EPA/600/A-97/061
                DLR Jet-REMPI as a Continuous Emissions Monitor:
                    Measurements of Chlorinated Dibcnzodioxins
                     H. Oser*, R. Thanner, and H.-H. Grotheer
 Institute of Physical Chemistry of Combustion, Deutsche Forschungsanstalt fur Luft
                                und Raumfahrt (DLR)
                              Stuttgart, 70569, Germany

                                    B. K. GuIIett
                   US Environmental Protection Agency (MD-65)
                      Research Triangle Park, NC, 27711, USA

                                  N. Bergan French
                                        Sky +
                              Oakland, CA, 94611, USA

                                     D. Natschke
                         Acurei Environmental Corporation
                      Research Triangle Park, NC, 27709, USA
* presenting author
ABSTRACT

       REMPI (Resonance Enhanced Multi-Photon lonization) mass spectrometer systems are known
for high selectivity, good on-line capabilities, and sensitivities to about 1 ppbv. Use of REMPI as a
continuous emissions monitor (CEM) for chlorinated aromatic compounds in flue gases, such as
polychlorinated dibenzodioxin (PCDD) and polychlorinated dibenzofuran (PCDF), will require much
greater sensitivities. As an improvement to traditional REMPI, the DLR Jet-REMPI™ system has
measured compounds such as chlorophenols and chlorobenzenes at pptv levels. These compounds have
been shown to be precursors for PCDD and PCDF formation. Direct measurements of PCDD and PCDF
will probably require even greater (ppqv) sensitivities. In addition, due to spectroscopic effects, REMPI
sensitivities decrease with increasing chlorination of PCDDs and PCDFs, making use of REMPI as a
CEM extremely challenging.

       In this paper we present new data showing DLR Jet-REMPI measurements of tri- and tetra-
chlorinated dibenzodioxins. We believe these are the first data of their kind, and note their significance in
demonstrating that single-color (1 wavelength) Jet-REMPI can measure PCDD congeners at this level of
cnlorination. The current instrument sensitivity is in the low (60) pptv region, and further work will focus
on improving sensitivity by at  least 1 or 2 orders of magnitude. In particular, sample cooling in the
expansion nozzle appears to be insufficient to resolve the more highly chlorinated molecules, likely due to
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 the heating required in the transfer line to avoid sample condensation.  Redesign of the inlet valve
 assembly will be aimed at correcting this problem.
 INTRODUCTION

        Current techniques to monitor emissions of polychlorinated dibenzodioxin (PCDD) and
 polychlorinated dibenzofuran (PCDF) use sampling times in excess of hours, during which the analytes
 are collected on adsorbing materials followed by sample extraction and preparation for subsequent gas
 chromatography / mass spectrometry (GC/MS) analysis III. These costly and time demanding methods
 have drawbacks in that compliance measurements are made only infrequently (perhaps once or twice per
 year). The consequences are over-designed air pollution control systems and regulatory strategies that
 rely on indirect process monitoring rather than direct monitoring and dioxin prevention strategies.

        In light of these limitations, a continuous emission monitor (CEM) for PCDD and PCDF offers
 four benefits to users:

 1.      Direct, rapid detection of PCDD and PCDF congeners, their indicators (compounds measured in
        lieu of PCDDs and PCDFs that indicate the parallel presence of PCDDs and PCDFs), or their
        precursors (compounds that have been shown to be chemical progenitors of PCDDs and PCDFs);
 2.      combustion  system optimization through continuous, on-line monitoring and process control;
 3.      a method to advance prevention of PCDD and PCDF formation rather than rely on flue gas
        cleaning controls; and
 4.      assurance to stakeholders (permit writers, the public, etc.) that the process is operating safely.

        For compliance monitoring, CEMs will limit the uncertainty and cost of compliance based on
 infrequent, extractive sampling efforts.  Development and use of a CEM for compliance purposes will
 likely require higher performance capabilities (especially for sensitivity) than if the CEM were used for
 research purposes or as a method of combustion optimization. These CEM sensitivity needs will be
 lessened with the development of a short duration sampling, concentration, and analysis method.

