COMPARISON OF AMBIENT AIR MEASUREMENT AND
SOURCE MEASUREMENT
Herbert C. McKee
Southwest Research Institute
Houston, Texas
April 1971
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PB 205 935
COMPARISON OF AMB1KN I AIR MKASUKKMF.NT
AND SOURCE MEASUREMENT
Contract CPA 70-40
SwRI Project 21-2811
Prepared for:
Office ol Me.isureinenl S(aiidai(li/a(i<»ii
Division of Cheinisliy and Physics
Air Pollution Control Olfiee
Knvironniental Protection Agency
April, 1971
Sw
NATIONAL'T'ECHNICAL
INFORMATION SERVICE
SOUTHWEST RESEARCH INSTITUTE
SAN ANTON IO HOU', ION
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
APTD-0902
3. Recipient's Accession No.
4. Title and Subtitle
Comparison of Ambient Air Measurement and Source Measurement
5' Report Date
April 1971
6.
7. Author(s)
Herbert C. McKee
&• Performing Organization Kept.
No.
9. Performing Organization Name and Address
Southwest Research Institute
3600 Yoakum
Houston, Texas 77006
10. Project/Task/Work Unit No.
SwRI Project 21-2811
11. Contract /GfeS* No.
CPA 70-40
1 2. Sponsoring Organization Name and Address
Office of Measurement Standardization
Division of Chemistry and Physics
Air Pollution Control Office
Environmental Protection Agency
13. Type of Report & Period
Covered
14.
15. Supplementary Notes DISCLAIMER; This report was furnished to the Environmental Protection
Agency, Air Pollution Control Office, in fulfillment of Contract No. CPA 70-40.
16. Abstracts
Many differences exist between methods used for ambient air measurement and source
measurement, related to the differences in concentration, temperature and humidity of
the sample streams, interferences that affect analytical results, and other factors. The
differences in the two types of methods have been substantial, therefore results obtainejd
with these different methods likely are not equivalent. Emissions cannot be related ac-
curately to ambient air measurements, which makes the job of planning and developing
standards much more difficult. Emission standards have little meaning unless a method
of measurement is specified, and specific methods or general guidelines have usually
been published with such standards. The need for a standardization program is outlined.
17. Key Words and Document Analysis. 17o. Descriptors
Air pollution
Gas analysis
Particles
Measurement
Sources
Exhaust emissions
Atmospheric composition
Temperature
Humidity
Standards
17b. Identifiers/Open-End ed Terms
17c. COSATI Field/Group
14/Q2
18. Availability Statement
Unlimited
19.. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
UNCLASSIFIED
21. No. of Pages
23
22. Price
FORM NTIS-38 ('10-70)
USCOMM-OC 40329-P71
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COMPARISON OF AMBIENT AIR MEASUREMENT
AND SOURCE MEASUREMENT
Contract CPA 70-40
SwRI Project 21 2811
Prepared for:
Office of Measurement Standardization
Division of Chemistry and Physics
Air Pollution Control Office
Environmental Protection Agency
By:
Herbert C. McKee
April, 1971
APPROVED BY:
Herbert C. McKee
Assistant Director
Department of Chemistry
and Chemical Engineering
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SUMMARY AND CONCLUSIONS
This report was prepared to aid in planning a program to stan-
dardize methods of source measurement used in air pollution control.
Standardization of methods used for ambient air measurement has been
in progress for some time, and new requirements established by recent
federal legislation make it necessary to provide standard methods for
source measurement as well.
Many differences exist between methods used for ambient air
measurement and source measurement, related to the differences in
concentration, temperature and humidity of the sample streams, inter-
ferences that affect analytical results, and other factors. Because of
these factors, methods used in the past for ambient air measurement
have been substantially different from methods used for source measure-
ment, and therefore results obtained with these different methods likely
are not equivalent. This in turn means that various emissions as mea-
sured by the available methods cannot be related accurately to ambient
air measurements, which makes the job of planning and developing
standards much more difficult.
Emission standards have been developed in the past by a number
of air pollution control agencies, and will be required in the future as
a part of all implementation plans. The method used most frequently in
the past has been the Ringelmann chart for controlling emission of black
smoke. Other emission standards have also been used to control visible
emissions based on equivalent opacity, particulates measured on a weight
basis, and sulfur dioxide as measured by a chemical procedure. A few
agencies have developed unique emission standards to control specific
problems in their jurisdictions; examples include fluoride, beryllium,
hydrocarbons, and others.
