were two issues involved: One, whether visual opacity tests
are inherently inaccurate, and two, whether readings only at the low
range become unreliable. As to the second issues, EPA was required
to provide further consideration and explanation on remand, and a
showing that 10% opacity measurements can be made within reasonable
accuracy. In its response, EPA (1974) states that after revising the
opacity standard (Method 6), observations by trained observers are
both accurate and precise enough to serve as a standard and that they
are also less costly than the test methods for determining the mass
emission standards (Method 5). In addition, EPA has also addressed
the first issue and agrees that a single, constantly invariant and precise
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correlation between opacity and mass emission would not be reliable.
Therefore, opacity standards are developed "for each class of sources
at a level no more restrictive than the corresponding mass emission
limitation with due consideration given to all conditions of operation. "
The Appellate Court has accepted the reasoning in EPA's response.
3.3 EVIDENCE
A general discussion about documenting admissible evidence in
environmental cases was presented by Peirce and Quebedeaux (1973).
The authors state that environmental cases are actually no different
from any other, involving the same rules of evidence. Possibly the
only material difference is seen in that someone has to correlate a
large amount of individual test results into a concise presentation.
The final judgment in a civil suit is awarded to the side that has been
able to present a "preponderance of evidence". (This is in contrast
to a criminal case, in which the prosecution must supply evidence for
the judge or jury to find the defendant guilty "beyond a reasonable
doubt.") The authors make a plea for entering only a strong case:
"Unless I can satisfy myself there is no doubt that the violation of the
law occurred and was caused by the defendant, it is capricious and
arbitrary on my part to enter a courtroom with the case. " The authors
then discuss the different kinds of evidence; the more relevant ones
are listed in the iollowing:
Direct evidence (everything which can be determined by an individual
through his senses. Most of the inicial evidence in environ-
mental cases is of this nature).
Circumstantial evidence (if the relevancy of this type of evidence can
be shown, then the existence of facts in issue may be inferred
from the surrounding circumstances).
Demonstrative evidence (evidence directed to the senses of the jury
withcut intervention of testimony of a witness. In environmental
cases, it is quite important to be able to show samples about
which a witness is testifying.)
Supportive evidence (scientific literature, also photographs, engineering
drawings, etc.).
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The authors then describe the admissibility of evidence; the
importance of the identification by witness of items which cannot "talk"
is stressed. The presentation of records is found to be more success-
ful if all the documentary evidence is introduced as business records,
which can be done through the custodian of the files. He must testify
that the business for which the record is kept is a regular organized
activity; the memorandum of the records was made in the regular
course of business; it was made at or near the time of the incident;
in the regular course of the business, an employee made the record
or furnished the information for the report; the identity of the record
and the method of its preparation may be proven by the person making
the entry, the custodian, or some other qualified witness. Personal
knowledge on the part of the custodian is not required.
The authors stress that it is important that each of the above
items must have a signature of one of the employees of the department
who prepared it or had a part in making the report. Most of the docu-
ments are required for each and every sample collected by the labora-
tory and analyzed by them. In addition, sixteen potential entries in
the compilation of evidence are listed: (1) Profiled Sample Results;
(2) Pertinent Pictures; (3) Enlarged Photos (for introduction as evidence);
(4) Aerial Photos and Enlargements; (5) Maps Showing Extent of Con-
tamination; (6) Reports of Conferences with Plant Management;
(7) Reports of Investigations; (8) Reports Tracing Samples from T:.r a
of Collection through Laboratory Analysis; (9) Certified Copies cl
Certificate of Incorporation, T. A. C. B. Variance or T. W. Q. B. Permit;
(10) Available Copies of Correspondence between State Agencies and
Plant Management; (11) Copies of Harris County Correspondence with
Plant Management; (12) Reports from Other Agencies ? j tinent to the
Case; (13) Copies of Complaints Received and Verified by Harris County;
(14) Documents Showing Progress (or lack of) toward Pollution Abate-
ment; (15) Historical Summary of Cases based on Prior Violations-
and (16) Narrative Summary of Available Evidence Prepared for Con-
sideration of the Pollution Control Director.
At the conclusion, the authors stress the importance of proving
the "complete chain of custody" over the evidence, i. e., at every stage
of the way the files, the samples, and the records of the analyses be
kept in such a fashion that some witness can testify under oath there
has been no tampering with the sample.
We have also reviewed a report about presenting scientific
evidence (Rogers 1974). The document is primarily directed at water
27
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pollution control. At the outset, it is stated that through the application
of the National Permit Discharge Elimination System (NPDES), fewer
court cases will be based on the issue of public nuisance, requiring
expert witness. "The issue will be simply whether the effluent levels
have exceeded the permit terms; it will be much like a license vio-
lation case: the factual issue will be whether the permit was violated--
basically a monitoring chore—not whether deleterious effects occur by
discharging at that level. (This change in the burden of proof was one
of the major reasons for amending the Act to employ the permit system).
Of course, even with the NPDES program, there will be court actions
and the basic rules of evidence for presentation of expert testimony will
come into play. " The author then proceeds to discuss administrative
trial-type hearings and legislative hearings, the presenting of direct
evidence and discovery. The section on "Procedures of laboratory re-
search and field investigation which are subject to attack, " including
'chain of custody', corroborates the discussion of the previous paper
above. The Deport concludes with examples of cross-examinations in
Court. *
In the following, we have collected a number of legal opinions
about admissible evidence in environmental cases.
Within the case of North American Coal Corporation vs. Air
Pollution Commission, Justice Stern (279 A. 2d 356) gave the following
definition of "substantial evidence": to determine whether the findings
of the board are supported by the substantial and legally credible evi-
dence required by the statute and whether the conclusions deduced
therefrom are reasonable and not capricious. All orders and decrees
Of legal tribunals, including those of administrative boards and com-
missions, must be supported by evidence sufficient, to convince a rea-
sonable mind to a fair degree of certainty; otherwise our vaunted
system of justice would rest upon nothing higher than arbitrary edicts
of its administrators. 'Substantial evidence' is more than a mere
scintilla. It means such relevant evidence as a reasonable mind might
accept as adequate to support a conclusion... ".
Note added in proof: An extensive discussion can also be found in a
review article by J. L. Sullivan and R. J. Roberts, "Expert Witnesses
and Environmental Litigation" (JAPCA 25, 353, April 1975).
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In an annotation to this case, Brazener (1971) has discussed
the sufficiency of evidence of violation in administrative proceedings.
He states that although many jurisdictions take the position that ad-
ministrative tribunals are not bound by the rules of evidence governing
court proceedings, and that hearsay evidence may be permitted in
quasi-judicial proceedings, the decision of an administrative tribunal
must be supported by evidence of probative value, and if such evidence
is apparent to a reviewing court, it will not substitute its own judicial
determination on the facts. With regard to the more specific issue of
whether an abatement order issued by an administrative agency upon
a finding that air pollution laws had been violated was supported by
sufficient evidence, it has been held that the abatement order must be
justified by substantial evidence. As proof of the violation itself, it
has been held that a preponderance of the evidence, and not proof
beyond a reasonable doubt, is all that is required. It has also been
held that expert testimony carries little weight when it is based in
part upon assumptions made by the expert with regard to certain tech-
nical aspects of the polluting operation; however, another court did
hold as sufficient to support an abatement order testimony based upon
certain empirical assumptions drawn from technical jour mis, where
the validity of the assumptions as stated in the hournals was not chal-
lenged.
In a treatise about Environmental Law, Grad (1973) argues
that to date the many sophisticated air pollution measuring and moni-
toring devices, have not as yet been challenged by litigation ana :;ieir
use has not as yet been accepted judicially. It is certain that scienti-
fically sound and technically validated measuring devices and moni-
toring techniques will have little difficulty in gaining acceptance in
the courts, in view of the fact that far more subjective devices, such
as the Ringelmann Chart, have found such acceptance, largely because
their was nothing more accurate to use. In the past, testimony in air
pollution enforcement cases has largely relied on personal obsirwuon
of enforcement personnel. Photographs of plumes and of visible emis-
sions have generally been accepted. Evidence of air pollution mea-
surements by more sophisticated apparatus will require expert testi-
mony regarding the nature of emissions—including validation of the
results of chemical analysis through testimony to the effect that tests
were performed in a scientifically and technically acceptable manner
and that the measuring instruments were functioning properly and were
accurately calibrated.
29
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Because of the absence,of court cases involving analytical
methods in siack emission measurements, we have been looking for
cases other than environmental ones to establish "admissible evidence
by expert witnesses". The case involving a blood test taken with a
new instrument (gas chromatograph) can serve as an illustrative
example. This case was argued after appeal before the Supreme
Court of Kansas (202 Kan. 636, 1969). The major findings of the
case are summarized in the following:
• A witness to evaluate findings of chemical tests for alcoholic
content of blood must be an expert on that subject (proper
academic background and practical experience).
* Results of tests are admissible as long as a qualified expert
testifies that the method employed is, in his opinion, reliable
and accurate and also that it is generally accepted as such by
other experts in the field.
• The fact that there may be some disagreement in the scientific
community as to the reliability of certain tests is a matter
affecting the weight of such evidence, but not its admissibility.
Appellate courts have generally held that the fact there may be
some disagreement on the part of a few in the scientific and
medical community as to the reliability of a particular test
method is a matter affecting the weight of such evidence and
not its admissibility. They have held such evidence admis-
sible as long as a qualified expert witness testifies that the
particular test method employed in a given case is reliable and
accurate In his opinion, and also that It is generally accepted
as such by other experts in the field.
• The fact that the chemist who conducted the tests with a newly
introduced gas chromatograph (Beckman GC-4) did not under-
stand the intricate functioning of sophisticated electronic de-
tector and recording device was not material to admissibility
of test results because before making the tests with the blood
of the defendent, "tests were made on known concentration of
blood and alcohol samples to check accuracy of instrument's
operation. "
• Experts who performed the tests may be cross-examined in
detail as to procedures followed (quantity of sample, tempera-
ture, working order of all equipment involved, etc.)
30
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3. 4 NEW LEGAL ISSUES
In two cases before the United States Court of Appeals in
Washington, D. C., important rulings were made affecting the pro-
cess of setting standards and monitoring compliance. The first case,
Portland Cement Association vs. W. D. Ruckelshaus (1973), involves
the visual observation of smoke plumes and the equivalency of test
methods. The second case, AMOCO OIL vs. EPA (1974), involves
the issue of measurement accuracy.
The Portland Cement Association challenged EPA for not com-
plying with the statutory language of Section 111 of the Clean Air Actt
This Section directs EPA to promulgate "standards of performance"
governing emissions of air pollutants by new stationary sources con-
structed or modified. Any of the challenges is based upon the con-
tention that the achievability of the standards was not adequately
demonstrated. The arguments go as follows: The regulation requires
that participate matter emitted from Portland Cament plants shall not
be (1) in excess of 0. 15 kg per metric ton, maximum 2-hour average;
(2) greater than 10% opacity, except in the presence of uncombined
water. Subsequent to the issuance of the rule, EPA discussed two
tests (dry-process Dragon Cement Plant and wet-process Oregon-
Portland Cement Plant) in a supplemental statement, together with a
principal literature source (HEW report 1967, ''Atmospheric Emissions
from the Manufacture of Portland Cement"). Therefore, the court
felt that the supplemental tests and the literature cited formed a basis
of the above rule. However, when the petitioner disputed the validity
of the first test, EPA stated in a brief that the two tests were only
used to assist in determining the emission levels of properly main-
tained equipment and not used as the primary basis for the cement
standards. The court then held that the court w.,s no; competent to
decide if the conclusions by the petitioner were correct. However,
the court felt that the criticism required EPA to discuss on remand.
But more important, the court stated that EPA cannoc disclaim re-
liance on reasons offered by EPA in its statement of reasons. With
other words, tests and literature used in support of a rule must be
an integral part and must conform with the statute and congressional
intent of the Clean Air Act and cannot be retracted when challenged.
This is further underlined in the court's ruling about the literature
sources cited. The principal literature source was called into question
by the petitioner since the test methods used to compile the results
31
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of the study were at odds with those used by EPA in its own tests.
The court held that if such literature is relied upon, EPA should
indicate which findings of that literature are significant to the parti-
cular rule it is supposed to support.
We now come to the part in which the court specifically re-
quires that the methods used to establish a standard should be the
same as used to determine compliance in an enforcement proceeding.
EPA has adopted the opacity standard in addition to the standard
regulating the particulate concentration. The court held that it may
be that the opacity test is an important enforcement tool, and that the
results of ar opacity test, which is normally performed at some dis-
tance from the plant by trained observers, offers a cheaper and faster
method of determining compliance than enforcement of the particulate
concentration standards. However, it is one thing to use a method of
testing to observe possible violations of a standard; it is another to
constitute that method as the standard itself. The court held further
that if the opacity test is to be a standard, and if violations can result
in enforcement actions without further testing, the standard must be
consistent w.th the statute and congressional intent. Furthermore,
the court found that the statute expressly requires—for the standards
EPA promulgates—that technology be achievable. The record pre-
sented apparently revealed a lack of an adequate opportunity of the
manufacturers to comment on the proposed standards, due to the
absence of d-sclcsure of the detailed findings and procedures of the
tests. In addition, the court found that the necessity to review agency
decisions requires enough steeping in technical matters to determine
whether the igency 'has exercised a reasoned discretion'.
In summary, the important points in this case were:
• The court did not specify any requirements for the use of a
method of testing to observe possible violations of a standard.
• However, if the method is to be substituted as the standard
itself, then requirements consistent with the statute and
congressional intent are placed upon the agency
(a) to demonstrate in well-conducted tests that the method
produces result with "reasonable accuracy" and make
results and procedures available in a timely fashion;
32
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(b) to respond to subsequent comments and disputes by
the manufacturers;
(c) if and when scientific literature is relied upon in the
promulgation of rules and standards, to indicate the
specific findings which are significant.
In the second case, one of the points the petitioner alleged was
that the EPA "Regulation of Fuels and Fuel Additives" fails to include
"specific findings" supporting the Administrators many regulatory
decisions, and that the 0. 05 g/gallon ceiling on lead in "unleaded
gasoline" is not sufficiently justified. While in the previous case
the court seemed to emphasize "specificity" in the promulgation of
rules and standards, the court seems to rule against "specificity" in
the present case. "We are satisfied that Congress wished the AdminiS"
trator... to read the 'findings'* requirements [of the relevant Section
211 in the Clean Air Act] in light of that imperative need for adminisr
trative flexibility and expedition which we have already recognized as
coloring EPA's statutory duty to state the 'basis and purpose' of its
regulation. Findings there must be, but they need not be "specific"
in the sense of being detailed and voluminous... in rule-making, ...
an agency task is not to test raw evidence against a single, pre-
established standard; rather the agency is to fashion a host of new
legal standards—regulations—having prospective effect".
However, in the following, the court refers to a certain Section
of the Clean Air Act that "requires particular factual determinations
be made concerning the threshold necessity of embarking upon full
regulation. Because these findings requirements are reasonably
precise and comprehensive, they are compatible with the mechanics
of rule-making and with the exigencies of judicial review".
In the second complaint about the 0. 05 g/gallon ceiling on lead,
the petitioner argues (amongst others) that the rationality of the pres-
cribed ceiling must remain in doubt until the Agency announces the
'test methods' it will use in measuring trace levels of lead. The court
found that it would be better practice of the Agency to promulgate its
* The provisions speak only of "findings", not of "specific findings".
The House version of the legislation required specificity; the Senate
version did not. The Senate version was adopted.
33
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standards and test methods at the same time, but there is no fixed
requirement to this effect. The court then affirms its statements
made in the Portland Cement Association case above that a signifi-
cant difference between techniques used by the Agency in arriving at
standards, and requirements presently prescribed for determining
compliance with standards, raises serious questions about the validity
of the standard. Should such a 'significant difference' appear upon
final promulgation of test methods, the court reviewing those methods
may have to regard their promulgation as an effective alteration in
the lead content ceiling.
The court then deals with the petitioner's argument that any
test methods adopted will involve a certain capacity for statistical
error. The court makes the following important statements: "We fail
to appreciate the force of this argument. The possibility of statistical
measurement error, which is often unavoidable where regulations set
qualitative standards, does not detract from an agency's power to set
such standards. It merely deprives the agency of the power to find a
violation of the standards, in enforcement proceedings, where the
measured departure from them is within the boundaries of probable
measurement error. Furthermore, if the vest methods eventually
adopted raise a greater potential for error than is practical or neces-
ary, a reviewing court may order revisions".
In summary, the important points in this case were:
• There is no fixed requirement to promulgate standards and
test methods at the same time.
• There should not be a significant difference between techniques
used in arriving at standards and used in determining com-
pliance with standards.
• The possibility of statistical measurement error does not
detract from the ability to set standards. However, the
departure of the compliance test results from the standards
must be greater than the probable measurement error before
a violation in enforcement proceedings is found.
In its response to the remand ordered by the Appellate Court
in the case of Portland Cement Assoc. vs. Ruckelshaus, EPA (1973)
addressed all of ihe above issues which are summarized in the following:
34
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In the courts questioning whether the validity of a standard
is affected by the different testing method required by EPA
in the promulgated standards and that used by EPA in its
tests in developing the standards, EPA responded by stating
that if a known relationship is established, "the change in test
methods in no way invalidated EPA's test results. "
To the issue of specifity what literature is relied on to support
the standard, EPA responded that the principal literature
source provided basic information regarding details about
cement plants, process details, equipment etc. and that the
source test data included in the report were not relied on to
show that the standard was being met.
The EPA's response to the question of opacity was already
described in Section 3. 2.
3. 5 PERFORMANCE SPECIFICATIONS AND
SPECIFICATION TEST PROCEDURES
FOR THE USE OF REMOTE MONITORS
In this section, we develop the basis for the performance speci-
fication and operating parameter for the use of remote monitors. For
the application to enforcement monitoring, the specifications can be
based upon the ones proposed or promulgated by EPA for the continuous
emission monitors of stationary sources. In the application of estab-
lishing the ambient air quality trends, the specifications must be con-
sistent with the ones promulgated for the ambient air monitors.
Thus, we give first an overview (Section 3. 5.1.) of the new
source performance standards, including the performance specifi-
cations for continuous monitors, and of the national primary and
secondary air quality standards including the test procedures that
establish reference and equivalent methods.
In Section 3. 5. 2., we outline a set of general performance
specifications and specifications test procedures for the use of
remote monitors in enforcement monitoring.
35
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3. 5.1 Background and Overview
In order to assess the sensitivity remote monitoring instru-
ments must have, we have listed the new source performance stand-
ards of 19 industrial plants in Table 3-1. It can be seen that the
performance standards for the opacity can be lower than 10 percent,
and for the cDncentrations of SO2 and CO lower than 650 ppm and
550 ppm by \olume, respectively. All other standards are given in
pounds per f lei or in pounds per product, a measure which requires
additional information to determine compliance. Thus we find that
for an effective application of remote techniques in enforcement moni-
toring, new standards should be developed that do not utilize the mea-
sure of "pounds per product" or "pounds per fuel."
As a basis for the formulation of performance specifications
of the remote techniques for enforcement monitoring, we have re-
viewed the continuous emission monitoring requirements and perform-
ance testing methods proposed by EPA as amendments to 40CFR60.
EPA nas proposed and promulgated Standards of Performance
for a number of new stationary sources. These new or modified
sources are required to demonstrate compliance with standards of
performance by means of performance tests. In order that sources
remain in compliance, provisions were included which require source
owners to install systems which continuously monitor levels of emis-
sions; these specific monitoring requirements are for:
1. Opacity fossil fuel-fired steam generators, petroleum
refineries;
2. SO2 fossil fuel-fired steam generators, sulfuric
acid plants, petroleum refineries;
3. NO fossil fuel-fired steam generators, nitric
acid plants;
4. HuS petroleum refineries;
5. CO petroleum refineries;
6. O2 petroleum refineries, fossil fuel-fired steam
generators; (in support for measurements with
excessive air flow).
36
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TABLE 3-1. New Source Performance Standards
Plant
Status Ref.
Standards
(1) Fossil fueled
steam generator
Pm
(2) Incinerators
(3) Portland Cement
Plant
(4) Nitric Acid Plant
(6) Asphalt Concrete
Plant
(7) Petroleum
(8) Storage Vessels tor
Petroleum Liquids
(9) Secondary Lead
Smelters
(10) Secondary Brass
and Bronze Ingot
Production Plant
(11) Iron and Steel
Plant
(12) Sewage Treatment
Plant
(13) Primary Copper
Smelters
Pm
Pm
Pm
(5) Sulfuric Acid Plant Pm
Pm
Pm
Pm
Pm
Pm
Pp
36 FR
24876
36 FR
24876
36 FR
24876
36 FR
24876
36 FR
24876
38 FR
9308
39 FR
9308
39 FR
9308
39 FR
9308
39 FR
9308
39 FR
9308
39 FR
9308
39 FR
37040
Opacity: 20%,
SO2: 0.8 lb/106BTU (liquid fuel)
1. 2 lb/106BTU (solid fuel)
NOX: 0. 2 lb/106BTU (gas fuel)
0. 3 lb/106BTU (liquid fuel)
0.7 lb/106BTU (solid fuel)
Particle: 0.18 g/m3com. (to ,2% CO2)
Opacity: 10%
NO : 3 Ib/ton acid produced
10% opacity
Acid Mist: 10% opacity and
0.15 Ib/ton acid product
Opacity: *20%
Opacity: s30%
CO: * 500 ppm v
HjS: s 230 mg/dscm in fuel gas
SO,: alternate method equivalent
to HjS standard
Hydrocarbons: If p > 78 torr, vapor
recovery system required
Opacity: * 20% (blast furnace)
* 10% (pot furnace)
Opacity: i 20% (reverbatory furnace)
* 10% (blast or electric furnace)
(excluding uncombined water)
Particles: * 50 mg/dscm
Opacity: * 20% (except for uncombined
water ^
Opacity: * 20% (except for 2 min. in
any one hour and except
for uncombined water)
SO,: * 650 ppm v
37
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Plant
(14) Primary Zinc
S.-nelter
(15) Primary Lead
Smelter
Status*
Pp
Pp
Ref.
39 FR
37040
39 FR
37040
Opacity
Opacity
SO,: *
Standards
: * 20% (except for 2 min. in
any one hour and except
for uncombined water)
: s 20% (except for 2 min. in
any one hour and except
for uncombined water)
850 ppm v
(16) Sreel Plant: Pp
Electric Air Furnace
(17) Fsrro-a)loy
Production
Facility
Pp
39 F Opacity: * 5% (exit from a control
37466 device)
* 0% {exit from the shop for
more than 1 min. in any
one hour)
* 20% (exit from the shop during
changing a furnace and
3 minutes thereafter)
< 40% (exit from the shop during
tapping a furnace and 3
minutes after)
* 10% (from dust handling
equipment)
39 FR Opacity: * 20% (except for 0% from
37470 control system)
* (ft from control system
(after tapping at least
60% of each tapping
period)
* 5,0% (from dust handling
equipment)
CO:
: 200, 000 ppm v
(18) Aluminum Plant
(19) Coal Preparation
P ant
39 FR
37730
39 FR
37922
Total fluorides: < 1 kg/ton of aluminum
produced
Opacity: * 10% (from pot room)
< 20% (from anode bake plant)
Opacity: « 30% from, any thermal
dryer gases
s 20% from any pneumatic
coal, cleaning
equipment gases
< 20% from any coal processing
and conveying equipment,
coaJ storage systems, or
coal transfer and loading
systems gases.
* Pm means promulgated and Pp means proposed.
38
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Initially EPA intended that the selection and use of continuous
instruments be in the form of instrument specifications and calibration
procedures, i. e., a formal EPA instrumentation certification program.
Once certified, an instrument from a particular product line of a given
instrument vendor could be installed in fulfillment of the monitoring
requirements for that source.
However, the "product line certification" approach was soon
considered undesirable because an instrument so certified may not
perform properly at the source due to
• unexpected or disregarded interferences
• improper installation
• undetected damages from handling.
It was realized that no one instrument model would be expected
to provide accurate results for each of the wide variety oi' (new) sources.
Therefore, a different approach has been adopted which raquires the
source owner to demonstrate at each source the capability of continuous
monitoring systems to meet the performance specifications for systems
which monitor
1. Opacity
2. SO0 and NO
fj X
3. 02
Specifications for systems which monitor
H2S
CO
will be proposed by EPA at a later date. The validity of these speci-
fications for the above four systems has been evaluated in depth by
extensive testing programs at steam generating facilities. The tech-
nical support for these specifications are contained in a report
"Performance Specifications for Stationary Source Monitoring Systems
for Gases and Visible Emissions" (EPA-650/2-74-013, January 1974).
39
-------
The provisions specifying general continuous emission moni-
toring requirements (40CFR60, App. B) have been proposed by EPA
in Sept. 1974 (39FR 32852). These include the performance specifi-
cations and specification test procedures (1) for transmissometer
systems for continuous measurement of the opacity of stack effluents,
(2) for monitors of SO9 and NOX from stationary sources, and (3) for
monitors of oxygen from stationary sources. The provisions for (2)
and (3) are generally broken down Into
1. Principle and Applicability
2. Apparatus
3. Definitions
4. Measurement System Performance Specifications
5. Performance Specification Test Procedures
6. Calculations, Data Analysis and Reporting
7. References
Additional provisions for (1) are given for the installation, op-
tional design specifications and determination of conformance with
design specifications.
As ar illustration o! the proposed performance specifications,
the requirements for th^ transmissometer :1) and the SO2 and NOx
monitors (2) are sumrr.arized in Tables 3-2 and 3-3, respectively.
TABLE 3-2. Performance Specifications for
Transmissometer
Parameter Specifications
Calibration error * 10% of test filter value*.
Zero drift (24 hour) £ 10% of emission standard*.
Calibration drift (24 hour) * 10% of emission standard*.
Response time 10 seconds (maximum).
Operational period 168 hour.
A report of all emission monitoring and a summary of excess
emissions must be given quarterly by the owner or operator of the
40
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stationary source, to be used by the Administrator to determine whether
acceptable operating and maintenance procedures are being used. The
continuous monitors are required on affected facilities where
• they can assist in minimizing pollutant emissions,
« the technical feasibility exists using currently
available continuous monitoring technology,
• the cost of the monitors is reasonable.
