EPA/600/A-92/277
INNOVATIVE SENSING TECHNIQUES FOR MONITORING AND
MEASURING SELECTED DIOXINS, FURANS, AND POLYCYCLIC
AROMATIC HYDROCARBONS IN STACK GAS
Dr. Jeffrey A. Draves
Radian Corporation
P. O. Box 201088
Austin, Texas 78720-1088
Mr. Dave-Paul Dayton
Radian Corporation
P. O. Box 13000
Research Triangle Park, North Carolina 27709
Mr. Thomas J. Logan
U.S. Environmental Protection Agency
Atmospheric Research and Exposure Assessment Laboratory
Methods Research and Development Division
Source Methods Research Branch
Research Triangle Park, North Carolina 27711
ABSTRACT
The U.S. Environmental Protection Agency (EPA) has determined the need to develop in situ
continuous or semi-continuous emissions monitoring (CEM) techniques for assessing dioxin, furan,
and polycyclic aromatic hydrocarbon (PAH) emissions from municipal solid waste (MSW)
incinerators and other sources. These species have a potential public health risk because of their
low associated exposure limits.
This paper discusses 12 innovative optical sensing techniques, which were evaluated for
application to continuous monitoring approaches. The ability of each of the techniques to function
as a CEM system is discussed. Two techniques, that appear to have the most potential for
successful application, are Ultraviolet (UV) Direct Measurement and Fluorescence Measurement.
Vapor phase UV spectral data for selected dioxins, furans, and polycyclic aromatic hydrocarbons
are being generated to determine limits of detection and assess applicability of the techniques.
INTRODUCTION
Dioxins and furans are formed as byproducts from combustion processes and from certain
industrial chemical processes using chlorine (e.g., paper bleaching and pesticide production). The
toxicity of these compounds makes them a great human health concern. Another class of
compounds, PAHs, is also associated with combustion processes. A number of the PAH
compounds are highly mutagenic and/or carcinogenic. A potential emission source of dioxins,
furans, and PAHs is MSW incinerators.
Current measurement techniques for dioxins and furans involve collecting samples using
U.S. EPA Method 23. Once collected, the dioxins and furans are identified and quantified using
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high resolution gas chromatography (HRGC) coupled with high resolution mass spectrometry
(HRMS). Approximately 2 months of processing time are required between Method 23 sample
collection and data reporting. Due to the acute and genetic toxicity of these compounds, the U.S.
EPA has determined that a continuous technique for monitoring dioxins, furans, and PAHs in stack
gas is needed1. Currently, there are no technologies at a state of development to continuously
quantitate or monitor these compounds or other trace organic constituents of stack gas. Therefore,
a fundamental research and development project is being conducted to address the need for
continuous monitoring of dioxins, furans, and PAHs.
The U.S. EPA has specified that the monitoring technique should provide for the following:
* Vapor phase measurements (continuously or semi-continuously);
• Capability of achieving a detection limit of 100 nanogram/normal cubic meter (ng/Nm3)
of total dioxin (the detection limits for the furans and PAHs were not specified);
• Particulate phase measurement (if feasible); and
• Speciated quantitation (if feasible).
Overview of the Research and Development Project
The research and development project is being conducted in five separate steps. These steps
are as follows:
» Step I - Feasibility Study;
• Step II - Spectral Measurements;
• Step III - Instrument Design and Fabrication;
• Step IV - Pilot Scale Testing; and
» Step V - Full Scale Field Testing.
The primary objectives of Step I, the Feasibility Study, are:
• To conduct a technology investigation to identify and evaluate applicable candidate
measurement techniques; and
• To provide a plan for development of the technique(s), that would have the greatest
potential for successful application as a CEM system.