Most agencies have recognized the fact that emission standards
have little meaning unless a method of measurement is specified, and
specific methods or general guidelines have usually been published with
the standards. Various scientific and engineering societies have also
made some effort at standardization of source measurement methods.
None of these efforts have included either a detailed laboratory evaluation
of available methods or a collaborative test to establish statistical limits
of accuracy and precision.
A study of existing regulations emphasizes the need for an extensive
program of standardization of source measurement methods. Available
11
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methods should be compared to select the variations best suited for
different source measurement applications. Collaborative testing is
also needed, but will be difficult because of practical limitations on
the number of participants and number of samples that can be accom-
modated by the sampling facilities that can be provided on any reason-
able basis. Further development of new methods is also needed, so
that adequate emission standards can be established for many different
types of stationary sources. These methods should include both refer-
ence methods and techniques suitable for continuous monitoring and
process control.
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TABLE OF CONTENTS
Page
I. PURPOSE OF MEASUREMENTS 1
II. DIFFERENCES IN REQUIREMENTS 2
III. EMISSION STANDARDS AND MEASUREMENT 4
METHODS
IV. PRESENT USE OF STANDARD METHODS 10
V. CURRENT EFFORTS AT STANDARDIZATION 11
VI. FUTURE NEEDS 13
BIBLIOGRAPHY 17
IV
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I. PURPOSE OF MEASUREMENTS
In order to understand the differences between methods used for
ambient air measurement and those used for source measurement, it is
important to examine the reasons for making any measurement related
to air quality. A most important distinction here is the difference in
legal requirements. Ambient air measurements are used to evaluate
overall air quality within a community, usually over relatively long
periods of time. These measurements are useful for planning purposes
to set goals, to document progress in reaching those goals, and to identify
areas of a community in which additional control measures may be needed.
On a shorter time basis, they may also be useful in indicating when cer-
tain emergency measures need to be instituted, although most com-
munities have not yet developed or implemented comprehensive emergency
plans, and the difficulties involved in such implementation are quite
formidable. However, one important point here is that no immediate
legal action against an individual source of pollution is likely to occur,
based on ambient air measurements alone.
Source measurements present a different picture. Stack sam-
pling, in particular, is performed to measure emission rates over a
very short period of time, to determine whether or not that particular
source is exceeding some legally established emission rate. With con-
tinuous instruments, stack monitoring in some cases is possible on a
minute-by-minute basis. In other cases, limitations on available methods
of sampling may make it necessary to take several hours to complete a
single sample, but the objective is still to determine emission rates
over as short a period of time as possible. The results also provide
an immediate indication of legal or illegal operation of the source in
question, and may lead to demands for changes in the operation of the
source or, in the case of disagreement, to legal action.
These differences in legal requirements place a greater require-
ment on source sampling methods for short-term or single measurement
accuracy and reliability. Errors in a single measurement of ambient
air quality are of only minor importance when a large number of mea-
surements are averaged, unless a single measurement is high enough
to initiate some emergency action. A consistent error in long-term
measurements means primarily that planning may be done less efficiently
than desired. While this is regrettable, the errors inherent in the pro-
cess of developing ambient air standards are likely to be greater than
the errors of measurement. However, with source sampling methods,
any controversy over the error of even a single measurement may lead
to legal action under some circumstances.
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II. DIFFERENCES IN REQUIREMENTS
In addition to the different legal requirements for measurements,
many other differences exist between ambient air measurements and
source measurements. Obviously, there are exceptions, but a considera-
tion of the general differences is helpful in understanding some of the
problems involved in developing methods for source measurement.
The most obvious difference usually is one of concentration. As
a rule, the concentration of any given pollutant in a stack or duct in an
industrial plant can usually be several orders of magnitude higher than
levels that are tolerable in a community atmosphere. For example,
ambient air measurements of sulfur dioxide must be made in the range
of 0. 01 to perhaps 0. 5 ppm; measurement in a stack carrying tail gases
from a sulfuric acid plant may frequently show several hundred parts
per million, with legally acceptable concentrations in some areas running
as high as 2000 ppm.
Temperature and humidity variations also may be greater within
a stack or process stream than in the ambient atmosphere. Excluding
only infrequent periods in cold climates, ambient air temperatures
normally will be in the range of 20 to 100° F. Stack temperatures, on
the other hand, may range all the way from below ambient to 1500° F or
above. Humidity can vary correspondingly since the absolute humidity
required for saturation is temperature-dependent.