Only a limited amount of cost data is available so far. About
$5K to $15K and 10 man-days for installation is needed for either the
opacity or oxygen monitors, and $10K to $20K and 20 man-days for
either SC>2 or NOX monitors. These estimates assume the monitoring
system tests will be performed both before and during the source per-
formance test.
TABLE 3-3. Performance Specifications for
SOQ and NO_. Monitors
£i A
Parameter Specifications
Accuracy * 20% of reference mean value
Calibration error* * 5% of each (50%, 90%) calibration
gas mixture value
Zero drift (2 hours)* s 2% of emission standard
Zero drift (24-hour)* S4% of emission standard
Calibration drift (2 hours)* * 2% of emission standard
Calibration drift (24-hour)* £ 5% of emission standard
Response time 15 minutes maximum
Operational period 168 hours minimum
The parameters with an asterisk are expressed as the sum of
the absolute mean value plus 95 percent confidence interval of a series
of tests, according to
x.
n
41
-------
where Xj aro the Individual values, £ is the sum of the individual
values, x" is the mean value, and n are the number of data points.
The 95 percent confidence interval (two-sided) is calculated according
to
r " - • J' *• /-nSTv''^ (TV \
<~. i.. g^ - • V n\l; X. : - (LX.)
1
where Sx^ is the sum of all data points, t 975 = tj -a/2, and C. L g§
is the 95 percent confidence interval estimate of the average mean value.
VM.TOBS wm 'ff!6
n . >#f5
a ----------- -. ..... . ............. - 18.706
3 _____________________________ „ ____ 4^0S
4 ___ . ................ „ ..... -------- s.isa
f> ............................. ------ 2.776
6 ............................. ------ 2.671
7 „ ------------------ ,—. --------- 2.*47
0
}'4r .. .. , 3.ISO
jr. a.i*s
K- —, a.•-•;!
w -tec lor f~l dojiress oj ireodom. 1J«« tt oqiud
The above provisions are not applicable to sources for which
monitoring equipment has already been contracted for. However,
this equipment must have the capability to monitor emission levels
to within +20 percent with a confidence level of 95 percent. Com-
pliance with .be requirements is determined by subjecting the con-
tinuous monitoring system to evaluation with a variety of known
opacity neutral density filters or a variety of Known concentration
calibration gases as applicable. In addition, owners or operators
of all continuous monitoring systems are required to record the
zero and span drift and to adjust them at leas-; once daily, ( or more
often if prescribed by the instrument manufacturer), using zero and
span gas introduced into the measurement system for extractive
methods and certified calibration gas cells for non-extractive
methods.
42
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In addition, records must be maintained that induce the occur-
rence and duration of any startup, shutdown, or malfunction of the
facility as well as the air pollution control equipment. Also, files
must be kept as to the results of any tests conducted in accordance with
the procedures listed in the monitoring performance specifications.
When the remote techniques are to be applied to establish the
ambient air quality trends, the performance of the instruments must
be consistent with the National primary and secondary air quality
standards, which are given in Table 3-4, together with the levels that
show an effect on human health and welfare (crops and structures)
(Ross 1972).
TABLE 3-4. National Air Quality Standards
and Level Effects
FEDERAL AIR QUALITY STANDARDS
Primary Secondary
attainment by no time limit
summer 1975 on enforcement
LEVEL EFFECT SHOWS OF:
Human Health Welfare •*
according to
federal criteria
Particulates
mlcrogramg/cu. water
annual geometric mean
max. 24-hr. cone.*
Sullur oxides
micrograms/cu. mater
annual artth. aver.
max. 24-hr. cone. *
max. 3-hr. cone. •
Carbon monoxide
mlIHgrams/eu. meter
max. 6-hr. cone. *
max. 1-hr. cone. •
Photochemical oxldanti
75
260
80 (. 03 pom)
365 (. 14 ppm)
60
150
10 (8 ppm)
40 (35 ppm)
1,300 (.5 ppm)
10
40
microgram«/cu. mater
one-hr. max. • ISO (. 08 ppm)
Hydrocarbons
160
mlcrograms/cu. mater
max. 3-hr. cone. *
6-8 am
Nitrogen oxides
mlcrograms/cu. meter
annual arith. aver.
24-hr. max. aver.
16Q(.S4ppm) 180
100 (. OS ppm) 100
80
200
115
100
12
58
ISO
100
118
60
ISO
85
2«S
100
470 •••
• not to be exceeded more than one* a year
•• structures and crop!
••• bated on damage to vegetation only
43
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On the local basis, the regulations of the Air Pollution Control
Districts may vary from those of the Federal regulations. In the
Los Angeles APCD, as an example, three stages of alert are defined.
The first alert constitutes the close approach to maximum allowable
concentration for the population at large, at which preventative action
is required. The second alert constitutes the pollution level at which
a serious health menace exists. The third alert constitutes the pollu-
tion level at which a dangerous health menace exists. In Table 3-5,
the pollution levels of the four major pollutants in the Los Angeles
APCD are given for the three alerts.
TABLE 3-5. Alert Stages for Toxic Air Pollutants
Rule '56. Alert Stages ?or Toxic Air Pollutants*
(In parts per million parts of air)
First Alert Second Alert Third Alert
Carbon Monoxide 50 100 150
Nitrogen Oxides* 3 5 10
SuH-T Dioxide 3 5 10
Ozo ie 0.5 •- 1.5
* Sun of nitrogen dioxide and nitric oxide.
In addition to the ambient air quality standards, EPA had in-
cluded certain test procedures for the determination of the levels of
the six pollutants. These measurement procedures were codified as
"reference methods", where equivalency was defined as any method
of sampling and analyzing for an air pollutant which can be demon-
strated to have a consistent relationship to the reference method.
At a later date (1975) a distinction was made between manual and
equivalent methods, codified in 40CFR53 (40FR7042, Feb. 18, 1975).
Subpart A of Part 53 contains the general requirements for a
determination of a reference and equivalent method for both manual
and automatic methods. An overview is given in Table 3-6.
44
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TABLE 3-6. Applicability of 40CFR50 and 53 (40FR7042)
Reference Method Equivalent Method
Manual Those methods as given in the Any method that satisfies
Appendices to Part 50, except the requirements in Sub-
at present, App. C (for CO) part C of Part 53.
and App. D (for oxidants)
Automatic Those methods whose Any method that satisfies
"measurement principles and the requirements in Sub-
calibration procedures" are parts B and C of Part 53.
specified in the Appendices
of Part 50 (namely App. C
and D at present).
In any application submitted to EPA for reference or equivalent
determination, the following information must be supplied: A
clear identification of the candidate method which will distinguish
it from all other methods and by which it may be referred to unam-
biguously. A detailed description of the candidate method. The
measurement principle, manufacturer, name, model number, and
other forms of identification; a listing of the significant components;
schematic diagrams; and a detailed description of the apparatus and
measurement procedures. A comprehensive operation or instruction
manual providing a complete and detailed description of tne operational
and calibration procedures prescribed for field use cf the candidate
method and all instruments utilized as part of that method, adequate
warning of potential safety hazards that may result from normal use,
or (if the method is automated) from normal use or malfunction of
the method and a description of necessary safety precaut-on, a clear
description of installation and operation procedures and of necessary
periodic maintenance, as well as comprehensive trouble-shoot ing
and corrective maintenance procedures and parts identification
diagrams. A statement that the candidate method has been tested in
accordance with the procedures described in Subpart B and/or
Subpart C of Part 53, as applicable, including test data, records
calculations, and test results as specified. A statement that the
Statements to the effect that the method or analysis tested is repre-
sentative and that a quality control program will be followed.
45
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Subpart B contains the performance specifications which are
summarized in Table 3-7.
TABLE 3-7.
Performance Specifications
for Automated Methods
1
?
ft
4
ft
A
r.
8.
8
10
Performance pnraineter
Noise
Lower detectable limit .
Interfprenc* "quivalent
TotH Intxrff r»nt . ..
Zero .
6323 (•)
1 To contort (ram pvrt« per million to tnlcirogrem ptr cubic mnlrr at l!i" C «rd 7M> mm Bg, maltlp'sy by M/O.02U7,
whtre M n the molecular weight o( tb* giu.
Subpart C contains the procedures for determining a consistent
relationship between candidate methods and reference methods.
Equivalency (consistent relationship) is shown when the differ-
ences between measurements made by a candidate manual or automatic
method and measurements made simultaneously by a reference method
are less than or equal to the value specified in the last column of Table 3-8.
TABLE 3-8.
Test Concentration Ranges, Number
of Measurements Required, and
Maximum Discrepancy Specification
Bhnoltaruotu mmmremmo miuired
PolluUct
Oild.'»nta_
Carbon
monoxide.
SrOlur flioxM»~_ .
ConwntraHon rang*
Low 0 09-0 10
M«4linn 0 15-0 a
11: -h 0.35-0 4S
Total
Low 7-1 1
Ui^h J5-45
Total
1.0 9T 0 02-0 (Vi
Medium 0 10-0 15
High 0 10-0 60 ....
Tote!
Ihr
FlrUMt
5
5
4
14
1
£
4
14
7
7
Second Mt
C
6 .
6 .
18 .
-« .
6 .
8 .
18 .
ft
8
24 hr dUc
First set Second »t ~*"~
1 8
2 3
2 2
7 S
timom
repancy
ilkaUou
a 01
.OS
.04
1.6
2.0
3.0
.02
.03
.M
46
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Then, provisions are given for the selection of the test sites,
test atmosphere, submission of test and other data, and the selection
of a proper sample manifold.
3. 5. 2 Outline of Performance and Test Procedures
for the Use of Remote Monitors
The generalized performance specifications and specification
test procedures outlined here for the use of remote monitors in
evidentiary monitoring for case development follow the format given
in 40CFR60, App. B.; Nader (1975) has suggested that the present
specifications can be worded such as to apply not only to the extrac-
tive and in-situ mode, but also to the remote mode. Nader states
that some evaluation of present specifications may require modifi-
cation but preferably after the regulation (wording) is appropriately
modified. It appears that, in many paragraphs of the Performance
Specifications, this can be accomplished without great difficulty.
On the other hand, the calibration procedures required for a remote
monitor are quite different and the regulations would require—in our
opinion—significant modifications. In the following, we give the titles
of the suggested performance specifications, followed by general
statements about the requested additional wordings for remote sensors.
(1) Principle ana Applicability
Must include statements to the effect that opacity ind/or gases
are sampled remotely, that specifications are given in terms of
performance specifications and that test procedures are given to
determine the capability of the remote monitors to conform to the
performance specifications prior to approving the system for evi-
dentiary monitoring in case developments.
(2) Apparatus
Must include a listing of all auxiliary equipment needed to
perform the test procedures to determine conformance with the
performance specification and to perform the field measurements.
(3) Definitions
All definitions for the measurements of the opacity and gases
are essentially applicables as given in 40CFR60, App. A and B.
47
-------
Definitions of subsystems must include receiver, transmitter and/or
remote reflector units, where appropriate. Maximum output of mea-
surement system must take account of specific source, stack diameter,
and source temperatures.
(4) Measurement System Performance Specifications
Statement needed to the effect that the measurement system
(remote monitor) must meet certain performance specifications to
be considered acceptable under this method. These performance
specifications can be patterned after the ones proposed in 40CFR60
App. A and B. However, since the measurements are influenced by
the interfering atmosphere, these performance specifications are
only valid urder a specified set of conditions given in the performance
specification test procedures as outlined below. For field measure-
ments made under conditions significantly different from the ones
given in the performance specification test procedures, well described
and documented "field measurements procedures" must be developed.
(5) Performance Specification Test Procedures
These procedures involve the calibration tests, field tests
for accuracy (relative), drift and response time.
Some of the calibration tests may be conducted in the
laboratory. Relatively large calibration cells will be required
whose wall effects on the pollutant concentration and on the light
transmission (reflections) must be either negligible or accountable.
For passive remote monitors, the cells must be heated to simulate
the stack emission at elevated temperatures. The self emission of
the windows must be accounted for. The simulation of atmospheric
interference and sky background is very difficult, and, in the case
of water vapor interference, impractible. In the case of opacity
measurements, special "neutral density filters" simulating specific
particulate emission must be used; some simulation of field conditions
must be made such as illumination by direct or indirect sun light.
All tests that cannot be simulated in the laboratory must be
performed during the field tests conducted for accuracy, drift and
response time. The procedures should follow the certification
procedures developed by EPA for reference Method 9 (Visual
48
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determination of the opacity of emissions for stationary sources). In
these procedures, the candidate remote monitor must be lested and
demonstrate the ability to measure the opacity and/or pollutant gas
concentrations under different conditions in the plume, intervening
atmosphere, and sky background. Similarly, as in Reference
Method 9, a "stack emission generator" must be specified; it must be
equipped with in-situ meters for smoke and gases, that can be related
to reference methods. In addition to the specification of a "stack
emission generator, " the sky background and the atmosphere slant
path between the stack and the candidate remote monitor must be
specified. This can be accomplished by monitoring the atmosphere
and sky background by ambient air monitors that include measurements
of interfering species (H2O, CO2, CO, CH4, N2O, particles, etc.)
and meteorological parameters (temperature, wind, clouds, etc.)
Instead of using a "stack emission generator, " it may be possi-
ble to utilize well-instrumented actual smoke stacks, whose behavior
under different fuel and load conditions are known. Of course, certain
tests such as the one for response time, may be impractical to con-
duct with an actual smoke stack.
In addition to the above special requirements for the use of
remote monitors, the performance specification test procedures must
include provisions to account for the expected change in sky back-
ground and intervening atmospheric conditions between the "test
range" and the field. These additional provisions must include the
determination of the effect of interference by "normal" and/or addi-
tional atmospheric species present at the time of the observation;
this interference arises not only from the path between source and
sensor, but also from the sky background. In the UV and visible
spectrum, scattering of sunlight presents an interference, while
the thermal radiation from the sky and/or clouds (total or partial
cover) cause an interference in the infrared. For active systems,
narrow band optical filtering minimizes the background effects, and
for passive methods, measurements adjacent to the target plume
provides the necessary information about the background radiation,
although care must be taken that the background is uniform for these
two measurements.
(6) Calculations, Data Analysis and Reporting
In addition to the procedures for determination of mean values
49
-------
and confidence intervals, analysis of accuracy (relative), calibration
error, zero drift, calibration drift, response time and operational
test period, as required for extractive or in-Situ continuous monitors,
field records must be kept which indicate the
time
observer location (distance, direction, weight)
background description
sky conditions (cloud cover, sun position)
weather conditions (wind direction and speed, temperature)
plume description (if visible)
(7) References
Adequate references must be provided to document the con-
sistent relationship of remote monitors with in-situ or extractive
devices, as well as the consistent relationship of remotely measured
pollution levels during the performance specification tests and the
field applications.
50
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PRESENT DEVELOPMENT OF
REMOTE MONITORING TECHNIQUES
4. 1 OVERVIEW
Considerable work has been done in recent years on the develop-
ment of active and passive systems to remotely measure gaseous and
particulate pollutants in emissions from stationary sources, around the
perimeter of multiple stationary sources, and in the ambient air. Some
developments are still in the theoretical feasibility s:age; others have
been demonstrated in the laboratory, and some have been used in the field.
Passive techniques for gases rely on measurements of infrared,
visible or ultraviolet radiation containing the absorption or emission
spectrum of the gas of interest. In the UV/visible region the radiation
is either scattered sunlight or direct sunlight; in the infrared the radiation
is emitted by the gas itself and its background. For particulate measure-
ments, visible observations of sunlight scattered by the particles are
made by trained visual observers or instruments. Infrared techniques
have the great advantage of working during both day and night, whereas,
in general, the UV/visible techniques are useful only during the day.
An exception to this latter statement could occur for opacity measure-
ments if low-light-level image enhancement instrumentation is used, or
if the stack plume is artificially illuminated for visual observation.
For gaseous measurements the techniques generally require high
spectral resolution to distinguish the spectral characteristics of the gas
of interest from those of interfering species. This high resolution may
presently be achieved by high resolution interferometer spectrometers,
by conventional spectrometers, by gas filter correlation, or by laser
heterodyne detection. Other methods, not relying on high resolution,
utilize the matched-filter technique or several narrow band filters to-
gether with a computer for interpretation of the data. Other techniques
51
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.which appear-not to have been applied to remote sensing of air pollution
include derivative spectroscopy and Hadamard spectroscopy.
:Tfee:main problem with passive techniques is the data interpre-
tation. "In the infrared there is generally spectral interference from
gases in the source of pollution and in the atmosphere. This spectral
overlap together with the dependence of the radiant intensity on the tem-
perature of thecsource and of the intervening atmosphere makes the
inversion of the radiative transfer equation to obtain the pollutant con-
•centration very difficult. In the UV/visible the data interpretation for
-gases is complex due to scattering by atmospheric aerosols and particles
in the source of pollution. The scattering depends on the particle type,
; number, size distribution and spatial distribution, all of which are
generally unknown, and on the sun angle. For observations of particles,
in a plume or in the ambient air, the same problems due to the com-
plexities of scattering apply.
The techniques presently being investigated for active laser
systems are Raman scattering, resonance Raman scattering, fluores-
tcence scattering, and differential absorption, for gaseous pollutants;
and elastic backscattering for participate pollutants. All methods involve
the projection of laser pulses into the atmosphere, and measurement of
an inelastic ^r elastic backscattered signal from the pollutant, and, in
theory, are capable of giving range resolution, and hence the spatial
distribution of the pollutants.
In Raman scattering the laser radiation is changed in frequency
when it is scattered by the molecule; this shift is characteristic of the
laoiecuie, and the amplitude of the scattered signal is related to the
^rarniber~:density of that molecule. This technique has been demonstrated
in the field, in both stack emissions and ambient air. However, its
"•applicability is restricted in concentration range and/or distance.
Increased sensitivity may be obtained-by using resonance Raman
scattering, in which the laser frequency is chosen to be close to an
afrsorptixm line of the molecule. The theoretical resonance enhancement
of the^Raman scattering cross-section is of the order of 10^; this en-
.hancement has been observed in laboratory experiments.
Sensitivity similar to that of resonance-Raman is theoretically
possible with fluorescence. In this method the laser radiation is ab-
sorbed toy tha molecule which re-radiates over several lines. The life-
time of this phenomenon is relatively long, and collisional quenching
52
-------
at atmospheric pressures reduces the effective cross-section, but it
is still comparable to that of resonance Raman. Fluorescence has been
observed in the laboratory, in a closed chamber, and possibly in a
stack plume. Quantitative interpretation of fluorescence signals is
difficult, and there is considerable interference by aerosol fluorescence.
The laser systems with the greatest potential (both in terms of
sensitivity and specificity) appear to be the technique of differential
absorption by scattering (DAS) for the single-ended measurement of
gaseous pollutants. In this method, two signals at frequencies on and
off a pollutant absorption line are projected into the atmosphere. The
difference in the signals backscattered from atmospheric molecules and
aerosols or solid surfaces is related to the pollutant absorption. This
technique has been demonstrated in the field, in both stack emissions
and ambient air.
The elastic (Mie) backscattering lidar technique for detecting
particulate pollution has long been used semi-quantitatively to map the
relative concentrations of particles as a function of time ind space.
The method has been more recently used in the field to measure the
opacity of a smoke plume by comparing the return signal from the near
side with that from the far side of the plume.
An overview of the tuning characteristics of known broadly tunable
coherent light sources was given recently by Kuhl and Schmidt (1974).
Their figure is reproduced here as Figure 4-la, where the sohu lines
indicate the regions for which reliable sources are available and have
proved their potential, and the dashed lines indicate the regions for
which sources are being developed.
More details of the diode laser regime is shewn in Figure 4-lb,
which is taken from Hinkley and Calawa (1974).
A particular application of both passive and active techniques is
the so-called "perimeter monitoring", in which the emission from a
stack or a complex of stacks can be determined without direct observa-
tion of the plume at the stack. In this technique, an up-looking instru-
ment measures the vertical loading of the pollutant continuously along
a closed path around the source. These measurements together with
knowledge of the wind velocity allow the mass flow rate of the pollutant
from the source to be calculated.
53
-------
!M<> /<7<,er
Dye Msr/
H/g/> pressure gas /aser
H H C— ZZ3
Parametric oscillator
CM «m^MnM«m*^^^^^^^MB^W«^ ••• ^3
Sum ant^ difference frequency ^.
^ our wavp parametric mixing
f)pin -flip Woman la -,er
a = c:
I 'tilanton /aser
cs sz; ss 2! ns
Dy° /osor pumped Raman /a'iPf
Power
cw
70 '
70 '
to
10 '
'
-
[wall]
puke ~~
10
to"
t
10 '
70
70'
<70'
.„'
10
j [
70'
07
;oo
7(700
Figure 4-la. Summary of Tuning Characteristics
of Known Laser Sources (Kuhl and Schmidt, 1974)
WAVENUMBER (cm <
5000 3000 2000 1500 1000 900 800
T
PbS, Se
l-x x
HC1 0
H2CO
CH4
3 3
CS2 H2O
CO NO
Figure 4-lb,
CH,
NO,
I ! I
NH
3H6
6 8
WAVELENGTH
10
14
Nominal wavelength regions covered by
three Pb-salt semiconductors at 12°K.
Strongly-absorbing wavelengths of some
common gaseous pollutants are also indicated
(Hinkley and Calawa, 1974).
-------
Measurement of the vertical loading may be made with both
matched filter correlation (MFC) and gas filter correlation (GFC) in-
struments mounted in a truck. Another method of measuring the vertical
loading from the ground could be with a differential absorption laser
system pointed vertically up, with the range being set above the maxi-
mum effluent altitude.
Possible airborne methods include the MFC instrument, the GFC
instrument, and the differential absorption using laser radiation back-
scattered from the earth's surface. The MFC is useful only during the
day, and the data interpretation is complicated by aerosols and by the
varying surface reflectivity. The GFC method can be used both day and
night, but depends on their being a difference in temperature between the
pollution and the ground, and thus would be limited in ma;iy instances.
The best airborne method appears to be the differential aosorption using
a laser system.
4.2 THEORY
4.2.1 CW Infrared System
The ability of any detector-noise-limited electro-Dptical instru
ment to detect the change in environmental parameters can be q^'vntiiie
generally by the signal-to-aoise ratio (SNR)
SNH =
S.dX R.P.dX
A A A
_,__ _ __
where S\ is the signal voltage per unit wavelength, IN s the r^is-
noise voltage, E\ is the instrument responsivity (Volts/Watt) at trie
wavelength X and P\ the radiant power per unit wavelength, It is
customary in infrared systems to combine the responsivity and tne noise
voltage into the detectivity:
D = R/N (4-2)
55
-------
which is equivalent to the inverse of the noise-equivalent-power:
(4"3)
where A^j is the detector area, Af is the bandpass, D^(f, TB) is the
wavelength-dependent specific detectivity at the chopping frequency f,
background temperature Tg ,
The available radiant power from an extended source (filling the
field -of -view) is proportional to the throughput of the system and the
spectral radiance seen by the detector:
PxdX = (7)xAono)dX/N(T,x)dTx(x) (4-4)
where 1?\ is the efficiency of the instrument, A0 is the entrance area,
O0 is the solid angle, N°.(T, x) is the blackbody radiance (W/cm^sr-nm)
at the temperature T(K), T\(X) is the transmission, and x is the position
along the line-of -sight. The general expression for the transmissivity is
given by
T\ - ToT»,
X as
where Ta is the transmissivity of gases, and rs is the transmissivity
of particles.
Then,
= n ra.(X) = exp [.yb x.(x) C.W pt(x)dx] (4-5)
where t|(X) is the spectral absorption coefficient, Cj(x) is the concen-
tration (mix'.ng ratio) of species i at location x, and pj- is the total
pressure, and
T = exp -/Ea.n.(x)dx! (4-6)
s L 'i i i
56
-------
-------
-------
where tfj is the sum of the absorption and scattering cross sections,
and nj(x) is the number density of species i at location x .
The Equation (4-4) can be rewritten for the special cases of
interest. In Figure 4-2, we show the principal applications of the
passive (a and c) and the active CW systems (b and d).
For the case (a), Equation (4-4) is the proper expression, where
the integration limits go from x = O(T(O) = 1) to x = * .
For the case (b), Equation (4-4) can be written (in general,
assuming a homogeneous atmosphere between the transmitter and
receiver) as
PxdX =
where ef is the spectral emissivity of the source, which has the tem-
perature Tg, TX is the transmission of the atmosphere between source
and receiver and TA is the atmospheric temperature. The solid angle
of the receiver should be larger than Ag/R^ , where Ag is the aperture
of the transmitter and R is the distance, in order to reduce scintillation
effects. However, the effective throughput is given by A0Ag/R^. By
chopping the source, the second term in the square brackets in Equation
(4-7) is eliminated. Thus, in this case
A Ac
PxdX = (7?x_Jl5S.)dX€^N°(Ts)Tx (4-8)
R
For the case (c), Equation (4-7) can be written as
x=h
(4-9)
n. a.
x=0
where h is the altitude of the aircraft [with r(h) = 1], e/ is the spectral
emissivity of the ground, which has the temperature TQ and r\ is the
integrated atmospheric transmissivity. At the shorter wavelengths
(X < 5 jj,m), the sun reflection must be accounted for, which is given by
57
-------
Figure 4-2. The principal CW applications
58
-------
sec
/-I
where p\ is the ground diffuse reflectivity, 0 is the sun zenith angle,
is the sun irradiance at the top of the atmosphere, T\(h) is the
vertical atmospheric transmission from the ground to the height of the
aircraft and T\(*) is the atmospheric transmission to the entire atmo-
sphere traversed by the sun rays.
For the case d, Equation (4-7) can be written as
(4-1D
where P is the spectral radiant power transmitted by tie laser source,
R is the height of the aircraft, A is the surface area viewed by the re-
ceiver (thus A/R^ = Q0) and AL is the area of the laser beam at the
surface. It is assumed that A ^ AL ; for optimum signal to background
ratio A =
A special expression is used for a laser heterodyne radiometer.
