EPA/600/R-10/050 

April 2010 

Temporal and modal characterization of DoD source air toxic emission 

factors 

Final Report 

SERDP Project Number: WP/CP1247 

Brian K. Gullett 
 

Air Pollution Prevention and Control Division 
 

National Risk Management Research Laboratory 
 

Office of Research and Development 
 

U.S. Environmental Protection Agency 
 

Research Triangle Park, North Carolina 27711 
 

Prepared for 
 

Strategic Environmental Research and Development Program
 


Department of Defense 
 

901 North Stuart Street, Suite 303 
 

Arlington, VA 22203 
 

EPA Interagency Agreement # RW-96-92280901-0 
 

RW969398430, RW969394437, RW969398433, RW969398434, RW969398435. 
 
EPA/600/R-10/050 

April 2010 

Table of Contents 

List of Tables ................................................................................................................................. iv
 


List of Figures................................................................................................................................ iv
 


List of Acronyms ......................................................................................................................... viii
 


Keywords:........................................................................................................................................x
 


Acknowledgements........................................................................................................................ xi
 


Abstract......................................................................................................................................... xii
 


Executive Summary..................................................................................................................... xiii
 


Objectives ................................................................................................................................... xvii
 


1.	 Background................................................................................................................................1
 


1.1 Emission Factors ...................................................................................................................1
 


1.2 Monitoring for Organic Toxics .............................................................................................1
 


1.3 Related Real-time Technologies for Monitoring of Trace Organic Pollutants .....................2
 


1.4 Related REMPI-TOFMS Studies on Vehicle Exhausts ........................................................2
 


1.5 Monitoring for Metals ...........................................................................................................3
 


1.6 Optical Path Methods and Field Measurements....................................................................3
 


2. Description of Equipment and Methods ....................................................................................5
 


2.1 REMPI-TOFMS ....................................................................................................................5
 


2.1.1 Laser Systems................................................................................................................7
 


2.1.2 Valve Inlet Systems.......................................................................................................9
 


2.1.3 Time of Flight Mass Spectrometer ..............................................................................10
 


2.1.4 REMPI-TOFMS Instrument........................................................................................11
 


2.1.5 Operating Procedures REMPI-TOFMS.......................................................................12
 


2.2 LIBS ....................................................................................................................................14
 


2.3 ORS .....................................................................................................................................15
 


3.	 REMPI-TOFMS: Field Ready Development and Performance Evaluation and 
 

Improvement............................................................................................................................17
 


3.1 Laser Systems......................................................................................................................17
 


3.1.1 Continuum Laser .........................................................................................................17
 


3.1.2 OPOTEK Laser............................................................................................................17
 


3.2 Pulsed Valve Operation.......................................................................................................18
 


3.3 Data Acquisition Software ..................................................................................................19
 


3.4 Calibration of REMPI-TOFMS System ..............................................................................20
 


4.	 Sampling from DoD Sources...................................................................................................21
 


5.	 Source 1: Validation of REMPI-TOFMS Measurements on a U.S. Marine Corps 
 

Diesel Generator ......................................................................................................................22
 


5.1 Experimental section ...........................................................................................................22
 


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April 2010 

5.2 Results and Discussion........................................................................................................23
 


5.2.1 Steady State Diesel Generator Results ........................................................................23
 


5.2.2 Transient Diesel Generator Results .............................................................................31
 


6. Source 1: U.S. Marine Corps Diesel Generator Air Toxic Emission Characterization...........34
 


6.1 Experimental .......................................................................................................................34
 


6.2 Results and Discussion........................................................................................................37
 


6.2.1 Steady State Emissions................................................................................................37
 


6.2.2 Emissions during Startups ...........................................................................................37
 


6.2.3 Emissions during Load Variation................................................................................41
 


7.	 Source 2: Real-Time Measurement of Trace Aromatics during Operation of Aircraft 
 

Ground Equipment...................................................................................................................44
 


7.1 Experimental .......................................................................................................................44
 


7.1.1 AGE.............................................................................................................................44
 


7.1.2 Operating and Sampling Procedures ...........................................................................45
 


7.2 Results and Discussion........................................................................................................46
 


7.3 ORS Measurements during AGE sampling.........................................................................56
 


7.3.1 Experimental Design ...................................................................................................56
 


7.3.2 ORS Instrument-Retro reflector Distance ...................................................................57
 


7.4 Data Processing ...................................................................................................................57
 


7.4.1 ORS Results.................................................................................................................58
 


8.	 Source 3: Verification Results of REMPI-TOFMS as a Real-Time PCDD/F Emission 
 

Monitor ....................................................................................................................................61
 


8.1 Materials and Methods ........................................................................................................61
 


8.1.1 Boiler testing................................................................................................................61
 


8.1.2 REMPI-TOFMS Testing .............................................................................................62
 


8.1.3 Indicator Compounds ..................................................................................................63
 


8.2 Results and Discussion........................................................................................................64
 


8.2.1 Pre-ETV results ...........................................................................................................64
 


8.2.2 ETV Results.................................................................................................................64
 


9. Source 4: Sampling from MWC Flue Gas...............................................................................68
 


9.1 Portsmouth Naval Shipyard Waste Combustor 2004..........................................................68
 


9.2 Experimental Approach.......................................................................................................68
 


9.3 Test Matrix ..........................................................................................................................69
 


9.4 Results .................................................................................................................................70
 


9.4.1 General On-site REMPI-TOFMS Instrument Performance ........................................70
 


9.4.2 REMPI-TOFMS results...............................................................................................70
 


9.4.3 Method 0023 and Method 0010 Results......................................................................73
 


9.5 Portsmouth Naval Shipyard Waste Combustor 2006..........................................................73
 


9.6 Materials and Methods ........................................................................................................75
 


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April 2010 

9.7 Results .................................................................................................................................76
 


10. Source 5: Emission Responses from HMMWVs, the M1 Abrams Tank, and the 
 

Bradley IFV .............................................................................................................................79
 


10.1Experimental .......................................................................................................................79
 


10.1.1 Platforms Tested..........................................................................................................79
 


10.1.2 Test Protocols ..............................................................................................................80
 


10.1.3 Sampling Approach .....................................................................................................80
 


10.2Results and Discussion........................................................................................................82
 


10.2.1 WV Cycle ....................................................................................................................83
 


10.2.2 HWFET Cycle .............................................................................................................85
 


10.2.3 Velocity/Gradient Cycle ..............................................................................................85
 


10.2.4 Startups ........................................................................................................................86
 


10.2.5 Bradley and Abrams ....................................................................................................87
 


10.2.6 Number Size Distributions (NSDs) .............................................................................90
 


10.3Emission Correlations .........................................................................................................90
 


11. Source 6: F-15 and F-22 Aircraft Engine Emissions...............................................................93
 


11.1Experimental Method..........................................................................................................93
 


11.1.1 Aircraft/Engine ............................................................................................................93
 


11.1.2 Testing Venue..............................................................................................................94
 


11.1.3 Exhaust Sampling........................................................................................................95
 


11.1.4 REMPI-TOFMS Sampling Approach .........................................................................95
 


11.1.5 REMPI-TOFMS Data Analysis Procedure..................................................................96
 


11.2Results .................................................................................................................................97
 


11.2.1 F-15 Tests ....................................................................................................................97
 


11.2.2 F-22 Tests ..................................................................................................................100
 


12. Conclusions............................................................................................................................108
 


13. References..............................................................................................................................110
 


14. Appendix A: List of Scientific/Technical Publications .........................................................116
 


14.1.1 Journal Articles..........................................................................................................116
 


14.2Oral and Poster Presentations............................................................................................116
 


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April 2010 

List of Tables 

Table 4-1. Source testing............................................................................................................21
 


Table 6-1. EPA sampling methods.............................................................................................35
 


Table 6-2. Air toxic emission factors determined by jet REMPI-TOFMS, OLGC, and 
 

EPA reference methods, and listed in AP-42. ..........................................................39
 


Table 6-3. RA of the three measurement methods during parallel sampling.............................40
 


Table 7-1. Emission factors for BTEX compounds during idle and full load operation. 
 

Comparison with published values...........................................................................52
 


Table 7-2. Emission factors for PAH compounds during idle and full load operation. 
 