        A more likely application for such a monitor is first as a research tool in laboratories studying
 PCDD and PCDF formation and control. As such, the instrument would need to make rapid, accurate
 measurements of PCDDs and PCDFs but could do this at concentrations much higher than needed for a
 compliance CEM.  Instrument sensitivities around ppfv levels are probably adequate so long as congeners
 (up to octa-substituted) can be identified. This type  of instrument would greatly accelerate our
 understanding of PCDD and PCDF formation and the availability of prevention and control techniques.
 Researchers have limited understanding of how combustion processes affect PCDD and PCDF formation,
 largely due to their need to relate time-integrated sampling data with dynamic formation mechanisms and
combustor conditions after an often multi-week analysis lag period.  A real-time CEM would provide
 immediate feedback on how variations in combustion operating parameters affect PCDD and PCDF
 formation and/or destruction,  thus allowing more accurate correlations and much more comprehensive
 data analysis.

        Finally, as our understanding of PCDD and PCDF formation improves, it would be valuable to
build a database using emissions from actual waste treatment processes to correlate operating conditions
with PCDD and PCDF formation. Such a database could be used to devise operating strategies to prevent
formation of PCDDs and PCDFs. This database could also be used to identify surrogates or indicators that
can be monitored more easily  and cheaply than the PCDDs and PCDFs themselves, leading to less
expensive, more widely implemented compliance and control strategies.
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        CEMs also provide data important for stakeholders* assurance that the combustion processes are
operating safely.  Stakeholders such as public interest groups, permit writers, and local citizens groups,
can play a major role in permitting waste treatment facilities. Real-time emissions data may accelerate
their acceptance, saving time and money during the permitting process.

The REMPI Technique
        REMPI (Resonance Enhanced Multi-Photon lonization) mass spectrometer systems are a highly
sensiti%re, highly species-selective, gas-phase analysis technology 121, REMPI appears promising to
measure PCDDs and PCDFs at extremely low concentrations, distinguishing between very similar species
and congeners, as required for a PCDD and PCDF CEM. One or two lasers are used to ionize the cooled
gas molecules in a small volume by absorption of two or more photons, one of which is resonant with an
electronic transition in the target molecule. Aromatic molecules have conveniently accessible vibrational
levels of the first excited singlet states (Si level),  at energies just exceeding half of the molecular
ionization energy. Thus, single color, resonant two-photon ionization schemes (1+1 REMPI) can be used
for these species. An advantage of this  approach is that "soft ionization" at relatively low laser intensities
is feasible. Typically an unfocused laser beam is used, and there is minimal fragmentation of the parent
ion. In contrast; the three-photon (2+1  REMPI) approach used for molecules such as alkyl chlorides
requires the use of higher laser intensities which  may result in significant ion fragmentation and, thus,
may compromise selectivity for some molecules.  When coupled with a Time-of-Flight Mass Spectrometer
(TOF-MS), this two-dimensional detection scheme by mass and wavelength provides high species
selectivity.

REMPI Test Requirements
        Measurement of PCDDs and PCDFs with REMPI methods requires consideration of several
issues:

»       Only PCDD and PCDF homologues which have at least all of the 2,3,7, and 8 positions occupied
        by  chorine atoms are important in determining toxicity.  There are 17 of these congeners from the
        tetrachlorinated dibenzodioxin (TCDD)  to the octachlorodibenzodioxin (OCDD). The TCDD
        congener 2,3,7,8-TCDD and the pentachlorodibenzodioxin (PeCDD) congener 1,2,3,7,8- PeCDD
        are especially important because of their large contribution to toxic equivalency, or TEQ
        (equivalence factors of 1 and 0.5,  respectively). In a CEM that measures congener-specific
        PCDDs and PCDFs, yet is limited to measurement of a subset  of these 17 congeners comprising
        the TEQ value, it  is not yet clear which specific congeners should be measured, and to what level
        of sensitivity, to be of value as a process-specific CEM.

»       The non-rigidity of PCDD and PCDF molecules, in particular the "butterfly" vibration around the
        axis through the oxygen atom(s), may demand very intense cooling to increase the electronic
        ground state population.

*•       The work of Zimmermann et al. /3/ indicates that chlorination of aromatic compounds increases
        the ionization energy and shifts the SI state towards lower levels. As a consequence, for the
        lower chlorinated  dioxins, the  SI state is more than half the ionization gap. However, for higher
        chlorinated dioxins, the SI state will be less than half the ionization gap, which could require a
        two-color (2 wavelength) REMPI  system to excite.  Previous research /4/ indicates that the
        transition of the SI state from  greater to  less than half the ionization energy may occur near the
        tetrachlorinated congeners. This is important because the TCDD isomers contain the most toxic
        congener, 2,3,7,8-TCDD, and  are therefore significant toward TEQ determination. Therefore,
        the potential ability of the relatively inexpensive one-color (1+1) REMPI method, described in
        this work, to excite the TCDD to over half of the ionization  gap would drastically simplify
        detection of this important congener.
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 *      Increased chlorination of the parent dioxin (or fiiran) molecule results in a decrease in the
        lifetime of the first excited state (increased intersystem crossing), leading to reduced REMPI
        sensitivities or precluding the single wavelength method altogether,

 »      Highly chlorinated PCDDs and PCDFs have extremely low vapor pressure.  Since REMPI is a
        gas-phase measurement technique, all sample lines, valves, and pumps must be heated to species-
        specific temperatures to prevent condensation of the target molecules.