Interferences in analysis may also change drastically in going
from a source sampling situation to an ambient air problem. Again, to
use sulfur dioxide as an example, interference with a chemical method
of measurement in a stack may occur due to the presence of several
hundred parts per million of nitric oxide. In the atmosphere, however,
much of the NO will have been converted to NOg, while a portion of the
SOs will disappear by oxidation to SQa or reaction with alkaline particu-
lates. Thus, the absolute quantities of the NO and other interfering
substances change drastically as well as the ratios of these various
substances to the sulfur dioxide being measured. The formation of
secondary pollutants in an ambient atmosphere by photochemical reaction
and in other ways also introduces other intereferences not originally
present in the process gas measured at the source.
For these various reasons, measurements at the source and
measurements in the ambient atmosphere may not be related to each
other. In other words, a measurement which indicates a pound of SOg
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in a stack may not correspond to an ambient air measurement indicating
a pound of SQs distributed in a certain volume of the atmosphere. Like-
wise, a source measurement indicating a pound of SOa in the gases from
a sulfuric acid plant may be subject to entirely different errors than a
measurement indicating a pound of SOa in the flue gas from a coal-fired
boiler.
One suggestion for reducing the impact of these variations in
interfering substances is to use the same method for stack sampling
that is used for ambient air measurements, and dilute the stack gas
sufficiently to reach the same concentration range. This would allow
the use of continuous monitoring instruments and other techniques of
measurement commonly used in ambient air sampling for stack measure-
ments. While this suggestion has some merit, differences in interfering
substances and the difficulties involved in maintaining an accurate dilu-
tion ratio make this something less than a cure-all for all of the problems
which exist.
The differences in working conditions for sampling also increase
the cost of making measurements and exert a psychological effect on
persons involved in such work. Ambient air measurements are usually
made at or near ground level. By bringing air into a building through
a suitable air inlet, an investigator can work in air-conditioned comfort.
In most stack sampling, however, the actual work of sample collection
must be conducted by manual methods immediately adjacent to a duct
or stack carrying the gases to be emitted. The only suitable sampling
points may be located on a stack 100 feet or more above ground level.
Construction of access ports, sampling platforms, and other mechanical
facilities may require major construction and alteration of facilities,
and may only be possible when the entire unit is shut down for routine
maintenance. During sampling, much lost time and personal incon-
venience occurs due to the necessity for climbing up and down ladders,
hauling equipment up and down with a block and tackle, running extension
cords for several hundred feet to obtain electrical power, and other
similar tasks. This means that workers must be more highly motivated
in order to obtain high quality data, and the cost per sample will usually
be much higher than the cost of ambient air sampling and analysis. The
only partial solution for these problems in the near future is the develop-
ment of automatic instruments for stack monitoring, which can reduce
the amount of work which must be done by manual methods but cannot
eliminate such work.
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III. EMISSION STANDARDS AND MEASUREMENT METHODS
In order to understand the problems in evaluating source sampling
methods, it is helpful to examine the regulations which are now in use
and the methods of measurement which are specified. These two must be
considered together, since no emission standard has much meaning unless
the method of measurement is specified. To do this, a number of air
pollution control ordinances and regulations were examined to identify
the emission standards and methods of measurement that are now in use.
"While not complete, this brief survey gives a general summary of the
methods now being used throughout the country. These are divided into
two categories: (1) those that are in general use in many jurisdictions
and (2) those in use in only a few jurisdictions because of special problems
or as a result of pioneering efforts by the agencies involved.
The most general emission standard is a limit on black smoke
based on evaluation by the well known Ringelmann chart. This standard
appears in practically all air pollution control ordinances and regulations
that deal with emission standards of any type. For many years, emissions
were limited to No. 2 Ringelmann in most jurisdictions, but recently
there has been a tendency to impose a No. 1 limitation.
Perhaps the second most used method is the regulation of visible
emissions other than black smoke by the concept of equivalent opacity.
There are valid scientific objections to this concept, and margins for
error in measurement are greater than desired; nevertheless, the con-
cept is a valid one and can be used satisfactorily if inspectors are trained
properly. It is also legally acceptable, having been upheld in courts of
law up to and including the U. S. Supreme Court.
Another type of emission standard which appears frequently is
the imposition of emission limits based on the weight of material emitted.
A major limitation here is that the adverse effects of an emission may
not be directly related to weight because of differences in particle size,
corrosivity, or other characteristics; nevertheless, weight is a conve-
nient unit of measure that has been widely used. Regulations of this
type appear to have been developed initially to limit emissions of fly
ash and other particulate matter from coal-burning equipment, and more
recently weight limitations have been applied to incinerators and other
combustion sources as well as process units not involving combustion.