Step II, Spectral Measurements, is designed to obtain measurements of the vapor phase
absorption spectra and measurements of the fluorescent lifetimes and to determine the fluorescence
profiles of three of the 75 chlorinated dibenzodioxins, two of the 155 chlorinated dibenzofurans,
and one representative PAH species. Candidate compounds are as follows:
• 2,3,7,8-tetrachlorodibenzo-p-dioxin;
* 1,2,3,7,8-pentachlorodibenzo-p-dioxin;
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• Octachlorodibenzo-p-dioxin;
• 2,3,7,8-tetrachlorodibenzofuran;
* Octachlorodibenzofuran; and
• Benzo-a-pyrene.
These six compounds present a representative cross-section of these classes of toxic species and
were chosen because of their level of toxicity and their likelihood of being emitted. (Step II is in
progress.)
Step in involves the actual design and fabrication of the monitoring instrumentation.
Step IV involves testing the instrument produced in Step HI, at a small well-characterized
emissions source or simulated emissions source.
Step V involves refining the instrument, based on information obtained during Step IV, and
then performing a field evaluation at a full scale operating emissions source.
This paper specifically presents the results of Step I and the objectives of Step n of the research
and development project.
Evaluating Optical Sensing Techniques
The term optical sensing (OS), as used in this paper, refers to the interaction of light with
matter (i.e., molecules, atoms or aerosols/paniculate) to yield qualitative and quantitative
information. The OS techniques are, for the most part, common laboratory spectroscopic
techniques that are applied to environmental monitoring. The advantages of OS techniques over
conventional analysis methods include real-time data analysis, structural specificity, and, in many
instances, in-situ monitoring capacity.
Requirements of Optical Sensing Techniques
During the investigation, desired minimum performance criteria of OS systems were determined
to ensure both accurate and rapid monitoring of dioxins, furans and PAHs. The categories "tor
which instrument performance was evaluated are stated below:
• Frequency of Measurement. This indicates whether the instrument is a continuous or
semi-continuous monitor. The more frequently a measured value is obtained the higher
the frequency of measurement. The evaluation is expressed in measurements per hour.
• Sensitivity. This indicates whether the instrument can meet the desired 100 ng/Nm3
detection limit and can distinguish between individual dioxin and furan isomers, and
PAH compounds. The 100 ng/Nm3 sensitivity level was specified by the U.S. EPA as
the minimum sensitivity necessary for preliminary technique consideration. The 100
ng/Nm3 is based on the measured emissions from MSWs currently in operation..
However, new regulations require that newly constructed MSWs meet a 30 ng/Nm3
emission level. While the techniques selected for further investigation will likely meet
the 100 ng/Nm3 sensitivity level, their actual detection limits are uncertain because no
vapor phase spectra of the compounds of interest are currently available. Once the
measured spectra are obtained, a more accurate assessment of the minimum detectable
limits will be made.
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• Constraints (Analytical and Physical). This indicates the expected level of development
required to achieve the capability of continuous monitoring. Analytical constraints refer
to the need to develop computer control software. Physical constraints refer to
development required to enable the technique to be used in a stack environment. The
evaluation is expressed in person-years required to complete development.
• Paniculate Matter. This indicates whether the instrument can measure the compounds
of interest on paniculate matter.
• Ease of Use. This is an estimate of the amount of training necessary to operate the
instrument on a day-to-day basis. The evaluation is expressed in person-hours required
to complete training.
• Maintenance. This is an estimate of the amount of routine maintenance that may be
required by the instrument. Maintenance includes down-loading of data, optics
alignment, diagnostic checks, etc. The evaluation is expressed in person-hours required
to perform maintenance.
• In situ Monitoring. This indicates whether the instrument can measure the compounds
of interest in the stack, as opposed to extracting samples from the stack for
measurement.
• Cost. This is an estimate of the expected associated cost of the instrument (based on
a combination of the prototype and production costs of the apparatus only).
Optical Sensing Techniques Considered for Investigation
Twelve OS techniques were considered for dioxin, furan, and PAH monitoring. The techniques
were selected for evaluation by reviewing available literature and through discussions with experts
in OS applications. The structural properties of the compounds of interest were also used as
criteria for selection. The techniques are presented in Table I and divided according to their
spectral region of operation. Most of the OS systems considered operate using either UV or
infrared (IR) light. Two techniques, photoacoustic spectroscopy (PAS) and Multiphoton lonization
(MPI), are listed as "consequence" techniques because the result of light absorption is monitored,
instead of the increase or the decrease of the light intensity itself.