The thermal radiance ISh in a spectral channel of bandwidth 0 centered
at frequency f j is mixed with a laser signal at VL to provide a signal
at the difference frequency V-Q = |f j - VL| (Seals 1974). The system
responds to the sum of signals in the channels centered at, ^L - yD •
For a quantum -limited system with no excess noise, the SNR becomes
SNR =
where c is the velocity of light, h is the Planck constant, v is the
spectral frequency (in Hz), t is the postdetection integration time, and
j3 is the spectral bandwidth (in Hz). N is the radiant power per unit
emitter area and solid angle for the signal channel and its image.
59
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4. 2. 2 Pulsed Laser Systems
The basic concept of single-ended Laser probing of ambient air
and stationary source emissions is illustrated in Figure 4-3 and Figure
4-4 for the case of a Raman system (Inaba and tfobayasi, 1972). The
laser is transmitted through a collimating telescope and scattered from
mixtures of particulate and molecular scatterers in the atmosphere.
The spectrum of the backscattered energy consists of Rayleigh and Mie
scattering components of the frequency, centered at VQ identical with
the transmitted laser frequency, and the Raman-shifted frequencies at
vi, v%, ... 5 vn due to various Raman active gases in the atmosphere.
These spectral components are analyzed and detected simultaneously
through a spectrum analyzer in conjunction with optical filtering devices
(narrow band filters or a monochromator) and an array of sensitive
photodetectors. Then, via a data processor, the multichannel informa-
tion such as location and concentration of gaseous contaminants, and
their correlation with the particulate matters may be displayed in real
time, and at the same time, if necessary, sent to the pollution alarm/
control system.
The systems for the fluorescence, differential absorption and
lidar methods are basically the same, but with differences in the fre-
quencies and in the data processing. All these laser systems are
sophisticated and expensive, but may be made mobile for enforcement
monitoring purposes.
The sensitivity of these techniques, of course, are determined
by the desigr. of the system and by the signal strength relative to the
system noise and background noise. The latter, due to scattered solar
radiation, is generally the dominant noise in daytime operation.
In considering laser systems we can write the basic equation in
a form common to all the techniques discussed in the following
P(R) = €Pt LN(R)J3AR~2TA(R)TG(R) per pulse (4-12
where P(R) is instantaneous received energy from resolution element
L at range R, ?t is transmitted energy (generally given in joules or
photons) at tg, L is effective pulse length, (L = cAt/2, where c is
the velocity of light and At is pulse duration; it is the range interval
60
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DETECTORS
TO POLLUTION
ALARMXCONTROL
SYSTEM
Figure 4-3. System diagram showing the basic concept of the laser-
Raman radar as a single-ended and range-resolved probe
for constituent analysis of air pollution and ordinary at-
mosphere in real time (Inaba and Kobayasi, 1972).
HflMAN SCATTERING
SCHEME
TRANSMITTED
BEAM
Figure 4-4. Schematic of the Raman scattering scheme showing the
transmitting laser, receiving optics, and spectrometer.
61
-------
from which signals are simultaneously received at: time t), R is
range R = c't-t0)/2, where tg is the time of transmission of pulse,
A is the effective receiver aperture, c is the optical efficiency of
the system, N(R) is the number density of the relevant pollutant,
j3 is the backscattering cross-section appropriate to the scattering
phenomenon under consideration, and TA(R) is the atmospheric
attenuation by interferents along the laser path, and TQ(E) is the
pollutant attenuation, both at range R .
The noise (N) in a well-designed laser system should be due
only to the photomultiplier current caused by signal photons, back-
ground photons and the dark current. Thus
N = (77 Nr +T?NB+ND)1/2 (4-13)
where 77 is the quantum efficiency, P(R) is the signal photons, Pg
is the background photons, and ND is the dark current equivalent noise
input. The background radiance collected by the receiver is given by
V/B = BAOAX (watt)
(4-14)
BAOAX , . , , ..
= hc/X" (photons/second)
where B is the radiance in Wcm"^l~^sr"~, h is the Planck constant^
and Afi is tJaoe throughput of the receiver in cm sr.
Thus, at the cathode, the number of background photons in a
gated system, with a gate width tg sec, is given by
The dark current noise may be neglected in comparison with
background noise, particularly when the phot ©multiplier is cooled.
Thus, the signal-to-noise ratio becomes
62
-------
T?P(R)
SNR =
(r?P(R)
per pulse
(4-16a)
For n pulses,
SNR =
TjP(R)- n
1/2
(T?P(R)
(4-16b)
Assuming that no data processing noise is added to the detector
noise, then the ultimate sensitivity of the system is determined by
Equation (4-16), and is obtained when SNR = 1.
o
The daytime background noise is typically about 10° greater than
the nighttime noise, i. e., Pg(day) = 10& PB (night). The significance of
this background noise varies with the technique, system, and range, as
illustrated in Figure 4-5 and 4-6.
Care must be taken in estimating the atmospheric attenuation
since the outgoing and return pulses are at different frequencies for the
Raman and fluorescence techniques.
Thus, knowing the system parameters, the atmospheric atten-
uation, and the relevant scattering cross-section, the number density
(concentration) of the pollutant may be determined from tie return signal,
Typical cross-sections for the different phenomena are g.ven in Table 4-1
(Derr and Little 1970).
TABLE 4-1. Typical Optical Scattering
Cross Sections (Per Particle)
Process
Mie
Rayleigh
Raman
Resonance Raman
Fluorescence *
Cross section (cm /sr)
10"27 to 10'8
ID'27
10-28tolO-31
ID'22
1 ft
10" and smaller (broadband emission)
* These cross-sections are reduced (a factor of about 10 )
by collisional quenching.
63
-------
e
z
10 IOZ IOJ
Ronge in Meters (P)
Figure 4-4. Fluorescence, Raman and DAS signals
versus range for sulphur dioxide
Night
Noisi
10
10"
Ronge in Meters (R)
Figure ^--5. Fluorescence and DAS signals
versus range for nitrogen dioxide
64
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Based on Equation (4-12), comparison of the techniques may be
made for detecting gaseous pollutants. The results of such a comparison
for S(>2 and NO2 in ambient air by Measures and Pilon (1972) are shown
in Figures 4-5 and 4-6, where DAS refers to the difi'ereniial absorption
method. There is no Raman calculation for NQg since this molecule
apparently fluoresces at all visible wavelengths, thus obscuring any
Raman effect. It is clear that the differential absorption method shows
the highest sensitivity, with fluorescence being better than Raman.
Some of the system parameters used in the calculations axe given in
Table 4-2. These comparisons are strictly on a theoretical basis without
considerations of problems such as fluorescence of aerosols and inter-
fering species, imprecise knowledge of quenching effects on the fluores-
cence cross-section, and the practical problem of optically filtering out
unwanted frequencies.
TABLE 4-2. System Parameters
Total Output Power
Pulse Duration
Collector Diameter
Optical Efficiency
Filter Bandwidth
Quantum Efficiency
Resolution (ARpgg)
X (Diff. Abs. )
X (Fluorescence)
100 kW
10 nsec
25 cm
75%
10 A (NO,
S0)
6 m
3020 A (SO2); 4480 A (NO2 :
3020 A (SO2); 4544 A (NO2
4. 2. 3 Perimeter Monitoring
Using optical techniques to measure the vertical loading provides
a measure of the vertical optical thickness which can be converted to
ppm-m, which in turn can be converted to g m~2.
The mass flow (M g sec"1) of pollutant across a line is given by
M = L v s sin
(4-17)
65
-------
where s is the line length in meters, L is the mean vertical loading
of pollutant Li grams per square meter, and v is the mean wind velocity
across the line in meters per sec. , and 9 is the angle between the wind
direction and the line.
If this vertical burden is measured continuously along a closed
path around a source or a complex of sources, the net mass flow out of
this closed path gives the source emission rate (Ms) , viz.
M = v L(s) sin 6(s) ds. (4-18)
s
If the emitted pollutant is known to be of relatively low concentration in
the ambient atmosphere, then a single traverse across the plume, 90°
to the wind direction, can be made, and the mass flow rate determined.
by Equation (4-17). The dimension of the plume(s) can be determined
from the shape of the signal recorded by the up-looking sensor (and the
sensor's ground speed), and the velocity (v) determined by some inde-
pendent method (laser doppler, UV or IR imagery, or anemometer).
4. 3 REVIEW OF ACTIVE SYSTEMS
Theoretical comparisons of single-ended .active systems for
monitoring pollutants have been made by several authors (Kildal and
Byer 1971, Measures and Pilon 1972, Ahmed 1973, and Hirschfeld 1974).
These-studies suggest that differential absorption is the most sensitive,
followed by fluorescence and resonance Raman, and finally Raman.
However, in reviewing the literature, field measurements appear to have
been achieved only with the differential absorption and the Raman methods,
and these field measurements were all for NO2 and SO2- The fluores-
cence and resonance Raman methods appear not to have developed beyond
the laboratory, and the differential absorption and Raman methods have
not beenTcleveloped for other species of interest.
4. 3.1 Differential Absorption
The differential absorption method has been used to measure
in urban atnr.ospb.eres (Rothe et al. 1974a) and in stack emissions (Rothe
et al. 1974b . They used a tunable dye laser in the 4600 A region. For
66
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the urban measurements, a mean concentration of 0. 23 ppm of NC>2 was
found over the distance 1. 73 to 3. 74 km. The measurement was made
at nighttime and took about 13 minutes; no comparison was made with
other data. The same laser system was used to measure NC>2 in stack
emissions in a chemical factory. Measurements were made 300 m from
the stack exit at a range of 750 m. The distribution across the plume
indicates that 1 ppm was detectable. Again the measurement time was
long, being about 33 minutes. The same publication shows ambient air
contours of NC>2 over the chemical factory, and indicate a measurement
sensitivity of 0. 5 ppm at a range of 500 m with each data point requiring
20 seconds measurement time. No comparison with other data or a
discussion of accuracy is given.
Grant et al. (1974) using a tunable dye laser in the 4500 A region
made nighttime measurements of NO2 in a closed chamber at a range of
365 m. A sensitivity equivalent to 5 ppm with a 10 m resolution element
at this range was determined, but no discussion of the integration time
required was given. The results showed good agreement with independent
transmissometer readings across the chamber.
Igarashi (1973) reported a differential absorption measurement
of NO2 using the 4480 I region, and SO2 using the 3000 A region. Details
of the experiment are not given, but 0. 1 ppm of the gases were measured
at a range of 300 m, with a resolution element of 100 m, using a 1 mJ
laser output.
An interesting variation of this technique due to Ziromb (1974)
does not require a tunable laser. It uses the Raman backscattered signals
from oxygen and nitrogen, which coincide with absorption bands of NC$2
and SO2- A system is presently being built to measure 23-70 ppm of SC>2
and 5-25 ppm of NO2 at a range of 200 m. The same sysr.em will also
measure 1000 ppm of CO2 using the direct Raman signal 3f CO2- No
further details are presently available.
Another similar technique (Granatstein et al. 197o) uses the back-
scatter of laser radiation from droplets (or smoke particles) in a stack
effluent. Laboratory measurements of CH4 and CC>2 wer^ made by tuning
a He-Ne laser at either 3. 391 urn or 4. 217 ^m, respectively. Measure-
ments were made using gas concentrations greater than 1000 ppm, and It
was concluded that the attenuation properties of the scatterers are needed
to interpret the data. It would appear that two adjacent wavelengths are
needed for each gas, instead of just one, and then of course, the method
is the same as the other differential absorption methods which use the
visible/UV.
67
-------
Feasibility studies have been conducted by Ahmed (1973) and
Byer and Garbuny (1973). Ahmed estimates a sensitivity of 0. 4 ppm
for NO2 in a 100 m resolution element at a range of 1 km for a 1 mJ
laser in the 4000 A region. Byer and Garbuny, for NC^, estimate
. 85 ppm in 15 m, at 1 km range, using 1 pulse from a 100 mJ laser;
they also estimate that . 14 ppm of CO can be determined under the same
conditions. Schotland (1974) discusses the errors involved ih the dif-
ferential absorption, and using the example of measuring vertical water
vapor profiles estimates errors of less than 8% for altitudes below 3 km.
Byer and Garbuny (1973) also considered differential absorption
using topographic reflectors. This, of course, does not give range
information; it gives only the mean concentration between the laser system
and the reflector. They estimate that pollutant concentrations of . 01 ppm
over a range of 100 m or 10 "^ ppm over 10 km can be measured. The
same technique is being developed by Melfi (1974) to measure tropospheric
ozone from aircraft using the earth's surface as the reflector. The system
uses two-tuned CO2 lasers and will be used to conduct rapid area surveys.
Grant and Hake (1975) have recently made DAS measurements of
SO2 and 03 at 2900 A using a 15 mJ dye laser which can meet the Federal
eye safety requirements with the addition of a 2 in. diameter beam ex-
pander. The gas was contained in a 2. 5 m chamber at about 250 m range.
Averaging eight pulses, they found an uncertainty of + 60 ppm-m for SO2
and + 130 ppm-m for 03. These large errors are attributable to variations
in the atmospheric backscatter since the measurements were spread over
one hour. They estimate that + 10 ppm-m for SO2 and + 13 ppm-m for 03
can be achieved by taking all the data within one minute.
Two preliminary reports from the Radio Research Laboratories
in Tokyo (Inomata and Igarashi 1974, Asai and Igarashi 1974) discussed
the development of two systems suitable for making the two DAS wave-
length measurements simultaneously or within 1 nsec of each other,
to minimize scintillation effects. The simultaneous measurement
uses two linearly polarized components (independently tunable) of a dye
laser cavity. The results of laboratory NO2 measurements with this
system are discussed in detail in Section 5. 3.1. The other report (Asai
and Igarashi 1975) concerned the measurement of 63 using a CO2 laser
and a retroreflector in a long-path measurement. The P(14) and R(14)
lines of a single laser were used, and alternately transmitted through
the atmosphere at 130 Hz. In controlled tests, they determined a sensi-
tivity of 12. 4 ppm-m, but by improving the stability of the laser and by
using digital processing, they anticipate a sensitivity of about 5 ppm-m.
68
-------
The properties of the various differential absorption systems dis-
cussed above are summarized in Table 4-3.
4. 3. 2 Raman Scattering
The only quantitative measurement of stack emissions using the
Raman method appears to be that by Nakahara et al. (1972). They used
a frequency doubled Nd: YAG laser at 0. 532 ^m to obtain a Raman signal
from SC>2 in a smokestack plume at a range of 228 m at nighttime. Using
4 mJ pulses, they measured 1850 ppm whereas the actual concentration
was 1000 ppm. They attributed the discrepancy to uncertainties in the
Raman cross -section for SC>2, and in the system's parameters. (It could
possibly be due to NO2 fluorescence interfering with the SC>2 Raman signal
as reported by three of the authors in the later paper (Nakahara 1973)).
They calculate that 80 ppm of SC>2 can be detected at nighitime with a 10 mJ
laser, at a range of 283 m? with a resolution element of 9 m, using an
integration time of about 4 minutes. In addition to measuring SO2, they
use the Raman signal from N2 to measure the scattering optical thickness
(opacity) of the plume, by observations from the same range through and
off the plume.
Melfi et al. (1973) made a qualitative nighttime observation of SC>2
in a plume 5 m above the top of the stack using a ruby laser at 6943 A.
Using 1. 5 J pulses at a repetition rate of 1 pps averaged over 100 seconds,
they detected SC>2 at a range of 210 m with a 3. 7 m resolution element.
They found good qualitative agreement between the SO2 Raman intensity
and the plant's electrical power output.
Although the two Raman systems discussed above were designed
for SO2, Inaba and Kobayasi (1972) report on a N2 laser (3371 A) demon-
stration system with a monochromator rather than a filte-' system. Using
this system at a range of 30 m and a resolution of 3 :m thf y analyzed the
Raman spectrum from oil smoke and automobile exhaust ^as. Using
0. 2 mJ pulses with a repetition of 50 pps and a 5 sec integration time,
they identified signals from SC>2, C2H4, H2CO, NO, CO, H2S, CH4, in
addition to the usual CO2, O2, N2 and
The only other field measurements using the Raman method appear
to be those by groups from Block Engineering and Edgewood Arsenal
(DeLong 1974). The system uses a frequency doubled ruby laser (0. 347 ^
operating with 80 to 160 mJ per pulse at two pulses per sacond. Daytime
field tests have measured controlled amounts of SO2 (30 ppm), kerosene
69
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(1. 7 ppm), HNO3 (7 ppm) and organo phosphate (. 04 ppm) at a range
200 m with a resolution length of 10 m, using an integration time of
about 1 minute. Based on these measurements and relative Raman
cross-sections, DeLong{1974) projected the sensitivity of the present
system to other gases, and compared them with calculated values, as
shown in Table 4-4. Note that the nighttime sensitivities are about a
factor of two better than those in daytime.
TABLE 4-4.
Projected and Calculated Sensitivities
and System Parameters (DeLong 1974)
Pioiecied
Material
Nj
Oj
CO
COj
COj
NO
N^O
H20
SOj
ca,
H2S
NHj
Clj
C,H4
HI
Spectral
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2331
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2145
1388
1288
1877
1290
3652
1151
2914
2611
3340
540
2650
530
Spectral
Position (A)
3777
3670
375 1
3647
3634
37!3
3634
3976
36i6
3862
38.8
3927
3538
3813
3534
Day Sentiiiviiy
(ppm) Rcf.(21)
313
262
317
210
330
682
108
125
58
41
57
79
91
57
50
86
62
19
5
9
12
Calculated Sensitivity
Day (ppm)
215
179
217
144
227
468
74
86
39
28
39
54
62
39
34
Night (ppti1.)
124
103
125
83
130
269
43
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23
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22
3!
36
22
20
Present Instrument Parameters
Collector Diameter, cm 91.4
Transmitter Efficiency 0.9
Receiver Efficiency 0.075
Detector Quantum Efficiency 0.3
Laser Energy® 3471.5A\J 0.083
Receiver Bandwidth, u 0.0005
Receiver Field of View, sr 1 x 10'6
Atmospheric Transmission 0.89
Range, cm 2 x 104
Range Gate, cm 10^
71
-------
Smith (1974), Barrett (1974), and Klainer (1974) have suggested
a method of enhancing the Raman sensitivity by using a Fabry-Perot
interferometer in conjunction with the rotational Raman lines instead
of the vibrational lines used in the systems discussed above. The
rotational, lines are periodically spaced and may be multiplexed by
using the Fabry-Perot as a filter with similar periodic transmission
peaks. Klainer suggests an increased sensitivity factors over vibra-
tional Raman of 50 for HC1 and 150 for CO2-
Gelbwachs and Birnbaum (1973) have suggested a problem with
the Raman technique due to fluorescence of aerosols which they observed
in some in-situ measurements. They estimate that the aerosol fluores-
cence signal can be equivalent to the Raman signal from 600 ppm of SOo,
or 6000 ppm of NO, or 3000 ppm of CO. In light of the results reported
previously ir, this section, it appears that these estimated aerosol effects
must be much too high. Of course, the discrepancy reported by Nakahara
et al. (1972) might be due to aerosol fluorescence, rather than the
fluorescence suggested by later work (Nakahara et al., 1973).
The properties of the various Raman systems discussed above
are summarized in Table 4-5.
4. 3. 3 Resonance Raman
The resonance Raman method does not appear to have been deve-
loped much beyond the theoretical stage. Inafoa and Kobayasi (1972)
report that the resonance effect has been observed for some gaseous
molecules in the laboratory. However, they point out that fluorescence
scattering should be expected to be superimposed on the resonance Raman
spectrum, since both phenomena require similar exciting frequencies
and the emitted frequencies are in the same region. This probable super-
position would make accurate determination of the pollutant concentration
very difficult, if not impossible. Possibly adjacent frequencies on and
off the Raman frequency could be used in a differencing technique to
subtract out the fluorescence signal; this method may not be amenable
to present filter capabilities.
Fowler and Berger (1974), under EPA sponsorship, investigated
the feasibility of measuring SO2 in stack emissions using fluorescence
and resonance Raman methods. In laboratory measurements they found
a resonance Haman signal 1. 8 times greater than the fluorescence signal
around 3000 i; this ratio could be improved with a narrower spectral
72
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bandpass (they used 24 1). The authors also confirm the problems of
fluorescence from other species and particles making quantitative mea-
surements unlikely.
Laboratory measurements of the resonance Raman cross-sections
have reported for SC>2 (Rosen et al. 1974).
4. 3. 4 Fluorescence
Although there have been several theoretical discussions of the
usefulness of fluorescence in the remote sensing of pollutants, there
appears to be only one report of actual measurements. These were
measurements of NC>2 by Nakahara et al. (1973), who apparently ob-
tained them as a result of NQ2 fluorescence interfering with their Raman
measurement of SC>2 in the visible region.
It is clear from this and the preceding discussion on resonance
Raman that there are problems in the interpretation of fluorescence
(and, of course, Raman) signals. In addition, Kildal and Byer (1971)
state that there is no straightforward relationship between the fluores-
cence intensify and the pollutant concentration, making quantitative mea-
surements very difficult. Presumably this latter problem can be over-
come with careful laboratory studies, and, in fact, has been investigated
in the infrared by Robinson and Dake (1973). They found that at atmo-
spheric pressure the 3R:fluorescence intensity is linearly related to the
laser power, and to the 6/5 power of the concentration, suggesting that
remote monitoring of fluorescence is possible at least in the IR. The
same authors (1974) extrapolate some laboratory measurements of
ethylene'fluorescence using a CO2 laser to infer that 0. 1 ppm of ethylene
could be detected at 10 km, or 100 ppm at 1000 km, (Their graphs
actually appear to give 0. 2 ppm at 10 km and 1000 ppm at 1000 km.)
They suggest this latter sensitivity would allow satellite monitoring of
stack effluents. However, it appears that they have not considered
problems such as the field-of-view being greater than the stack plume
dimensions, and background noise.
Pikus et ai. (1971) have also considered a satellite-borne system
for detecting NO based on fluorescence at 1927 cm~l. The calculations
assume a 5-joule pulse CO laser and compute a threshold NO concentra-
tion sensitivity of 2 x 10llcm-3 (7. 4 ppb) at sea level. Even assuming
that a 5-jouh: laser were available for satellite use, these results may
be optimistic since the calculations neglect detector and system noise
74
-------
sources, 80 cm diameter collecting optics are required, i, 50/o optical
efficiency is assumed, and interferences due to other species are neg-
lected. (At 1927 cm"*, H2O is a strong absorber over the 0.1 micron
band pass assumed.)
Another estimate (Menzies 1971) of the capability of remote
sensing of NO fluorescence using a 1 mJ pulse CO laser and sensitive
heterodyne detection indicates that 0. 1 ppm in a 300 m path can be mea-
sured at a 1 km range, if the relative humidity is 50% (quenching by
H2O is faster than that of other constituents for this case).
For fluorescence in the visible/UV region, Kildal and Byer (1971)
have estimated that at nighttime about 0. 5 ppm of NO2 anc SO2 in a 15 m
path can be detected at a range of 100 m using a 0.1 mJ pulse laser.
They state that this sensitivity drops by a factor of 200 during the day.
Penney et al. (1973) have made laboratory observations of NO2
and 03 fluorescence using a 0. 488 Jim argon laser, and of SO2 fluores-
cence using a dye laser tuned near 0. 3 |im. They found SO2 fluores-
cence to be strongest, and estimate that it should be feasible to measure
10-3 ppm of SO2 with a resolution element of 100 m at a range of 1 km.
Gelbwachs et al. (1972, 1973) have also made laboratory observa-
tions of NO2 fluorescence using laser excitation at 4416 and 4880 1.
They then developed an in-situ fluorescence technique to measure am-
bient NC>2. They do not discuss the possibility of extending the method
to remote sensing, except to point out that they observed aerosol fluores-
cence which may interfere with remote sensing applications.
The sensitivities of the various fluorescence systems discussed
in this section are summarized in Table 4-6.
4. 3. 5 Lidar
Much of the work to date on lidar systems for measuring particu-
late (Mie) elastic scattering has been done by the group at Stanford
Research Institute. Collis and Uthe (1972) discuss the capabilities of
lidar systems.
The backscatter from particles is, of course, dependent on the
shapes, size distribution and refractive index of the particles, so that
return signals will vary from plume to plume. Hence, ir, order to apply
the technique to enforcement monitoring, it will be necessary to make
calibrations for the different types of particles.
75
-------
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Collis and Uthe (1972) summarized the status of lidar systems in
1972 as follows: "Lidar techniques of remote observation of atmospheric
pacniwrala!:*: WMCPD&rat ions have obvious value in a wide rs,nge of air pol-
lution applications where semi-quantitative spatial and temporal data
are needed, and are already in regular use in research. For routine
operational use, lower cost, eye safe instrumentation must be developed.
The degree to which lidar can be used for making objective, remote mea-
surements of significant parameters (i. e., turbiditys opacity or mass
concentration) has not been fully established. Considerable progress is
being made in this difficult area and already quantitative data can be
derived in research applications. For routine use in emission source
monitoring however, while work in progress appears promising, the
development of a legally acceptable, low cost operational technique is
still some way off. "
Progress has been made in the meantime and an operational system
was fabricated by GE for EPA. It is shown in its operating configuration
at the Barbados Island Station of the Philadelphia Electric Company in
Figure 4-7.
Figure 4-7. EPA Mobile Lidar System developed
by GE shown in operating configuration
at the Barbados Island Station at the
Philadelphia Electric Company
77
-------
Cook et ai. (1972) report a method in which the plume transmit -
tance is measured by comparing the clear1 air lidar return from the near
side of the plume with that from the far side. They made field measure-
ments on a power plant smoke plume with a van-mounted ruby laser
system at a range of 487 m. A comparison was made with the passive
telephotometer (Conner and Hodkinson 1967), which makes a contrast
measurement and relies on having a target with contrast (e. g. sky and
hillside) behind the plume. The passive technique is somewhat sensitive
to the illumination conditions (e.g. sun position, cloud cover). The lidar
accuracy is .imited by the PM tube aft erpul sing, but within the error
limits both methods agreed. The lidar system errors are estimated to
be < 12% for an opacity of < 0. 5, and < 2. 5?c for opacity < 0. 2.