Comparison with published values...........................................................................53
 


Table 7-3. Emission factors for aldehydes compounds during idle and full load 
 

operation. Comparison with published values..........................................................54
 


Table 8-1. Candidate TEQ surrogate compounds from pre-ETV Method 0010 
 

sampling....................................................................................................................63
 


Table 9-1. R2 for PCDD/F TEQ based on 36, 5-min samples at the MWI. ...............................75
 


Table 9-2. PCDD/F TEQ emission rates from HRGC/HRMS analyses. ...................................76
 


Table 10-1. Emission factors of M1097 and M1114 HMMWVs. ...............................................84
 


Table 11-1. Engine power settings tested.....................................................................................94
 


Table 11-2. Summary of F-15 engine tests. .................................................................................97
 


Table 11-3. Test schedule for the F-22 engine tests...................................................................101
 


Table 11-4. A comparison between Summa canister, REMPI-TOFMS and PTR-MS data 
 

with the PTR-MS average calculated from provided Battelle data and 

canister sampling time. ...........................................................................................102
 


List of Figures 

Figure 2-1. REMPI-TOFMS instrument........................................................................................5
 


Figure 2-2 (a, b, c). REMPI ionization principles.........................................................................6
 


Figure 2-3. Top View of the Movable Inlet Mounting Plate.......................................................10
 


Figure 2-4. Schematic of LR10 compact 19” rack-mount reflectron TOFMS............................11
 


Figure 2-5. Two views of large REMPI-TOFMS system............................................................11
 


Figure 2-6. Compact REMPI-TOFMS instrument. .....................................................................12
 


Figure 2-7. Detection of multiple analytes using wavelength-dependent ionization. .................13
 


Figure 2-8. Transient benzene concentrations detected in vehicle exhaust while running 
 

a dynamometer-based RS. ........................................................................................13
 


Figure 2-9. REMPI-TOFMS mass spectrum at benzene (78) wavelength as observed in 
 

vehicle exhaust..........................................................................................................14
 


Figure 2-10. Schematic setup of LIBS system. ............................................................................15
 


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Figure 2-11. Setup ORS during sampling......................................................................................16
 


Figure 3-1. Wavelength emitted from laser with increased ambient temperature 

(increase in temperature for scan 1 to 9)...................................................................18
 


Figure 3-2. Snapshot of data acquisition software in operation. .................................................20
 


Figure 5-1. U.S. Marine Corps tactical utility generator. ............................................................23
 


Figure 5-2. A 3D survey scan (mass, wavelength, ion signal) ....................................................24
 


Figure 5-3. Time-of-flight mass spectrum recorded at (A) optimum styrene (287.7 nm) 

and (B) Benzene (259.0 nm) ionization wavelength in diesel generator 

exhaust. .....................................................................................................................25
 


Figure 5-4. Comparison of 1+1 REMPI wavelength spectrum recorded for toluene in 

diesel generator exhaust and from calibration gas standard (the latter scaled 

to equal intensity). ....................................................................................................26
 


Figure 5-5. Monitored REMPI-TOFMS signal for reference gas (C6D6) and benzene in 
 

exhaust diesel generator............................................................................................26
 


Figure 5-6. On-line REMPI-TOFMS ion signal traces of nine individual target analytes, 
 

labeled with mass, chemical name and used, most favorable ionization 

wavelength................................................................................................................27
 


Figure 5-7. Recorded ion signals during nine repeats of the analyte cycle. ................................28
 


Figure 5-8. Observed day to day variations in estimated concentrations of BTEX-like 
 

analytes in exhaust diesel generator..........................................................................29
 


Figure 5-9. Comparison between extractive and REMPI-TOFMS concentrations for 
 

three exhaust analytes. ..............................................................................................30
 


Figure 5-10 (a, b). (a) Real-time transient benzene emissions following a cold start. (b) 
 

Normalized ion signal traces for single aromatic ring (thin lines) and double 

aromatic ring (fat lines) analytes. .............................................................................32
 


Figure 5-11. Transient REMPI-TOFMS results. ...........................................................................33
 


Figure 6-1. Cold and hot start-up emissions of benzene, naphthalene, CO, and CO2 with 
 

exhaust temperature. .................................................................................................38
 


Figure 6-2. Temporal temperature and particle-bound PAH concentrations in the diesel 
 

exhaust. .....................................................................................................................41
 


Figure 6-3. Load change emissions of benzene, naphthalene, CO, and CO2 with exhaust 
 

temperature. ..............................................................................................................42
 


Figure 6-4. Temperature distribution and particle-bound PAH concentrations under 
 

varying loads.............................................................................................................43
 


Figure 7-1. Aircraft ground equipment outside EPA facilities....................................................45
 


Figure 7-2. REMPI-TOFMS time-resolved trace of cold startup, idle (low) load, and 
 

high load conditions..................................................................................................47
 


Figure 7-3. REMPI-TOFMS wavelength-resolved trace during idle (low) load condition.
 


..................................................................................................................................48
 


Figure 7-4. Comparison of (selected) AGE wavelength spectra versus the TO-14 
 

calibrated gas standard..............................................................................................49
 


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April 2010 

Figure 7-5. Comparison between GC/MS and REMPI-TOFMS analysis of summa 

canister gases. ...........................................................................................................50
 


Figure 7-6. Comparison between REMPI-TOFMS measurements at low load and TO15 
 

method analyses by two laboratories........................................................................50
 


Figure 7-7. REMPI-TOFMS and CO and CO2 CEM concentrations during a series of 

startups (the initial startup was a cold start) and shutdowns (for refueling), 

operating at high, high, then idle load. Range of data (barely visible) are 

shown for benzene. ...................................................................................................51
 


Figure 7-8. Comparison of startup responses of benzene and naphthalene for the AGE 

and diesel generator. .................................................................................................56
 


Figure 7-9. ORS measurement configuration..............................................................................57
 


Figure 7-10. Comparison of the reference spectrum of formaldehyde (blue trace) to a 
 

measured spectrum of the turbine plume (red trace) ................................................59
 


Figure 7-11. Comparison of the reference spectrum of ethylene (red trace) to a measured 
 

spectrum of the turbine plume (blue trace)...............................................................59
 


Figure 7-12. Comparison of the reference spectrum of n-octane (red trace) to a measured 
 

spectrum of the turbine plume (blue trace)...............................................................60
 


Figure 7-13. Comparison between CEM and ORS measurements................................................60
 


Figure 8-1. Marine package boiler at EPA facilities. ..................................................................62
 


Figure 8-2. Pre-ETV phase determination of MClBz as a PCDD/F TEQ surrogate...................65
 


Figure 8-3. REMPI-TOFMS mass spectrum of MClBz with inset of relevant mass range. 
 

0.1 ppb for a 4 min averaging period, S/N = 3. ........................................................65
 


Figure 8-4. ETV phase comparison of TEQ from Method 23 and MClBz prediction 
 

Figure 8-5. Comparison of M-10 and time-integrated REMPI predictions of PCDD/F 
 

Figure 9-1. Comparison between real time results for PAHs acquired with REMPITOFMS at identical Boiler A and Boiler B for two 4-h intervals that were
 


Figure 9-2. Emissions of PAHs during shutdown of boiler. Break in data during filter 
 

Figure 9-3. A 3-dimensional qualitative depiction PAH emissions during the startup of a 
 

Figure 9-4. Emissions of selected PAHs and monochlorobenzene during startup of 
 

Figure 9-5. Comparison between REMPI-TOFMS time averaged concentrations and 
 

those from conventional Method 0010 sampling during the course of the 
 

from REMPI-TOFMS measurements.......................................................................66
 


TEQ with actual M-23 measurements. .....................................................................67
 


typical of the normal (steady state) operation...........................................................71
 


change. ......................................................................................................................71
 


boiler (at ~ t=10 min)................................................................................................72
 


boiler (at ~ 9:00 AM)................................................................................................72
 


sampling campaign. ..................................................................................................74
 


Figure 9-6. Mass spectrum recorded at monochlorobenzene wavelength (~ 270.8 nm).............74
 


Figure 9-7. PCDD/F TEQ, conventional 1,2,4 triClBz and mass 18- REMPI-TOFMS 
 

ion signal over the coarse of the four day sampling campaign.................................77
 


Figure 9-8. Recorded REMPI-TOFMS ion signals for mass 180/182/184. ................................78
 


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April 2010 

Figure 10-1. Emission transients for the M1097 and M1114 HMMWVs. A: West 

Virginia and B: Highway HWFET cycles. ...............................................................80
 


Figure 10-2. Steady-state benzene, naphthalene, methylnaphthalene, CO, and CO2
 


emissions from the M1097 and M1114 HMMWVs during a velocity and 

gradient stepped cycle...............................................................................................86
 


Figure 10-3. Cold start emissions of benzene, naphthalene, methylnaphthalene, CO, and 

CO2 and PM size distribution for the M1097 (left) and M1114 (right) 

HMMWVs. ...............................................................................................................87
 


Figure 10-4. Steady state organic emissions at analyte-specific wavelengths, A: M1 

Abrams, low and high idle conditions, and B: Bradley IFV, idle 0 and 2 
 

trials. Inset: real-time variance of organics at low idle.............................................88
 


Figure 10-5. Cold and warm start emissions of benzene, naphthalene, and 
 

methylnaphthalene for the Bradley IFV and M1 Abrams. .......................................89
 


Figure 10-6. Benzene, naphthalene, and methylnaphthalene emissions during a shutdown 
 

Figure 10-7. Steady state PM size distribution for the M1097 HMMWV (top) and M1114 
 

Figure 10-8. Steady state REMPI, ELPI, and CEM data for the M1097 (left) and M1114 
 

Figure 11-11. Comparison REMPI-TOFMS with PTR-MS for benzene and naphthalene.
 