Table II presents possible operating configurations (e.g., extractive and/or in-situ) for eacrrof
the techniques presented in Table I. Figures 1 and 2 illustrate conceptual operating configurations
of OS systems in extractive and in-situ monitoring modes. In either operating configuration, the
light beam is multipassed to extend the measured path length.
Techniques Considered for Further Investigation
Each of the techniques presented in Table I was evaluated in reference to the performance
criteria categories listed above. The results of this evaluation are given in Table III.
The techniques were ranked for each category on a scale of 0 to 10, with 10 indicating the best
result. The scores from the individual categories were then summed. The two techniques having
the highest summed scores were selected for further consideration. When summed, the highest
ranking techniques were UV absorption and laser induced fluorescence (LIF). The operation
principles of each of these methods are described below.
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Ultraviolet Absorbance Spectroscopy
The UV absorbanee spectroscopy is conventional absorption spectroscopy using an appropriate
broad-band excitation source, such as a Xenon arc lamp . The technique is well developed and
requires about 1 minute or less, depending on the signal-to-noise ratio (S/N), to identity and
quantitate the concentration of a single species. It is also possible to use laser light sources (e.g.,
an excimer pumped dye laser). The laser techniques are not, however, as well developed as the
broad-band technique. Typically, UV provides better sensitivity than IR because the UV band
strengths are greater and light sources are more intense. However, not alt compounds are
observable in the UV region. Further investigation will be necessary to evaluate possible dioxin or
ftiran detection in the UV or near visible region.
The literature review and feasibility study yielded no vapor phase UV spectra for the
compounds of interest. However, liquid phase spectra2 and subsequent detection limits do exist
for several furan compounds. Extrapolation of the liquid phase detection limits to the vapor phase
has been performed. The extrapolation is difficult for the following reasons:
• The type of solvent used can have a large effect on both the position of the absorbanee
peak and its intensity.
• The solvent interacts with the dioxins, furans, and PAHs to hinder rotational motion,
causing significant changes in the width and intensity of the spectral features.
• The temperature difference between vapor and liquid phases can significantly increase
the population of higher rotational states, causing a decrease in peak intensity and a
broadening of the spectral feature. However, the lower frequency of collisions in the
vapor phase will lead to longer lifetimes and narrower absorption features. The overall
result of these two processes is difficult to predict a priori, but a factor of 10 increase
in intensity is possible.
Although not exact, these extrapolations indicate the order of magnitude of the detection limits
that can be expected in the vapor phase for the compounds of interest.
As is shown in Table IV, the expected UV detection limits increase as the molecular weight of
the furan increases. Over a 100-m path, the detection limits range from 18.6 ng/Nm3 for
dibenzofuran to 2,353 ng/Nm3 for the heptachlorofurans. The detection limit for the most toxic
isomer, the tetraehlorodibenzofuran is 25.6 ng/Nm3. Considering the increase in spectral intensity
(about an order of magnitude in most cases) upon going from the liquid phase to the vapor phase,
detection limits of 1.86, 235.3, and 2.56 ng/Nm3 can be expected for these three furans. These
detection limits, while only an order of magnitude estimate at best, are encouraging and fall within
the required detection limit of 100 ng/Nm3 for several of the furans.
In the UV region of the spectrum, background interferences are minimal. While water vapor
and CO2 can significantly hamper IR detection limits, they have negligible effects in the UV region.
Other compounds present in the stack gas may interfere with UV detection. Potential interfering
compounds include dioxins, furans, PAHs not of interest, and other compounds attached to the
surface of the paniculate matter. The lack of spectral information on dioxins, furans, and PAHs
makes exact identification of interferants presently impossible.