 This leads to three key questions:

 »      Can TCDD isomers be measured with one-color (1+1) REMPI?
 »      Does REMPI show promise for measuring PCDDs and PCDFs, indicators, or precursors with
        sufficient sensitivity and species selectivity to be useful as a CEM?
 »      What are the performance requirements for a PCDD and PCDF,  indicator, or precursor CEM?

        This paper addresses the first two questions by presenting data from the DLR Jet-REMPI system
 measuring PCDD isomers with two to four chlorines.   The third question is much broader and requires, a
 combination of research in mechanistic studies and a prototype PCDD and PCDF CEM to collect data for
 identifying surrogates or indicators that can be more easily measured.
EXPERIMENTAL SYSTEM

Jet-REMPI Principle and Apparatus
        REMPI is a highly sensitive, highly species-selective gas-phase analysis technique (see e.g., /2/).
To achieve good wavelength resolution, the gas sample has to be cooled by expansion through a nozzle.
Adiabatic expansion results in low sample temperatures which increase the electronic ground state
population. The enhanced population of the ground state gives an increase in sensitivity and very sharp
REMPI transitions.

        A major improvement in REMPI sensitivity without loss in selectivity was achieved with DLR's
Jet-REMPI. In a supersonic jet, the temperature drop occurs only in a relatively narrow zone downstream
of the nozzle (i. e,, the zone where the beam still forms a jet). If ionization is carried out farther
downstream (i. e., in the molecular regime),  as in conventional REMPI setups, then the sensitivity drops
due to a decrease in beam density. Conversely, when ionizing directly in the transition zone between the
jet regime and the molecular regime, the highest sensitivities in conjunction with the lowest temperatures
are obtained.

       One or two lasers (one in our case) are used to ionize the cooled ps molecules in a small volume
by absorption of two or more (two in our case) photons, one of which is resonant with an electronic
transition (mostly Si state) in the target molecule. The laser beam is brought in orthogonal to both the
vertical molecular beam axis and the horizontal axis of the mass spectrometer. Tunable REMPI pulses
between 275 and  320 nm are generated by a frequency-doubled Nd:YAG (neodymium: yttrium,
aluminum,  garnet) pumped laser (model Infinity 40-IOOTM made by Coherent Inc., Santa Clara, CA),
system [model Scanmate OPPO™ (optical parametric power oscillator) made by Lambda Physic,
Goettingen, Germany].

       A linear  Reflectron-Time-of-Flight Mass Spectrometer (TOF-MS) (made by Stefan Kaesdorf,
Munich, Germany) analyzes the ions by mass. This two-dimensional detection scheme by mass and
wavelength provides high species selectivity. Figure 1 shows the arrangement of the DLR Jet REMPI.
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        The potential for REMPI as a CEM for combustion emissions has been discussed in the literature
 15,61 although the determined detection limits around 1 ppb were not sufficient for practical, target
 molecule applications.  A major improvement in sensitivity without loss in selectivity was achieved with
 Jet-REMPI, In a supersonic jet the temperature drop occurs only in a  relatively narrow zone downstream
 of the nozzle (i. e;, the zone where the beam still forms a jet). If ionization is carried out farther
 downstream (i. e., in the molecular regime), as in conventional REMPI setups, then the sensitivity drops
 due to a decrease in beam density. Conversely, when ionizing in the transition zone, between the jet
 regime and the molecular regime, the highest sensitivities are obtained in conjunction with the lowest
 temperatures. This simple and effective configuration cannot be implemented with conventional laser
 ionization sources, so special ion extraction optics were designed.

        Sensitivity has been further improved by increasing the ionization volume (without loss in
 resolution due to focusing techniques) and by minimizing  collisions of charged particles with the walls.
 To implement these improvements a skimmer nozzle (to reduce the pressure in the ion source) is no
 longer necessary; a pulsed sample valve (General Valve Corporation, Fairfield, NJ) is used instead to jet
 the samples into the ionization chamber.  This valve delivers a 250 ms sample pulse at a repetition rate of
 30 Hz.