Figure 11-12. Comparison between time averaged REMPI-TOFMS benzene data and 
 

of the M1 Abrams.....................................................................................................89
 


HMMWV (bottom) during a stepped velocity and gradient cycle. ..........................91
 


(right). .......................................................................................................................92
 


Figure 11-1. Trimpad and location of probe and instrument trailers with respect to aircraft........95
 


Figure 11-2. Concentration profiles during F-15 engines testing..................................................98
 


Figure 11-3. Concentration profiles during second sequence of F-15 engine testing. ..................98
 


Figure 11-4. Concentration profiles during the 30 minute test 2B1..............................................99
 


Figure 11-5. Complete 2B series. ..................................................................................................99
 


Figure 11-6. Concentration during first sampling of F-22 engine...............................................103
 


Figure 11-7. Concentrations during 4A and 4B sampling of F-22 engine. .................................103
 


Figure 11-8. Concentrations for other REMPI-TOFMS detectable analytes. .............................104
 


Figure 11-9. Comparison between REMPI-TOFMS and PTR-MS.............................................104
 


Figure 11-10. Benzene and PAHs response during afterburner test.........................................105
 


106
 


Summa canister results. ..........................................................................................106
 


Figure 11-13. Benzene concentrations as function of thrust level F-22 engine........................107
 


Figure 11-14. Benzene emission factor (μg/g carbon burned) for F-22 engines. .....................107
 


vii 
AFB Air Force Base 

AGE Aircraft Ground Equipment 

APCS Air Pollution Control System 

APIMS Air Permit Information Management System 

APU Auxiliary Power Unit 

AVG Average 

AWMA Air and Waste Management Association 

AZ Arizona 

BTEX Benzene, Toluene, Ethylbenzene, and Xylenes 

CAA Clean Air Act 

CEM Continuous Emission Monitors 

CLS Classical Least Squares 

CO Carbon monoxide 

CO2 Carbon Dioxide 

DNPH 2,4-Dinitrophenylhydrazine 

DoD Department of Defense 

DOE Department of Energy 

ECD Electron Capture Detector 

ELPI Electrical Low Pressure Impactor 

EPA Environmental Protection Agency 

ETV Environmental Technology Verification 

FID Flame Ionization Detector 

FTIR Fourier Transform Infrared Spectroscopy 

FWHM Full Width Half Maximum 

GC Gas Chromatography 

GC/MS Gas Chromatography/Mass Spectrometry 

GHz Gigahertz 

HAP Hazardous Air Pollutants 

HEPA High Efficiency Particulate Arresting 

HMMWV High Mobility Multipurpose Wheeled Vehicle 

HPLC High Performance Liquid Chromatography 

HRGC High Resolution Gas Chromatography 

HRMS High Resolution Mass Spectroscopy 

HWFET Highway Fuel Economy Test 

IFV Infantry Fighting Vehicles 

LACEA Laser Applications to Chemical and Environmental Analysis 

LIBS Laser Induced Breakdown Spectroscopy 

LRMS Low Resolution Mass Spectrometry 

LTA Low Temperature Ashing 

MHz Megahertz 

MS Mass Spectrometry 

MWC Municipal Waste Combustor 

ND Non Detect 

NDIR Non-dispersive Infrared Analyzer 

EPA/600/R-10/050 

April 2010 

List of Acronyms 

viii 
NIST 	 

NO 

National Institute of Standards and Technology 

Nitric Oxide 

NSD 	 Number Size Distributions 

OLGC 	 

OP-FTIR 	 

OPO 	 

ORS 	 

PAC 	 

PAH 

PAS 	 

On Line Gas Chromatography 

Open Path Fourier Transform Infrared 

Optical Parametric Oscillators 

Optical Remote Sensing 

Path Average Concentration 

Polycyclic Aromatic Hydrocarbons 

Photoelectric Aerosol Sensor 

PCDD 

PCDD/F 

Polychlorinated Dibenzodioxins Dibenzofurans 

PolyChlorinated Dibenzo-p-Dioxin and polychlorinated 

dibenzoFuran 

PIC 	 

PM 

Products of Incomplete Combustion 

Particulate Matter 

PTFE 

PTRMS 	 

PTR-MS 	 

RA 

RDF 	 

PolyTetraFluoroEthylene 

Proton Transfer Reaction Mass Spectrometer 

Proton Transfer Reaction - Mass Spectrometry 

Relative Accuracy 

Refuse Derived Fuel 

REMPI 	 Resonance Enhanced Multi Photon Ionization 

REMPI-TOFMS 	 

RPM 

RSD 	 

Time of Flight Mass Spectrometry 

Revolutions per Minute 

Relative Standard Deviation 

RTP 	 

RWS 

S/N 

SDA 	 

STP 

Research Triangle Park 

Roadway Simulator 

Signal Noise 

Spray Dryer Catwalk Area 

Standard Pressure 

SVOC 	 

TEF 	 

TEQ 

TIC 

TOFMS 	 

U.S. 

Semi Volatile Organic Compounds 

Toxic Equivalency Factor 

Toxicity Equivalent 

Tentatively Identified Compounds 

Time of Flight Mass Spectrometry 

United States 

UV Ultraviolet 

VOC Volatile Organic Compounds 

EPA/600/R-10/050 

April 2010 

ix 
Resonance-enhanced multiphoton ionization spectroscopy 

REMPI 

Time of flight mass spectrometry 

TOFMS 

Laser-induced breakdown spectroscopy 

LIBS 

Open path measurements 

Air toxics 

Air pollutants 

Measurement 

Emission factors 

Diesel generator 

Auxiliary power unit 

Municipal waste combustor 

HMMWV 

Abrams tank 

Bradley Infantry Fighting Vehicle 

F-15 

F-22 

EPA/600/R-10/050 

April 2010 

Keywords: 

x 
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April 2010 

Acknowledgements 

The investigators and authors would like to extend their appreciation and acknowledge to the 

SERDP organization for funding this research program, and would also like to thank the 

following organizations and individuals that contributed to the success of this project: 

•	 Drs. Abderrahmane Touati and Lukas Oudejans of Arcadis U.S., Inc. enacted the testing 

programs and performed the organic measurements throughout this project. 

•	 Drs. Harald Oser and Michael Coggiola of SRI International were critical providers of the 

resonance enhanced multi photon ionization (REMPI) technology and able consultants 

throughout the program. 

•	 Dr. Andrzej Miziolek of the Army Research Laboratory was the primary motivator of the 

laser induced breakdown spectroscopy (LIBS)-related work. 

•	 Drs. Shannon Serre and Emily Gibb-Snyder (United States (U.S.) Environmental 

Protection Agency (EPA), National Homeland Security Research Center) provided 

critical expertise with the LIBS instrument and experimentation. 

•	 Messrs. Whaley, Huffman, and Winberry from U.S. Marine Corps at Camp Lejeune for 

loan of the tactical generator 

•	 Col. Steven Aylor, SMSgt David Caldwell, and Sgts. Thomas Clemens, George Garnot, 

and James Scaccia from Pope Air Force Base (AFB) for the loan of the AGE. 

•	 Dr. Ken Cowen from Battelle Memorial Institute 

•	 Messrs. Michael Barnett and Jeff Landrum from the Southern Public Service Authority 

Power Plant (Portsmouth, Virginia) 

•	 Messrs. William Bolt, Jason Jack, and Gregg Schultz from the Aberdeen Test Center, 

Maryland, for access to vehicles and the Roadway Simulator (RWS). 

•	 Dr. Howard Mayfield from Tyndall AFB, Panama City, Florida 

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Abstract 

This project tested three, real-/near real-time monitoring techniques to develop air toxic emission 

factors for Department of Defense (DoD) platform sources. These techniques included: 

resonance enhanced multi photon ionization time of flight mass spectrometry (REMPI-TOFMS) 

for organic air toxics, laser induced breakdown spectroscopy (LIBS) for metallic air toxics, and 

optical remote sensing (ORS) methods for measurement of criteria pollutants and other 

hazardous air pollutants (HAPs). Conventional emission measurements were used for 

verification of the real-time monitoring results. The REMPI-TOFMS system was demonstrated 

on the following: 

•	 a United States U.S. Marine Corps (USMC) diesel generator, 

•	 a U.S. Air Force auxiliary power unit (APU), 

•	 the waste combustor at the Portsmouth Naval Shipyard, during a multi-monitor 

Environmental Technology Verification (ETV) test for dioxin monitoring systems, 

•	 two dynamometer-driven high mobility multi-purpose wheeled vehicles (HMMWVs), 

•	 an idling Abrams battle tank, 

•	 a Bradley infantry fighting vehicle (IFV), and 

•	 an F-15 and multiple F-22 U.S. Air Force aircraft engines. 

LIBS was tested and applied solely to the U.S. Marine Corps diesel generator. The high detection 

limits of LIBS for toxic metals limited its usefulness as a real time analyzer for most DoD 

sources. ORS was tested only on the APU with satisfactory results for non-condensable 

combustion products [carbon monoxide (CO), carbon dioxide (CO2)] but with limited success on 

condensable volatile organic by-products. This program demonstrated the ability to measure 

trace aromatics with REMPI-TOFMS in harsh environments and with a high degree of accuracy 

and precision. 

xii 
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April 2010 

Executive Summary 

The Department of Defense (DoD) quantifies air pollutant emissions from its facilities and 

weapon platforms in order to identify potential sources needing remediation and to comply with 

base permitting requirements. These pollutants include the so-called criteria pollutants such as 

nitrogen oxides and particulate matter (PM) as well as trace air toxics. This information further 

enables DoD to employ measures such as adoption of preventive operational modes or 

equipment substitution in order to minimize disruption of training and operational activities. 