This system has been recently improved by replacing the PM tube
and hence eliminating the afterpulsing. Conner (1975) considers that in
good atmospaerie conditions the method can ROW measure the opacity
within 2%. Good atmospheric conditions mean that the atmospheric
aerosol content is the same on both sides of the plume. Under poor
atmospheric conditions, readings are variable and must be averaged
over a period of time.
The technique of Cook et al. is basically the same as that of
Nakahara et al. (1972) who used the Raman signal from N£ in front and
through the plume. Nakahara et al. considers their method to be more
accurate sinse the N2 concentration and Raman baekscatter are better
known than tie atmospheric particle concentration and backscatter.
This latter technique appears advantageous since the signal is readily
obtained from a Raman system for gases, so that a separate system
for particle observations is not required. However, due to the low
Raman signals, the range capability would be less, and sky background
noise would be more significant.
It would appear that the remote laser method should be preferred
to passive (instrument or trained observers) observations which depend
so much on ambient lighting conditions. The laser method can give an
absolute transinittance, and only requires a clear line-of-sight to the
plume. In addition, the laser method is not restricted to daytime ob-
servations like the passive one. However, Belanger (1974) discusses a
night vision instrument which uses an image intensifier to provide a
nighttime image of the scene (including the stack plume) on a phosphor
screen. Th? author considers that the method would be suitable for en-
forcement o: regulations, but does not discuss the possible effects of
variations o:.' ambient light.
78
-------
Conner (1975) considers that the present pulsed laser system
may be limited for operational use due to eye safety hazards (see also
discussion in Section 5. 2). SRI, under EPA funding, is investigating
the use of a CW laser system, to measure opacity, which would meet
safety requirements, and would be smaller and less expensive. Conner
is hopeful that the price might be less than $20, 000 for the system.
It should be noted that optical techniques, as presently known,
cannot separate the scattering by particles and by water droplets. The
remote sensor will have to examine the plume some distance from the
stack exit where visual observation indicates that the droplets have
evaporated.
In light of the court rulings on opacity observations discussed
in Section 3*2, it seems very desirable to implement instrument mea-
surements rather than using trained observers, particularly for low
opacity conditions.
4. 3. 6 Intercomparison of Measurements of Gases
In order to compare the measurements and predictions for the
various methods for remotely measuring gaseous pollutants, the results
discussed in Sections 4. 3.1 to 4. 3. 4 are normalized to a certain extent
and presented in Figure 4-8. The results are normalized to a pollutant
thickness (resolution element) of 10 m. (It should be noted that in an ex-
tended source the fluorescence technique cannot achieve 10 m resolution
due to the long lifetime of the phenomenon; this lifetime restricts re-
solution to 100-300 m depending on the molecule.) On tho basis of DeLong's
(1974) estimate, we assume that at nighttime the Ranian method is twice
as sensitive as during the day; all other published results are for night-
time. In normalizing for the resolution element, it is assumed that the
sensitivity is inversely proportional to the resolution length (see Equation
4-12)). No normalization nas been made for the systems parameters
such as receiver aperture, laser energy and repetition rate, integration
time, wavelength, atmospheric effects, type of detector and assumptions
about the relevant scattering cross-section.
The results do snow that in general the field measurements are
lagging behind the theoretical predictions, which, of course, are all
based on reasonable systems parameters. It appears that predictions
for the important gases are indicating a lower sensitivity limit shown
by the dashed line in Figure 4-8, ranging from about 0. 1 ppm at 100 m
to about 2. 5 ppm at 1000 m.
79
-------
100
10
CO
c
0)
CO
Nighttime, 10 rn Thlcknc-KB
* Measurements
x Theory
100
1000
Range (m)
10000
References:
(1) Kildal et al. 1971
(2) Rothe et al. 1974a
(3) Rothe et al. 1974b
(4) Grant et al. 1974
(5) Ahmed, 1973
(6) Nakahara et al. 1972
(7) Inaba et al. 1972
(8) DeLong, 1974
(9)Mer.zies, 1971
Figure 4-8. Sensitivity vs. Range. Normalized to 10 m thickness
at nighttime. The data points are labeled as [species
(reference) technique] where D is differential ab-
sorption, R is Raman and F is fluorescence.
80
-------
4. 3. 7 Stack Effluent Velocity Measurements
Since many emission standards for stationary sources are based
on a mass emission rate, a remote measurement of effluent concentra-
tion alone is insufficient for determination of non-compliance. The
perimeter measurement and area surveys can provide the mass emission
rate, but, of course, it will not always be possible to isolate a single
source in that type of measurement. Other remote sensiog methods
provide only a concentration measurement, and a measurement of ef-
fluent velocity must be obtained to determine the mass emission rate.
In addition to the two vidicon methods being developed for deter-
mining the velocity, EPA and NASA have been supporting the evaluation
of a laser-doppler velocimeter (LDV) at the Raytheon Company (Herget
et al. 1975, Herget 1975). Their LDV system consists of a 20-watt CO2
laser, solid invar interferometer, 30 cm diameter f/8 transmitting and
receiving telescope, and a Ge:Cu detector. An elliptically-shaped flat
tracking mirror and a bore-sighted telescope are used to aim the laser
beam at the stack plume. The difference frequency at th*3 detector pro-
duced by the local oscillator (the laser) and the energy backscattered
and doppler-shifted by the particles in the plume is monitored visually
on a Hewlett-Packard spectrum analyzer. The detector output is re-
corded on separate magnetic tape channels after processing by the
spectrum analyzer and also by a specially built frequency tracker.
The system was tested on a power plant stack (Herget ec al. 1975,
Herget 1975), and showed good agreement with in-situ measurements of
the velocity as shown in Table 4-7. The in-situ data, were averaged over
a 30-minute period, and the LDV velocity is obtained by analyzing a
series of 50 msec intervals over a period of 2 seconds. Such data show
wide fluctuations in velocity and amplitude. For each velocity deter-
mination, the resultant spectrum is a Lorentzian-shapea curve of ampli-
tude versus velocity extending from about zero to 2V. The plume velocity
V is taken as the peak amplitude of the spectrum.
These tests also showed that a linear relationship exists between
the intensity of the laser return signal and the in-stack measured opacity
of the plume. Since there is probably a relationship (determined empi-
rically by in-situ methods) between opacity and the mass loading for each
type of source (Conner 1975), the LDV system has the potential to pro-
vide a mass emission rate for particles from a source.
81
-------
TABLE 4-7. In-Stack and Remote
Velocity Data (Herget 1975)
Load
MW
83
83
83
92
96
ee
97
97
109
109
111
in
122
122
124
124
130
j 130
i 130
\ !S5
] 135
j 137
137
Pttot
Velocity
Ft/Sec
87.3
87.3
100
110
107
107
102
102
118
118
118
118
129
129
136
136
136
142
142
148
146
146
146
Doppler I
Velocity I
Ft/Sec !
80 1
83 }
|
90 *
l
95 1
83
90
90
92
too
107
100
103
113
119
112
118
125
117
125
120
130
125 ,
135 |
4.4 REVIEW OF PASSIVE SYSTEMS
There seems to be less work on passive methods for source
monitoring than on active systems, no doubt due to the data interpre-
tation problems of the passive techniques. However, due to their
generally lower cost, it would appear that passive methods would be
more attractive for routine monitoring, even though, with their complex
data interpretation, they might be more difficult to be introduced in
court as admissible evidence. On the other hand, passive methods may
be best suited for surveillance monitoring.
Passive methods may be used in either direct observation of
the plume, as discussed in this section, or indirect observation by the
perimeter monitoring technique, as discussed in Section 4. 5.
82
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Two instruments so far developed, the matched-filter spectro-
meter and the gas filter correlation radiometer, are small, portable
and relatively inexpensive, and are thus appealing for enforcement
monitoring, whereas other passive systems are larger, more expensive
and often require a computer for data processing.
4.4.1 Passive Opacity Techniques
The main passive technique used at the present time is that of
the trained visual observer. The observers are trained at EPA smoke
schools, using controlled smokestacks, to make the meaiurements
according to Ref. Method 9, taking into account the prevailing illumina-
tion conditions. The training method is such it is generally agreed that
the observer in the field will underestimate, rather than overestimate,
the opacity.
Instrumental techniques for passive opacity measurements have
been discussed by Conner and Hodkinson (1967) and include telephoto-
meters, photography, Volz sun photometers, and observers with com-
parators. In addition, there is the night vision image intensifier for
night observations of opacity. All of these techniques, except for the
Volz sun photometer are subjective due to their dependence on the il-
lumination conditions.
The Volz photometer method requires a direct lina-of-sight to
the sun through the plume and alongside it; these conditions will not
always be available, and so the technique is limited.
The telephotometer and photography method make an observation
of a contrast target (e. g. sky and hillside) through and alongside the
plume and use the theory of contrast reduction to estimata the plume
transmittance; clearly, a suitable target will not always be available.
Comparators may be used by an observer to estimate the plume
opacity. The comparator, which contains scattering panicles of varying
number densities, is viewed in comparison with the plume under the
same illumination conditions. Comparators have been developed for
both black and white plumes.
The night vision image intensifier is being evaluated by personnel
in EPA Region III (Smith 1974), and they consider that it should be suit-
able for use by observers who take a training course. Of course, it will
have the same limitations due to illumination variations.
83
-------
EPA Region III uses photography, both on the ground and from
the air, in their surveillance program. They find that showing a photo-
graph of emissions to the offender usually brings about compliance.
Smith (1974) suggests that the contrast reduction of ground features
might be measured by densitometry of the aerial photographs. Due to
illumination effects and the difficulty of finding constant extensive ground
contrast targets, it is doubtful whether this method can be useful.
However, Pressman (1975) is working on another aerial photography
technique for measuring opacity, illustrated in Figure 4-9. Measurements
Opacity = 1 - T = l--
Figure 4-9. Opacity measurement from aircraft
of radiance sxe made in and alongside the plume shadow on a homo-
geneous reflecting ground surface. It is clear from Figure 4-9 that
the ratio of the radiances gives the transmittance of the plume, assuming
that the diffuse radiance over each area is the same, and that there are
no other sources of radiation, such as reflected sunlight, illuminating
the surface. An analysis of this technique is being conducted at EPA-
Las Vegas, taking into consideration the film processing requirements,
spectral variations of ground features, interference due to sunlight
scattered from other structures on to the target surface, and the fre-
quency of su.table targets in photographs of industrial areas. Pressman
thinks that this method can be more accurate than the visual observer,
and anticipates having some results to report by mid-1975.
84
-------
This technique is, of course, limited to daytime operation, and
is best used early morning and late afternoon to obtain clear shadows.
The wind must also be in the right direction so that the shadow lies over
a homogeneous target area. However, within these limitations the
technique does appear promising.
It would appear from publications and from the court cases pre-
viously discussed that the usefulness of passive opacity measurements
is limited since they cannot be used under all conditions, and the inter-
pretation of the data is somewhat subjective due to variations in illumina-
tion. The active laser technique appears to be potentially best suited for
use under most conditions.
4.4.2 Matched-Filter Spectrometer
This technique, in which the spectrum of the incoming radiation
is automatically compared with a stored (in the spectrometer) replica of
the spectrum of the gas being measured, was pioneered for remote sensing
of air pollution by Barringer (1966), and appears to be the first electro-
optical instrument for air pollution. It uses scattered sunlight and is
restricted to daytime use, and has been developed only for SO2 (at 3100 1)
and NO2 (at 4400 I). The instrument has been refined over the years and
is presently marketed as COSPEC II, which is small and portable. The
instrument, shown in Figure 4-10, consists of two telescopes to collect
light from a distant source (scattered solar radiation), a two-grating
•ran
Figure 4-10. The Barringer COSPEC II.
85
-------
monochromator for light dispersion, a disc-shaped multislit mask, and
an electronics system for signal processing. The disc is composed of
circular slits photo-etched in aluminum on quartz, and provides a high
contrast reference spectrum for matching against the incoming ab-
sorption spectra. The arrangement is designed to correlate succes
sively in a positive and a negative sense with the SCty absorption bands
via disc rotation in the exit plane on the monochromator. The detector
used is the XP 1118 photomultiplier tube. Signal processing results in
a voltage output proportional to the optical depth in ppm-m of gas being
observed. A schematic of one telescope and associated optics is shown
in Figure 4-11.
Ml, M2.M3 MIRRORS
INCIDENT I LIGHT
I / I i
PHOTOMULTIPLIER / I
TUBE / , »
/CALIBRATION CELLS
t
, / FIELD I LENS
; I A,MI \, ^
Ex^Sr-tr '-^=£ss»&*s.
i ; i REFRACTOR
i i PLATES
MJ
Figure 4-11. Schematic layout of the Barringer remote sensor
The dynamic range of the instrument is 100-10, 000 ppm-m.
Calibration is effected using four fused-silica cells containing known
concentrations of SC>2 that are incorporated into the instrument. The
instrument is 50 x 25 x 37 cm in size, weighs approximately 18 kg and
can be operated by either a 12V DC battery or conventional 115V 60 Hz.
The COSPEC II was recently tested by EPA (Barnes et al. 1974)
in comparison with in-stack measurements for SC*). The results of the
tests are shown in Table 4-8.
86
-------
TABLE 4-8. Comparison of In-Stack and Remote
SO2 Concentration Measurements
Range
(meters)
20
20
200
300
300
300
In-Stack
(ppm)
500
585
700
460
450
700
HemotP
(ppm)
465
520
240
224
205
275
(IS) - (REM)
(IS)
7
10
65
52
54
60
x ICO
From the table it is seen that agreement with the in-stack readings
at the closest range is quite good. However, at greater distances cor-
relation becomes quite poor. The value at 200 m is suspect since it re-
presents only one hour of data taken on one day. On that day the plant
experienced an outage terminating further work during the study. At
300 m the results are low, but reasonably consistent (54% to 60%). The
authors consider that this consistency could possibly be applicable in
using the instrument at extended ranges if the range correction factor is
constant under different meteorological conditions, such as rain, haze,
and smog, but that much more work would be needed before a firm con-
clusion could be reached on this matter.
A more serious problem was discussed by Barnes et al. (1974).
In their tests they varied the plume opacity by sequentially inactivating
the electrostatic precipitators in the stack. When the second bank of
precipitators was turned off, resulting in a 20% opacity reading (by in-
stack transmissometer), the COSPEC II signal level dropped to an un-
measurable level although the in-stack SO2 monitors showed no change
in SO2 readings. Since this level (20% opacity) is within federal regula-
tions, it would appear that the COSPEC instrument would not be suitable
for enforcement monitoring, and not even for semi-quantitative screening
of sources.
One other problem encountered during the field tests was that of
the plume not remaining in the field-of-view of the COSPEC n. This
occurred even on moderately windy days. This point should, of course,
be noted in the design of any remote sensor. The COSPEC II FOV is
3 mr x 10 mr. Reducing that to 3 mr x 3 mr or perhaps 3 mr x 5 mr
should allow operation during moderately windy days when the plume is
not reasonably vertical for more than one or two stack diameters.
87
-------
Barnes et al. (1974), in their summary, state "In conclusion,
the COSPEC II in its present design is inadequate for EPA use for
routine monitoring purposes. The main limitation, as has been noted,
is inadequate AGC compensation for scattering effects by particulates
both in the plume and in the intervening atmosphere. The less serious
problem of f ield-of-view is perhaps a more readily rectified one. It
should be no,ed hsre that EMI, Inc. recommends usage of the COSPEC
in two other modes, namely as a mobile perimeter monitor (looking
vertically into the sky) and from helicopters (sighting horizontally
through plumes)."
4.4. 3 Gas Filter Correlation '
Another small portable remote sensor is the Gas Filter Corre-
lation (GFC) instrument, for measuring SO2, under development for
EPA (Bartle 1974a). It operates in the infrared and can be used both dayJ
and night.
GFC is a modification of N on -Dispersive Infra-Red (NDIR) tech-
nique that has been known for some time. In contrast to pure radiometry
or dispersive spectroscopy, a GFC (non-dispersive) device uses the gas
itself to obtain the ultimate high-spectral resolution filter (provided by
the line-width of the gas). High spectral resolution is the most im-
portant parameter in obtaining specificity and accuracy in pollutant
analysis.
GFC combines the high energy throughput feature of radiometers
and the high-resolution features of dispersive instruments. It makes
use of the contributions of all spectral lines of a band system of a parti-
cular species to obtain sensitivity. Specificity is obtained by making use
of the correlation between spectra arising from the particular species
in the source and in the instrument gas cell. Discrimination for many
pollutant species against many interfering species occurring naturally
and in pollutsd atmospheres has been studied previously (Bartle 1972).
In addition, a ratioing technique may be employed that minimizes effects
of changes in source intensity, background radiation, and continuum 4
absorption due to aerosols, water vapor, or other molecular species.
The incoming radiation at the sensor is chopped so that it alternately
passes through two optical paths, one through a transparent cell and
one containing the specific gas. Thus, the radiation is modulated only
at the wavelengths at which the pollutant absorbs and high specificity
results.
88
-------
The JRB instrument operates in the 4 ^m combination band of
SC>2 and is designed to minimize the effects of not knowing the plume
temperature, and uses a dual split design, shown in Figure 4-12. It
has been shown (Bartle 1972) that the signal generated by chopping
between two cells is a non-linear function depending upon the SO2 in the
plume and fixed instrument parameters and the difference between the
radiance emitted by the plume and background atmosphere. By ratioing
two GFC signals obtained using different amounts of SC>2 ^n the specifying
cells, the effects of plume and atmospheric radiance are greatly mini-
mized, so that the plume temperature does not have to be measured.
Separate tuning fork choppers are used for each cell pair. The cells
are 10 cm in length. The image of the stack plume is focused by an
f/2. 46 (at 4 urn) lens on a 1 x 1 mm detector which defines the field-of-
view to be 8 milliradians (8 m at 1 km). An ambient temperature oper-
ation (ATO) PbSe detector is used, but a single-stage thermoelectric
cooler is used to provide temperature control.
B * A
rB r
Dual Split Cell -
Windows
Objective Lens
Plane of AV Tuning
Fork Choppers
T. E. Cooler
PbSe Detector
4. 0 Jim Filter
— 800 Hz Tuning Fork
AV-1
AV-2
Section 3-B
Section A-A
Figure 4-12. Optical system schematic of the JRB remote SC>2 monitor
89
-------
Section A-A of Figure 4-12 shows the configuration of the dual
split cell. The two gas cells contain different partial pressures of SO2
and are pressurised to 1 atm with pure N2 to pressure-broaden the SC>2
lines. The reference cells contain relatively low pressures of SO2 and
are also pressurized to 1 atm with pure N2- The cell areas are the
maximum al'owed by the tuning fork choppers, about 8 mm wide x 1. 9 mm
long.
Section B-B of Figure 4-12 shows the dual tuning fork configuration.
Fork-1 is shown closed, allowing radiation to pass through the V-l re-
ference cells; Fork-2 is shown open, allowing radiation to pass through the
AV-2 gas cell. Fork-1 operates a frequency of 40 Hz and Fork-2 at a
frequency of 100 Hz. Because a single lens serves both AV-1 and AV-2
systems have exactly the same field-of-view at the stack plume, as is
essential for proper cancellation of the stack effluent temperature factor.
The superimposed image signals of the two AV systems are electronically
separated by the signal processing. A third tuning fork chopper, operating
at 800 Hz, is located immediately ahead of the detector aperture to elim-
inate the low frequency 1/f detector noise from the PbSe detector.
The instrument has a sensitivity of 70 ppm-m at a plume tem-
perature of J-70 C and 290 ppm-m at 170 C using an instrument integra-
tion time of 10 sec. The physical specifications are listed in Table 4-8,
and a photograph of the instrument is shown in Figure 4-13.
The JRB instrument was used in a field test conducted by EPA
(Bartle 1974b), in which remote measurements were compared with in-
situ extractive techniques (DuPont Analyzer and EPA Method 6). The
results shown in Table 4-9 show fairly good agreement within the experi-
mental error between the methods. It appears that the quoted errors in
Table 4-9 are greater than would be expected from the previously quoted
instrument sensitivities, but this may be due to instrument balancing
problems exaerienced in the field. There does not appear to be any
effect of raneje. The data on 8-14-74 were apparently taken in very hazy
conditions, but there was no significant effect due to the haze. On this
same day, the stack precipitators were sequentially turned off giving a
maximum opacity of about 37%, but there was apparently no effect on the
remote SO2 iata, These tests revealed some shortcomings in the design
for operational field use, but these are presently being corrected, to-
gether with a change in the detector, reducing the field-of-view to 2 mrad "
x 2 mrad and at the same time achieving better sensitivity (Bartle 1975).
90
-------
Weight: 22 pounds
Size: 38 cm length x 18 cm width x 23 cm height
Field-of-view: 8. 0 m rad x 8.0 m rad
Power requirements: 3. 3 watt.s
Power source: 8 Eveready EDI NiCd (1. 2 arnp-hr, 6. 25 V);
(Batteries) 2 Eveready R6 NiCd (6 amp-hr, 1. 25 V)
Battery operating lifetime: >£ hours
Warm-up time: 3 minutes
Time constant (to 1 - 1/e signal level): 1, 3, 10, 30, and
90 seconds
Attenuation: 1, 5, 10, 50 and 100
Gain selection: 1, 5, 10, 50'and 100
Recording;: 1% panel meter; rocorder jacks for
AV,
AV2 and AV2/AV1 signals
Figure 4-13. Photograph and physical specifications
of JRB 862 remote sensor
TABLE 4-9. Summary of Average Values of
Remote GFC and Extractive Data
Range
(m)
160
390
390
390
390
390
160
date
8-12-74
8-12-74
8-13-74
8-13-74
8-14-74
8-14-74
8-15-74
Time
10:00-11:45
13:45-16:50
09:00-12:00
18;45-2l:00
09:15-12:45
14:30-16:30
09:30-11:45
[SO2], ppm
Remote
T,°C
150
15)
150
15 J
120
150
110
Cone.
540 ± 200
G30 + 170
530 ±120
550 ± 120
400 ± 160
440 ± 110
750 + 70
Extractive*
buPont
Analyzer
—
—
412±18
422 + 28
472 + 32
519 ± 21
Ei>..
Mcthoi 6
525 ± 25
398 ± 23
....
401 i 17
475 ± 7
4991. 11
%
Donation
-17
-25
-25
-1G
+• 7
-32
* All extractive data taken from plume with a temperature ol 150 ± 5 C.
91
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4.4.4 Medium Resolution Dispersive Spectrometer System
The dispersive spectrometer system, which bears the acronym
ROSE (Remote Optical Sensing of Emissions), was designed and fabri-
cated for EPA by General Dynamics/Convair. The basic purpose of
the ROSE system is to study the spectra of various stationary source
emissions so as to determine which spectral regions are most suitable
for measurement of particular species and to verify which species are
actually present in the effluent. This information can then be used to
assist in the design of simple instruments for specific pollutants. The
instrument is generally not considered by SPA for routine monitoring
due to its bulk and cost, although it is mounted in a truck like the laser
systems. The contractor's final report (Streiff and Claysmith 1972)
describes tha ROSE system in detail. Figure 4-14 shows the principal
parts of the receiver section: Dall-Kirkham telescope optics with a
60-cm diameter primary mirror, Perkin-Elmer Model 210 linear wave
number drive monochromator, and detector housing with a portion of a
Cryogenic Technology closed-cycle helium refrigeration system. The
monochromator contains two gratings that are each used in first order
with long-wave pass filters to cover the spectral ranges 2. 8-6. 5 and
6. 5-14 microns. The spectral resolution is variable, depending on the
Figure 4-14. The ROSE system receiver section
with electronics during field tests
92
-------
the slit opening, but 1 cm"1 at 10 (jim and 4 cm"1 at 5 urn are achievable
in the absorption mode. The Ge:Hg detector is operated at 28°K. The
source unit (not shown) contains identical telescopic optics, and a black-
body radiation source is located at the telescope focus. The blackbody
is operable over the range 1100-1800°K and is optically chopped for long-
path (^ 2 km) absorption measurements. In the remote emission mode,
optical chopping occurs just in front of the monochromator entrance slit.
For intensity calibration purposes the source unit is placed just in front
of the receiver unit so that the blackbody radiation (unchopped) fills the
field-of-view of the receiver unit. Both source and receiver units con-
tain bore-sighting attachments to allow visual alignment of the telescopes.
An example of the type of spectra obtained with the ROSE system
by EPA in a field test (Barnes et al. 1974) is shown in Figure 4-15. SO2
emission bands are readily distinguished, and, if the plume temperature
is known, the SC>2 concentration in the plume may be calculated. The authors
calculated 650 ppm for a 400°K plume, which compared tD 710 ppm using
an extractive method, and to 680 ppm measured with an in-stack optical
method. They show that an uncertainty of 6% in the plume temperature
at 400°K produces an error of about 12% in the concentration.
MM II-OT "50
PUJME •» SKY
ex" t
MH
. *<:*•• t • 1M.« ! ; . - i ' ' ' i ! C.O,
-.E. CSOH.W-.w, 'I-!—i ;.. , '--L-r-t-j • ^ui
.
Figure 4-15. Plume and sky spectra from 7-13 microns
(Barnes et al. 1974)
93
-------
The problem with the dispersive technique is the determination of
the plume temperature. Barnes et al. (1974) state that spectral reso-
lution better than 0. 5 cm"* and a computerized data reduction program
would be needed to obtain the plume temperature, but they do not elabo-
rate on the method.
Chen et al. (1974) have suggested a method which utilizes the fact
that the spectral location of the peak of a vibratiorial-rotational band of a
gas depends on its temperature; the peak 01 the P or R branch shifts away
from its band center as the temperature increases. Assuming that there
is a region of no spectral overlap of gases in the plume, they estimate
that in the 8. 6 ym SO2 band, the P and R branches separation changes by
0. 5 cm~l per 10°K change in temperature (over the range 375°K to 575°K).
They consider that an interferometer-spectrometer can provide spectra
so that the plume temperature can be measured within 10°K. They also
estimate tha; at 400°K, a 2% error in temperature results in a 10% error
in SC>2 concentration. They point out that the temperature uncertainty
increases in the presence of particles in the plume.