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Fluorescence
Fluorescence relies on the excitation of the molecule of interest to a known state by the
absorption of a photon from a light source (e.g., Xenon arc). The photon is either emitted at the
same frequency (or more likely at a lower frequency) and monitored by a spectrometer. The
response times will generally be similar to those for the UV absorbance. However, because
photoemissions can take on the order of seconds, it will be necessary to investigate the fluorescence
spectra and lifetimes.
As with UV absorption, the sources are capable of accommodating long path lengths, but the
fluorescence volume and, therefore, the solid angle relative to the detector is important and must
be considered. The amount of fluorescence is governed by Equations 1 and 2:
F = 2.3 « 1(0) * f(0) * g(?) « A (v) [Equation 1]
where: 1(0) = the incident light intensity
f(0) = solid angle of irradiated volume falling on the detector
g(i>) = the detector's response
A(p) = the Beer's Law absorbance of the sample.
Replacing A with the components of Beer's Law gives the following:
F = 2.3 * 1(0) * f(0) « g(v) * a(»>) * c * 1 [Equation 2]
where: a(i>) = the molecular absorbance strength
1 = is the path length
c = concentrations
No vapor phase fluorescence spectra of the compounds of interest were found during the
literature review. However, liquid phase detection limits do exist. In this case, extrapolation of
the liquid phase detection limits to the vapor phase is difficult for the same reasons stated above
and for the following additional reasons:
» The limits of detection are not solely dependent on the path length, but are also
dependent upon the solid angle of the excitation volume that is visible to the detector.
• Species that can absorb the emitted photon by being located between the emitting
species and the detector may exist,
« The emission of light requires a finite amount of tune. The species emitting the light
are moving, both up the stack and out of the original excitation volume. This motion
may require the detector to be placed up the stack from the source. Diffusion out of the
excitation volume will make the detection limits higher as the excited volume is
increasing.
Expected fluorescence detection limits are presented in Table V.
Trace components, such as the PAHs, the polychlorinated biphenyls (PCBs), and other dioxins
and furans, may interfere with the fluorescence technique. The measurement of a single compound
will depend upon its fluorescence lifetime.
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Laser Induced Fluorescence. The LIF technique is conceptually similar to the fluorescence
technique described above. The UF technique uses a carefully tuned laser to excite the molecule
of interest. This careful tuning allows for very specific excitations and more specific compound
identifications. As with the fluorescence technique above, the emitted photon can then be
monitored as a function of frequency with a spectrometer of appropriate resolution. This gives the
ability to both selectively excite and selectively detect the compounds of interest. The LIF
technique has been shown to be very sensitive for detecting PAH compounds.
The advantages of LIF over fluorescence are twofold. The first advantage is. that a laser light
source is much more specific in terms of which species are excited. Consequently, the species will
be excited to a narrow band of states, making the emission spectra less complicated and easier to
interpret. The second advantage is the increase in light intensity that is obtained when using a
laser source. Because fluorescence is directly related to the intensity of the light source, lasers
offering greatly increased light intensity at the specific wavelength of interest will cause an increase
in the fluorescence.
As with the fluorescence technique discussed above there is no vapor phase information
available concerning the compounds of interest. This lack of information makes identifying of the
appropriate laser source difficult. The frequency of measurement will again depend on the
fluorescence lifetime, but should be similar to UV absorption (on the order of 1 minute or less),
depending on the S/N ratio, per species.
Actual vapor phase absorption spectra, emission spectra, and emission lifetimes must be
obtained to better characterize the ability of these techniques to measure the compounds of
interest.
Measurement of Vapor Phase Spectra
One of the limiting factors in the feasibility study was the absence of vapor phase spectral data
for the dioxin, furan, and PAH compounds. Lack of spectral information not only made identifying
the appropriate OS techniques difficult, but also affect the implementation of the technique
because reference spectra are generally needed to identify and quantify species.
Vapor phase spectral data are being obtained, in a temperature range typical of incinerator
stack emissions, for the six selected dioxins, furans, and PAHs presented above.