        These improvements  have been shown to increase REMPI sensitivity substantially; e.g., by a
 factor of 200  for dichlorotoluene and by a factor of 1000 for naphthalene. Further sensitivity
 improvements are possible if desired (for instance by simply increasing the laser repetition rate). For more
 details see /7-10/.

        The prototype Jet-REMPI analyzer was built at DLR Stuttgart.  DLR holds a European patent on
 several features of the system II I/, and a Japanese patent and U.S. patent are pending. The first field test
 of this prototype was conducted on a small pilot scale incinerator in Karlsruhe, Germany.  No PCDDs
 and PCDFs were measured and, unfortunately, no reference methods were available to compare with Jet-
 REMPI  measurements.  However, data showing well-resolved time profiles of particular products of
 incomplete combustion (PICs) showed an unreliable correlation between PIC formation and carbon
 monoxide (CO) levels. One disadvantage of this test was the abundance of paniculate matter in the
 ionization zone, which led to a strong background signal. It is essential to prevent particles from entering
 the ion source by using a sampling system equipped with suitable filters.

 Feeder System
        To test the ability of Jet-REMPI to measure dioxin species, a temperature-sensitive permeation
 vial system /12, 13/ (described more fully in /14/) was developed to deliver gaseous species to the Jet-
 REMPI  system. The permeation vial was housed in a glass spiral mounted in the oven of a Hewlett
 Packard model 5890 gas chromatograph (GC) which acted as a constant temperature (± 1 C) bath.
 Nitrogen was used to carry the volatilized test compound from the permeation vial to the inlet of the Jet-
 REMPI analytical system. The mass volatilized was determined by mass loss of the permeation vial and,
 coupled with a mass flow controller, allowed calculation of concentrations.
EXPERIMENTAL RESULTS

Unchlorinated Dibenzodioxin (UCDD)
        Generally, REMPI sensitivities decrease with chlorination by a factor of approximately 6 per
substituted chlorine atom /10A This is due to enhanced intersystem crossing; i.e., a reduction of the
lifetime of the excited state (S1).  Although the measurement of UCDD is not difficult with regard to
sensitivity, it plays an important role in testing Jet-REMPI for the detection of PCDDs and PCDFs in
general. All of these compounds possess a so-called butterfly vibration around the symmetry line through


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 the oxygen (O) atoms. The force constant for this bending vibration is very low, which results in very
 narrow spacing between the energy levels. If the molecules are insufficiently cooled, the closely adjacent,
 vibrationally excited states will be populated in addition to the ground state.  This leads to more
 complicated or even clogged spectra.  Such an effect may be expected in particular in the case of Jet-
 REMPI with its characteristic short distance between the nozzle and skimmer.

        Figure 2 shows a well-resolved spectrum for UCDD with line widths (full width, half maximum,
 FWHM) of typically less than 0.1 run and clearly separated lines. Spectra are shown for the I2C- and 1JC-
 containing parent ions. The cooling achieved with DLR Jet REMPI is obviously sufficient to avoid
 spectral clogging caused by the high population of excited states. The different peaks in the wavelength-
 dependent spectra represent the excitation into different vibrational energy levels of the excited electronic
 state.

        The wavelength shift in Figure 2 of the ion signals containing 13C towards higher energies is
 expected for the vibrations of the heavier isotope. This discrimination between "C and I3C isotopes is an
 indication of our high selectivity. In GC/MS, 13C congeners can be separated by mass, whereas the
 retention times are virtually identical for the 12C and the IJC compounds. By contrast, with Jet REMPI one
 can use both the mass and the ionization wavelength to discriminate between isomers.

        Figure 3 shows the UCDD mass spectrum at a resonance wavelength of 295.82 nm with
 contributions due to the forementioned parent ions. No fragmentation is observed and this is typical for
 the soft ionization achieved with our low photon densities.

 2,7-dichlorodibenzodioxin (2,7-DCDD)
       The wavelength spectrum of 2,7-DCDD is shown in Figure 4. There are many more transitions
 than for UCDD, but each of them is well-resolved. According to the literature /15, 16/ the greater
 complexity in the 2,7-DCDD spectrum is due to the fewer degrees of symmetry in this molecule in
 comparison with UCDD. Again the Jet-REMPI mass spectrum exhibits no fragmentation. Therefore, only
 the parent signals are shown as an inset in Figure 4.