Another method of estimating plume temperatures relies on the
use of an interferometer-spectrometer and is discussed in the next section
4.4. 5 Interferometer-Spectrometer
Interferometer-spectrometers have an advantage over conventional
scanning spectrometers with their high optical throughput and rapid ac-
quisition of the spectrum (assuming an on-line special purpose computer
is available). They have been used to remotely sense stack emissions by
Low and Clancy (1974) and the General Dynamics/Pomona group (Streiff
and Ludwig 1973) both of whom have made qualitative measurements,
and by Prengle et al. (1973) who report some quantitative measurements.
The GD/Pomona system, which is installed in a van for mobility,
was used in comparison with the ROSE system described above. Two
Michelson-type interferometer-spectrometers were used to obtain spectra
data over the 2 to 14 micron region. One interferometer using an LN2
cooled InSb 'PV) detector covered the region from. 2-5.4 microns while
the second interferometer equipped with an LN2 cooled HgCdTe detector
obtained useful data from 3. 5-14 microns. The characteristics of both
interferome:ers are tabulated in Table 4-10.
94
-------
TABLE 4-10. Principal Interferometer Characteristics
Hem
Model Designation
(Drive Mechanism)
Wavenumber Region
of Operation
Optical Resolution
Spectrum Recording
Rates
Detector
Detector Lens
Detector Cooling
Foreoptlcs/Field-
ot-View (50%)
Wavelength
Reference
Interferometer #1
1F-3
1850 to 5000 cm*1
-2.5cm"1
1 per 2. 5 sec.
1.0 mm dia. InSb(PV)
1/4" dia. silicon
Liquid Nitrogen
10" dia. /2 m rad.
0. 63282 n
HeNe Laser
Interferometer #2
IF -3
7 16 to 2500 cm"1
~ 1 cm"1
1 per 4. 5 sec.
2x2 mm HgCdTe
1 1/4" dia. Germanium
Liquid Nitrogen
12" dia. /6 m rad.
0. 63282 u
HeNe Laser
The principal element in the interferometer is an optical cube
consisting of a GD/Pomona developed beam splitter, a fixed front sur-
faced mirror and a moving mirror driven by a servo-controlled system
developed by Idealab, Incorporated, in a triangular sweep to obtain
linear mirror movement.
The optical cube is shown in schematic form in Figure 4-16.
As indicated in the schematic, the single cube is used for the informa-
tion channel, a laser reference and a white light synchronization pulse.
The sync pulse is used to locate the exact center of the interferogram
for coherent averaging of successive interferograms (when desired).
The laser provides the digitizing clock and wavelength reference.
Both instruments were equipped with f/8 collecting optics with
the 2-5 micron interferometer having a 10-inch diameter collecting
mirror and the 3. 5-14 micron interferometer having a 12-inch dia-
meter collecting mirror. The design allows for variations in the field-
of-view from a few milliradian to several degrees by means of quick-
change foreoptics elements.
95
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LASER DETECTOR
/
f/1 LENS
TARGET
DETECTOR
f/8
FOREOPTICS
/ JL \ ^ WHITE LIGHT DETECTOR
/\ j »—iIU—
SYNC PULSE
1 ----- »---\/\/\A/~ INTERFEROGRAM
-1AAAAA/1 LASER CLOCK
Figure 4-16. Optical layout of Michelson interferometer
Some typical spectra of a stack plume, obtained at a range of
about 500 m, are shown in Figure 4-17, with the inset giving the plume
concentrations of some gases, measured in-stack. The plume tempera-
ture was not known, and no attempt was made to determine it from the
remote spectra, so no estimate of the gas concentrations were made.
It is of interest to compare these spectra with those of the ROSE system,
see Figure 4-18, obtained on the same stack. The ROSE system,
with its somewhat lower spectral resolution, detects SO2 in the
8. 6 (Lim and 1. 6 M^I regions, whereas these bands are not obvious
in the interferometer spectrum.
Pren^le et al. (1973) have made interferometer spectrometer
measuremerts of stack emissions with a mobile system shown in Figure
4-19. The Cassegrain telescope has a 25 cm diameter primary mirror,
and the interferometer is a Block Engineering Co. Model 296, covering
the 2. 8-15 jum range with 0. 5 cm"* resolution.
The authors propose a method to obtain the plume temperature
which is applicable only to the interferometer spectrometer sensor. At
zero retardation of the interferometer mirrors all frequencies have the
same phase and add to give a narrow spike in the interferogram. The
amplitude of this spike represents the total flux incident on the inter-
ferometer, integrated over the 2. 8-15 ^m region. This total flux pro-
vides a measure of the plume temperature (this would appear to be true
only if the plume emissivity is constant with time and is known). The
spike amplitude is calibrated against temperature using a blackbody.
96
-------
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HUM 1 >\
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ADDITIONAL MMPUAITIES
OIL & WAttB
STACK IffLUENT
S'ICIf
O. _ . . MOT
L 2SOO 3000
0.000
2000. 2200 2400 2600 2800 3000 3200 3400 3600 3800 4COO
WRVENUttBER (I/CM)
Figure 4-17. Emission spectra of the gaseous effluents
from a sinter plant stack measured at
Kaiser Steel Corporation, Fontana
97
-------
8 n
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CO
• r-l
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98
-------
Figure 4-19. Assembled mobile interferomeier-
spectrometer system (Prengle et al., 1973)
Measurements were made of a power plant stack plume at a range
of about 65 m. A single measurement typically consisted of averaging a
total of 20 to 100 scans (mirror scans), each scan taking 3 sec. The
results, compared with in-stack measurements, are given in Table 4-11.
TABLE 4-11. Interferometer Compared with In-Stack
Remote
In-Stack
Temp(K)
560
561
CO(ppm)
5550
4130
NO(ppm)
324
376
CH4(ppm)
858
878
02^4 (ppm)
296
292
99
-------
The agreement is very good; details of the data interpretation
are not given, but it appears that some sort of calibration of the system
is required using in-stack measurements, i. e., quantitative measure-
ments cannot be made on a plume without prior access to the stack to
empirically calibrate the interferometer for that particular stack and
its emissions.
It seems that this approach for measuring the temperature of
the plume is not suitable for routine monitoring. Hence the interfero-
meter-spectrometer does not appear to have a significant advantage
over the dispersive spectrometer. Of course, it does have a greater
throughput and makes rapid spectral scans. These advantages must be
balanced against the disadvantages of the greater expense and complexity
of the interferometer system.
4.4. 6 Filter Wheel Sensor
A filter wheel remote sensor was built by Bendix (Prostak and
Dye 1970) for EPA, for measuring pollutant spectra in the 7-14 jjm region.
The wavelength is scanned by rotating a continuously variable filter wheel,
which has a resolution of about 1 percent. The radiation is collected by
a 28 cm Dall-Kirkham telescope, and passed through the filter wheel on
to a mercury-doped germanium detector mechanically cooled to 28 °K.
An on-line computer is used to analyze the spectra in terms of pollutant
concentration using regression analysis based on previous calibration data.
This device is much simpler, optically (see schematic in Figure
4-20), than the scanning spectrometer or interferometer, but due to the
poor spectral resolution, the data interpretation is difficult even with
help of the on-line computer. The system was also tested in the long-
path active mode at the same time as the ROSE and the GD/Pomona
interferometer systems, but had problems with its computer. The filter
wheel technique does not seem to have been pursued since that time.
4. 4.1 Laser Heterodyne Technique
The passive laser heterodyne technique (illustrated in Figure
4-21), discussed by Hinkley (1972), Menzies and Shumate (1974), and
Seals (1974) does not appear to have been applied to field measurements
of stack emissions (or ambient air).
100
-------
RECEIVER
AUXILIARY
DETECTOR xPASSiVE-MODE
CHOPPER
SAMPLED REGION '
"II 6 KM NOMINAL LENGTH)
ELECTRONICS CONSOLE
POSITION FEED BACK
INTEGRATOR
1
1MULTI- |
PLEXER 1—
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INTEGRATOR
-n
i
SYNCHRONOUS
RECTIFIER
PHASE-LOCK
SYNCHRONOUS
RECTIFIER
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AMPLIFIER
t
1
1
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AMPLIFIER
---i I r~r"-
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1
j
r*-
-
STEP 'Eft j
MOTOR 1
PRE^MP I
PREAMP [•
MAIN SIGNAL FLOW
COMPUTfO-CONTHOLLED
COMMAND SIGNALS
Figure 4-20. Block diagram of Bendix filter wheel sensor
(passive mode does not use transmitter)
-KAM-SPLITTlft
(
ctececcion 01 poilucant gases f."orr, a
smokestack using a tunable-diode-
laser local oscillator
101
-------
The laser heterodyne technique may be used to selectively detect
a pollutant emission line if a local oscillator (laser) frequency is found
to coincide with that emission line. If this line is relatively free from
interference due to other species, the technique can be better than cor-
relation techniques in certain spectral regions where interference is
relatively high, such as in water vapor bands.
The basic detection technique is illustrated in Figure 4-22. The
laser can be at a fixed frequency, or it can be tunable so that it scans
across the emission line of interest, and a beat frequency is produced
whenever the difference frequency is within the bandpass of the electronics
The sensitive spectral width in this technique can be less than
0. 06 cm-1 (corresponding to an IF bandwidth of 10^ Hz), and the NEP
is typically ICT^W in the 5-12 |Lim region for a 1 sec integration time.
DETECTOR
LOCK-IN AMPLIFIER
CMOtttR
V
AMP AMP
LASER LOCAL «£
C5C11AATO** OC
••r
IMS -
GKAVOR
Figure 4-22. Schematic of heterodyne technique
Hinkley (1972) shows that by scanning the laser wavelength through
that of the pollutant emission line, a beat frequency is produced whenever
the difference frequency between the two infra-red signals is within the
bandpass of r.he detector/amplifier system; the amplitude of the signal is
related to pollutant concentration. The signal-to-noise ratio is given by
_exp(hi//kT )-:
o
8xp(hf/kT. ) -
(4-19)
102
-------
where ot' is the absorption coefficient of the line per ppm of gas con-
centration (c), L the thickness of the plume, Tg its temperature,
cjj the emissivity of the background at temperature T^, > is the infra-
red frequency, h is Planck's constant, k is Boltzmann's constant,
B the system bandwidth, and r the post -detection integration time.
Equation (4-19) is also based on the following assumptions: (i) that the
IF bandwidth is less than the emission linewidth; (ii) that the emission
and absorption due to the pollutant in the ambient atmosphere is not
important because of a low concentration there relative to that in the
plume; (iii) that the background attenuation from the wings of other
molecular absorption lines is negligible; and (iv) that the local oscil-
lator has sufficient power to overcome the other sources of noise.
Equation (4-19) holds, regardless of range, as long as the field-of-view
of the collecting telescope is filled by the plume; in the infrared,
with collection optics only a few centimeters in diameter, it should
be possible to detect pollutants 1 kilometer away.
Under these conditions the minimum detectable concentrations
for pollutant gases with line strengths of 1 x 10-5cm~Vppm are shown
in Figure 4-23 as a function of wavelength and for different source tem-
peratures and background emissivities. Concentrations of a few ppm
of NO and CO at 400 to 600° C can be detected; and similar sensitivities
are achievable for C2H4 and NH3 (at longer wavelengths) at a temperature
of only 50° C. Since SO2 in the 8. 7 ym region has a measured absorption
strength almost ten times smaller, the minimum detectable concentra-
tions for this gas should be raised accordingly.
The local oscillator power necessary to satisfy assumption (iv)
above is given by the equation
(kTA)(ht>)
= • (4-20)
where TA. is the noise temperature of the amplifier, G the infra-red
detector gain and r\ its quantum efficiency, RL the load resistance,
and e the electronic charge. For an amplifier with a noise temperature
of 240°K (noise figure of 2. 4 dB), and assuming T) = 0. 5, G = 0. 12,
= 50 ohms, and X = c/v = 10 pm, we obtain PLQ ~ 12 mW.
103
-------
loco cr
Figure 4-23. Theoretical wavelength dependence for remote
heterodyne pollutant monitoring for various gas
temperatures, and for background emissivities
of 0. 2 and 1. 0. Useful wavelengths for some
pollutant gases are indicated on the abcissa.
Other parameters are shown in the figure.
Using state-of-the-art infra-red detectors and low-noise ampli-
fiers, .the local oscillator power of 12 mW is prohibitive, producing not
only excessive heating of the detector, but a substantial liquid helium
boil-off. When wide band (> 500 MHz) photodiodes having nearly unit
quantum efficiency become available, the local oscillator power re-
quirement will be less than 100 yW, a more realistic value.
104
-------
Of course, as with most other passive techniques, knowledge of
the plume temperature is required for quantitative measurements of
the pollutant.
Shumate and Menzies (1974) have developed a heterodyne radio-
meter, with a CO2 laser as a local oscillator, and used it to remotely
detect several laboratory samples of gaseous pollutants at ambient tem-
perature. Previous demonstrations of heterodyne radiometer sensiti-
vities to SO2 and CO2 were accomplished by heating the gas samples.
The sensitivities to 03, NHs, and C2H4 were found to be adequate for
detection of ambient concentrations in the parts per billion (ppb) region.
The sensitivities to SO2 are on the border line for detection of ambient
concentrations around 50 ppb, and it may be possible to improve this by
a factor of 4 if detection wavelengths near 8. 8 urn are being used instead
of their operating region around 9. 0 jim. A CO laser, operating, near
5. 2 ym, has also been used as a local oscillator in the detection of nitric
oxide (NO) at a temperature of 390°K. The passive heterodyne radio-
meter does not appear to be capable of detecting ambient NO at normal
smog concentrations; however, the authors suggest that it can be used
to monitor NO concentrations in stationary source emissions which are
at elevated temperatures.
The sensitivities to the various gases are shown i:i Table 4-12.
The minimum detectable amounts in the second column (in units of con-
centration times path length give a signal -to -noise ratio of one when a
time constant, r of 10 seconds is used. For these measurements,
B = 600 MHz. This corresponds to a spectral resolution of 0. 04 cm'1.
TABLE 4-12. Experimental Sensitivities to Pollutant G^ses
(Menzies and Shumate 1974). The gases vere
at 298°K, except for NO, which was at 3SO°K.
The band designations I and II refer to the upper
and lower of the two mixed (10°0, 02 °0) states.
Nitric oxide 10-' "C"O: 7-6, P(15) 5.19
Sulfur dioxide 10-« "Cl"O-: OO^-H, K(40) 9.02
Ozone ^ X 10-' '=C"O.: 00°1-U, ^(40) 9.50
2 x 10-* "XT'O,: 00°1-II, />(14) 9.50
Ethylene 5 x 10" "C"O.: 00»l-l, P(14) 10.5J
Ammonia 10-* i;C"Oj: 00»1-I, /»(32) 10.72
105
-------
To date, much of the work in the laboratory on heterodyning has
used helium-cooled detectors, and conventional laser sources, as well
as helium-cooled tunable laser diodes. For field applications, higher
temperatures must be used; developments of both detectors and tunable
laser diodes are progressing along these lines. The HgCdTe detector,
which operates at a higher temperature, has the added advantage of
requiring considerably less local oscillator power than doped germanium
and pyroelec;ric detectors (Koehler 1974).
4.4. 8 Dispersive Hadamard Transform Spectrometer
Hadamard transform spectroscopy (HTS), which appears not to
have been applied to remote monitoring of air pollution, utilizes the
multiplex technique by means of a conventional spectrometer with entrance
and exit masss containing many slits. Spectral scanning is achieved by
moving the slits rather than the grating. The detector output is decoded
by use of Hadamard matrices in a computer. The basic concept is il-
lustrated in /figure 4-24 (Decker 1971). The dispersed radiation is "de-
dispersed" by being returned through the spectrometer on to a detector
adjacent to the entrance slit.
Although spatial information alone, or spectral information alone,
can be Hadamard multiplexed, a combined system (imaging spectrometer)
is possible OJwift and Wattson 1974). The object or field of interest is
focused onto a field stop at the entrance plane of a dispersion spectro-
graph by a conveDtional lens or telescope (a field stop replaces the usual
entrance slit). A two-dimensional Hadamard mask is then scanned across
the field stop, thus transmitting a time-varying light intensity that con-
tains information about all spatial resolution elements in terms of the
mask patterr,. In this way, the spatial information is encoded. The
transmitted radiation is in turn dispersed, and focused as a spectrum
at the exit focal plane of the spectrograph. A one-dimensional Hadamard
mask is placed across the spectrum and stepped one element of its cycle
for each complete scan of the spatial mask. This, too, produces a tem-
poral modulation which contains encoded spectral information.
A laboratory instrument having a spatial field of 31 x 33 elements
(each one typically 0. 1 mm x 3. 5 mm) and a spectral array of 63 elements,
with the detector and gratings covering the 6 um to 25 pm region with a
resolution of 0. 02 |um or better has been built (Swift and Wattson 1974).
106
-------
25.5 mm x 1.0 mm
Field Stop Silts-
90 corner
Reflector
509-Total-Slut
S255 " Matrix Mask,
at Exit Foca. Plane
150-groove/ton
Grating,Blazed
for 2.0 mlcrona
Mlnuteman Instrument Company
Model 305 0.5-m«ter
Corrected Czerny-Turner
Spectrograph
Detector,
mm Square Active An.a
to Preamplifier i Data Recorder
g-Pork Optical Chopper
Figure 4-24. Schematic of Hadamard transform spectrometer
(Decker 1971)
Theoretical analysis (Larson et al. 1974) shows Uat HTS is best
suited for spectra which are characterized by a few well-defined and
intense peaks on a low intensity background. Conversely for spectra
with high backgrounds, for dense spectra, or for weak spectral features,
HTS has no advantage over a conventional scanning spectrometer. On
the basis of this analysis it would appear that, in general, HTS has no
special advantage for remote sensing of pollutants, since their spectra
are generally weak and mixed with interfering spectra.
107
-------
4.4.9 Passive Vidicon Instrumentation
A UV vidicon system for the measurement of SC>2 and plume
velocity is being developed at NASA-Langley (Exton 1974). The vidicon
is sensitive to a bandpass of 50-100 A in the SO2 absorption band at
3100 A, and detects scattering solar radiation (similar to the COSPEC).
Hence the intensity of the plume image on the vidicon screen provides
a measure o:' the SO2 in the plume. The quoted accuracy is + 20-30 ppm
at a concentration of 100 ppm. However, the instrument has been tested
only with low opacity (< 1%) plumes, and presumably, like the COSPEC,
the accuracy will deteriorate with increasing plume opacity, range, and
increasing atmospheric haze.
It would appear that this device would be most useful as a quali-
tative device for imaging invisible SO2 plume; it could show the location
of the plume with respect to the stack so that other remote sensors could
optimize their pointing location. Exton (1974) indicated that on one oc-
casion the device showed downwash of the plume around the stack, which
would change the SO2 path length observed by remote sensors.
This vidicon device has also been used to estimate the effluent
velocity. The plume has eddy inhomogeneities which show as "blobs"
on the SC*2 image of the plume. The plume velocity is obtained by tracking
these eddies as a function of time.
Another vidicon device operating in the IR (3-4. 5 jjm) is planned
for evaluation by Aerospace Corporation under EPA support (Herget 1975).
This too will provide an image of SC«2 in the plume due to emission in the
4. 0 fj,m SC>2 band. It is also hoped to obtain velocity by tracking the plume
inhomogeneities. Presumably it will not provide quantitative SO2 data
independently, since the plume temperature will not be known, at least
not remotely.
4. 5 AREA SURVEYS
Area surveys of air pollutants can be useful for episode monitoring,
for selecting plant sites, for evaluating environmental degradation, for
assisting in the design of contact monitoring networks, and for tracking
plumes to study atmospheric dispersion, diffusion and fate of pollutants.
Area surveys can be conducted from airborne platforms such as aircraft,
108
-------
helicopters or blimps; from vehicles driven through and around the
area, and from long-path observation networks traversing; the area.
It would appear that space observations of pollutants will not be suit-
able for local purposes since the spatial resolution, both horizontal
and vertical, is too coarse.
From the point-of-view of enforcement, area surveys of ambient
air pollution levels are not relevant except where the area surveyed
includes stationary sources. Since the sources of emissions are mostly
above ground level, ground level long-path measurements of ambient
pollutant amounts will not, in general, provide a measure of the source
emissions. However, if a measure of the pollutant in a vertical column
can be made continuously around the perimeter of an area source, a
knowledge of the mean wind velocity enables the rate of emissions within
that area to be estimated. Measurements of the vertical loading may be
made with ground-based instruments looking up, or airborne instruments
looking down from above the upper altitude limit of the emissions. Con-
siderations of this technique seem to have been limited to gaseous pol-
lutants. Similar measurements for particulate pollutants would be dif-
ficult, although qualitative three-dimensional mapping of particle con-
centrations over an area may be done with an airborne lidar system.
The COSPEC instrument has been used for perimeter monitoring
of NO2 and SO2, in the vertical up-looking mode in which the scattered
(by molecules and aerosols) solar radiation is measured t'Langan 197la).
The instrument is periodically calibrated by placing cells containing
known amounts of each gas in the line-of-sight within the instrument.
The problems of multiple scattering, varying sun an[ le and varying
aerosol amounts and distribution makes quantitative interpretation very
difficult. Some measurements (Langan 1971b) of SO« arojnd a single
stack gave an emission rate of about 24 metric tons/day (iveraged over
a 50 minute measurement period), whereas an in-stack c :emical method
gave 17. 3 metric tons/day (averaged over a 60 minute measurement
period). The report suggests that some of the discrepancy can be attri-
buted to fluctuating winds.
Barringer Research Ltd. (1974) has also used a GFC instrument
for measuring CO at 4. 6 ^m in the up-looking mode, but no quantitative
results were reported.
109
-------
An up-looking differential absorption laser system installed in a
van would seem to be well suited for perimeter monitoring by measuring
the return signal from an altitude above the emissions to give the vertical
integrated pollutant optical thickness.
This basic technique appears also to be the most suitable for air-
borne measurements. Two instruments are being developed for aircraft
operation, u sing downward looking laser systems, and utilizing the earth-
reflected laser radiation. EPA, Las Vegas (Melfi 1974) is developing a
system for measuring 03, using two pulsed CO2 lasers, tuned to different
wavelengths. The laser beams must be accurately boresighted so they
are illuminating the same ground patch, and it is assumed that the wave-
lengths are close enough that the ground reflectivity is the same for each.
This basic system could be used for other gases as well, such as SC>2,
C2H4 amd WA%, either by tuning or by using isotopic CC>2 laser.
NASA-Langley (Allerio 1975) is also supporting a similar program
at JPL to develop a tunable CO2 laser heterodyne aircraft system for 03.
Another aircraft laser system is being developed at NASA-Langley
(Hess 1975) for the measurement of CO. This DAS system uses hetero-
dyne detection of the earth-reflected radiation from a CW tunable diode
laser. The shape (due to pressure broadening) of the pollutant line ob-
tained by the spectral tuning apparently can be mathematically analyzed
to provide coarse information on the pollutant height distribution.
In all of these differential absorption methods, a careful analysis
must be made of possible errors due to the earth/atmosphere fluctuating
background; to the effects of the aircraft moving over different targets
between pulses or during the laser tuning; and to variations in the laser
output.
A summary of on-going programs in perimeter and area moni-
toring of different agencies is given in Table 4-13.
4. 6 ON-GOING AND PLANNED RESEARCH PROGRAMS
In addition to the literature search for remote sensing work rele-
vant to this program, we have learned from various government agencies
and laboratories their relevant on-going and planned programs. A listing
of these programs and the names of the persons contacted are given in
Table 4-14 and 4-15.
110
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TABLE 4-13. Area Survey Techniques
NASA/MAPS
(Planned)
NASA/ERTS
(Feasibility Shown)
NASA
(Suggested)
EPA
EPA
NASA
POLARIMETER
NASA
BARRINGER RESEARCH
NA8A/CIMATS
SPACE
IR. Uses GFC method. Not suitable for enforcement—£Tea too large--
gives Integrated tropospheric amount.
Visible. Radiometer. Not suitable for enforcement—gi/es vertical
burden of aerosols over water surfaces.
Visible polarimeter. Not suitable. Tropospheric aerosol amounts—data
interpretation difficult for quantitative information.
AIRCRAFT - BLIMP - HELICOPTER
Airborne lidar system. 3-dimensional mapping of relative participate distributions.
IR. 2 wavelength CO, laser. Earth reflection giving vertical integrated
amount. Looks promising in theory—needs flight demonstration.
IR. Tunable diode laser. Earth reflection. Same comments as for EPA
program above.
Visible—same comments as for space application.
IR. GFC. 2 flight models tested by NASA--gtves vertical integrated amount-
needs temperature profile—in general, not sensitive to lowest 1 km, so not
suitable tor enforcement.
Visible. COSPEC matched filter—severe data interpretation problems due
to scattering.
IR. Correlation interferometer—uses reflected sunlight—data problems due
to varying surface reflectance—gives vertical integrated amount, so no good
for enforcement.
BARRINGER RESEARCH
BARRINGER RESEARCH
SAI
GROUND - MOBILE
Visible. COSPEC looking upward from van—for area emission monitoring—
quantitative interpretation is a problem due to scattering.
DR. GFC looking upward from van—for perimeter monitoring.
BARRINGER RESEARCH
BENDIX
EPA/ROSE
GD/POMONA
SAI
SAI
GE/EPA
LINCOLN LAB/EPA
SAI
GROUND - FIXED LONG PATH
Visible. COSPEC. Xenon source. SO2, NO2 only- Aerosol attenuation may
be significant. Present range: 100-930 m.
IR. Filter wheel. Blackbody source—computer problem—not pursued.
Present range: 1.6 km.
IB. Scanning spectrometer. Blackbody source. Used ;.s research tool.
Present range: 400 m - 4 km.
IR. Interferometer spectrometer. Blackbody source. Present range:
2-4 km.
IR. GFC. Blackbody source—for factory emissions. Present range: SO m.
IR. GFC. Blackbody source—for highway CO emissions. Present range:
SO m.
IR. 10.6 ym CO, laser source for O,. Present range: 670m.
IR. 4.7 urn tuned diode laser source for CO. Present range: 610 m - 2 km.