Weight limits applicable to combustion sources are expressed in many
different ways such as grains per cubic foot, pounds per hour, pounds
per thousand pounds of air, etc. Units based on volume of gas discharged
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are usually corrected to some standard condition such as 12% COg to
compensate for changes in the amount of dilution air which may be present;
this correction also avoids circumvention through the deliberate addition
of dilution air. The ASME Power Test Codes provide the basic standard
methods that have been widely used in measuring the particulate content
of stack gases. Various modifications have been made, especially to
collect condensable vapors as in the PHS Method for incinerator testing.
Obviously, these different methods will give substantially different results
depending on the temperature of filtration to collect samples, and on
other variations such as whether or not condensable vapors are also
collected and measured.
With some variations in mechanical equipment and procedures,
all of these methods are similar in nature. First, a velocity traverse
is made with a pitot tube to determine velocity distribution across the
duct or stack. Isokinetic sampling is then performed, by controlling
the sampling rate so that the linear velocity of the gas stream entering
the sampling probe is equal to the linear velocity of the stack gases at
that point; this avoids centrifugal effects which would result in samples
not representative of the flue gas stream. Particles are collected with
an alundum thimble, cyclone collector, filter, or some combination
of these. Water is condensed and measured, and other condensable
vapors may also be collected for measurement. Simultaneous velocity
measurement and sample collection is also possible, using a probe
which is equipped with both a pitot tube and a sampling inlet. After
collection, samples are dried and weighed, and further laboratory work
may be conducted to determine particle size distribution, chemical
composition, or other necessary data.
When attempts were made to apply some of these emission stan-
dards to process emissions, difficulties arose because of great variations
in the volume of gas emitted along with the particulate matter. In some
jurisdictions, units of measurement such as weight per unit volume were
retained despite these difficulties, but in others the so-called process
weight principle has been used. This concept was originally developed
in Los Angeles County to apply to the foundry industry. It allows for
consideration of the fact that a small foundry cannot do as good a job of
controlling emissions, on a percentage basis, as a large foundry. Since
its original adoption, the same table with the same numbers has been
copied in many other jurisdictions and applied indiscriminately to any
and all types of processes. While a detailed study of this matter appar-
ently has never been made, it would appear likely that the use of the
same table for different types of industrial operations would impose
much more severe restrictions on some industries than on others.
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Sulfur compounds have been regulated in a number of jurisdictions
and the present regulations seem to have been based in part on a per-
centage reduction believed necessary to achieve certain ambient air
quality goals, and in part on limitations of the available technology for
process applications. An example of the first type is the limitation of
sulfur in fuel, which serves to reduce emissions of sulfur dioxide though
these limits do not constitute "emission standards" in the usual way.
The measurement of sulfur in coal and fuel oil has been well known with
adequate standard methods for a number of years, and no significant
problems of measurement have arisen. For process applications, how-
ever, most of the emission standards now in use depend on either a
maximum concentration in the stack as measured by stack sampling,
or on a maximum concentration in the ambient atmosphere surrounding
the plant as measured by conventional ambient air measurement methods.
For many years, stack gas concentrations from process sources have
been limited to 2000 ppm, with a recent trend in some jurisdictions to
reduce this to 500 ppm. This concept was originally developed for appli-
cation to sulfuric acid manufacturing and has been applied to other process
operations involving sulfur dioxide. Most regulations specify one or
more of the stack sampling methods contained in PHS Publication 999-
AP-13, or their equivalent. These are essentially acid-base titration
methods.
Turning now to the more unique emission standards, special
problems in certain localities have led to the development of new emis-
sion standards by the responsible agencies. Since cities in California
led in the development of photochemical smog, it was only natural that
the control districts in Los Angeles County and the San Francisco Bay
area have led in the development of source sampling relative to hydro-
carbons. Los Angeles County, with some exceptions, has operated
primarily on the basis of total hydrocarbons, limiting emissions from
storage tanks, loading docks, and other facilities handling large quantities
of various hydrocarbon mixtures. The San Francisco Bay area, on the
other hand, has followed a slightly different approach which places more
emphasis on photochemical reactivity, and therefore measurement of
individual hydrocarbons is required. This is not a clear-cut distinction,
as shown by the fact that Los Angeles County's Rule 66 relating to solvent
vapor is also based on reactivity. However, this partial difference in
philosophy has led to differences in methods of measurement as outlined
in the applicable publications of these two agencies.