The measurement program consists of measuring the UV absorbance cross-sections for each
of the selected compounds. The absorbance spectra will be used to identify features for use in
detection, as well as to pick the appropriate laser excitation sources for LIF measurements. The
fluorescence wavelengths and cross-sections will then be identified. Finally, the fluorescence
lifetime will be measured for each selected compound.
CONCLUSIONS
The feasibility study yielded two techniques, UV absorption and OF, that have the potential
to be applied to real-time monitoring of dioxins, furans and PAHs, The lack of vapor phase
spectral information precludes narrowing the field further. Further information is needed to
definitively specify the most applicable technique.
A program designed to obtain vapor phase spectral information for selected compounds of
interest is presently ongoing. The spectral information that is obtained will consist of measured
UV absorbance spectra, LIF spectra, and fluorescence lifetimes.
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REFERENCES
1. J.A. Draves, D-P. Dayton, and J.T. Bursey, Innovative Sensing Techniques for
Monitoring and Measuring Selected Dioxins. Furans. and Polycyclic Aromatic
Hydrocarbons in Stack Gas. Final Report. DCN No. 91-275-065-10-09, Radian
Corporation, October 1991.
2. E.B. Gonzalez, R.A. Baumann, C. Gooijer, N.H. Velthorst, and R.W. Frei,
Chemosphere, 16 pp 1123-1135, (1987).
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Table I. Spectra! regions of the optical sensing techniques.
Ultraviolet
Infrared
Consequence
UV Absorbance
Fluorescence
Laser Induced
Fluorescence (LIF)
ShpoPskii Spectroscopy
(SS)
Laser Induced Breakdown
Spectroscopy (LIBS)
Fourier Transform Infrared
Spectroscopy (FTIR)
Matrix Isolation/FITR
(MI/FTIR)
Gas Chromatography/
MI/FTIR (GC/MI/FTIR)
Laser Absorbance
Gas Filter Correlation
(GFC)
Photoacoustic
Spectroscopy (PAS)
Multiphoton lonization
(MPI)
Table II. Extractive and non-extractive techniques.
Category
UV Techniques
IR Techniques
Consequence Techniques
Technique
UV Absorbance
Fluorescence
LIF
SS
LIBS
GC/MI/FTIR
MI/FTIR
FTIR
Laser Absorption
PAS
MPI
Extractive
X
X
X
X
X
X
X
X
X
X
X
In-situ
X
X
X
X
X
X
X
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Table III. Summary of techniques.
Technique
UV
Absorbance
Fluorescence
LIF
SS
LIBS
FTIR
MI/FTIR
GC/MI/FTIR
GFC
Laser
Absorbance
PAS
MPI
MS/MS
Frequency or
Measurements
[Number/Hour]
60
60
60
25
300
6
—
—
60
60
300
Sensitivity '
Within
specifications
Within
specifications
Within
specifications
Within
specifications
Out of
specification
Out of
specification
Possibly within
specification
Within
specification
Out of
specification
Out of
specification
Within
specification
No information
Within
specification
Analytical and Physical Partlculate
Constraint Matter
None No
Needs analysis software Yes
Will need stabilizers for Yes
optics; analysis software
Sampling and separation will No
need to be developed as will
solvent mixing system. Also
needs analysis software.
Needs development of a No
separation method
Needs development of No
software for control and
timing
Needs sample delivery Yes
system; computer software
Needs sample delivery No
system
Need downsizing and sample No
delivery system
Ease of Use
[Person-
Hour]
8
8
40
40
12
40
40
40
40
Maintenance
[Person-
Hour/Month]
2
2
5
10
10
10
15
10
12
In-
Situ
Yes
Yes
Yes
NcJ
No
No
No
No
No
Capital
Costs
(Thousands)
250
250
200
300
200
250
150
300
300
'Ability to meet a 100 ng/Nm ' detection limit and distinguish among various congeners.
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Table IV. Expected UV detection limits.