IR. GFC Blackbody source—H.S, VC - for area surveys. Present range: 1 km.
Ill
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TABLE 4-15. Review of Other Agency Programs
HASA/LANGLEY
Evaluation of AAFE instruments for A/C use
CIMATS - correlation Interferometer
MAPS - GFC
HSI - interferometer spectrometer
2. In-house DARS program--CO from A/C looking down at earth reflected signal from CW tunable
diode laser, plus heterodyne detection. Scanning across pollutant line .dlows mathematical
unfolding of coarse information of height distribution. On A/C Spring 1975.
3. JPL program same as above, but with tunable (X>2 laser for Oj. On A/C Spring 1977.
4. AIL program—passive radiometry using CO. laser heterodyne for O,, NH., C.H,. On A/C
May 1978.
5. Tunable diode laser plus retroreflector on A/C wing for CO. In-house development.
6. Differential absorption for SO. using 3000 A dye laser. Have SOj spec .rum with 0.2 A resolution.
Will test on stack emission, tfien install on A/C for ambient SO,.
7. SAI program--GFC with retroreflector on A/C wing for HC1 and CO.
8. Differential absorption in IR (1.5-4. 5 urn) with tunable diode lasers. (Joint NASA, EPA,
AF, Army program).
9. Differential absorption for NO2 with tunable dye laser. In-house Investigation of difference
between sequential and simultaneous pulsing of the laser.
10. Differential absorption for H2O using 7000 A tunable dye laser. Will use in up-looking mode
for humidity profiles.
11. UV camera for SOg and velocity in plumes.
EDGEWOOD
ARSENAL
1. Passive LOPAIR, advanced development, 8-12 ym, 16-channel filter instrument. Looks at sky
at low elevation angle. Uses on-line computer using selected channels and weighting functions for
Dimethylmethylphosphonate (DMMP).
2. Isotopic CO, laser using topographic reflector. Exploratory programs,.
>. Differential absorption program (with EPA)--Ahmed of New York. Visible laser (. 09 ppm NO.
at 1 km).
4. Raman. Currently planning on using Ruby laser without doubling to pe. increased S/N.
NSF
SRL. SO., O,, NO*- -Differential absorption laser system.
2 «5 <-
EPA-LAS VEGAS 1.
2.
In-house O, 2X CO, laser on A/C—area survey.
Aerial photography for opacity.
USAF 1. Brooks AFB-JRB -- GFC in-situ for HC1 and HF designed for ready acaptation to long-path measurements.
2. RADC-Block Engineering -- Remote detection, tracking and quantitative measurement of HC1 in the
residual effluent plumes of solid booster launches.
DOT
GFC long path (50 m) with retroreflector across highway to mcritor CO (car emissions) and SF.
(released tracer),
6
NCAR
Transportable syste/n: Lidar for aerosols
Doppler velocimeter
Can also do Raman scattering.
Acoustic soundings for inversion height.
113
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114
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PRACTICAL CONSIDERATIONS
5. 1 OVERVIEW
In this section we consider the practical systems constraints
due to safety considerations and to instrument and source parameters.
One of the first constraints to consider is the eye safety re-
quirements. Thus, an analysis of the performance standards for laser
products as proposed by the DREW is made and the maximum permis-
sible exposure and minimum safe range are determined. The resulting
instrument parameters are then used as an input into the error analysis
of the different laser systems. It is obvious that the errors of hingle-
ended pulsed laser systems vary due to the method of data intr,.• De-
lation, the scattering cross sections, and the assumptions mac, about
the pollutant and the atmosphere. A detailed analysis to inter compare
techniques is very much dependent on the system design, and on the
assumptions made about the atmospheric properties (teirporal, spatial
and spectral). A true comparison will ultimately be mac e only by
simultaneous field tests on a plume with coincident in-siiu measure-
ments of the pollutant. However, when the instrument a:;d atmospheric
parameters are made equal for the most promising systems (DAS,
Raman and Lidar), operating at 4500 A, with a minimum eye safe range
(MSR) of 50 m, which is probably acceptable for operational use, the
calculations show that the Raman system probably does rot have an
acceptable range and accuracy capability during nighttime use, and is
not at all useful for daytime operation. The lidar system and the DAS
system appear to have useful accuracies up to at least 1000 m range
for the integration times permitted by the existing Federal Regulations
(15 seconds for opacity and 15 minutes for gas concentration). The day-
time use of DAS may be limited to smaller ranges at large gas concen-
trations.
115
-------
In the case of passive remote monitors, a different set of re-
quirements must be met. The source radiation is dependent on pol-
lutant and interfering species concentration, as well as gas temperature
for infrared methods, and on the plume and atmospheric particle con-
centration for UV/visible methods. Hence, knowledge about, or a
technique to eliminate, these latter parameters is required in the data
interpretation. The degree of accuracy with which the temperature
and particle effects can be measured/eliminated is directly reflected
in the ability to determine the pollutant concentration. It is found that
instruments which utilize optical correlation and ratio techniques are
better suited than other spectroscopic instruments. However, the
sensitivity of the infrared method is still dependent on the source
strength, i. e., blackbody temperature, so that cool exhaust plumes
near ambient temperatures will be very difficult to observe. The UV/
visible method is considerably hampered by variations in the plume
opacity and atmospheric particle amounts. Active systems are not
constrained by these limitations.
5. 2 EYE SAFETY HAZARDS FROM LASER SYSTEMS
A consideration in evaluating remote sensing laser systems for
air pollution is the potential safety problem. The most obvious hazard
with the laser beam is direct axial viewing, but specular reflections
are also a risk, and considerable care must be exercised in the use of
laser systems. The skin can be burned, by some laser beams, but the
main hazard is damage to the eye. The danger varies with wavelength
of the laser radiation due to the wavelength dependent optical properties
of the eye.
The most sensitive region is the visible region, 400 to 7000 A,
since the cornea, aqueous humor and the lens readily transmit this
radiation. Thus, the full laser beam energy is focused on the retina
in an image 10-20 u,m in diameter resulting in high power densities of
kilowatts/cm2 OR the retina even for milliwatt powers incident on the
pupil of the eye. These high power densities can cause severe damage
to the retina, and the fovea, resulting in loss of visual acuity.
In the UV region, the radiation below about 4000 A is absorbed
by the lens, and below about 3150 1 it is absorbed by the cornea, so
that UV hazards are mostly limited to these parts of the eye. The ra-
diation is absorbed over a larger area than is the focused visible light
116
-------
on the retina, so the power densities are not so high. Exposure to ex-
cessive UV results in inflammation of the cornea and conjunctiva at the
shorter wavelengths, and cataract formation at the longer wavelengths.
In the ER region, up to 1.4 ym, the ocular transmission is less
than that of the visible, and varies with wavelength. From 1. 4 to 1. 9
essentially all radiation is absorbed by the cornea and the aqueous humor
Beyond 1.9 jjim all the radiation is absorbed by the cornea alone. The
absorbed energy can be conducted to the interior of the eye, raising the
temperature of the lens, and resulting in the formation oi cataracts.
5. 2.1 The Maximum Permissible Exposure and Minimum Safety Range
The Department of Health, Education, and Welfare has proposed
(1974) Performance Standards f
-------
reduce its divergence). If the laser beam has a divergence solid angle
O and an energy of p joules, then the radiant exposure (irradiance),
E, at a distance R cm is given by
(5-1)
When E is the MPE, then R is the MSR, i. e.,
When the MSR is computed for the promising laser techniques,
Raman, DAS, Lidar and LDV, it appears that the existing Raman and
lidar systems cannot safely be used operationally in the visible region,
since the beam would present a hazard at great distances. The existing
DAS system is possibly acceptable in the visible, and all systems appear
acceptable ii the near UV and IR. The MSR could be reduced by in-
creasing the laser beam divergence. The present typical system di-
vergence of 0. 3 m rad results in a 0.1 m beam width at 300 m. A larger
divergence of 3 m rad, (1 m at 300 m) would seem still small enough
for use with most stacks.
It is theoretically possible to further reduce the MSR by con-
sidering the basic laser system equation, given by Equation (4-12). From
this equation it is seen that, for a fixed return power, P(R), the trans-
mitted signal, P£, can be reduced by increasing the product L x N(R);
this product is proportional to the optical thickness which is the mea-
sured parameter in the DAS and lidar techniques. This means the mini-
mum detectable concentration is increased, since increasing L does
not help in the case of a stack plume where L> plume width. In addition,
the integration time of the system may be increased, so that n pulses
are integrated rather than the single pulse represented by Equation (4-12).
This enables P{. to be reduced in proportion to n^/2.
5.2. 2 Required Modifications
Sensitivity Change: The minimum detectable optical thickness
should not be increased for the Raman system since it is already quite
high (~ 300 ppm-m for SC>2, see Table 4-5).
118
-------
The DAS sensitivity is about 1 ppm in a plume at r,'50 m range
(see Table 4-3), and could be relaxed to at least 10 ppm ior enforce-
ment monitoring; this would reduce the DAS visible MSR, by a factor
of 3. 2 to 0. 05 km (including the divergence modification).
The accuracy of the present GE lidar system is 2. 5% at 0. 2
opacity, and could reasonably be relaxed to say 10%, giving a reduction
by a factor of 4 in PJ-, resulting in a lidar MSR of about 2. 8 km (in-
cluding the divergence modification).
Integration Time Modification: In evaluating the possibility of
increasing the integration time to decrease the MSR, the Proposed
Performance Specifications of Continuous Monitoring Systems must be
considered. These specifications for opacity monitoring with an in-
stack transmissometer call for a 10 second maximum response time,
although the visual determination of opacity (Method 9) calls for readings
at 15 second intervals. Thus, presumably the integration time for a
lidar system should not exceed 15 seconds. For in-stack monitoring
of SO2 and NOX, a 15 minute maximum response time is required.
Hence, the integration time for the DAS and Raman systems should
not exceed 15 minutes.
The GE lidar system is a single pulse device and is capable of
only 3 pulses per minute, so it can obtain a reading every 20 seconds,
slightly exceeding the 15 seconds suggested above. It is clear that the
integration time of this system cannot be changed.
The DAS integration time is already long (10-30 nin.) so that
within the specifications constraints discussed above, no significant
improvement of MSR is possible, and, in fact, it would worsen for the
system which must reduce its integration time to 15 minutes.
The Raman integration time is typically about 1 n.in., so
lengthening this to the permitted 15 min. allows about a fourfold de-
crease in P{., resulting in a Raman visible MSR of about 1. 0 km (in-
cluding the divergence modification).
5. 2. 3 Final System Parameters
In summary, the present systems might be considered safe for
near UV and IR operational use, but some modifications must be made
for their use in the visible as discussed above. The suggested simple
modifications result in MSR's, for all methods, of 2. 8 kin and less as
shown in Table 5-1.
119
-------
TABLE 5-1. Proposed System Parameters
and Achievable MSR's
Dtvcrccncc p ^S"0" Sensitivity MSR Beam
Diameter
DAS (Visible) 3 x 10~3 ra.J lO^J 15 min. 10 ppm 50 m 15 cm
Raman (Visible) 3 x I0~3 rad 40 x 10"3J 15 min. 30C ppm-m 1000m 300 cm
Lidar 'Visible) 3 x io~3 rad 250x 10"3J 20 sec. 10% accuracy 2800m 540 cm
LDV (IR) 3xlO"3rart 20 W 2 sec. 20% accuracy 150m* 45cm*
* One second exposure
In order to make these systems eye safe at the exit of the trans-
mitter, the beam diameter at the transmitter must be equal to the beam
diameter at the MSR. These values are shown in Table 5-1. The values
for DAS and LDV are not unreasonable for a practical system, but for
the existing Raman and Lidar systems, the beam diameters are im-
practicable.
It is seen that both the MSR and the safe beam diameter of the
Lidar are probably excessive using the present GE approach even with
the proposed modifications. However, it would appear that the DAS
system, which has reasonable values of MSR and safe beam diameter
could be used for opacity measurements since, like the Lidar, it mea-
sures the transmittance of a plume. In terms of system sensitivity,
it does not matter whether gas or particle transmittance is measured.
In fact, due to the four signal measurements required for DAS com-
pared to the two required for the Lidar, the Lidar system is more
accurate for a given transmittance, as shown in Section 5. 3. 4.
It should be noted the MPE is much larger, and hence the MSR
and safe beam diameter are much smaller, in the near UV (< 4000 A)
and in the IR (> 1.4 ^m). Thus, systems should preferably operate in
these regions; they have the additional advantage that the solar radia-
tion background is greatly reduced or is negligible. The use of these
regions appears possible for the detection of gases using Raman (in
the UV) and DAS (in the UV and IR). However, opacity measurements
are traditionally based on observations in the visible, and the Federal
Regulations are based on visible measurements, so that opacity mea-
surements in the UV may not be readily accepted. Lidar opacity
120
-------
measurements below 4000 A could probably be related to conventional
visible measurements on a theoretical or empirical basis for all types
of particles.
5. 3 ERROR ANALYSIS OF ACTIVE SYSTEMS
The errors involved in the various remote sensing techniques
can be estimated by consideration of the equations describing the signal
and noise of the system, although very little error analysis of systems
has appeared in the literature. Of course, the final estimate of the
accuracy of a system will be made in controlled tests in comparison
with in-situ standard methods.
5. 3. 1 DAS Systems
In DAS the laser radiation is transmitted (and received) at the
line center (wavelength 1) and at the wing (wavelength 2). The values
of N(R) and j8 here refer to the Rayleigh and Mie scatters behind the
plume and are assumed constant during the measurements.
may also be assumed constant so that Equation (4-12)
may be rewritten:
InP(R) = In C-2 InR+lnrr(R) (5-3)
where C = ePtLN(R)j3AT^(R) and is assumed to be constant with time
and wavelength. Now
-2 /R(p(R)k +o)dR
TG(R) = e o
where p(R) is the pollutant density at range R and k is the absorp-
tion coefficient of the pollutant, cr is the attenuation coefficient of
particles in the atmosphere or plume, so we have
In
rE
P(R) - In C - 2 In R - 2J (p(R)k + c?)dR (5-4)
121
-------
At range (R + AR)
R+AR
/.
In P (R+AR) = lnC-21n(R H AR) - 2/ (D(R)k+0)dR
J
(5-5)
Differencing (5-4) and (5-5) for wavelengths 1 and 2:
lnP1(R) -InPjfR -i-AR) - 2 In (R * ^ + 2p(R)k1^R+2aJAR
(5-6)
In P2'R) - In P2(R + AR) = 2 In
2 p(R)
(5-7)
where p(R) is the mean pollutant density over the distance AR.
Assuming CTJ = ^j tne difference of (5-6) and (5-7) gives
p(R)AH = -r
-kg)
?r
In ^ /T^x - In
. .
+ "i>y
+AR)
InO
Au W
, /«.
where Q =
/r-n\
(5-8)
In deriving Equation (5-8) it was assumed that the atmospheric
and pollutan; properties are constant while the data are taken at the
two wavelengths. This is true if they are taken simultaneously, but if
it takes more than 1 msec to tune the laser between wavelengths, then
atmospheric scintillation and air motion adds an error term to Equation
(5-8). Schotland (1974) discussed these errors but did not provide an
estimate of their magnitudes. It is clear that simultaneous measurements
at the two wavelengths are preferred.
In Equation (5-8) the absorption coefficients may be uncertain
by as much as ± 20% (Schotland 1974), but this would be merely a sy-
stematic error which could be eliminated by careful calibration. Random
errors in the absorption coefficient can arise by variation of pressure
122
-------
and temperature of the pollutant, and by fluctuations in the laser wave-
length. The other errors in using Equation (5-8) to estimate p(R)AR
occur in the measurement of the received power as a function of range
and wavelength. The received power can possibly be measured to
within 1% (implying a signal-to-noise ratio of 100), but s.nce four power
outputs must be measured in Equation (5-8), Q has an error of 4%, and
when Q is close to unity, then the error in In Q, and hence, in
p(R)AR is large.
This latter conclusion is verified by Inomata and Igarashi (1975),
who have developed a DAS system with simultaneous wavelength oscil-
lation of a dye laser. Two linearly polarized components of a dye laser
cavity were independently tuned and used to measure 85 ppm-m of NO2
in a test cell. The laser power fluctuates by more than iO%, and it was
necessary to monitor the output power at each wavelength. Their results
are shown in Figure 5-1 which shows the standard deviation of a series
of measurements. (V/P)0 and (V/P) correspond to P2(R)/Pi(R) and
P2(R + AR)/Pi(R + AR) respectively, in Equation (5-8). These errors
also include those due to wavelength instabilities of the laser, although
the authors measured them and found them to be negligible.
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-------
The advantage of simultaneous wavelength measurements is
demonstrated by the reduction in the fluctuations in (c) and (f) compared
with (a), (b), (d) and (e). The error in Q [Equation (5-8)] for this set
of data, is only 4% [(c) + (d) errors], but translates strikingly into a
47. 5% error in the measurement of pollutant optical thickness. This
error will be even larger if the SNR is less than the apparent value 100
for each power measurement, as will occur for increasing range.
Of course, for larger optical thicknesses this error is reduced.
For 850 ppra-m, which might be more representative of a plume, and
4% error in Q, the error in the optical thickness is about 25%. For
increasingly larger optical thicknesses, the transmission of the plume
will decrease so that the resulting return signal decreases and the mea-
surement errors increase, and finally cannot be measured due to sy-
system or background noise.
It should be noted that these measurement errors could be re-
duced by averaging more pulses [SNR o: (number of pulses)1/2], but a
long averaging time may not always be practicable, particularly if the
source and atmosphere are fluctuating.
5. 3. 2 Raman Systems
In the Raman-technique, the transmitted laser radiation is shifted
in wavelength when it is scattered by the pollutant, so that in Equation (4-1
we can consider TA.(R) to be the atmospheric attenuation of the out-
going laser beam, and TQ(R) to be the atmospheric attenuation of the
return Raman radiation. If it is assumed that-these atmospheric at-
tenuations are constant then
P(R) = KN(R) (5-9)
where
K = ePtL0AR-2TA(R)rG(R)
124
-------
i. e. , the pollutant number density is directly proportional to the mea-
sured return signal, so that the precision of the pollutant measurement
is the same as that of the power measurement: if SNR = 10, N(R) is
determined within 10%.
There are uncertainties in the value of K due to instrument un-
certainties, due to the value of (3 , which is uncertain by up to 1 20%
(DeLong 1974) and due to the atmospheric attenuation uncertainties. All
of these may be considered as systematic errors, although the atmo-
spheric attenuation may fluctuate during a series of pulses being averaged.
A common method to obtain the pollutant concentration in ambient
air directly, and to minimize the uncertainties, is to ratio the return
signals from the pollutant and from nitrogen, the concentration of which
is assumed known and constant in the atmosphere:
(5
N(R)N2
This method must be used with caution for plumes, since they may be
oxygen enriched, and at varying exit pressures and temperatures. If
the Raman returns of the pollutant and nitrogen are close together so
that atmospheric scattering losses can be assumed the same, and do
not exhibit different atmospheric absorption losses, then the only random
uncertainties in obtaining the pollutant concentration occur in the power
measurements, and may be reduced by pulse averaging without concern
for atmospheric fluctuations. If SNR = 10, then the pollutant concen-
tration error is 20% since two power measurements are needed.
An error source in Raman scattering, not described in the above
equations, is that due to overlapping of Raman spectra of different species
contained in a pollutant source. The Raman system measures the Q-
branch of the vibrational -rotational Raman spectrum, but, as shown in
Figure 5-2, the S- and O-branches of strongly scattering, high concen-
tration species may overlap and mask the weaker Q -branch of another
species. To retain specificity, narrow band interference filters with
high rejection ratios must be used.
Typical Raman signals are small and the SNR is low so that
nighttime operation provides greater sensitivity and range. Daytime
125
-------
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J = DRj T^) (5-11)
and the signal from behind the plume is given by
P(Ra) = P R2-2 TA(R2) rp2 (5-12)
where
D = ePtLN(R)j3A
Hence
1/2
T
P
2
(5-13)
Since Rj is not greatly different from R£, it may be assumed that
TA(RI) and TA(R2) are equal. Hence, the error in Tp is determined
by the errors in measuring the powers. Since the square root of the
power ratio is involved, the percentage error in Tp is the same as in
the power measurement, i. e., if SNR = 100, then me uncertainty in
Tp is 1%. It must be noted that the error in opacity is greater than
that in Tp, especially for low opacities. For example, a 1% error in
Tp results in 4% and 9% opacity errors when the opacity ,s 0. 2 and 0.1
respectively.
The assumption of the backscatter being the same on both sides
of the plume may not be a good one, particularly in an industrial atmo-
sphere where measurements would be made. This error is difficult to
estimate, but could be eliminated by using the Raman scacter of nitrogen
as the scattering source, but of course, the SNR would decrease and
maybe result in uncertainties larger than those eliminated.
Another error source in this lidar technique is that of thermal
lensing (Cook et al 1972) by the hot plume gases, which causes some
127
-------
of the radiation from behind the plume to refract in and out of the re-
ceiver field-of-view, and hence causes the return signal to fluctuate;
the magnitude of this effect is uncertain. This thermal lensing effect
(which is similar to scintillation) does not affect the DAS technique if
simultaneous measurements at two wavelengths are made.
5. 3. 4 Inter comparison of Laser Techniques
A comparison of the promising laser techniques has been made
on the basis of the error considerations discussed above. Let us con-
sider the signal-to-noise relationship (Equation 4-16b):
1/2
SNR = * P
-------
Figure 5-2. System Parameters
X
AX
L
•i :
o
< =
pt
t)
n «
B
4500 1
51
10 m
10" sec (> pulse width)
500 cm2
10"5sr
0.1
10 J (based on DAS MPE eye safety
requirements)
0.2
900 pulses (based on 1 pps and 15 minute
Integration time permitted by
Federal Regulations for gas
measurements)
lO'VcuT'sr'1!'1
Using these values:
P(R) = 1.14 x!015N(R)jS-4 Tp photons (R in m) (5-16)
R
PB = 5.66 x 102 photons (5-17)
and
SNR = 13.4 7 P(R) Vf7y during the day (5-18)
1?
SNR = 13.4 (p(R))1/2 during the night (5-19)
129
-------
The values of N(R) and 0 assumed for this comparison are
given in Table 5-3.
Table 5-3. Backscatter Parameters
DAS and Lidar
Raman
Raleigh
Mie
10
-27
10"
N(R){cm-
10
19
10
-8
10*
10
ID'28
1015 (100 ppm)
-6
10
-13
The Mie parameters, given here for a clear day (25 km visibility), will,
of course, vary with the particle type and size distribution and with the
visibility. The Raman parameters vary with the gas and with the con-
centration. All of the values of 3 depend on wavelength.
Thes9 values of SN(R) are consistent with independent estimates
by Collis and Uthe (1972) for Rayleigh scattering:
N(R) =
where CTR is the Rayleigh attenuation coefficient (cm-1) and by Measures
and Pilon (1972) for Mie scattering:
N(R) = 4 x 10"2 a
M
where Oj^ is the Mie attenuation coefficient (cm~^). The value of
TA(R) is based on the model atmosphere (Elterman 1968) (25 km visi-
bility), and ranges from 1. 0 at 10 m to . 12 at 5000 m for the 2-way
transmission. The parameter TQ does not appear in the Raman equa-
tion, and in the lidar equation it represents the 2-way particulate trans-
mittance of the plume. In the DAS equation 21ntQ is used, so that
the difference in the absorption coefficient on and off an absorption line,
is used directly. We have assumed that kj = 16 (atm-cm) and
130
-------
k2 = 8 (atm-cm)~l based on the work of Grant et al (1974) in using DAS
for NO2 measurements. Thus, the effective value of TQ for 100 ppm
with aim stack exit diameter is given by
= .92
for passage once through plume. This same transmittance for particles
in the lidar system represents an opacity of 0. 08.
Using the above values of the systems parameters, and Equations
(5-18) and (5-19), calculations were made of the SNR of the backscattered
signal for DAS, Raman and lidar, both day and night, for 100 ppm of the
gas in a 1 m exit diameter (or 0. 08 opacity). It is assumed in these cal-
culations that the transmitter and receiver fields-of-view completely
overlap at all ranges, and that the effective backscattering cross-sec-
tions and system efficiency are constant at all ranges.
Figure 5-3 shows the results for DAS and lidar at a single wave-
length. These values are computed for the backscatterec signal in front
of the plume, and are the same for each DAS wavelength. The SNR is
slightly smaller from behind the plume and different for oach DAS wave-
length. The SNR for the Raman system is not shown in Figure 5-3 since
the values are very low: SNR = 13. 4 at 10 m and 1. 31 at 100 m during
the night, and SNR < 1 during the day.
In order to compute the concentration (opacity) measurement
errors, the SNR values were used in conjunction with the data analysis
procedures developed in Section 5. 3. It is assumed that SNR = 100
represents 1% signal error, SNR = 40 represents 2. 5% signal error,
etc. These error estimates must be considered as optimistic since
(a) the value of N(R)/3 is likely to vary during the measurement period,
(b) the value of N(R)8 may not be the same on each side of the plume,
(c) signal processing errors are not considered, (d) laser wavelength
and intensity fluctuations are not considered, (e) thermal lensing
effects by the plume are not considered, and (f) spectral interference
effects of other species are not considered. There is also a systematic
error due to lack of precise knowledge of the absorption coefficient and
its variation with temperature, but this can be eliminated by careful
laboratory and field calibration.
131
-------
alfW
toy.
Figure 5-3.
SNR calculations for DAS and Lidar
(900 pulses at one wavelength) for a
1 m plume (100 ppm) at range R
The calculated measurement errors, shown in Figure 5-4,
indicate that DAS and lidar are probably useful (20% error) out to 1 to
3 km, but that Raman docs not have a useful range capability. It should
be noted that the lidar system, to comply with the present Federal
Regulations for opacity/, cannot use a 15 minute integration time, but
must use 15 seconds. Figure 5-4 is strictly for intercomparison of
the techniques and does not represent optimized systems, although it
does indicate that a Raman system designed for eye safe operation in
the visible does not have a useful range capability. Figure 5-5 shows
the effect on the lidar accuracy of reducing the integration time to 15
seconds and indicates a.useful (20% error) range of 650 m during the
day and 840 m at night. The calculations shown in Figures 5-4 and 5-5
are for 100 ppm in a 1 m stack exit diameter, and for 0. 08 opacity in
the case of lidar. The 100 ppm-m of gas is probably a lower limit of
interest in enforcement monitoring. For opacity, 0. 08 is less than
the 0.10 and 0. 20 limits prescribed for most sources in the Federal
Regulations; presumably enforcement personnel will be most concerned
with monitoring larger opacities which are exceeding the limits.