The first method used for source measurements of hydrocarbons
was developed by the Los Angeles County Air Pollution Control District.
Samples are taken in evacuated glass bulbs and transferred to the gas
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cell of an infrared instrument for measurement of total hydrocarbons by
infrared absorption at a wave length of 3. 4 microns. Results are cal-
culated as ppm hexane, since a major concern there is evaporation of
gasoline in storage and handling, and hexane was picked as being repre-
sentative of the molecular weight range and infrared absorptivity of
gasoline vapor.
With the adoption of Rule 66 relating to organic solvents and
vapors, a different method was developed for use with the greater variety
of organic vapors which had to be measured under that regulation. Sam-
ples are still taken in evacuated glass bulbs to measure process emissions,
vapors in storage areas, or other source sampling involving organic
solvents and vapors. These samples are then passed through a com-
bustion tube in which all organic matter is converted to COa which is
then measured with a nondispersive infrared analyzer. While based on
a different principle, this method also gives a measure of total organic
materials without regard to individual organic compounds present. Other
methods have been used for special purposes to evaluate classes of com-
pounds or individual compounds by the Los Angeles County Air Pollution
Control District. An example of the first type is the use of the fluorescent
indicator analysis (FIA) to measure olefins, aromatics, and saturates
in hydrocarbon samples. Gas chromatography has been used to measure
individual chemical compounds in various organic mixtures but this has
been done primarily for research purposes or to meet unique problems,
and methods based on gas chromatography have not been widely adopted
for generalized application in connection with emission standards.
As mentioned previously, the Bay Area Air Pollution Control
District has emphasized photochemical reactivity in Regulation 3 relating
to the control of organic emissions. Therefore, the emission standards
are stated in terms of reactive components with special emphasis on
olefins and substituted aromatics. The determination of these constitu-
ents in gaseous effluents is made by absorbing the olefins and substituted
aromatics on silica gel, after which they are removed with an appro-
priate organic solvent and determined by gas chromatography. A similar
chromatographic procedure is used for other samples to determine com-
pliance with the various portions of Regulation 3. For solvents and other
organic liquids, olefins and substituted aromatics are determined by a
sulfonation procedure which is a modification of ASTM Method D-1019-62.
For source sampling, however, gas chromatography is the method most
frequently used. Another interesting variation is a provision for using
a combustible gas indicator for purposes of conducting preliminary tests.
Organic gases of less than the allowable limit of 50 ppm (as hexane)
when measured in this way are assumed to be in compliance with the
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regulation. Emissions showing more than this amount are suspected of
being in violation and additional tests are conducted by gas chromato-
graphy or other suitable methods, depending on the type of source in
question.
A limited number of other process emissions have been covered
by emission regulations where specific problems are known to occur.
For example, Florida sets a limit for fluoride emissions based on the
weight of phosphate (PsOg) processed, in order to limit the emission of
fluorides by fertilizer manufacturing operations. Texas sets a fluoride
limit which is calculated based on meteorological dispersion equations
starting with maximum downwind levels off the plant site thought to be
acceptable. Very strict limits on beryllium have been adopted in a
number of states, based primarily on a comprehensive study originally
initiated because of specific problems near beryllium processing opera-
tions in Pennsylvania. Some limits have been established on lead and
other metals, based at least in large part on previous work done by
industrial hygienists to protect industrial workers from toxic metals.
"Fugitive dust" may constitute the most important category of
pollutant that is covered in only a very few jurisdictions. Most of the
various emission standards are based on measurements which must be
made in a stack or duct prior to emission to the atmosphere. The first
exception to this principle was the use in California of atmospheric
monitoring instruments around industrial plants to measure sulfur dioxide,
which was originally introduced as a further check on the stack emission
limit of 2000 ppm which was determined by stack sampling. This principle
has been further extended by Pennsylvania and Texas in order to permit
quantitative measurements of fugitive dust, which is defined as dust which
is not emitted through a stack or duct and therefore cannot be measured
by conventional stack sampling methods. Examples here might be dust
from metallurgical operations which drifts out the side of a building, dust
raised by vehicle traffic either on a plant site or on streets and freeways
throughout the community, dust blown from an open conveyor or storage
pile, dust arising from construction activities, and many others. Regula-
tions in these two states provide for measuring fugitive dust by making
ambient air measurements downwind from the suspected source, using
a conventional high-volume sampler. Another sampler located upwind or
in another suitable location to measure community background levels is
also used, with the difference between the two results being the contribu-
tion of the source in question to the ambient air levels. Because of
variations in background between upwind and downwind locations, margins
of error in such measurements may be significant and therefore this
8
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method cannot be used to measure emissions which are relatively small.