       Figure 5 shows a series of measurements at different concentrations used to estimate the
 minimum detectability for 2,7-DCDD. Dioxin concentrations were varied by altering the temperature of
 the dioxin feeder. The concentration at each temperature was determined by pumping the dioxin flow over
a trap for several hours and then using gravimetric analysis. These data, when extrapolated to S/N = 3,
yield a detection limit of 30 ng/dscm at a pulse energy of 0.3 mJ. Actually, we could show that increasing
 the pulse energy to 1 mJ is possible without fragmentation. In this case we would get a detection limit of 9
 ng/dscm which translates into 75 ppt by weight or 60 ppt by volume for DCDD. This is  the first on-line
detection limit reported for a DCDD isomer.  It is very favorable and surprisingly close to what  we
 recently found  for o-chlorobenzene /10/.

       These experiments showed that efforts must also be taken to ensure that the inlet valve can be
 sufficently heated to prevent condensation of dioxins.  Such heating influences the beam cooling
 mechanism and requires careful optimization of the inlet system design.

 l,7,8-trichlorodibenzodioxin(l,7,8-TrCDD)
       The wavelength spectrum for 1,7,8-TrCDD is much more complicated than that for 2,7-DCDD,
as shown in Figure 6. In addition the prototype instrument may not be providing sufficient cooling (to be
discussed later). The mass spectrum is again fragment free.  However, there are more parent peaks due to
the larger number of possibilities in the "C1/57C1 and I2C/°C distribution as shown in the inset of Figure 6.

Tetrachlorodibenzodioxins (TCDD)


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        Two problems must be addressed, which may turn out to be limiting factors for reliable
 measurement of tetra- and higher chlorinated dioxins.  From the vapor-pressure data for these species 111,
 18/ it is obvious that the sampling line and the inlet valve must be heated very carefully to avoid
 condensation.  As the degree of chlorination increases, it becomes more important to ensure that all parts
 are well heated. This heat requirement will not only increase the initial sample temperature, but it will
 also decrease the cooling effect of the jet.

        The other important aspect concerns the change in the relative positions of the energy levels upon
 chlorination, as reported in the literature 131. In the case of PCDDs and PCDFs, the ionization potential
 rises while the energy level of the SI state (which is resonantly excited by the first photon absorbed)
 decreases. This may jeopardize the applicability of the simple (1+1) single color REMPI scheme.

        Figures 7 and 8 show the REMPI spectra of 1,3,7,9-TCDD and 2,3,7,8-TCDD, respectively.
 These spectra are the first REMPI spectra of TCDDs. Although they show sharp lines, the two spectra are
 very complicated and there is considerable overlap of the spectra for the two isomers. We regard these
 spectra as preliminary and it is yet not clear whether we ionized the molecules by excitation of populated
 rotational and vibrational levels of the electronic groundstate via the vibrationless SI state or the band
 origin, the SO electronic groundstate. From Figures 7 and 8 it would appear possible that a simple single-
 color REMPI scheme can be used for the detection of TCCD.

        The REMPI mass spectrum for  1,3,7,9-TCDD (see Figure 9) is again fragment free. This
 advantage is fully appreciated by comparison with an electron impact mass spectrum of the congener.
DISCUSSION

        We suspect that the complexity of the TrCDD and TCDD wavelength spectra shown in Figures 6
through 8 is at least partly a result of insufficient cooling.  The 0.5 mm diameter gated inlet valve has
been routinely heated to 100'C, and has appeared to produce adequate jet cooling for a series of rigid
organic molecules. I1-IQI. However, for these dibenzodioxin tests, to avoid condensation of TrCDD and
TCDD, we heated the sample lines,  including the inlet valve, to 225*C.  This higher initial temperature
results in the final temperature rising approximately quadratically. Not only does the cooling process start
from a higher initial temperature, but the cooling effect itself is reduced because of the increased mean
free path resulting in fewer collisions in the expansion zone. Whereas a higher final temperature might
be acceptable for rigid molecules, in the case of dioxins, one has to assume that due to the outer ring
flexing about the central oxygens (so-called  "butterfly vibrations"), the  molecules may, to a significant
extent, remain within these vibrational excited states.  Insufficient molecular cooling results in a finite
population remaining within the exited vibrational energy levels in the electronic ground state. This
results in a crowded wavelength-dependent REMPI spectrum and a reduction of sensitivity, because the
excitation takes place from many different groundstate energy levels. The question of cooling and final
temperature will be checked in subsequent experiments by redesigning the inlet system.