Path Length [M]: 0.0047
100
100
Species
DF
DF2
DF4
DF5
DF6
DF7
ng
0.008
0.038
0.11
0.11
0.44
1.01
tng/L]
400
1900
5500
5500
22000
50500
Dig/Mm3]
400
1900
5500
5500
22000
50500
[ng/Nm3]
18.64
88.54
256.3
256.3
1025.2
23533
[ppt]
02.7
09.1
20.5
18.4
66.8
140.5
DF = Dibenzofuran. Number after "DF indicates number of chlorines.
Table V. Expected fluorescence detection limits.
Species
Dibenzofuran*
1,2,3,4
2,3,7,8
Dibenzodioxin
1,2,3,4
1,2,7,8
1,3,7,8
2,3,7,8
1,2,3,7,8
1,2,4,7,8
1,2,3,4,7,8
1,2,3,4,6,7,8
1,2,3,4,6,7,8,9
Wavelength
Excitation
285 246
292 252
307 257
230
230
232
235
232
232
230
232
232
[nm]
Emission
316 327
338 407
340
342 418
346
343
343
342 416
343
340 409
343 405
341
LOD
[ng/ml]
0.02
0.015
0.025
2
0.07
4
1.3
1.8
5.5
4.5
0.5
2.5
100 M
(ng/Nm3)
02
0.15
0.25
20
0.7
40
13
18
55
45
5
25
100 M
[PPt]
0.03
0.01
0.02
1.52
0.05
3.04
0.99
1.23
3.77
2.81
0.29
1.33
The numbers in the column indicate the chlorinated positions.
11
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Moisture
Removal
Heated
Paniculate Fitter
Data Aquls'rtion
Sample Stream
From
Incinerator
Sample
Figure 1. Conceptual configuration of an optical sensing system in an extractive mode.
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DISCLAIMER
This paper has been reviewed in accordance with the U.S. Environmental Protection Agency's
peer and administrative review policies and approved for presentation and publication. Mention
of trade names or commercial products does not constitute endorsement or recommendation for
use.
14
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TECHNICAL REPORT DATA
1. REPORT HO.
EPA/600/A-92/277
2.
4. TITLE AND SUBTITLE
5.REPORT DATE
Innovative Sensing Techniques for Monitoring and
Measuring Selected Dioxins, Furans, and Polycyelic
Aromatic Hydrocarbons in Stack Gas
6,PERFORMING ORGANIZATION CODE
7. AUIHOR(S)
Thomas J. Logan, Dave-Paul Dayton, Jeffrey A. Braves
8,PERFORMING ORGANIZATION REPORT HO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corp., P.O. Box 201088, Austin, TX 78720-
1088; Radian Corp., P.O. Box 13000, Research
Triangle Park, NC 27709
10.PROGRAM ELEMENT NO.
11. COKTRACT/GRANf NO.
68-D1-0010
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
AREAL/MRBD/SMRB/PPIS (MD-77A)
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
Proceedings Paper
1*. SPOHSORIHG AGENCY CODE
15. SUPPLEMENTARY BOIES
16. ABSTRACT
The U.S. Environmental Protection Agency (EPA) has determined the need to develop
in-situ continuous or semi-continuous emissions monitoring (CEM) techniques for
assessing dioxin, furan, and polycyclic aromatic hydrocarbon (PAH) emissions from
municipal solid waste (MSW) incinerators and other sources. These species have a
potential public health risk because of their low associated exposure limits. This-
paper discusses 12 innovative optical sensing techniques, which were evaluated for
application to continuous monitoring approaches. The ability of each of the
techniques to function as a CEM system is discussed. Two techniques that appear to
have the most potential for successful application are Ultraviolet (UV) Direct
Measurement and Fluorescence Measurement. Vapor phase UV spectral data for
selected dioxins, furans, and polycyclic aromatic hydrocarbons are being generated ~
to determine limits of detection and assess applicability of the techniques.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED TERMS
c.COSATI
IS. DISTRIBUTION STATEMENT
19, SECURITY CLASS (This Report)
21.NO. OF PAGES
14
20. SECURITY CLASS (This Page)
22. PRICE
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