However, gross sources of emissions sometimes give short-term readings
of many hundred or several thousand micrograms per cubic meter, in
which case the contribution of the source is much greater than the limits
of accuracy of measurement, and this method can be used. This type of
measurement has been very useful in making easier the control of severe
dust nuisances resulting from fugitive dust emissions.
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IV. PRESENT USE OF STANDARD METHODS
Most of the emission standards outlined previously contain some
specification of a method of measurement or provide for such specification
by an air pollution control agency or other governmental entity. In many
cases legal regulations will not specify a method but will state that
measurements are to be made by methods acceptable to the commissioner
of health, the air pollution control officer, or other official. Frequently,
printed methods are provided either as a part of the regulation or as a
supplement prepared by the agency itself. Some of these give specific
directions for conducting source testing, while others contain background
information and/or literature references, and leave the specific choice
of methods and techniques to the investigator.
One of the most complete and widely used of these publications
is the Source Testing Manual published by the Los Angeles County Air
Pollution Control District. In the San Francisco Bay area, appendices
are provided for each regulation which outline details of methods of
source measurement. These publications might not be considered
"standard methods" in the usual sense of the word in that they are more
guidelines than standards and leave some discretion to the judgment of
the person making such measurements. This may be more desirable in
the case of source measurements than ambient air measurements, and
such judgment may always be required to allow the investigator to com-
pensate for the great differences in temperature, flow conditions, humidity,
and other variables which affect the results.
Historically, the methods for source sampling which have been
quoted most often in emission standards are the Power Test Codes
published by the American Society of Mechanical Engineers. Some
effort at standardization has also been made by ASTM, APCA, and other
professional groups.
Within the past few months, the necessity to develop implemen-
tation plans under the provisions of the federal Air Quality Act of 1967
has forced many air pollution control agencies to take a closer look at
emission standards and at methods of source measurement. Much more
activity along this line can be expected on the part of most, if not all,
air pollution control agencies. The requirements of the 1970 amendments
to the federal Clean Air Act have also focused more attention on the
development of emission standards and source measurement methods.
10
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V. CURRENT EFFORTS AT STANDARDIZATION
In addition to the efforts of various governmental agencies to
develop emission standards and the concurrent necessity for specifying
methods of source measurement, attempts at standardization have been
and are being pursued by various scientific groups. The longest "track
record" is that of the American Society of Mechanical Engineers which
published the first version of the well known Power Test Codes in 1927.
At present, the most concerted activity is being conducted by the
American Society for Testing and Materials. Committee D-22 of that
organization is working in the field of standard methods for measure-
ment of the atmosphere, and Subcommittee 06 of that committee is
devoted to methods for source sampling. The following methods have
been adopted or are under consideration by Committee D-22:
Particulate Matter. One method, D-2928-71 "Sampling Stacks
for Particulate Matter", has been published as a tentative standard.
It is similar to the ASME Power Test Code method except for some
technical details regarding sample collection.
Black Smoke. The subcommittee has developed a method to
evaluate black smoke by the conventional Ringelmann method, and
approval by the full committee is expected within a few months.
Equivalent Opacity. Work is underway by the subcommittee to
develop standard methods for equivalent opacity, following the regula-
tions in use in many jurisdictions. Preliminary indications are that
subcommittee members believe that severe limitations on the use of
this concept will be necessary because of possible sources of error.
Instrumental Methods for Particulates. Subcommittee 06 is
evaluating the need for a separate method covering instrumental methods
such as the smokescope, transmissometer, etc. Such methods might
cover black smoke, emissions other than black as indicated by equi-
valent opacity, or both.
Sulfur Compounds. Methods are being developed by the sub-
committee for sulfur dioxide and sulfur trioxide from fossil fuel com-
bustion sources. These likely will be based on previously published
methods such as the so-called Shell method and Monsanto method (PHS
Publication 999-AP-13).
11
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General Considerations. Work is being planned by Subcommittee
06 to develop standard methods applicable to most types of sources, cover-
ing such items as the measurement of velocity and volume by methods
other than pitot tube, possible changes in the pitot tube method specified
in D-2928-71, and other general considerations in sample collection.
Additional methods for source measurement of gaseous contaminants
are also under consideration.