Information on source air toxics is particularly limited, primarily due to lack of automated 

methods of sample analysis, underscoring the need for innovative approaches, instruments, and 

methods to achieve these ends. Since a large portion of DoD sources are mobile sources that 

operate under non-steady state modes, most of the current extractive methods cannot resolve 

modal or temporal changes in emissions that result from such type of sources, leading to gaps in 

the overall DoD air toxics emissions inventory. The United States Environmental Protection 

Agency (EPA), under a DoD Strategic Environmental Research and Development Program, 

“Source and Ambient Air Monitoring for DoD Operations (WP/CP1247),” initiated and 

completed a research project to develop and validate the latest state-of-the-art technologies for 

these measurements. These technologies would provide modal and time resolved measurements 

of air toxics emissions from various types of point- and mobile-sources. Such information could 

be used, for example, in the Air Force's Air Permit Information Management System (APIMS), 

an emission inventory system currently used by Hill AFB and being adopted DoD-wide, as well 

as to improve EPA's AP-42 emission factor system. This report presents the results of this 

project. 

The project objective was approached through the applied development of a combination of three 

unique, versatile, field-ready, real or near real-time monitoring techniques that can measure trace 

air toxic levels: resonance enhanced multi photon ionization time of flight mass spectrometry 

(REMPI-TOFMS) for organic air toxics, laser induced breakdown spectroscopy (LIBS) for 

metallic air toxics, and optical remote sensing (ORS) methods for verification and measurements 

of criteria pollutants and other hazardous air pollutants (HAPs). Conventional emission 

measurements were used for verification of the real-time monitoring results and assessment of 

their accuracy. A fast sampling method that separates particles from gases was successfully 

integrated in an overall sampling scheme designed to conserve the integrity of the sample, avoid 

any particle/gas partitioning, while bringing the quantity of target compounds above the 

detection limit of the REMPI-TOFMS measurement technique. 

Satisfactory development of the REMPI-TOFMS system, from laboratory to a field-ready real or 

near real time monitor of trace organic aromatic pollutants system, was performed at the EPA 

research facility in Research Triangle Park (RTP), North Carolina. The system has been 

demonstrated on the following: 

•	 a U.S. Marine Corps (USMC) diesel generator, 

•	 a U.S. Air Force auxiliary power unit (APU), 

•	 the waste combustor at the Portsmouth Naval Shipyard, during a multi-monitor 

Environmental Technology Verification (ETV) test for dioxin monitoring systems, 

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EPA/600/R-10/050 

April 2010 

•	 two dynamometer-driven High Mobility Multi-purpose Wheeled Vehicles (HMMWVs), 

•	 an idling Abrams battle tank, 

•	 a Bradley infantry fighting vehicle (IFV), and 

•	 an F-15 and multiple F-22 U.S. Air Force aircraft engines. 

LIBS was tested and applied solely to the U.S. Marine Corps diesel generator. The high detection 

limits of LIBS for toxic metals limited its usefulness as a real time analyzer for most DoD 

sources, resulting in the withdrawal of the U.S. Army Research Laboratory from the SERDP 

project. ORS was tested only on the APU with satisfactory results for non-condensable 

combustion products [carbon monoxide (CO), carbon dioxide (CO2)] but with limited success on 

condensable volatile organic by-products thereby eliminating the opportunity to directly compare 

the ORS and REMPI-TOFMS technology. 

During the SERDP funding period 2003-2008, the following (in approximate chronological 

order) achievements were made: 

•	 A large laboratory scale size REMPI-TOFMS system has been applied to the exhaust of 

an USMC diesel generator. Steady state benzene, toluene, ethylbenzene, and xylenes 

(BTEX) emissions on the order of 100 ppb were observed. Cold start benzene emissions 

were observed on the order of 14 ppm, which lasted ~ 20-30 seconds. The REMPITOFMS results were successfully compared to measurements obtained by conventional 

certified EPA methods, and validated the system as responsive and functional with 

complex mixtures. LIBS results from the USMC diesel generator study were found to be 

unsatisfactory due to the lack of sensitivity for real time detection of metals in the 

exhaust gas and limited detection of metals on soot loaded filters collected during the 

sampling of the exhaust. LIBS plus low temperature ashing (LTA) showed positive 

results, improving metal discrimination from highly carbonaceous backgrounds. 

However, the examined DoD sources to date did not show sufficient metal emissions to 

be quantified by LIBS with LTA. 

•	 Testing by SRI International on a compact REMPI-TOFMS indicated a minimal sacrifice 

of system quality and so the small system was approved for design and construction by 

SERDP. A first compact REMPI-TOFMS system was delivered to EPA in April 2004. 

•	 REMPI-TOFMS emission measurements were completed on an Auxiliary Power 

Unit/Aircraft Ground Equipment (APU/AGE). This was a turbine engine compressor 

from Pope AFB (type A/M32A-95). Modal-dependent results for benzene, toluene, 

ethylbenzene, o-, m-, p-xylenes, and styrene showed excellent agreement with standard 

EPA sampling methods and gas chromatography/mass spectrometry (GC/MS) analysis. 

The ORS system was applied to this source, and measurements for criteria pollutants 

such as CO2 and CO emissions were completed. In addition to these species, absorption 

bands for formaldehyde, ethylene, and aliphatic mixtures that originated from the fuels 

were found in the measured spectra. 

•	 A prototype compact REMPI-TOFMS developed under another project was taken into 

the field (December 2004) to the Portsmouth Naval Shipyard waste combustor and tested 

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on the flue gas prior to the air-pollution-cleaning-device. The sampling system platform 

consisted of the REMPI-TOFMS system and a novel rotating filtering system designed to 

conserve the integrity of the sample and avoid or minimize any particle or gas 

partitioning. Real time detection of various small polycyclic aromatic hydrocarbons 

(PAHs) and monochlorobenzene in the flue gas of the combustor was accomplished. 

Results from parallel conventional sampling for dioxins and furans and semivolatiles 

were used to establish correlations between the aforementioned analyte classes. 

•	 The design for the SERDP-funded REMPI-TOFMS field unit was submitted in February 

2004 as a required SERDP “Go/No Go” deliverable. The design consisted primarily of a 

compact laser system and rack mounted TOFMS for organics measurements, with two 

distinct inlet types for increased flexibility. The simpler inlet system could be used with a 

fixed frequency laser system. 

•	 The compact REMPI-TOFMS system was delivered to EPA in May, 2005 after an initial 

evaluation at SRI International. 

•	 The REMPI-TOFMS system participated in an EPA ETV test at the EPA laboratories in 

RTP, NC. The ETV test verified the performance of four different detection systems for 

chlorinated dioxins, trace air toxics. This was the first fully international ETV test, with 

participants from Japan, Austria, and Germany complementing the EPA-SRI 

International participation. The ETV verification reports are available at 

http://www.epa.gov/etv/vt-ams.html#dems. 

•	 The capabilities of REMPI-TOFMS towards detection of higher-chlorinated benzenes 

were extended after the addition of a second (fixed) wavelength option for a two color 

REMPI approach on one of the two compact systems. Results showed minimal loss in 

REMPI-TOFMS sensitivity with increasing level of chlorination while maintaining the 

ability to separate individual isomers. 

•	 The REMPI-TOFMS instrument was taken to the Aberdeen Test Center’s RWS for 

sampling of exhausts from two different (M1097 and M1114) HMMWVs as driven on 

various simulated roadway profiles as well as steady state velocity profiles. It included 

parallel sampling for CO, CO2 and PM [via an electrical low pressure impactor, (ELPI)]. 

Additional data were obtained from the exhausts of M1 Abrams and Bradley track 

vehicles under start-up, shutdown, and stationary idle conditions. A journal paper 

detailing the performance of REMPI-TOFMS in characterizing real-time air toxic 

emissions during the Aberdeen RWS tests has been submitted to Atmospheric 

Environment entitled “Transient PAH, PM, CO, and CO2 Emission Responses from 

HMMWVs, the M1 Abrams tank, and the Bradley Infantry Fighting Vehicle” by Brian 

Gullett, Lukas Oudejans, and Abderrahmane Touati (2009). 

•	 Two compact REMPI-TOFMS instruments were taken into the field (December 2006) to 

the Portsmouth Naval Shipyard waste combustor and tested on the flue gas before the gas 

entered the air-pollution-cleaning-system. One instrument monitored PAHs while the 

other (two-color) REMPI-TOFMS instrument was focused on real time detection of 

1,2,4-trichlorobenzene as a potential indicator of dioxin toxicity based on previously 

obtained results at the same combustor facility. 

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•	 The REMPI-TOFMS instrument was deployed to Tyndall AFB, Florida, for sampling of 

jet engine exhausts in collaboration with Battelle Memorial Institute. Emission factors 

were obtained for individual engines from an F-15 jet aircraft and four F-22 aircraft as 

operated on a trimpad. Results were consistent and found to be in good (benzene) to fair 

(naphthalene) agreement with proton transfer reaction MS (PTRMS), another real time 

detection method for these compounds. A comparison of the time averaged REMPITOFMS data with conventionally sampled summa canisters was good across the whole 

(benzene) dataset. The results are currently (July, 2009) being written into a paper primeauthored by Battelle. 