        These effects, however, do not necessarily influence whether TCDD can be ionized with a single-
color (1+1) REMPI. If the ground state SI is less than half the ionization gap (as discussed in /4/), one
could still try to achieve ionization with a (1+1) single-color system via a vibrationally excited SI state.
This ionization would be unaffected by the sample temperature. Since we were able to measure ion signals
from TCDDs with the present arrangement, one can expect that sensitivity will improve only when the
sample is more sufficiently cooled. We conclude that monitoring of TCDD is possible with a (1+1)
single-color REMPI.

        A remaining question is how promising is REMPI as a CEM to measure PCDD and PCDF


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congeners, their indicators, or their precursors in combustion flue gas.  Sensitivity and species selectivity
are both important parts to this question.  REMPI certainly has adequate species selectivity, and data
presented in this paper show that levels of chlorination up to TCDD can be measured using the simple
one-color (1+1) Jet-REMPI approach. Sensitivity is affected by the conflicting requirements to heat the
molecules in the sample line to avoid condensation and cooling them in the expansion nozzle to facilitate
spectral resolution.  These requirements begin to conflict at around TCDD and larger homologues.
However, there are several ways around this conflict.

        First, the availability of real-time PCDD data may allow the establishment of correlations
between measured concentrations of lower-chlorinated dioxins and TEQ. This would allow establishment
of TEQ values using measurements of the more REMPI-accessible PCDD homologues. Second, other
molecules, such as PCDFs, when coupled with dioxin measurements, may provide strengthened
correlations with TEQ. PCDFs have a significantly higher vapor pressure than dioxins (0.43 Pa for
2,3,7,8-TCDD at 150*C and about 6 Pa for 2,3,7,8-TCDF at the same temperature) /17, 18/.
Consequently, less heating of the sample lines is required for PCDFs.  In addition, due to the relatively
rigid carbon-carbon (C-C) bond, PCDFs are less susceptible to the effect of insufficient cooling. Moreover,
it is known (see e.g., /19/) that PCDFs are present in incinerator emissions generally more abundantly
than PCDDs. This may lead to situations when 50% of the total TEQ consists of a single congener,
2,3,4,7,8-pentachlorodibenzofuran (2,3,4,7,8-PeCDF). The main disadvantage of PCDFs seems to be that
polychlorinated congeners require a two color (1+1) REMPI /4/, making a CEM somewhat more
complicated. However, we will continue to investigate the use of PCDFs as a surrogate for TEQ-related
CEM measurements.
CONCLUSIONS

        Application of Jet-REMPI in this work has determined the first detection limit for a DCDD
species and obtained the first known spectra for TrCDD and TCDD species.  The detection limit (30
ng/dscm) is too high to make use of Jet-REMPI as a compliance CEM but efforts underway reasonably
anticipate 2 orders of magnitude improvement in sensitivity. With less stringent sensitivity limits, Jet-
REMPI will be applicable to combustion process control and research studies on PCDD and PCDF
formation. As research efforts improve our understanding of PCDD and PCDF formation, it is likely that
correlations between indicators or precursors, including the lower chlorinated species measured in this
work, will enable us to predict TEQ values from these more REMPI-measurable species. In this manner,
a PCDD/PCDF compliance CEM can be developed that will derive continuous measurements from
correlative, rather than direct, measurements.
ACKNOWLEDGEMENTS

        This paper describes results of tests conducted during 1996 at EPA's National Risk Management
Research Laboratory (NRMRL) in Research Triangle Park, NC. These tests were jointly funded by
EPA/NRMRL, DOE's Office of Environmental Management Mixed Waste Focus Area, and DLR.  Sky +
provided technical management and Westinghouse Savannah River provided contractual management.
REFERENCES

1.    Ballschmiter, Bacher, Dioxine, VCH, Weinheim, Germany, 1996.
2.    U. Boesl, R. Zimmermann, C. Weickhardt, D. Lenoir, K.-W- Schramm, A. Kettrup, E.W. Schlag,
     Chemosphere 29, 1429 (1994).