132
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i! t j. Raman 100 ppm
tth: LidJ.r 0. 08 opacity
1000
10000
Range ,(m)
Figure 5-4. Inter comparison of measurement errors for plume
at various ranges. These results are not optimized
for each system, but are strictly for intercom-
parison of techniques.
0.8 Opacity
Integration 15 sec 15 mln
Tlmc: Day Night Day Night
10000
Range (m)
Figure 5-5. Lidar errors as a function of integration time
133
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As the gas concentration in a stack plume increases, so the
Raman return signal will increase, and the errors will decrease.
However, for DAS and lidar, the transmittance of the plume decreases
with iraei-eastog. gas (particle) amounts, and the errors will decrease at
first, and then increase. The signal-to-noise of the measurement
behind the plume, of course, decreases continuously with increasing
gas (particle) amounts, but this decrease is initially outweighed by
the increase in the values of Q and opacity, so that initially the per-
centage errors in concentration (opacity) decrease. However, at
larger amounts the- signal-to-noise decrease outweighs the increase in
Q and opacity, and the errors increase again.
Figure 5-6 shows the increasing range capability of the Raman
technique with increasing, gas concentration. However, even at very
high cmncentrati«5H& (10rOQQ ppm) the system does not have a,useful
daytime range capability. Figure 5-7 shows the variation of lidar errors
with increasing opacity mp to an opacity of 0. 8. It is seen that 0. 8 opa-
city is not large enough to increase the errors during nighttime operation,
but during the day the errors start to increase between 0.4 and 0. 8 opa-
city values. Figure 5-8 shows that at nighttime the DAS errors decrease
eo
10000 100 100C
ppm ppm ppro
Day Night Night
10000
ppm
Night
ts*
'* 40
100
Range(m)
1000
Figure 5-6. Raman errors as a function of gas concentration
134
-------
80
Curve Opacity
108 Day
. 08 Night
10
10000
Figure 5-7. Lidar errors as a function of opacity
so
60
fii1' .;:„ j;,.'; • | .! •--^^:-
^' ' '
Jffiii
s
nta
-HH
20
Dl - 100 ppm-m Day
Ml - 100 ppm-m Wight
D2 = 1000 ppm-m Day jl'!!,'-!
N2 « 1000 ppm-m Night Pli.fj:
D3 » 2500 ppm-m Day ^\"\'\l'
N3 » 2500 ppm-m Night j| ]•'/! |
r-rl
10
100
Range (m)
1000
10000
Figure 5-8. DAS errors as a function of gas optical thickness
135
-------
up to 1000 ppm-m, but increase between 1000 and 2500 ppm-m. During
the day the errors decrease slightly going from 100 ppm-m to 1000
ppm-m; however, increasing the gas optical thickness to 2500 ppm-m,
dramatically increases the errors and greatly reduces the daytime range
capability of this DAS system.
5. 4 ERROR ANALYSIS OF PASSIVF INFRARED SYSTEMS
In the following, results of calculations are presented which show
that the influence of source and atmospheric parameters is significant
in the data interpretation of passive systems. Because of the importance
of the pollutant SO2, the calculations were made for this species. Since
SO2 has several infrared bands, some calculations were made for more
than one band in order to show that the proper selection of the infrared
spectral region is important, and also that the device is dependent upon
many competing parameters and requirements.
5.4.1 Source Strength
In order to assess the plume radiation and the required noise-
equivalent-radiance, the radiated energy of SO2 in the 4 jrni spectral
region was calculated in a line-by-line model. The line parameters
(position, shape, strength and lower energy level) were developed pre-
viously (Ludwig et al. 1974). The results are shown in Figure 5-9 in whicl
a normalized filter function with a bandwidth of 60 cm"* at half-height was
used (2465-2525 cm'1).
The influence of other species in the plume and of the atmo-
sphere between the observer and the plume and beyond was found to
be negligible. (For a pathlength of 130 m between observer and plume,
the atmospheric absorption transmission is 0. 998 for 50% relative
humidity, 0, 3 ppm N2O, 320 ppm CO2, 1. 4 ppm CELj, and 0. 01 ppm
SO2. The radiance of the clear sky was calculated to be less than 2
percent than that of the plume having 500 ppm-m SO2 at 650°K).
From the results shown in Figure 5-9, it is clearly seen that
the emitted radiance is a sensitive function of the plume temperature.
(An uncertainty of + 10% in temperature at 500°K results in an uncer-
tainty of over + 100% in SO2 concentration). Thus,, in order to determine
136
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Figure 5-9. Emitted radiance as a function of SO2 optical thickness
the SO2 concentration in the plume, a method must be found to either
eliminate the temperature dependency or to determine the plume tem-
perature accurately by an independent measurement. (One such method
is the SAI-GFC analyzer that was described in Section 4. 4. 3 and whose
field test results indicated an uncertainty of about + 25% in the deter-
mination of SO2 concentration.)
For the case of perimter monitoring in the up-looking mode,
which was schematically shown in Figure 2-1 , line-by-hne calculations
were made for measuring SO2 at 4 jim and 8. 6 ym. The results for
the received radiance at 4 urn as a function of SC>2 loadin,; (ppm-m) are
shown in Figure 5-10 with a given filter function. The atmosphere has
no significant influence in this spectral region and different amounts
of water vapor would not give significantly different radiance values.
However, the influence of the atmospheric temperature is significant,
as shown in Figure 5-11, where the mean atmospheric temperature
was varied between 270 and 300°K. It is easily seen that a pure radio-
meter measurement would not be very sensitive to the SO2 vertical
loading, but much more to the atmospheric temperature.
137
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100
ppm-m
1000
Figure 5-10, Radiance versus SO« vertical loading in 4 iim band
Figure 5-11, Radiance as a function of SQ2 vertical loading in the
4 ym band for three different average atmospheric
temperatures
138
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This situation is reversed for the 8. 6 ym region, where SC>2 has
a fundamental band. Here, the influence of the mean atmospheric tem-
perature is somewhat reduced, as shown in the comparison between the
Figures 5-11 and 5-12, even though an accurate radiometer measure-
ment of the SC>2 vertical loading remains impossible. The influence
of three different water vapor concentrations (0. 5, 1. 0 and 1. 5 normal
Gutnick corresponding to about 30, 60 and 90 percent relative humidity)
on the effect of the observed radiance is shown in Figure 5-13.
5.4. 2 The Measurements of Signal Differences:
The influence of the atmospheric temperature and the water
vapor can be reduced by using the signal differencing method, as is
being done in the gas filter correlation instruments. In this case, the
instrument measures the difference of the incoming energy as it passes
through the gas channel, containing SO2, and the reference channel,
containing N2-
ppm-m
" Idoo
Figure 5-12. Radiance versus vertical SC>2 loading in the 8. 6
region for three different mean atmospheric temperatures
139
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3 4 J « 7 8 » !
1 > 5 « 7 8 1 !
1 4 JtTIII-
2 J 4 S t ' C 1000 2 J « 5 * ' « 10000
101'
•10
Figure 5-13. Radiance versus vertical SOg loading in the 8. 6
band for three different water concentrations
We have calculated the correlation term AV for several atmo-
spheric conditions with different SO2 vertical loadings in the two infra-
red rotation-vibration bands at 4 nm and 8, 6 ^m. The 4 jim band is
essentially free of interfering species, whereas the 8. 6 um band has
many interfering water vapor lines. It is apparent from the following
analysis that although the signal in the 8. 6 &m is stronger, its uncer-
tainty, due to water vapor interference, is significantly greater than
in the 4 fim band. The GFC signal in the 4 y,m band for SO2 amounts
from 10 ppir-m to 5000 ppm-m for the effective atmospheric tempera-
tures of 275; 286 and 3001C is shown in Figure 5-14.
The ~esults show that the AV signal is a strong function of
the SO2 concentration, but that its dependence on the atmospheric tem-
perature is relatively small; an uncertainty in temperature of + 2°K
results in an uncertainty of only about ± 10 ppm-m at 100 ppm-m. The
influence of the normal atmosphere was also considered. It was found
140
-------
10
-8 t
Figure 5-14. GFC signal as a function of SO2 loading at 4 ym
for three temperatures
that about 1000 very weak lines of N22, 53 lines of
CH4 and the water vapor continuum contribute in this spectral interval.
The influence of these species was found to be negligible. The effect
of clouds in the field-of-view was also investigated. It was found that
stratus clouds decrease the AV signal. High clouds will, of course,
have less influence.
The results of the calculations as a function of the vertical
loading of SO2 at 8. 6 ^m are shown in Figure 5-15. The results show
that the AV signal is stronger than in the case for the 4 y,m due to the
higher radiance values in the blackbody function and the somewhat
larger band strength. Because the slope of the Planck function is much
less in this spectral region than in the 4 ym region, the error due to
+ 2°C in atmospheric temperature is only i 2 ppm-m at 100 ppm-m.
However, the influence of the other atmospheric species, especially that
of water vapor, is considerably greater than in the 4 ym region. There
141
-------
10
10
io;ooo
Figure 5-15. GFC signal as a function of SC>2 loading at 8. 6
for three temperatures without^ interfering atmosphere
are 262 lines of CO2, 2518 lines of 03, 1078 lines of N2O, 89 lines of
CH4 and 497 lines of water vapor plus its continuum radiation in this
spectral region. A change in concentration of any of these species will
influence the determination of SO2 vertical loading;.
The influence of water vapor variation was investigated in
greater detail. The effect manifests itself both in terms of a "cor-
relation sigr-al" (water lines on SC>2 lines) as well as an "uncorrelated
emission signal". Representative results are shown in Figure 5-16
for the AV signal as a function of SC>2 loading at three different water
vapor concentrations. The water vapor concentrations chosen cor-
respond to the 0. 5, 1. 0 and 1. 5 normal Gutnick distribution. They
correspond to about 30%, 60% and 90% relative humidity at 286° K.
142
-------
io
Figure 5-16. GFC signal as a function of SC>2 loading for three
water vapor concentration (8. 6
If the water vapor profile were known, it would be possible to
correct the AV signal for the interference. However, it can be shown
that a single measurement of the relative humidity near the surface is
not representative of the total water vapor content in the atmosphere.
A single surface measurement can result in great errors and the un-
certainty is estimated as much as + 50% in total H2O loading in the
atmosphere, which results in an uncertainty of almost 100% in SO2
vertical loading at 100 ppm-m (see Figure 5-16). This error becomes
somewhat smaller at higher levels of SOj loading, but is significantly
larger at lower levels. In order to reduce these errors, it would be
necessary to include additional channels into the instrument which
would permit a better estimate of the water vapor content. However,
one single measurement, giving the total amount in precipitable centi-
meters would not be sufficient, since the radiance signal is both a
function of the water vapor vertical distribution and the atmospheric
temperature profile.
143
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5. 4. 3 Perimeter Monitoring Data Analysis (Infrared)
The radiative transfer equation shows that the downwelling
radiance depends on the atmospheric temperature profile and on the
vertical distribution of the pollutant and other species. However, in
perimeter monitoring the pollutant is confined to the lowest layers
of the atmosphere, probably below 500 m. Since the temperature lapse
rate is typically about 6°C km"*, the mean temperature of the 500 m
layer is only 1. 5°C different from the values at the top and bottom.
Hence, assuming the pollutant temperature has equilibrated with that of
the atmosphere, the radiance from the layer may be approximated
closely by a single slab model, i. e.,
Rx = N(X,T) (1 - TX)
Of course, the lapse rate will vary with the meteorological conditions,
but it is believed that the mean temperature of the 500 m layer can be
estimated within i 2*C by measuring the surface temperature, and by
knowing the typical diurnal meteorological variations for the location.,
Of course, a measured temperature at altitude may be available by
other means, such as a radiosonde, a tower or tethered balloon, in
which case the mean layer temperature would be known more accurately.
In using the perimeter monitoring technique, the pollutant may
be dispersed uniformly (or non-uniformly) through the lowest layers, or
it may be confined to a relatively thin layer, depending on the meteoro-
logical conditions and the distance from the source. These variations
of distribution mean that the pollutant mean temperature and pressure
varies, so that the GFC signal is expected to vary. However, since
the vertical variation of temperature and pressure is small within the
anticipated vertical extent of the pollutant, the effect of the pollutant
vertical distribution is small.
In our computer simulations for the GFC instrument, we found that
the single slab model AV signal at 8. 6 ium, in the range 100 ppm-m to
10, 000 ppm-m SO2, varies from the model using a profile by less than 1%,
and that the maximum effect of the variations in the SO2 vertical distributio
is an additional 1%. These uncertainties are small compared with the un- '
certainties in the 8. 6 urn water vapor effects. These single slab effects ar
approximately twice as great in the 4 Mm SO2 band due to the greater changi
of blackbody radiance with temperature, so that at 4 urn. there is a 4% un-
certainty in addition to the approximately +1G% uncertainty due to the 12° C
temperature uncertainty.
144
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6
ADVANTAGES AND DISADVANTAGES OF
REMOTE MONITORING TECHNIQUE3
6.1 OVERVIEW
In this section we summarize the advantages and limitations of
remote monitoring techniques in air enforcement and regulatory pro-
grams.
In general, one of the advantages of "remote sensing" from
elevated platforms, namely the coverage of large areas, has been re-
cognized for some time since the advent of Landsat 1 (previously known
as ERTS 1). Many interesting features of land and water areas could
be recognized, which would otherwise have remained undetected. Some
Landsat programs were even concerned with measurements of air pol-
lution (Griggs 1974), and others provided evidence in legal cases. For
example, spectral data taken by the Multi-Spectral-Scanner (MSS) on
board the spacecraft were used to determine that a major city water
intake pipe had been placed directly into a large pool of pollutants in
Lake Superior. The image was used in a court suit by the city against
a firm that was paid about $8 million, before the Landsat program, to
position the intake pipe in a clean water area. The suit was settled
out of court, according to the NASA official (AWST 1975), In the
same article it was stated that Landsat 1 has been used Li cases
involving the violation of pollution laws. In addition, the spacecraft
has been actively involved in enforcing water impoundment laws
governing the safety of damming facilities at about 50, 000 sites.
Inadequate damming was involved in at least one major fiital accident
in recent years involving the water containment areas now under
Landsat observation.
145
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Besides the advantage of,wide area coverage from elevated plat-
forms, there are several other advantages of either stationary or
mobile ground-based as well as airborne remote monitors, which can
be realized in enforcement and regulatory programs. These include
cost effectiveness, unannounced and non-interfering monitoring of
stack emissions, rapid response in air pollution episodes and objective-
ness in opacity observations. This latter advantage was pointed out al-
ready in Section 3. 2. Although visual observations by trained observers
are less cos:ly than the remote Lidar technique, the courts have begun
to put less weight on such "subjective evidence", especially at the lower
opacity range ( ^ 10%). Thus, the application of the Lidar technique is
not so much based upon reasons of economy, but more upon reasons of
producing "sufficient evidence".
There are, of course, certain disadvantages to remote monitoring,
which include the greater initial capital outlay of the instruments, the
effect of atmospheric interference on the measurements, the increased
requirements in calibration procedures of the instruments, and lastly,
the possible eye safety hazard of the more powerful lasers operating in
the visible soectrum.
In balance, however, we found that the advantage outweigh the
disadvantages.
6. 2 COST EFFECTIVENESS
We have attempted to estimate the costs involved in remote
monitoring and to compare them with present in-stack costs. We have
chosen the monitoring of 100 stacks as a basis. Basicially, there are
three types of costs: research and development, purchase price of the
operational field instrument, and operating costs, which include the
man hours needed for maintenance, calibration and operation. Ob-
viously, our estimates for the remote monitors must be regarded as
very tentative, since reliable cost data are not even available for in-
stack monitors which have been in use for several years. In the pro-
posed rules lor Emission Monitoring Requirements and Performance
Testing Methods (1974), it was stated that the costs associated with
continuous monitoring are difficult to assess due to limited industrial
monitoring experience. However, some cost data were given which
we have used in our cost estimates.
146
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The cost estimates given in the following are based on evi-
dentiary monitoring for case development. It is obvious that sur-
veillance monitoring requires less effort, and that greater effort is
required for evidentiary monitoring. This is true for both point
sampling as well as remote monitoring. In fact, the development
of portable in-stack monitors will make it possible to spend relatively
short time for surveillance, and possibly even for enforcement at the
stack(s) in question (Nader 1975). Nevertheless, indications are that
significantly more time will be required for case development because
of the number of samples and the extent of documentation needed. In
any case, our studies show that more time will be needed using the
in-situ and extractive sampling techniques than the remote ones.
6. 2.1 Opacity
In this case, we consider as the present methods, both the visual
observations of trained observers and the in-stack monitoring by trans-
missometers. An overview is given in Table 6-1. For the visual ob-
servations, we have assumed that approximately one-halt day is used
for observing each stack and one-half day to record and analyze the data.
For 100 stacks this amounts to about 0.4 man year. The initial cost of
$1K is assumed to be needed for the smoke school.
TABLE 6-1. Initial and Operational Costs for
Monitoring the Opacity of 100 Stacks
Man Years
Monitoring Mode
Present (visual)
Present (in-stack)
Initial Cost
1 K
5-10 K
Per 100 Stacks Remarks
0. 4 Initial Cost: Smoke School
2.5
Remote Monitor 20-80 K 0.4
147
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The cost figures are drastically different for in-stack transmis-
someters. New stationary sources are required to have continuous
monitors, installed and the results have to be reported to the appropriate
agencies Thus, it is difficult to assign any additional cost figures,
because the analysis of the company reports demand an uncertain
amount of man hours. However, if a state agency is compelled to
conduct in-siack monitoring for evidentiary purposes, the cost for
100 stacks increases significantly. The cost of an in-situ transmis-
someter is estimated to 5-10 K, and the additional effort to monitor
is estimated to be about 5 man days per stack (Smith 1974). Thus, for
100 stacks, 4000 man hours or about 2. 0 man years will be needed. In
contrast, the remote Lidar instrument is estimated to be in the price
range from about $20 K to $80 K, which is several times higher than
the in-stack instrumentation. However, the operational costs are lower,
and are judged to be the same as for the visual observations.
The estimate of the cost for enforcement monitoring with a tele-
photometer shows a low initial purchase price, but comparable opera-
tional costs.
The cost estimates for aerial surveillance from aircraft are
relatively low because of the large area coverage, assuming automatic
data analysis. Of course, the cost of operating the aircraft must be
added.
6. 2.2 Gas Concentration
An overview for gas instrumentation to measure gases is given
in Table 6-2. The present monitoring is conducted by analyzing the
company reports, required for new stationary sources. If in-stack
monitoring is required, for case development, the reference method
costs about SI. 5 K, and takes about 10 man days to collect the data.
Thus, for UDO stacks, 8000 man hours or 4 man years would be required.
However, if portable in-stack monitors were to be used, the operational
time would probably be reduced.
As in the case for opacity monitoring, the initial price of the
remote sensors is higher than the in-stack monitor, but the operational
costs are considerably less. We have assumed that the operational
laser systems will be about $20-$80 K; the passive instruments are
less expensive and will be in the range from about $10-$40 K. The
operational costs are assumed to be similar to the ones used for the
remote opacity measurements.
148
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TABLE 6-2. Initial and Operational Costs for
Monitoring Gases in 100 Stacks
Man Years
Monitoring Mode
Present (in-stack)
Active Remote Sensor
Passive Remote Sensor
Initial Cost
1. 5K
20-80 K
10-40 K
Per 100 Slacks
8.0
0.4
0.4
Remarks
Limited in concentration and
temperature range
* Velocimeter (50 K) needed tor mass flow.
The price for other spectroscopic instruments such as multi-
spectral photometers, interferometer-spectrometers, and monochrom-
ators can vary widely, depending on the complexity.
6. 3 OBJECTIVITY IN OPACITY MEASUREMENTS
The main passive technique used at the present time is tint of
the trained visual observer. The observers are trained at EPA smoke
schools, using controlled smokestacks, to make the measurements
according to Reference Method 9, taking into account the prevr. Jing
in illumination. For these reasons, several states have introduced
legislation that require the plant operators to install "reliable" and
continuous monitors into the stacks, and to provide a permanent recoru
for the preparation of periodic reports.
The same arguments apply to the remote lidar instruments and
opacity readings based on lidar measurements will be more acceptable
in litigations.
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6.4 UNANNOUNCED AND NON-INTERFERING MONITORING
The requirements to install continuous monitors in new stacks
keeping the records and making them available to enforcement personnel
does not appear to alleviate the need for "unannounced" enforcement
monitoring, including night observations. The remote techniques dis-
cussed in this report are the possible tools for this kind of monitoring.
The legal justification for their use was given by the Supreme Court
Decision in the case of Colo. Air Poll. Variance Board vs. Western
Alfalfa Corp, (see Section 3. 1).
In addition, remote techniques do not interfere with the normal
operation of the plant, by the requirement of installing temporary in-
stack monitors by the enforcement personnel.
6. r, SURVEY OF WIDE GEOGRAPHICAL AREAS
Surveys of wide geographical areas are required for the design
of contact monitoring networks, assessment of site selection and in the
evaluation of environmental degradation,
FOP the design of contact monitoring networks are based upon
extensive measurements of "dispersion meteorology" data. The term
"dispersion meteorology" used here refers to the air mass transport,
speed and wind direction, frequency distribution, and to the vertical
dimension available for dilution of contaminants. In addition, stream-
flow or streamline maps are useful in understanding how the air moves
from one area to another, and is influenced by the topography. The
complexity ia the streamline flow patterns is reflected in the conver-
gence and divergence of the streamlines and in the deflection by ele-
vated terrains. As a general rule, experience has shown that complex
flow patterns have more turbulent mixing associated with them than
do less complex flow patterns.
Based on these results the location of contact monitoring for
area sources should be concentrated in areas of convergence. In areas
where similar data are not available, remote monitors will be of great
assistance in setting up contact networks.
150
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Also the knowledge of point sources in relationship to the "dis-
persion meteorology" will influence the location of a contact monitor
network. The assessment of the impact to be encountered on the site
selection of a new industrial/power plant involves a great number of
aspects. Beside the aspects of the water and land requirements, the
most difficult ones are the requirements for minimum impact on air
quality. This involves a preliminary analysis of available meteorological
and background air quality data; plume simulation utilizing aerial smoke
techniques under a variety of adverse pollution weather conditions; in-
stallation of a meteorological and background air quality monitoring
system to obtain routinely ambient data and using tracer systems. The
releases of tracers are made in various combinations of cime periods
depending upon the prevailing weather conditions. To follow the trace
gases, an extensive sampling network must be established of radial
lines and concentric arcs in the downwind sector on ground level and
elevated terrain consisting of numerous individual bag samples and
sequential samplers. It is obvious that remote monitors mounted in
vans/aircraft would be of great assistance in these programs.
6. 6 RAPID RESPONSE IN POLLUTION EPISODES
The mobility and near real-time analysis of remcte sensed data
make it possible to monitor the sources and ambient air in pollution
episodes, where it is vital to determine early, whether or not the
emergency measures are effective.
For example, many local Air Pollution Control Districts have
defined alert stages. The ones given in the Los Angeles APCD have
been listed in Table 3-5. When any one of these alert stages is readied,
the LAAPCD prescribes certain actions that are to be undertaken to
prevent further increase of pollutant levels and to effect a decrease in
the pollutant levels. The public at large is to be informed about the
alert stages by public announcements, and through announcements of
the L. A. County Sheriff to its sub-stations, all city police departments
and California Highway Patrol as well as local public safety personnel,
air polluting industrial plants and processes which require "alert" data
in order to effect pre-arranged plans, are designed to reduce the output
of air contaminants.
151
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In the LAAPCD, the pollution levels are monitored by twelve
(12) widely separated local sampling stations (see Figure 6-1). In
addition, inspectors in radio-equipped cars are utilized to spot "ex-
cessive visible" emissions and odors. However, they are not equipped
to measure the ambient air in real time, and cannot determine, the
air pollution levels in alert episodes, when it is of vital importance.
Again, remote sensors mounted either in vans or on airborne plat-
forms would fulfill this aspect of monitoring tasks.
.A
r-
\
'"•"i-.r-vJ"
._j
81
Figure 6-1. Los Angeles County Air Pollution Control
District Air Monitoring Network
152
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6. 7 LIMITATION UNDER CERTAIN ATMOSPHERIC CONDITIONS
Remotely sensed data are influenced by the intervening atmo-
sphere, and extreme conditions such as fog and rain will limit the use-
fulness of those data. Although in many cases the direct influence is
accounted for (for example, by using multiple wavelength detection), the
transmission is, in general, reduced, thus reducing the signal levels.
In the limit of opaque atmospheres, no signals from the remote source
are obtained while extractive and in-situ samples continue to function.
6. 8 INCREASED REQUIREMENTS IN CALIBRATION
As pointed out in Section 3.5 the application of remote tech-
niques to evidentiary monitoring adds certain requirements which, in
turn, demand calibration procedures that are not required for in-situ
or extractive instruments. These additional requirements were listed
in Section 3. 5. 2.
6.9 SAFETY HAZARD
The potential health hazard for eye safety has been discussed in
Section 5. 2. It was pointed out that the most obvious hazard with the
laser beam is direct axial viewing, but specular reflections are also a
risk, and considerable care must be exercised in the use of laser systems.
The most sensitive region is the visible region, since the cornea,
aqueous humor and the lens readily transmit this radiation. Thus, the
full laser beam energy is focused on the retina in an image 10-20 (Ltm
in diameter resulting in high power densities of kilowatts/cm^ on the
retina even for milliwatt powers incident on the pupil of the eye.