A major activity in the standardization of atmospheric measure-
ment methods is being conducted by the Intersociety Committee,* but
this organization has not yet begun work on source sampling methods.
There has been some discussion in the Intersociety Committee of the
need for source sampling methods, and some effort in that direction
may be made in the near future. However, it is the opinion of various
persons in the Intersociety Committee that some of the subcommittees
would have to be restructured to bring in the proper knowledge and
capability to attack the problems of standardization of source measure-
ment methods. No specific plans of this nature have yet been developed.
The Intersociety Committee is a cooperative group consisting of
representatives of eight scientific and engineering societies:
Air Pollution Control Association
American Chemical Society
American Conference of Governmental Industrial Hygienists
American Industrial Hygiene Association
American Public Health Association
American Society for Testing and Materials
American Society of Mechanical Engineers
Association of Official Analytical Chemists
12
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VI. FUTURE NEEDS
The previous discussion has served to point up the obvious: There
is a great need for a much more concerted effort to develop and standard-
ize methods for source measurement. To many who have been involved
in the air pollution control field for many years, this realization is long
overdue. Nevertheless, this need is now widely recognized, and a con-
siderable emphasis in this area can be expected in the immediate future.
Much of this emphasis will come from air pollution control agencies who
are just beginning to realize the implications of the federal legislation
which requires emission standards as portions of overall implementation
plans. Many industrial pollution control people are now reaching the
same realization as they have interpreted for them the implications of
the same federal legislation by air pollution control agencies and by the
companies' own legal counsel.
The major difference in the overall status of source sampling
methods as compared to ambient air methods is the greater need for
development work in the source measurement area, which follows from
the greater variety of conditions likely to be encountered. These varia-
tions, as mentioned previously, may always require that a standard
method leave a greater amount of leeway for the individual judgment of
the investigator, and the degree of standardization probably can never
be as complete as in the case of ambient air measurement. In other
words, setting up and running a high-volume sampler in Cincinnati
involves essentially the same problems that are encountered in setting
up and operating a high-volume sampler in Dallas. In source sampling,
however, every industry is different, and even individual plants within
the same industry will show a considerable degree of variation in operr-
ating conditions which in turn influence the problems encountered in
source measurement. This may mean that a more rigorous control
over the skill and experience of the investigator may be required in
source measurements than will be the case in ambient air measurements.
If standard methods can be developed to the point where practically all
details are specified, then much of the work can be performed by tech-
nicians and others with a relatively low level of professional skill.
While this has not yet been accomplished in ambient air measurements
with any assurance of quality, the likelihood of accomplishing this appears
to be even less in considering source measurements.
The need for collaborative testing as a part of the process of
standardization is just as great in the development of methods for source
measurement. In fact, in view of the more restrictive legal require-
ments, it may be even greater. However, many practical difficulties
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can be anticipated in attempting to conduct multilaboratory collaborative
tests of source sampling methods. For any method involving particulate
contaminants, the generation of a test atmosphere for purposes of labora-
tory evaluation will be extremely difficult if not impossible. This means
that collaborative testing in some cases will probably have to be per-
formed by bringing a number of collaborators to the same point so that
all can sample the same source. For the usual type of stack sampling
operation, however, space on sampling platforms will be limited so
that only one or two groups can work at any one time and therefore changes
in operating conditions between different sampling periods may introduce
serious sources of error. Even if these problems can be resolved to
any reasonable degree, obtaining test results with a large number of
collaborators and/or a large number of samples will be much more
difficult than is usually the case in the collaborative testing of ambient
air methods. Obtaining a sufficient number of samples to insure statis-
tical validity may be very difficult or impossible.
In developing source sampling methods, there is a great need to
shorten the time required to collect and analyze samples. Since source
sampling is done to meet immediate needs to a greater extent than
ambient air measurement, the several days' time lag inherent in the
conventional particulate sampling methods is a severe limitation on the
use of such methods. This also raises the question of the availability
and suitability of continuous instruments for stack monitoring purposes.
Several companies are now developing and introducing new stack moni-
toring instruments to measure a variety of contaminants, and continued
activity in this field can be anticipated.
As with ambient air measurements, manual reference methods
can be used as a means of checking on the calibration of continuous
analytical instruments. Here again, however, the comparability of the
reference method and of the measurement obtained by a continuous
instrument must be established by detailed development work before
routine use of a stack monitoring instrument is feasible. Thus, in the
development and standardization of source sampling methods, a division
might be made similar to the division already being observed in ambient
air sampling methods. That is, reference methods should be developed
to provide a standard basis for measurement, and these in turn should
then be used as a means of checking the suitability of various stack
monitoring instruments for continuous process use. Once this com-
parability has been demonstrated, stack monitors can then be used for
routine operation and checks by a reference method can be limited to a
rather infrequent schedule.