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3.   R, Zimmermann, U. Boesl, D. Lenoir, A. Kettrup, Th.L. Grebner, HJ, Neusser, Int. J, Mass Spectr,
     and Ion Phys. 145, 97 (1995).
4.   R. Zimmermann, D. Lenoir, A. Kettrup, H. Nagel, U. Boesl, 26th Symp. (Int.) on Combustion, The
     Combustion Institute (1996), in press.
5.   E. A. Rohlfing, 22nd Symp. (Int) on Combustion, The Combustion Institute, 1843 (1988).
6.   B.A. Williams, T.N. Tanada, T.A. Cool, 24th Symp. (Int.) on Combustion, The Combustion
     Institute, 1587 (1992).
7.   H. Oser, R, Thanner, H.H. Grotheer, 8th Int. Symp. on Transport Phenomena in Combustion. San
     Francisco, July 1995, Proceedings, Vol. 2, pp. 1646-56.
8.   H. Oser, R. Thanner, H.H. Grotheer, European Symposium on Optics for Environmental and Public
     Safety, Munich, June 1995. SPIE 2504,15 (1995).
9.   H. Oser, R, Thanner, H.H. Grotheer, Fourth International Congress on Toxic Combustion
     Byproducts, June 1995. Comb. Sci. and Tech. 116, 567 (1996).
10.   H. Oser, R. Thanner, H.H, Grotheer, 1996 Int. Conf, on Incineration and Thermal Treatment
     Technologies. Proceedings pp. 387-392.
11.   H.H. Grotheer, H. Oser, R. Thanner, Patent No. DE-4441972, 1997.
12.   A. E. O'Keefle, G. C. Ortman, Anal. Chem. 38, 760 (1966).
13.   A. P. Altshuller, I.R. Cohen, Anal. Chem. 32, 802 (1960).
14.   H. Oser, R. Thanner, H.H. Grotheer, B,K. Gullett N. Bergan French, D. Natschke, The Japanese
     Flame Days, Osaka, May 1997, accepted for publication.
15.   C. Weickhardt, R. Zimmermann, U. Boesl, E. W. SchJag, Rapid Comm. Mass.Spectr. 7, 183
     (1993).
16.   C. Weickhardt, R. Zimmermann, K.-W. Schramm, U. Boesl, E.W. Schlag, Rapid Comm. Mass.
     Spectr. 8, 381 (1994).
17.   B.F. Rordorf, Thermochemica Acta 112, 117 (1987).
18.   K.W. Schramm, H. Fiedler,  O. Hutzinger, Staub - Reinhaltung der Luft 50, 281 (1990).
19.   R. Addink, K. Olie, Env. Sci. and Tech. 29, 1425 (1995).
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                           Sign*
                                                 295.0
                                                           't-UCDOSpeanjn(18S«mu|(x 10)
                                                      295.5   296.0  296.5
                                                         Wavelength [nm)
                                                                       297.0
                                             Fig. 2 Wavelength dependent Jet-REMPI
                                                 spectra for UCDD. Masses 184 and
                                                 185 are monitored.
Fig. 1 Setup of the DLR mobile Jet
    REMPI apparatus.  IS = ion source,
    SHG = second harmonic generation,
    PS=prism separator, OPPO =
    optical parametric power oscillator,
    DSO = digital signal oscilloscope,
    and GS/s = DSO sampling rate in
    gigasamples per second.
ton Signal [a, u.)
100

 80

 60

 40

 20
100

 80

 60

 40

 20-
     20
             60  80
                    100
                                                      140  160  180  200
                                                       Mass [amu]
                                             Fig. 3 Mass spectrum for UCDD at a
                                                 wavelength of 295.82 nm (split for
                                                 better resolution).
                                   Page 10 of 12

-------
      300   302   304   306   308
              Wavelength [nm]
 Ion Signal [a. u/

  0,5'

  0,4

  0,3

  0,2

  0,1'

  0,0

I
1

280 290
300
mass [amu]
                                                  300    304    308    312
                                                          Wavelength [nm]
                                                                          316
Fig 4 Wavelength dependent REMPI
     spectrum for 2,7-DCDD. Mass 252
     is monitored (Inset: Parent ions at a
     wavelength of 305.6 nm).
                                            Fig. 6 Wavelength dependent REMPI
                                                spectrum for 1,7,8-TrCDD. Mass
                                                286 is monitored (Inset: Parent ions
                                                at a wavelength of 304.9 nm).
Fig. 5 Jet-REMPI measurements of 2,7-
    DCDD, showing minimum
    detectability of approximately 30
    ng/dscm.
                                             Ion Signal [a. u.]
                                               OS-,
                                               0.4.

                                               0.3-
                                               0.2.

                                               o.t
                                               0.0.
                                                  310   312  314   316  318  320
                                                          Wavelength [nm]
Fig. 7 Wavelength dependent REMPI
    spectrum for 1,3,7,9-TCDD. Mass
    320 is monitored.
                                  Page 11 of 12

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  Ion Signal [a. u.]