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Objectives 

This project applied state-of-the-art trace pollutant detection technologies for the determination 

of emission factors for Department of Defense (DoD) sources. Results from these technologies 

were to be verified via comparisons with conventional extractive sampling measurement 

techniques. The ultimate results will provide temporal and spatial measurements of the air toxics 

at tested DoD sources. The state-of-the-art technologies are: 

•	 Jet Resonance Enhanced Multiphoton Ionization (REMPI)-Time of Flight Mass 
 

Spectrometer (TOFMS) 
 

•	 Laser Induced Breakdown Spectroscopy (LIBS) 

•	 Optical Remote Sensing (ORS) 

The United States Environmental Protection Agency (EPA) regulates emissions of air toxics 

under the EPA - Clean Air Act (CAA) and DoD needs to address the potential impacts of these 

regulations on its operations. Identification of potential DoD sources which contribute to ambient 

air toxic levels, mobile sources in particular, will permit DoD to devise strategies to control and 

minimize emissions of air toxic pollutants from its facilities and from its on-road and non-road 

sources. Currently, the major DoD air emission database for toxic air compounds is very limited 

in scope since measurement methods for many of the 188 air toxics listed in the CAA have not 

yet been developed; further, when these measurement methods have been developed, most of 

them do not produce temporally and spatially resolved measurements. Spatially and temporally 

resolved emission measurements are needed to assess their impact, if any, on ambient air toxic 

levels, and to determine what operational modes contribute significantly to these emissions. 

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1. Background 

1.1 Emission Factors 

Source-specific emission factors are often required in order to comply with state reporting 

regulations or permit requirements which requires a quantitative emissions inventory of more 

than 500 species of toxic air pollutants (Levy et al., 1993). Preference is usually given to 

sampled information rather than use of generic emission factors. However, both sampling data 

and emission factors are limited in breadth since relatively few sources have been characterized 

for the approximately 188 defined hazardous air pollutants (HAPs) which include both organic 

and metallic compounds (EPA, 2004). This fact reflects the difficulty and cost of assessing a 

multitude of emissions from a myriad of sources. A further complication of emissions 

quantification is that many of these methods were validated on specific sources and are of 

uncertain universal applicability. Very few of the current extractive methods can resolve modal 

or temporal changes in emissions that can be related to, for example, load changes or start-ups. 

For some sources these non-steady-state emissions are suspected to be a significant portion of the 

total air pollution emitted, and hence, their quantification may be important towards determining 

average emission factors, pollutant exposure, and mode-specific pollutant minimization. 

Protocols for source emissions characterization are a function of sampling and analytical 

limitations. Analytical detection limits also determine sampling protocols, primarily related to 

sample volume collection time necessary to avoid non-detects. For HAPs, these limitations can 

be particularly influential, since HAP concentrations are typically significantly lower than other 

pollutants such as criteria pollutants NOx, CO, and SO2. Hence, sampling protocols for HAPs 

typically require long-term, steady state monitoring and this requirement prevents observation of 

HAP transients. 

1.2 Monitoring for Organic Toxics 

Analyses for trace organic HAPs typically require a 4 h extractive sample taken on an annual or 

less frequent basis and lengthy laboratory analyses which are not conducive to prompt feedback. 

From a regulatory or public interest viewpoint, this results in an infrequent and potentially 

minimally representative monitoring scheme. The conventional methods also provide little 

assurance that subsequent emissions remain controlled, especially during periods of transient 

upsets, such as startups and shutdowns, when emissions are typically higher. 

Real time detection, high sensitivity, and high selectivity are three key requirements toward 

process control for combustion-derived HAPs. Recent technological advances in measurement of 

HAPs show promise for continuous, real time monitoring. This raises the possibility of 

minimizing their formation through feedback to the combustion process control, assurance to the 

public of compliance, and minimization of over-design of gas cleaning systems. Since the typical 

ppq-level concentrations of the toxic HAP congeners are beyond the detection limits (~ 100 ppt) 

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of developing monitoring technologies, two strategies have been adopted: (1) use of higher 

concentration indicator, or surrogate, compounds to infer HAP concentrations of trace HAP 

compounds such as polychlorinated dibenzodioxins/dibenzofurans (PCDDs/Fs), and (2) 

concentration of emissions on a sorbent followed by a purge and analysis. Indicator compounds 

are determined by conventional sampling and analysis (GC/MS) and are chemically similar 

compounds to the target HAPs. These indicator compounds may be precursors to PCDDs/Fs or 

pollutants formed in similar, parallel reactions. The universality of these indicator compounds 

across facility types remains to be investigated, but they likely vary somewhat depending on the 

plant type, the waste and fuel types, and plant operating and combustion conditions. 

The presence of a real time monitor raises the first possibility to provide operational feedback to 

minimize the formation of HAPs, such as polychlorinated dibenzo-p-doxin and polychlorinated 

dibenzofuran (PCDD/F), as well as characterization of emissions during operational transients. 

This would be an important capability for distinguishing effects of operating modes or air 

pollution control equipment failures on HAP emissions. Indeed recent work (Gass, 2002; Gullett 

et al., 2006) has demonstrated seven-fold increases in PCDD/F emissions during 1 h combustor 

shutdowns and startups, consistent with other work (Gross et al., 2004; Neuer-Etscheidt et al., 

2006) in which PCDD/F raw gas levels increased by one to two orders of magnitude during 

transient combustion conditions. The extent to which these transient emissions may affect shortand long-term stack emission values and, hence, compliance issues, is undetermined. The rapid 

variation of PCDD/F, as well as other co-pollutants, due to transients, fuel changes, and 

operating variations suggests that fast on-line monitoring is necessary in order to effect changes 

in operating conditions that will reduce or prevent conditions favorable to PCDD/F formation. 

Work with REMPI-TOFMS at an industrial hazardous waste incinerator was successfully able to 

monitor aromatics including monochlorobenzene during the introduction of barrels of liquid 

hazardous waste (Heger et al., 2001), finding transient evolution of the pollutants. The ability to 

measure facility transients for indicator concentrations with REMPI-TOFMS and to correlate 

their levels with toxicity equivalent (TEQ) values has yet to be established. 

1.3 Related Real-time Technologies for Monitoring of Trace Organic Pollutants 

Only a few studies exist in which low molecular weight hydrocarbons have been analyzed in 

detail for diesel trucks, air ground equipment or Army vehicles. The typical extractive method 

with GC or GC/MS analysis does not detect transient emission events, such as a cold starts, since 

the timescales of the event are much shorter than the typical sampling time of several minutes for 

extractive sampling. GC/MS also prevents full speciation of some isomers as in the case of 

xylenes. Developing technologies such as SPI-TOFMS or PTR-MS are able to detect most 

BTEX compounds as present in gasoline automobile exhaust in real time. However, these 

methods lack isomer selectivity and the generally encountered detection limits for SPI-TOFMS 

are insufficient to detect a fairly large subset of the aromatic compounds present in modern 

vehicle exhaust gas flows. 

1.4 Related REMPI-TOFMS Studies on Vehicle Exhausts 

The REMPI-TOFMS technique combined with a supersonic expansion has been developed over 

the last decade as an isomer selective, sensitive and real time monitor of aromatic organic 

compounds. The sensitivity and rapidity of REMPI-TOFMS outperforms current extractive 

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methods, enabling characterizations of transients and immediate feedback to the operator of the 

emissions source. The application of REMPI-TOFMS to vehicle exhaust so far has been limited 

to studies on exhaust gas emissions from gasoline engines and diesel engines (Franzen et al., 

1995, Weickhardt et al., 1993, Boesl, 1998) emphasizing the real time and selective capabilities 

of REMPI-TOFMS without providing extensive emission factors. Laser MS work by Frey et al. 

(1995) examined time-resolved concentrations of benzene, toluene, xylenes, and 

trimethylbenzene under dynamic engine operation, such as load and speed changes as well as 

misfires and fuel mixture changes. Their compact mass spectrometer had a sensitivity of 1 ppm 

for aromatic hydrocarbons and a sampling period of 20 ms. Other related work (Nagel et al., 

1996) examined formaldehyde and acetaldehyde emissions. Boesl et al. (1998, 2000) reviewed 

developments in REMPI with a time-of-flight mass spectrometer (REMPI-TOFMS) to measure 

engine transients on a spark-ignited, four-cylinder gasoline engine coupled to an electronic 

dynamometer. Extreme fluctuations of benzene, toluene, and xylenes concentrations were 

observed in the exhaust for the first 60 s of operation, after which levels dropped and stabilized. 

1.5 Monitoring for Metals 

LIBS is a simple, laser-based technique that characterizes the elemental composition of aerosols, 

liquids, gases, and solids in real time with a single laser pulse. LIBS instruments typically use a 

short pulse-duration laser (~ 3-10 nsec in duration and 20-150 mJ of pulse energy) that is focused 

through a lens onto a surface or into the volume to be analyzed. The high energy pulse creates a 

small plasma at the focal point of the system optics during the pulse. The resulting high 

temperature plasma (~ 20,000 K) is sufficient to vaporize, atomize, and electronically excite a 

small amount of the sample matter (pg to ng). These excited atoms and molecular fragments 

decay primarily by emission of photons whose wavelength spectrum is characteristic of the 

atoms in the plasma. The light from the emitting atoms is collected using standard optical 

techniques and dispersed in a monochromator or spectrograph depending on the design of the 

detector. The resulting frequency spectrum is a fingerprint of the elemental composition of the 

sample. Through calibration the intensity of each peak in the spectrum can be related to the 

quantity of the element giving rise to the spectral feature. 