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The use of stack monitoring instruments raises other questions
in connection with the legal aspects of developing and applying emission
standards. Nearly all of the standards now in effect require the use of
manual sampling and analytical methods which involve a considerable
time lag in obtaining results. There is a need for new concepts in the
legal field so that regulations and emission standards can be written
directly in terms of measurements made with continuous instruments.
One example of this concept has already been developed in the state of
Texas, where an instrumental method has been written into a legal
emission standard as a substitute for the visual estimation of equivalent
opacity. This eliminates problems inherent in visual observation, and
legal compliance with this regulation can be demonstrated only on the
basis of an instrumental measurement without the necessity to demon-
strate comparability between the instrumental method and a reference
method. In this particular instance, the instrumental method is more
accurate and reliable than the conventional visual method, and therefore
the question of comparability is not applicable. However, the further
development of legal concepts which would permit the use of emission
standards tied directly to instrumental readings would be of considerable
benefit in eliminating time lag, uncertainty, and confusion in the opera-
tion of various stationary sources subject to emission standards.
One other question which seems to have been partially overlooked
in the past is the comparability of ambient air measurements and source
measurements. No specific recommendations can be made to overcome
this limitation except the obvious one that further work done to develop
methods for both ambient air measurements and source measurements
should include some consideration of this problem. In the work which
is now in progress to evaluate methods for ambient air measurements
prior to collaborative testing and adoption of standards, some considera-
tion should be given where possible to the nature of the source sampling
methods which are available for the same contaminant. One example
here is the effect of particle size in measuring total particulates. The
conventional high-volume method for particulates includes very few
particles larger than 50 microns, whereas the conventional method for
source sampling is supposed to obtain a representative sample of the
material in the stack irrespective of particle size. If a large portion of
the emission consists of large particles, it is obvious that many of these
particles will fall to the ground within a short distance of the stack, partly
on the plant property. In this special situation, a stack measurement
could not relate directly to an ambient air measurement in the community
using a high-volume sampler.
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Another problem may occur with organic matter which would be
measured as a constituent of particulate matter by some stack sampling
methods or would be recovered in a condensate trap in sampling. In
actual fact, at least a portion of such organic matter probably would be
diluted in the atmosphere following emission and would remain in the
vapor phase. Thus, a stack measurement might reflect the presence
of organic matter but give an erroneous indication of the physical state
of such constituents after emission to the atmosphere. Problems of this
nature affect a. legal definition of particulate matter as well as the pro-
cedures used in sampling with respect to temperature, flow rate, con-
densate traps, etc. Similar examples of this lack of comparability
might be shown for sulfur dioxide, hydrogen chloride, hydrocarbons,
and many other contaminants subject to control through the use of
emission standards and source sampling methods.
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BIBLIOGRAPHY
Laws, Ordinances, Standards, and Regulations of the following states:
New Jersey Pennsylvania
Florida Oklahoma
California North Dakota
New York Iowa
Texas Delaware
Laws, Ordinances, Standards, and Regulations of the following local
governmental entities:
Los Angeles County Air Pollution Control District
Bay Area Air Pollution Control District (San Francisco Bay area)
Allegheny County, Pennsylvania
County of San Bernardino, California
Metropolitan Dade County, Florida
County of Sarasota, Florida
City of Chicago, Illinois
City of Cleveland, Ohio
City of Poughkeepsie, N. Y.
City of New York, N. Y.
City of Detroit, Michigan
City of St. Louis, Missouri
City of Cincinnati, Ohio
City of Cedar Rapids, Iowa
St. Louis County, Missouri
Air Pollution Control District, Los Angeles County, California. "Air
Pollution Source Testing Manual. " November, 1965.
Air Pollution Control District, Los Angeles County, California. "Recom-
mended Test Methods for Organic Solvents and Vapors (Rule 66)."
April, 1968.
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"Atmospheric Emissions from Sulfuric Acid Manufacturing Processes."
U. S. Public Health Service Publication 999-AP-13 (1965).
"Determining Dust Concentration in a Gas Stream." Power Test Codes
PTG-27, American Society of Mechanical Engineers. 1957.
1970 Book of ASTM Standards. Part 23, Water; Atmospheric Analysis.
American Society for Testing and Materials, Philadelphia, Penna.
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