In the spectral regions outside the visible one, the dangers are
reduced since the radiation is absorbed by the lens, cornea, and/or
aqueous humor. However, inflammation of the cornea and conjunctive
can result and cataracts may be formed.
153
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Thus, performance standards for laser products have already
been proposed to minimize these hazards. Any operational laser system
utilized in remote monitoring must conform to these standards. Clearly,
care will have to be taken in pointing the laser beam at the stack plume,
or vertically up for area monitoring. The beam could inadvertently be
directed intc an office window, at people on or in a building beyond the
plume, or at people in an overflying aircraft. Presumably safety locks
would be necessary to prevent the beam from being pointed in the hori-
zontal direction.
The analysis made in Section 5. 2 showed that the Minimum Safe
Range and safe beam diameter for existing laser systems vary widely.
While the present laser systems used in the differential absorption by
scattering method, in the visible, and the laser Doppler velocimeter
method, in the infrared, appear safe, with certain slight modifications,
the existing Raman and Lidar systems do not appear safe for operational
use in the visible regions.
154
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CONCLUSIONS AND RECOMMENDATIONS
7. 1 GENERAL CONCLUSIONS
Based upon the material presented in the body of this report,
the following conclusions are drawn:
Certain remote monitoring techniques can be successfully
applied to
• Enforcement Monitoring
• Research and Development of Regulations
• Ambient Air Trends
and that the advantages outweigh the possible disadvantages.
From the 36 air pollutants that were listed as important to ex-
pend research and development resources (see Table 7-1), 17 are judged
to be amenable to remote monitoring in the immediate/near term and
long term.
In addition to the species listed in Table 7-1, many newly
identified pollutants of interest can probably be monitored by remote
techniques, after their spectral characteristics are identified.
The results of the present survey of the published literature
on remote instruments/techniques are summarized in Tables 7-2 and
7-3 for the active and passive systems, respectively. In these tables,
only the generic terms of the techniques and/or instruments are given
and no specific instruments by manufacturer or model are identified.
The column entitled "Development Status" distinguishes between "field
tested", "under development", "lab study" and "theoretical"; "field
155
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TABLE 7-1. Pollutant Amenable to Remote Monitoring
IMMEDIATE/NEAR TERM _ LONG TERM __
Particles (Op.icity)*
SO,* Heavy HC
NC0* Oxides of Sulfur
CC» Certain Specific Elements
Light HC Chlorinated HC
HF*
HC1
NH3
N0"
HNO,
0
°3
Viryl chloride
N2
co2
* Standards of Performance for Now Stationary Sources
Proposed 01 I'i omulgated
** Species used for determining excess air flow
tested" qualifies an instrument to be ready immediately for field use
in "Case Development" and/or "Surveillance", if not otherwise noted
in the "Remarks ' column. This last column contains also the section
or table number(s) where more details are given.
In general, we believe that the active systems appear to have
a larger applicability in terms of range in plume temperature and
pollutant concentrations. This is because measurements made with
passive systems are more influenced by source and background para-
meters than the active systems. The measurements made by infrared
passive systems are particularly dependent upon the plume tempera-
ture. Thus, either multiwavelength and/or ratio techniques are re-
quired to minimize the temperature dependence. In addition, relatively
cool plumes will have lower signal strength. Thus, pollutant measure-
ments in these cool plumes will be more difficult to achieve with
passive systems. On the other hand, passive systems tend to be less
expensive than active systems, and appear therefore more attractive
for the application of surveillance monitoring, where the data are
not used in case development. The laser systems that are most
156
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TABLE 7-2. Active Systems
Technique/ Spectral
Instrument Region
Differential Vls/UV
Absorption
IR
Lidar Vis
Laser Doppler IR
Velocimeter
Long-Path Vis/UV
/IR
Raman Vls/UV
Resonance Vis/UV
Raman
Fluorescence Vls/UV
Fabry -Perot Vls/UV
Raman
Species/
Parameter
S02> N02
SO2, NO2
Many
Gases
Opacity
Particles
Velocity
Mass Flow
Many
Gases
so2
Many
Gases
All Gases
Many
Gases
Some
Gases
Development
Mode Application Status Remarks
Stack
Perimeter/
Area
Stack
Perimeter/
Area
Stack
Area
Stack/
Perimeter
Stack
Area
Stack
Stack/
Area
Stack/
Area
Stack/
Area
Stack/
Area
Evld/Surv Field Tested
Evid/Surv Available
Evid/Surv Under
Development
Evld/Surv Under
Development
for A/C
Evid/Surv Field Tested
Surv Field Tested
on A/C
Evtd Field Tested
Evld Under
Development
Surv Field Tested
Surv Field Tested
Surv Theoretical
Surv. Lab Study
? Lab Study
? Lab Study
Ground-based - Present instrumentation
as used not eye-safe (Section 4. 3. 1)
Has not been done, but feasible (Section
4. 5), both ground and aircraft based
See Table 4-15
See Table 4-15, at present for ozone
Not eye safe yet, (Section 4. 3. 5) eye-
safe system being developed
Gives 3-dimens:onal mapping of relative
concentrations (Section 4. 5)
Necessary for sjme emission standards
(Section 4. 3. 7 and Table 3-1)
Relates opacity and mass concentration
(Section 4. 3. 7)
Using remote transmitter or retro-
reflectoi-; can bo laser, dispersive or
non-dispersive .systems (Table 3-16);
useful mainly for ambient air monitoring
Limited in rang.;, especially during day
(Sections 4. 3. 2 and 5.3.2)
Usefulness limi ed (Section 4. 3. 2 and
5.3.2)
Needs to be demonstrated in field;
possible interfer ence due to fluorescence
by gases and othjr species (Section 4. 3. 3)
Looks doubtful in terms of sensitivity
and specificity; .Section 4. 3. 4)
Provides increased sensitivity over
vibrational Ramon; still limited in range,
especially durinj day (Section 4. 3. 2)
157
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TABLE 7-3. Passive Systems
Technique/
Instrument
Matched Filter
Correlation
Gas Filter
Correlation
Photography
Vidicon
Heterodyne
Radiometer
Dispersive
Spectrometer
Spectral Species/
Region Parameter
U//Vis S02,NO2
IF S02
CO
so2
Vis Opacity
uv so2
IP soz
IF Many
Gases
IF Many
Gases
Development
Mode Application Status Remarks
Stack/
Perimeter
Stack
Perimeter
Perimeter
Stack
Stack
Stack
Stack/
Perimeter/
Area
Stack
Surv. Field Tested
Evid/Surv Field Tested
Evid/Surv Field Tested
Evid/Surv Under
Development
Evid/Surv Field Tested
Ground &
Aircraft
Surv Field Tested
Surv Planned
Evid(?)/ Lab Study
Surv
Surv Field Tested
Quantitative Interpretation difficult due
to varying aerosols (Section 4. 4. 2 and
4.5)
Limited in concentration and tempera-
ture range (Section 4. 4. 3), but tem-
perature effect reduced
No quantitative data reported as yet
(Section 4. 5)
See Table 4-14
Needs further development for quantita
live analysis; nighttime observations
feasible with image intensifier (Section
4.4. 1)
Quantitative interpretation difficult due
to varying aerosols; has potential as a
velocimeter (Section 4. 4. 9)
Independent knowledge of plurne temper
ture required for quantitative analysis;
has potential as a velocimeter (Section
4.4.9)
Achieves high specificity; has yet to be
demonstrated In field (Section 4. 4. 7)
Includes scanning spectrometer ai\d in-
terferometer-spectrometer; requires
high sperlral resolution t'rr spprif">fy
|iari»lu«-B (detitum 444 «»»1 44%)
158
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promising for near-term operational use are differential absorption
Lidar and laser Doppler velocimeter. The most promisiig passive
systems are correlation instruments, vidicons and photographic
techniques. Of course, for area surveys, both active and passive
systems (ground-based and airborne) have application.
A suggested time frame for introducing these instruments for
enforcement monitoring and the development of performance specifi-
cations and criteria is shown in Table 7-4. Steps involved in this
overall plan to introduce measurements by remote techniques as evi-
dentiary material are:
make candidate technique available to trained field personnel;
field personnel satisfied that technique produces reliable data;
data introduced into court and test cases established;
EPA develops and proposes performance specifications for
remote monitors.
Summary of questions to be satisfied in order to obtain co^.rt
acceptance of remote monitors to provide "substantial evidence" (re-
quired in near-term initial test cases):
Is the scientific principle underlying the instrument's
operation valid?
Does the instrument successfully embody and apply thi
underlying principle ?
Was the instrument in proper working order and cali-
brated at the time of the test ?
Was the person conducting the test qualified to do so?
Did the person conducting the test use the proper
procedures?
If different from the person conducting the test, is the
person interpreting the test's results qualified to do so?
159
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TABLE 7-4.
The Overall Time Schedule of
Introducing Remote Techniques
for Enforcement Monitoring
CALENDAR YEAH
Initiate Tr; Inlng Program*
Establish "est Range
Particle - Opacity
Available
Initial court cases
Particles • Mass Flow
Available
Initial court cases
SOj/NOj
Available
Initial court cue*
Other Gases
Available
Initial court ewe*
1915
A
A
•MHW
A
A
1916
1911
J\--._
A
1978
,.
1979
~A
-A
1980
A____
1981
1982
7.2 RECOMMENDATIONS
Based upon the general conclusions and, in particular, upon
Table 7-2 and 7-3, we recommend that EPA continues, initiates and/
or participates in the development of several instruments discussed
below. Many agencies, in particular NASA, have been involved in
the development of remote sensing techniques for air pollutants. It
would appear cost-effective for EPA to coordinate (as is already
done in some developments), its research programs with these
agencies.
160
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Laser Doppler Velocimeter
• Stack Emission Monitoring
--Make system operational in a van, together with the
DAS system
—Make it available to field enforcement personnel
—Continue the development of the LDV system to relate
its output to opacity, and to mass flow, if possible.
Lidar
• Stack Emission Monitoring
-*
—Make the lidar system operational in a van for the
measurement of opacity;
—Make it available to field enforcement personnel.
• Perimeter and Area Monitoring
--Adapt lidar to airborne operations for the measurement
of mixing height, dispersion of plumes and air quality
assessment over wide geographical areas.
Differential Absorption
• Stack Emission Monitoring
—Make the DAS system operational in a van for the mea-
surement of SO2 and NO2;
—Make it available for field enforcement personnel;
--Develop the DAS system for the measurement of other
species (see Table 7-1), using the infrared spectrum.
• Perimeter and Area Monitoring
--Continue to develop the DAS system to airborne operation
to measure 63 between the aircraft and the ground for air
quality assessment over wide areas;
161
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—Initiate the development of the DAS! system to van and
aircraft based operations to measure all gases for
perimeter and area monitoring'.
Correlation Techniques
• Stack Emission Monitoring
—Continue the field testing of the passive GFC instrument
for the measurement of SO£ and ma.ke it available to
field enforcement personnel;
—Extend the techniques to other species, such as
CO, HC1, and light hydrocarbons.
• Perimeter and Area Monitoring
—Make available to field enforcement personnel the pas-
sive MFC instrument for SO2 and NO2 van based;
—Develop the correlation techniques in the IR for SO2
and other pollutants, van based.
Vidicons
• Stack Emission Monitoring
—Make vidicon system for SC>2 operational;
—Make it available to field enforcement personnel;
—Develop system to NC<2 in the UV arid to other gases
in the infrared;
--Investigate possibility to use vidicon as velocimeter.
Photographic Techniques
• Stack Emission Monitoring
--Continue development of image intensifier technique for
nighttime surveillance/compliance;
162
-------
—Develop aircraft based photographic techniques for
daytime surveillance/compliance (possible' evidentiary).
Long-Path Systems
• Perimeter/Area/Ambient Air Monitors
--Continue to develop laser systems;
--Continue to develop non-dispersive techniques.
Resonance Raman
—Conduct field tests to verify feasibility of resonance
Raman technique to measure SC^ in stack emissions.
Heterodyne Radiometry
—Conduct field tests to verify feasibility of resonance
Raman technique to measure SO2 in stack emissions.
Based on the specifications which EPA had proposed or pro-
mulgated for continuous in-stack and ambient air monitors, and based
on recent court decisions on the use of analytical instrument;: in en-
forcement proceedings, we recommend that performance specifications
for remote monitors be developed as more experience is gained in the
field with existing monitors.
The important instrument parameters specified by EPA for
continuous in-stack and ambient air monitors, which will also apply
to remote techniques when used in enforcement monitoring, include:
• Span (lower detectable limit to upper level which must be
than the emission standard by a given factor)
• Noise (usually 0. 5 of the lower detectable limits)
• Accuracy (percentage difference between values measured
by the sensor and the applicable reference method)
• Calibration error (absolute mean value plus 95 percent
confidence interval)
163
-------
• Zero and calibration drift (absolute mean value plus 95
percent confidence interval)
• Response time (rise and fall time to 95 percent)
• Interference equivalent (influence on pollutant signal by
interfering gases in plume)
Additional parameters that will have to be specified for
remote techniques will include, but may not be limited to the
following:
Range (minimum and maximum distance between source and
observer, in which the instrument must give data with the
specified accuracy)
Field-of-view (should be small enough for the source plume
to fill the fov)
Interference equivalent (influence on pollutant signal by the
interviewing atmosphere as well as sky radiation beyond the
plume)
Supporting plume data (velocity, temperature, etc.)
The information recorded during field observations should
include those given in Method 9 for the visual observation:
• Time
• Observer location (distance, direction, height)
• Background description
• Weather conditions (wind direction and speed,
ambient temperature)
• Sky conditions
• Plume description (if visible)
164
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KEFEREfclCES
Ahmed, S. A. (1973) Appl. Opt. 12, 901.
Allerio, F. (1975) private communication.
AMOCO OIL vs. EPA (1974) 8 ERG 1481.
Asai, K. and Igarashi, T. (1974) Preprint, private communication.
Aviation Week and Space Technology (1975), February 3.
Barnes, H. M., Herget, V7. F. and Bobbins, R. (1974) "Analytical
Methods Applied to Air Pollution Measurements", p. 245, Ann
Arbor Science Publishers, Inc., August.
Barrett, J. J. (1974) "Lacer Raman Gas Diagnostics", Ed. M. Lapp
and C. M. Penney, Plenum Press, New York.
Barringer, A. R. et ai. (..963) 4th Symposium on Remote Sensing,
Ann Arbor.
Barringer Research Ltd., Ontario (1974) Report TR74-235 to Canadian
Centre for Remote Sensing, February.
Bartle, E. R. et al., (1972) J. Spacecraft and Rockets U, 836.
Bartle, E. R. (1974a) EPA Contract 68-02-1208, JRB Assoc. Inc.,
La Jolla, CA, April.
Bartle, E. R. (1974b) EPA Contract 68-02-1481, Final Report,
October.
Bartle, E. R. (1975) private communication.
Belanger, W. E. (1974) Poll. Eng. 30, June.
165
-------
Bockrath, J. T. (1972), 51 ALR 3rd, 1007.
Brazeraer, FL A. (1971) "Air Pollution Control: Sufficiency of Evidence
of Violation in Administrative Proceeding Terminating in Abatement
Order", 48 ALR 3d, p. 795.
Byer, R. L. and Garbuny, M. (1973) Appl. Opt. 12, 1497.
Chen, S. H.. Lin, C. C. and Low, M. J. D. (1974) Environ. Sci. and
Techn. 7, 424.
Collis, R. T. H. and Uthe, E. E. (1972) Opto-electronics 4, 87.
Colorado Air Pollution Variance Board vs. Western Alfalfa Corp. (1974)
reported in Air/Water Pollution Report, p. 205.
Conner, W. (1975) EPA, private communication.
Conner, W. D. and Hodkinson, J. R. (1967) P. H. S. Publ. 999-AP-30.
Cook, C. S. „ Bethke, G. W. and Conner, W. D. (1972) Appl. Opt. 11,
1742. ~
Decker, J. A., Jr. (1971) Appl. Opt. 10, 510.
Derr, V. E., and Little, C. G. (1970) Appl. Opt. 9, 1976.
DREW (1974* 39 FR 32094.
DeLong, H. P. (1974) Opt. Eng. 13, 5.
Denney, R. J. (1974) private communication.
Ellison, A. H. (1974) EPA-650/2-74-015.
Elterman, L. (1968) AFCRL-68-0153, April.
Emission Monitoring Requirements and Performance Testing Methods
(1974) 39 FR 32852.
Environmental Law (1970-1974)
a. American Law Institute—American Bar Association, Environ•»
mental Law - IV Conference Study Materials (1974).
166
-------
Environmental Law (1970-1974) continued...
b. Attorney General of California, 1974 Guide to Environmental Law.
c. Bureau of National Affairs, Environmental Report (1970-74).
d. Commerce Cleaning House, Clean Air and Water jSlews.
e. Environmental Law Institute, Environmental Lav/ Reporter
(1971-74).
f. Environmental Law Institute, Federal Environmental Law (1974).
g. Krie.r, Environmental Law and Policy.
h. The Lawyers Cooperative Publishing Co., American Law Reports
Annotated.
EPA (1974) response to Remand Ordered by U. S. Court of Appeals for
the District of Columbia in Portland Cement Association vs.
Ruckelshaus (486 F. 2nd, 375, June 29, 1973), EPA-Research
Triangle Park, N. C., PB-237952 (EPA-450/2-74-023), November.
Exton, R. (1974) NASA-Larigley, private communication.
Fowler, M. C. and Berger, P. J. (1974) EPA Report No, EPA-650/
2-74-020, January.
Gelbwachs, J. A., Birnbaum, M., Tucker, A. W. and Finder, C. L.
(1972) Opto-electronics 4, 155.
Gelbwachs, J. A. and Birnbaum, M. (1973) Appl. Opt. 12, 2f .'.,
Grad, F. I. (1973) "Environmental Law Treatise" (Published -n Environ-
mental Law.
Granatstein, V. L., Rhinewine, M. and Fitch, A. H. (1S73) Appl. Opt.
12, 1511.
Grant, W. B., Hake, R. D., Jr., Listen, E. M., Bobbins, R. C. and
Proctor, E. K., Jr. (1974) Appl. Phys. Lett. 24_, 550.
Grant, W. B. and Hake, R. D., Jr., (1975) submitted to Appl. Phys.
Lett., February.
Griggs, M. (1975) "Measurements of Atmospheric AerosDl Optical
Thickness over Water Using ERTS-1 Data, J. Air Poll. Control
Assoc. (In press).
167
-------
Haythorne, R. E. and Rankin, J. W. (1974) "Visual Plume Readings—
Too Crude for Clean Air Laws", Natural Res. Law. Vol. VII,
No. 3, 457.
Henz, "D. J. (1970) '*The Ringelmann Number as an Irrebutable Pre-
sumption of Guilt—An Outdated Concept, 3 Natural Res. Law 292.
Herget, W. ?. (1975) private communication.
Herget, W. F., Miller, C. R., and Sonnenschein, C. M. (1975) Paper
WA7, Spring Conf. OSA, Anaheim, CA, March 19-21.
Hess, R. V. and Seals, R. K., Jr. (1974) "Applications of Tunable
High Energy/Pressure Pulsed Lasers to Atmospheric Transmission
and Remote Sensing", NASA TM X-72010.
Hinkley, E. D. (1972) Qpto-electronics_4, 69.
Hinkley, E. D. and Calawa, A. R. (1974) "Analytical Methods Applied
to Air Pollution Measurements", Ed. R. K. Stevens and W. F.
Herget, Ann Arbor Science Publishers, Inc.
Hirschfeld, T. B. (1974) Opt. Eng. 13, 15.
Igarashi, T. (1973) 5th Conference on Laser Radar Studies, Williams-
burg, Virginia, June.
Inaba, H. and Kobayasi, T. (1972) Opto-electronics 4, 101.
Inomata, H. and Igarashi, T. (1974) Radio Research Laboratories,
Tokyo, Preprint, private communication.
Kildal, H. and Byer, R. L. (1971) Proc. IEEE 59, 1644.
Klainer, S. M. (1974) SPIE Meeting, San Diego, August.
Koehler, T. (1974) Electro-Opt. Systems Design, page 24, October.
Kuhl, J. and Schmidt, W. (1974) Appl. Phys. 3, 251.
Langan, L. (197la) AIAA Meeting, Palo Alto, November.
Langan, L. Q971b) Environmental Measurement Inc., San Francisco,
Report EPA Contract No. 6H-02-0124.
168
-------
Larson, N. M., Crosmun, R., and Talmi, Y. (1974) Appl. Opt. 13,
2662.
Low, M. J. D. and Clancy, F. K. (1974) Environ. Sci. and Techn. 1,
73.
Ludwig, C. B., Griggs, M., Malkmus, W. and Bartle, E. R. (1974)
Appl. Opt. 13, 1494.
Measures, R. M. and Pilon, G. (1972) Opto-electronics 4, 141.
Menzies, R. T. (1971) Appl. Opt. 10, 1532.
Menzies, R. T. and Shumate, M. S. (1974) Science 184, 570.
Melfi, S. H., Brumfield, M. L. and Storey, R. W., Jr., (1973) Appl.
Phys. Lett. 22, 402.
Melfi, S. H. (1974) EPA, Las Vegas, private communication.
Nader, J. (1975) EPA-Research Triangle Park (private communication).
Nakahara, S., Ito, K., Ito, S., Fuke, A., Komatsu, S., Inaba, H.,
Kobayasi, T., (1972) Opto-electronics 4, 169.
Nakahara, S., Ito, K., and Ito, S. (1973) Abstract from 5th Conference
on Laser Radar Studies, Williamsburg, Va., June.
North American Coal Corp. vs. Air Poll. Comm., (1971; 279 A 2d 356.
Peirce, A. R., and Quebedeaux, W. A. (1973) "Documentation of
Admissible Evidence for Environmental Cases" presented at 76th
Annual Meeting, Texas Academy of Science, University of Houston.
Pikus, I. M., Goldstein, H. W. and Reithof, T. R., (1971) AIAA
Meeting, Palo Alto, November.
Penney, C. M., Morey, W. W., St. Peters, R. L., Silverstein, S. D.,
Lapp, M., and White D. R. (1973) NASA CR-132363, September.
Portland Cement Association vs. W. D. Ruckelshaus (1973)
(486 F 2d 375).
169
-------
Prengle, H. W., Jr., Morgan, C. A., Fang, Cheng-Shen, Huang,
Ling-Kim, Campani, P., and Wu, W. W. (1973) Environ. Sci.
and Techn. 7, 417.
Pressman, A. (1975) EPA-Las Vegas, private communication
Prostak, A. and Dye, R. H. (1970) Bendix Final Report, Contract
CPA 22-69-55, October.
Robinson, J. W. and Dake, J. D. (1973) Spectr. Lett. 6, 685.
Robinson, J. W. and Dake, J. D. (1974) Anal. Chem. Acta. 71, 277,.
Rogers, J. A. (1974) "A Primer for EPA Employees: Presenting
Seicneific Evidence", published by the Office of General Counsel,
EPA, Washington, D. C., September.
Rosen, H., Robrish, P. and Chamberlain, O. (1974) Lawrence
Berkeley Lab Report LBL-3215, October.
Ross, R. D. (1972) Air Pollution and Industry, Van Norstrand Reinhold
Co., New York.
Rothe, K. W., Brinkmann, U. and Walther, H. (1974a) Appl. Phys. 3,
115.
Rothe, K. W,, Brinkmann, U. and Walther, H. (1974b) Appl. Phys. 4,
181.
Schotland, R. M. (1974) J. Appl. Meteorol. 13, 71.
Seals, R. K., Jr., "Analysis of Tunable Laser Heterodyne Radiometry:
Remote Sensing of Atmospheric Gases", AIAA J. 12, 1118.
N "
\ Smith, W. (1972) Opto-electronics 4, 161.
\
Smith, H. (1975) EPA, private communication.
Streiff, M. L. and Claysmith, C. L. (1972) Contractor Report EPA-
R2-72-052.
170
-------
Streiff, M. L. and Ludwig, C. B. (1973) Contractor Report EPA-650/
2-73-026.
Swift, R. D. and Wattson, R. B. (1974) 9th Rem. Sens. Symp. Abstracts,
Ann Arbor, April.
Zaromb, S. (1974) Pittsburg Conference, Cleveland, March.
Zimpritch, J. B. (1975) "Administrative Searches and the Clean Air
Act: Constitutionality of On-Site Monitoring as a Function of Tech-
nological Sophistication" to be published.
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TECHNICAL REPORT DATA
(I'U'j-.c rt'iiil !>i^lrn-lioii\ on (/'.v rev* r\r bffoir cotn/>
n* r<;nr ;.r> 1
EPA 340/1-75-009
. 71 TL~ ..'>;, S'J'JTI n.t
Application of Remote Monitoring Techniques in Air
Enforcement
'. AUTHORiSS
CB Ludwing and M. Griggs
'. PERFORMING ORGANIZATION NAME AND ADDRESS
Science Applications Inc.
- La Jolla, California 92038
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Stationary Source Enforcement
401 M Street, S.W. , Washington, D.C. 20460
15. SUPPLEMENTARY NOTES
IftliU)
3. Ri:cii':iNrs ACCLSSIO.VNO
G HLPOHT DATfc
jl/15
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION HbPOHT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-03-2137
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
16. ABSTRACT
The usefulness of remote sensing techniques for routine field used by enforcement
agencies are discussed, taking into account the need for laser systems to comply
with eye safety regulations. This study confirms that the technique of differential
absorption has the best sensitivity for the single-ended measurement of gaseous pollu-
tants. Data interpretation problems of the passive techniques make them less accurate
in general, than the active methods. The legal aspects of enforcement monitoring
are also investigated.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Air Pollution Observations
b.lDENTIRERS/OPEN ENDED TERMS C. COSATI Fiekl/GlDUp
Remote Monitoring
14B
14D
?. DISTRIBUTION STATEMENT
19. SECURITY CLASS (I his kepo.-tl
Unclassified
21. NO OF PAGES
180
Unlimited
20. SECURITY CLASS (Th's page)
Unclassified
23, PRICE
EPA Form 2220-1 (9-73)
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INST! tlCT IONS
1. CirPORT NUMBER
!.: A rt the EPA report number as it appears on the cover of the pub!: ,>',
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