LIBS development, pioneered by Dr. David Cremers of Los Alamos National Laboratory, has 

shown the ability to detect many metals, including beryllium, lead, chromium, and uranium. 

ADA Technologies, Inc. has adapted Dr. Cremers’ technology in several instruments with the 

demonstrated capability of measuring beryllium at levels below 2 μg/m3

 in air with fieldable 

units. While LIBS is typically considered an in situ measurement, it can also be used to analyze 

solids (e.g., Be at 0.1 μg on a filter), enabling it to analyze PM-laden filters. This will be 

important to this effort, as many metals are expected to be below detection limits for real time 

sampling. 

1.6 Optical Path Methods and Field Measurements 

Researchers have developed strategies over the past decade to make measurements of gaseous 

and particulate pollutant emissions from agricultural operations and transportation activities 

using novel ORS and conventional point sampling techniques. This has included open-path 

Fourier transform infrared (OP-FTIR)) and laser-based technologies to estimate gaseous and PM 

emission fluxes and to map air pollution. OP-FTIR has the capability of identifying and detecting 

a wide range of gases and is an accepted technique to measure gaseous air toxics and volatile 

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organic compounds (VOCs). OP-FTIR instruments pass an infrared light along an open optical 

beam path up to 1 km long to measure and identify chemical contaminants directly in the field. 

This yields real-time data (<1 minute per sample) for multiple chemical species (25 of the 33 

UAT compounds) typically with ppb detection levels. Detection limits for chemicals measured 

by OP-FTIR systems will vary depending on the chemical species, atmospheric conditions 

(humidity and temperature), and whether interfering compounds are present. Typical system 

detection limits for a 100 meter separation between the transmitter/receiver telescope and the 

retroreflector is from 0.1 to 15 ppb for most infrared-active chemicals. Ambient values for many 

of the air toxics of interest are at or below these levels but these values represent integrated 

concentrations collected over significant periods of time and cannot be temporally resolved. In 

other words, using conventional ambient measurement methods, one cannot differentiate 

between low background levels that remain constant and short-duration “spikes” in concentration 

that occur infrequently during the entire sampling period. The strength of ORS techniques lies in 

their ability to measure changes in pollutant concentration on a near-real time scale. Our recent 

work, as well as developmental work done by instrument manufacturers indicates that for many 

of the air toxics of interest, event-related source emissions will be measurable using OP-FTIR. 

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2. Description of Equipment and Methods 

Aside from the conventional continuous emission monitors (CEM) for real time measurement of 

CO, CO2 and O2, three complementary technologies were used during this research project, 

namely REMPI-TOFMS, LIBS, and ORS. A description of these three methods is provided in 

the next sections. 

2.1 REMPI-TOFMS 

The REMPI-TOFMS instrument consists of multiple components as shown in Figure 2-1. 

Exhaust 

Time-of-Flight Mass Spectrometer 

Microchannel plate Detector 

Ion Beam Steering Plates Ion Extraction 

Optics 

Pulsed Valve 

Pulsed Laser 

C6D6 

Calibration Gas 

Filter Transfer line 

Ion Reflector 

REMPI-TOFMS 

Nd:YAG 

OPO 

Trigger 

PC 

Ionization 

Chamber 

Mass Flow 

Controllers Valve 

outlet 

Source 

Figure 2-1. REMPI-TOFMS instrument. 

REMPI is tailored as a wavelength-selective method of creating ions for mass separation and 

detection in a TOFMS. The REMPI approach to ionize molecules was established many years 

ago in academia for identification of reaction intermediates and end products. As the acronym 

5 
 
Ionization Continuum Ionization Continuum Ionization Continuum

 

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alludes to, the ion yield is enhanced when the laser wavelength is found to be in resonance with 

an intermediate molecular transition. Depending on the wavelength used, such intermediate state 

can be reached in a single step or with multiple albeit non-resonant photon steps. Depending on 

the internal energy level configuration, ionization may occur after absorption of single or 

multiple ions with the same initial color (one-color REMPI) or a different color (two-color 

REMPI). Ionization schemes are typically denoted as a combination of two numbers that are 

characteristic for the number of photons to reach the intermediate resonant state (first number) 

plus the number of photons to reach ionization (second number). For example, 1+3 REMPI 

means that one photon is needed for reaching the intermediate state and three photons are needed 

to create an ion from this intermediate state. The REMPI method of ionization as used during 

this SERDP project is always 1+1 REMPI (using a single wavelength) or 1+1′ REMPI (using 

two wavelengths as indicated by the ′ ). 

In general, the lowest electronic state for small aromatic organic analytes (S1) is located between 

4.1 and 5.0 eV. This corresponds to a wavelength range between 300 and 250 nm [ultraviolet 

(UV) range of the spectrum] when this lowest electronic state is reached using a single photon or 

alternatively between 600 and 500 nm (visible light of the spectrum) when using two photons to 

reach this electronic state. Since in the latter case the intermediate electronic state is reached 

through a non-resonant process, the ionization efficiency is typically much lower while much 

more laser energy is needed to accomplish such two photon absorption. Therefore, with the main 

objective to create a highly sensitive detection method, the two photon absorption to reach the 

intermediate state was not considered. The subsequent absorption of a second UV photon leads 

to ionization of the analyte if the ionization energy is below twice the photon energy as 

illustrated in Figure 2-2 (a). This is the case for the 1+1 REMPI ionization scheme. If the 

ionization energy is larger than twice the photon energy [Figure 2-2 (b)], no ionization occurs 

and the analyte will not be detected using TOFMS. This barrier can be overcome by using a 

second, more energetic shorter wavelength photon [Figure 2-2 (c)]. This is the case for a 1+1′

REMPI ionization scheme. 

S1

S0

S1

S0

S1 

S0 

Ionization Continuum 

S1 

S0 

Ionization Continuum Ionization Continuum 

a b c 

Figure 2-2 (a, b, c). REMPI ionization principles. 

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So far, the REMPI process has been described as if the intermediate electronic state is a single 

discreet state. In reality, each electronic state, including the electronic ground state (S0) consists 

of numerous discrete states due to the internal vibration and rotation of the analyte. This leads to 

an energy level structure that is unique for each molecule. Consequently, when the wavelength of 

the absorbing photon is changed, multiple discrete wavelengths will exist within a fairly short 

wavelength window where ionization can take place. Such wavelength scan yields an 

absorption/ionization spectrum that can be considered as a fingerprint of the target analyte and 

are even isomer specific. 

There are four main reasons why a wavelength spectrum may not show these transitions as 

discrete, sharp, lines. First, the lifetime of the excited state may be extremely short 

(microseconds or less) which results in a (lifetime) broadening of the energy transitions, or 

spectral lines. Second, insufficient cooling in the expansion can broaden transitions. Third, the 

actual ionization scheme may involve ionization via a higher electronic (SN; N > 1) state with a 

higher density of available states, and fourth, the laser source of ionization cannot be fine tuned 

over a short wavelength range due to its own linewidth. The latter aspect appears when a 

comparison is made between the two laser systems that were used throughout this SERDP 

project. The combination of these four reasons means isomer selectivity cannot always be 

accomplished using REMPI. This is especially the case for heavier aromatic analytes like larger 

PAHs. 

REMPI as applied here is a soft ionization technique. Therefore, no significant fragmentation 

takes place and a mass spectrum essentially consists of the parent ion only. 

The single color 1+1 REMPI process at the lowest wavelength used of 250 nm also excludes 

detection of molecules with ionization energies above 9.2 eV. Consequently, interferences with 

aldehydes, for example, can be ignored since most have ionization energies well above this 

value. Note that the ionization efficiency of higher order REMPI processes is significantly 

smaller than that of 1+1 REMPI. It also requires higher power densities that are not present in the 

unfocussed laser beam. For the same reasons, the far more abundant exhaust gases such as 

nitrogen, steam and CO2 cannot be ionized and, therefore, do not interfere. 

2.1.1 Laser Systems 

Optical parametric oscillators (OPO) are solid-state devices which use non-linear optical 

conversion to provide tunable laser light over a very broad wavelength range covering the visible 

and IR spectrum. In combination with a frequency doubling module, UV light can be created 

from the OPO signal beam. The technology eliminates the need for handling, replacement and 

swapping of multiple dyes that are used in the nearest competitive laser technology, the dye 

laser. By doing away with the need to change between multiple different laser dyes in order to 

scan across a broad tuning range, the OPO provides an extremely flexible system and facilitates 

measurements that are not otherwise possible to perform in a timely manner. 

Two laser systems were used during the SERDP funding period. The initial tests were performed 

with a Continuum Sunlite EX OPO with FX-1 UV frequency extension. This OPO is pumped by 

the third harmonic (355 nm) of a Powerlite Precision 9000 Nd:YAG laser system. Its two-stage 

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design combines a narrowband oscillator with a high efficiency optical parametric amplifier to 

produce coherent light between 445 and 1750 nm. A computer control system maintains 

optimum crystal performance (phase matching) while moving over wide wavelength ranges. UV 

output energy, using the signal beam output and the frequency doubler, is between 5 and 10 mJ 

across the tuning range, with between 5 mJ and 7 mJ in the 250-280 nm range. The laser spectral 

line width was tested by the manufacturer to be ~ 0.2 cm-1. 