   0.6-1
      309  310  311  312  313 314  315
             Wavelength [nm]
Fig. 8 Wavelength dependent REMPI
    spectrum for 2,3,7,8-TCDD. Mass
    320 is monitored.
Ion Signal (a. u.]
120-
100-
M-
60 •
40-
20-
0
120
too
M
60
40
20
0-





50 100





150 200





250 300 350 400
Mass [ami]
                                            Fig. 9 1,3,7,9-TCDD mass spectrum at a
                                                 wavelength of 315.65 nm (split for
                                                 better resolution).
                                  Page 12 of 12

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 NRMRL-RTP-P-207
              TECHNICAL REPORT DATA
        (Please read Instructions on the reverse before camplet
1. REPORT
  HfW/WlO/A-97/061
                           2.
4. TITLE ANDSUBTITLE
 DLR Jet-REMPI as a Continuous Emissions Monitor:
 Measurements of Chlorinated Dibenzodioxins
                                                      5. REPORT DATE
                                    6. PERFORMING ORGANIZATION CODE
7. AUTHOR.S) H. Oser> R> Thanner, H. -H. Grotheer (DLR);
 B.Gullett (EPA); N.B.French (Sky+), and D. Natschke
 (A cur ex)
                                    8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                      10. PROGRAM ELEMENT NO.
 DLR Stuttgart
 Stuttgart,  70569
 Germany
Sky +
Oakland,  CA
94611,  USA
Acurex Environmenta
PC Box 13109
RTF, NC 27709
11. CONTRACT/GRANT NO.
68-D4-0005 T3-035/-032
                                                      (A curex)
12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Air Pollution Prevention and Control Division
 Research Triangle Park, NC  27711
                                     13. TYPE OF REPORT AND PERIOD COVERED
                                     Published paper; 5/96-4/97
                                     14. SPONSORING AGENCY CODE
                                      EPA/600/13
15. SUPPLEMENTARY NOTES
                          project officer is Brian K. GuUctt, Mail Drop 65,  919 /
 541-1534. For presentation at Int. Conf. on Incineration and Thermal Treatment
 Technologies, Oakland, CA,  5/12-16/97. _
 s. ABSTRACT
             paper presents new data showing Deutsche Fo r s Chungs an st alt fur Luft
und Raumfahrt (DLR) Jet-Resonance Enhanced Multi- Photon lonization  (REMPI) mea-
surements of tri- and tetr a- chlorinated dibenzodioxins. It is believed that these are
the first data of their kind.  Their significance in demonstrating that single-color  (l-
wavelength) Jet-REMPI can measure polychlorinated dibenzodioxin (PCDD) congen-
ers at this level of chlorination is noted.  The current instrument sensitivity is in the
low (60) parts per trillion by volume (pptv)  region, and further work will focus on
improving sensitivity by at least  1 or 2 orders of magnitude. In particular, sample
cooling in the expansion nozzle appears to be insufficient to  resolve the more highly
chlorinated molecules, likely  due to the heating required in  the transfer line to avoid
sample condensation. Redesign of the inlet  valve assembly will be aimed at correc-
ting this problem.  REMPI  mass  spectrometer systems are  known for high selec-
tivity, good on-line capabilities,  and sensitivities to about 1 part per  billion by vol-
ume (ppbv). Use of REMPI as a continuous  emissions monitor  (CEM) for chlorinated
aromatic compounds in flue gases, such as PCDDs and polychlorinated dibenzofurans
(PCDFs), will require much greater sensitivities. DLR's Jet-REMPI system has
measured compounds at parts per trillion by volume (pptv).
17.
                             KEY WORDS AND DOCUMENT ANALYSIS
                DESCRIPTORS
                                          b.lOENTIFIERS/OPEN ENDED TERMS
                                                 c.  COS AT I Field/Group
Pollution
Measurement
lonization
Halohydrocarbons
Furans
Flue Gases
                         Pollution Control
                         Stationary Sources
                         Jet-Resonance Enhanced
                           Multi-Photon lonizatioi
                         Chlorinated Dibenzo-
                           dioxins
                         Dioxins
                                   13 B
                                   14G
                                   07B.07C
                                   21B
18. DISTRIBUTION STATEMENT
 Release to Public
                                          19. SECURITY CLASS (This Report)
                                          Unclassified
                                                                   21. NO. OF PAGES
                         20. SECURITY CLASS (Thispage)
                         Unclassified
                                                  22. PRICE
EPA Form 2220-1 (9-73)

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