The major drawback of this Continuum laser system is its size; it just fits on a 3’x 8’ table which 

makes it too large for field deployment. Therefore, the smaller REMPI-TOFMS systems (about 

2’ x 4’) utilized a more compact laser system. OPOTEK (Carlsbad, CA) manufactures efficient 

compact and widely tunable solid-state laser systems based on its patented OPO designs. The 

OPOTEK system is designed to be compact, and rugged. Their current Vibrant II-355nm with 

frequency-doubling laser system has sufficient power for sensitive measurements and produces 

continuously tunable light across a wide range of wavelengths to accommodate the detection of a 

large variety of species. This system is also compact and rugged enough to be used during field 

experiments. The standard Vibrant II-355 nm laser system from OPOTEK is a compact all-inone tunable laser system which can generate tunable output from 210 nm to 2.6 μm, based on 

OPO technology. Due to the all-solid state nature of this system, there is no need to circulate or 

change laser dyes that have typically been used to generate tunable light at these wavelengths. 

The system consists of the Nd:YAG pump laser, associated second and third harmonic 

generation, OPO, UV extensions, and control electronics all on one rigid frame. This packaging 

not only leads to a compact unit, but also significantly adds to the ruggedness of the product by 

eliminating the alignment problems that come from the scattered discrete components usually 

found in this type of system. These attributes made this system an ideal starting-point for the 

integration into a field capable system. The UV output energy is between 1.5 and 3.5 mJ across 

the tuning range, with between 2.0 mJ to 3.5 mJ in the 250 to 280 nm range used during our 

preliminary studies. The laser spectral linewidth was tested by the manufacturer to be 

approximately 4 cm-1. The assessment of the increase in linewidth with respect to the large laser 

system is part of the evaluation. 

When using a single color wavelength, the use of the REMPI method is restricted to analytes 

with an intermediate electronic state with an energy value above half that needed to create an 

ion. In the case of multiple chlorinated aromatics, the intermediate state lies below half the 

ionization energy and no ions are formed. In order to overcome this limitation, one of the 

OPOTEK laser systems was modified to include the generation of a higher energy laser photon 

as a second color / wavelength option for ionization. This is accomplished by generating 213nm 

(fifth overtone of fundamental of Nd:YAG) laser light through the mixing of residual 355 nm 

and 532 nm laser light onto a BBO crystal. This method generates 2 to 3 mJ of this highly 

energetic laser light which is combined with the tunable UV from the OPO system using a 

dichroic mirror. With the combination of the tunable UV and fixed wavelength 213 nm laser 

light, detection of higher chlorinated benzenes (up to hexachlorobenzene), chlorinated furans (up 

to tetrachlorofuran) have been confirmed with only moderate losses in sensitivity with increased 

chlorination. 

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2.1.2 Valve Inlet Systems 

Under atmospheric conditions, individual (ro)-vibrational lines are broadened due to collisions 

with abundant molecules like nitrogen, oxygen and air. Consequently, wavelength spectroscopy 

under these conditions will result in unresolved features which lead to low or no wavelength 

selectivity. This applies for recorded wavelength spectra when using an effusive inlet source. 

Such loss in selectivity can be avoided by the use of a pulsed valve inlet system. The adiabatic 

expansion into vacuum creates a supersonic jet in which rotational and vibrational cooling of the 

target analytes takes place. Consequently, the population in the electronic ground state that was 

originally spread over a large number of (ro-) vibrational states is transferred into only the lowest 

(ro-) vibrational states. This cooling results in more discernible spectra, enhancing the selectivity 

in comparison with effusive-source ionization spectra. In addition, since the ion signal is 

proportional to the population in the initial state, transitions starting from this smaller set of 

populated states appear stronger than in the case where the population is spread over a larger 

number of initial states. 

All results described in this report are obtained using Parker-Hannifin Corporation Series 99 

Pulse Valves that are mounted in various ways as described here. During the first part of the 

SERDP research efforts with the large time of flight mass spectrometer, four valves were 

mounted onto a single stainless steel block. Because the valve itself serves as a vacuum seal 

between the sample inlet line and the ion source chamber, removing the valve necessitates 

venting the entire instrument. While a sliding gate valve could be incorporated between the exit 

of the pulsed valve and the ion source, such an arrangement adds undesirable distance between 

the exit orifice and the ionization region. As an alternative to this approach, SRI International 

had previously developed a configuration that incorporates four pulsed valves on a single sliding 

mount. This arrangement allows any one of the four valves to be aligned with an entrance 

channel to the source region while keeping the remaining three valves isolated from the vacuum, 

and hence free to be removed and replaced as necessary. However, the size of this four-valve 

configuration restricts its use to the larger ion source chamber. 

Because of the migration of the laser ionization mass spectrometer to a smaller platform, a new 

multi-valve design was required. In order to incorporate a combined valve/GC capillary inlet unit 

on this instrument, it was necessary to have the manufacturer modify the valve-mount vacuum 

flange. The new flange design, which is shown in Figure 2-3, features a larger, flat surface in 

close proximity to the ionization region. Even with the modified flange design, the new valvemounting configuration can only accommodate two pulsed valves or one pulsed valve and one 

capillary inlet. The two inlet types are mounted onto a single, wedge-shaped plate that pivots 

near its apex. A system of slots and precision spring-loaded guides allows the plate to rotate ±30 ̊

about its midpoint while maintaining adequate compression of a high-temperature Kalrez o-ring 

seal placed around the sample entrance orifice on the vacuum flange. When the valve mounting 

plate is in either of its extreme positions, the exit aperture of the pulsed valve or capillary is 

precisely aligned with the sample entrance orifice. A positive detent mechanical lock secures the 

valve plate in either position, and ensures reproducible location. In addition, a third locking 

position is provide midway between the two extremes that effectively seals the vacuum chamber 

and allows either of the valve or the capillary to be removed. The design incorporates several 

other important features. The valve seat has been modified to significantly reduce the dead 

volume between the sample gas and the exit orifice. Rather than introducing the sample through 

9 
 
Spring-loaded detent 

General Valve series 99 

pulsed valve 

Capillary inlet 

Sample out 

Sample in 

EPA/600/R-10/050 

April 2010 

the conventional coaxial entrance channel, which results in essentially no flow and a large dead 

volume, the sample can be introduced through a small entrance channel cut near the sealing 

poppet. A corresponding exit channel is also provided on the opposite side of the valve thus 

allowing for continuous sample flow through the pulsed valve independent of its opening 

function. The use of a flowing sample results in the rapid removal of organic samples by the 

carrier gas flow, while also substantially reducing the dead volume of the valve. All results in 

this report were obtained with these modified valve systems unless explicitly noted. 

Spring-loaded guide 

Spring-loaded pivot 

Figure 2-3. Top View of the Movable Inlet Mounting Plate. 

An alternative method of adiabatic expansion can be obtained using a continuous inlet system 

with a small orifice (10-20 micrometer) as opposed to 0.5mm for the pulsed version. This 

approach was tested for determination of the optimum orifice opening (by SRI International) but 

has not been evaluated under field sampling conditions. 

2.1.3 Time of Flight Mass Spectrometer 

The first experiments supported by SERDP were performed using a Jordan reflectron time of 

flight mass spectrometer. It has a mass resolution as high as 4000 in combination with the 

supersonic jet inlet system. The size of the system prevented field operation (taking up a volume 

of 6’ x 4’ x 3’) and the mobile REMPI-TOFMS was therefore built around a 19” rack mounted 

TOFMS. While the initial goal was to design a compact mass spectrometer from standard 

materials, the need for very high level ion-optical engineering to obtain maximum mass 

resolution in a small package led to a commercial solution. An ideal solution is found in the ILR10 In-Line Reflectron Time-of-Flight Mass Spectrometer package from Stefan Kaesdorf 

Industries (Germany). This all-in-one unit, shown in Figure 2-4, contains the source region, 

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EPA/600/R-10/050 

April 2010 

Reflectron TOFMS, ion detector, electronics, and high-vacuum pumps in a single, compact 

standard 19” rack-mount package. 

Electronics 

Laser 

Window 

Gauge 

19” 

17.5 

Figure 2-4. Schematic of LR10 compact 19” rack-mount reflectron TOFMS. 

2.1.4 REMPI-TOFMS Instrument 

The three major components (laser, inlet valve and time of flight mass spectrometer) previously 

described make the REMPI-TOFMS instrument. Figure 2-5 shows the setup of the laboratoryonly large instrument while Figure 2-6 shows the system that can and has been deployed during 

multiple field sampling trips. 

Figure 2-5. Two views of large REMPI-TOFMS system. 

On the left is the time of flight mass spectrometer and on the right a view of the large table with 

OPO laser system 

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Figure 2-6. Compact REMPI-TOFMS instrument. 

2.1.5 Operating Procedures REMPI-TOFMS 

In contrast to the high voltage power supply for the Jordan TOFMS, the high voltage supply for 

the Kaesdorf reflectron TOFMS was found to be extremely stable with no noticeable drift of 

voltage values with time. Consequently, the mass calibration of the TOFMS was performed only 

when significant changes were made to the laser beam alignment through the ionization 

chamber. The mass calibration uses internal gas standards (usually benzene, 78 m/z and 

trimethylbenzene, 120 m/z). These two sets of mass and time-of-flight arrival time, and the 

constraint that the arrival time starts at t = 0.0 μs for zero m/z, are used to generate two constants 

for a second order polynomial fit to the data which is satisfactory up to mass 250. The calibrated 

time of flight versus mass curve is stored in the data acquisition software. 

REMPI-TOFMS can be operated in three different data acquisition modes: 

• Monitoring one or a range of masses as function of ionization wavelength 

• Monitoring one or a range of masses as function of time at one specific wavelength 

• Monitoring specific masses as linked to specific wavelengths 

An example of a wavelength spectrum for multiple masses (75-200 m/z) is shown in Figure 2-7. 

12 
 
Figure 2-7. 	 Detection of multiple analytes using wavelength-dependent ionization. 

EPA/600/R-10/050 

April 2010 

In Figure 2-7, the REMPI-TOFMS instrument was measuring analytes as present in the exhaust 

gas from a diesel generator. Depending on the degree of resolution required and the actual length 

in nanometers of the scan, these wavelength scans may take up to 30 minutes to complete. 

Consequently, such wavelength scan can only be determined when the emissions are constant 

(on the time scale of 30 minutes). This is the case for calibration gases or during steady state 

operations of combustion systems. Clearly, this is not the case during accelerations or changes in 

loading of an engine as shown in Figure 2-8. In such case it would have been impossible to 

obtain a reliable wavelength spectrum. This is an example where it is more advantageous to 

monitor multiple masses with one single wavelength. 

120 

100 

80 

60 

40 

20 

0 

time (min) 

Benzene Concentration (ppb) 

2 4 6 8 10 12 14 16 18 20 22 24 26 

Figure 2-8. 	 Transient benzene concentrations detected in vehicle exhaust while running a 

dynamometer-based roadway simulator. 

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One advantage of lower selectivity in wavelength is that at a specific wavelength, it is possible to 

ionize and detect multiple analytes with different mass. An example of this is shown in Figure 

2-9 where at the most favorable wavelength for benzene detection multiple PAH-like analytes 

are detected. As discussed earlier, overlap in absorption spectra provides information on a 

selected subset of analytes. Confirmation of the analyte identity should be performed with 

wavelength scans. 

m/Z

2.0 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

m/z 

REMPI Ion Signal (arb units) 

80 120 160 200 240 

Figure 2-9.	 	 REMPI-TOFMS mass spectrum at benzene (78) wavelength as observed in 

vehicle exhaust. 

The third method of data acquisition has become available only after conclusion of all field tests 

that were performed with the REMPI-TOFMS instruments. The data acquisition software uses a 

list of predetermined mass and wavelength combinations that are unique for detection of each 

analyte individually. The data acquisition system runs automatically through such sequence of 

wavelengths and acquires the ion intensity for the associated masses. This provides a much more 

hands-off approach that can be utilized in the detection of multiple analytes under “steady state” 

engine combustion conditions. This approach has been tested on a multi component calibration 

gas with satisfactory results. Further improvements could include changes in detector voltage 

(“gain”), using predetermined values (passive control) or based on observed intensity active 

control by enhancing the gain until a specific ion signal is present. 

2.2 LIBS 

In laser-induced breakdown spectroscopy, LIBS, a pulsed Nd:YAG laser beam is focused 

through a lens onto a substrate and plasma is formed. This plasma vaporizes and atomizes the 

sample, exciting the constituents of the sample. Light emitted from the plasma is characteristic of 

the interrogated sample. This light is collected with a spectrometer containing a charge coupled 

device, and a broadband spectrum (200-980 nm) is generated. Figure 2-10 shows the setup as 

used for interrogation of filter deposits as collected during vehicle sampling. 

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April 2010 

Broadband Spectrometer 

Pierced 

mirror 

Nd-YAG 

1064 nm 

Plasma 

Spark 

Focusing/ 

collecting optics 

Fiber Bundle 

OOLIBS 

software 

Figure 2-10. Schematic setup of LIBS system. 

2.3 ORS 

ORS measurements provide information on a path-integrated concentration of HAPs in 

emissions from, possibly, a diesel turbine engine. The OP-FTIR can also be set up to collect 

information on PM in the engine exhaust. The OP-FTIR spectrometer is designed for both fenceline monitoring applications, and real-time, on-site, remediation monitoring and source 

characterization. An infrared (IR) light beam, modulated by a Michelson interferometer is 

transmitted from a single telescope to a retro reflector (mirror) target as shown in Figure 2-11. 

The returned light signal is received by the single telescope and directed to a detector. The light 

is absorbed by the molecules in the beam path to the retro reflector and again as the light is 

reflected back to the analyzer. Thus, the round-trip path of the light doubles the chemical 

absorption signal. One advantage of OP-FTIR monitoring is that the concentrations of a 

multitude of infrared absorbing gaseous chemicals can be detected and measured simultaneously, 

with high temporal resolution. 

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Exhaust 

Stack 

Retroreflector 

OP-FTIR 

30 m 

Figure 2-11. Setup ORS during sampling. 

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3.	 REMPI-TOFMS: Field Ready Development and Performance Evaluation 

and Improvement 

At the onset of this SERDP project, a large REMPI-TOFMS system existed at the EPA facility 

which was suitable for emission characterization for sources located on-site. The experiences 

with this system were used to develop a smaller and field-ready unit. The evaluations of the 

critical instrument parts that were part of the SERDP project are described here. 

3.1 Laser Systems 

The performance of a laser system is in general sensitive to the environmental conditions in 

which it is placed. Although ultra-stable laser systems (both in laser energy output and absolute 

wavelength) exist, the laser systems used during the SERDP funded projects had limitations in 

their stability, especially considering their application in less favorable field conditions with 

potentially larger ambient temperature fluctuations and the presence of PM (dust) in air. 

3.1.1 Continuum Laser 

The large Continuum laser system is located in a laboratory equipped with an air conditioning 

system. However, slight changes in ambient temperature were found to have only a minimal 

effect on the emitted laser energy. The phase matching angles of the second and third harmonic 

crystals needed remote control adjustments only during the first 2-3 hours of operation). No 

appreciable wavelength shifts were noted over the course of a day of measurements. This in part 

due to the fact that the wavelength selection in this laser system is not determined by the OPO 

crystal (phase matching) angle but rather by a grating which is much less sensitive to 

temperature fluctuations. Phase matching angles adjustments of all crystals inside this 

Continuum Sunlite OPO system are performed using the software installed with the instrument. 

3.1.2 OPOTEK Laser 

Temperature changes inside the laser system, especially during the warm-up period, results in 

noticeable changes in laser energy as well as actual wavelength emitted from this laser. The 

changes in laser energy are due to changes in the phase matching angles of the second and third 

harmonic generating crystals which tend to shift when the temperature changes. Adjustments 

from the outside of the laser system can be made to correct for these changes and do not create a 

major concern in the performance of the laser system. OPOTEK has informed us that a more 

stable version with feedback control is now available but such improvement has not been 

implemented in the existing laser systems. Adjustments of the phase matching angle of the 

frequency doubling module can be performed using the software control of the OPOTEK laser 

system. Figure 3-1 shows an example of laser wavelength drift as a consequence of increased 

temperature inside the laser system. This is observed when the wavelength-dependent ion signal 

is monitored for a calibration gas. A suggested improvement to the manufacturer would be to 

elevate the temperature of the OPO crystal to well above ambient temperature in order to reduce 

these shifts. It should be noted that the application of this laser system for semi-high resolution 

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April 2010 

MS (HRMS) in combination with TOFMS is at the edge of its wavelength stability capabilities. 

Alternatively, a temperature stabilization of the air inside the laser system would be possible 

(without turbulence preferably). Note that the observed wavelength shifts were obtained despite 

the presence of a working air conditioning unit that was connected to the dust cover under which 

the laser is placed. The main function of the air conditioning unit was to maintain a relatively 

constant temperature inside the dust cover, independent of the ambient outside temperature. 

Fortunately, the drift in wavelength, if present, is constant across the typically used wavelength 

range of operation (255 to 290 nm). Therefore, it was implemented in all sampling procedures 

with the REMPI-TOFMS system to frequently monitor an internal standard, deuterated benzene, 

and correct established wavelengths of target analytes by the drift in wavelength for the internal 

standard. 

30 

25 

20 

15 

258.1 258.2 258.3 258.4 258.5 258.6 

Wavelength (nm) 

Ion Signal (arb. units) 

258.7 258.8 

1

 2

 3

 4

 5

 6

 7

 8

 9 

Figure 3-1.	 	 Wavelength emitted from laser with increased ambient temperature (increase 

in temperature for scan 1 to 9). 

Wavelength scans over extended ranges were found to result in an oscillating laser energy output 

which can be corrected by simultaneous recording of the laser energy at the exit window of the 

ionization chamber. This oscillation is primarily due to the use of high order polynomials to fit 

the OPO and UV stepper motor positions as controlled by the software. Deviations in motor 

position from this fit at intermediate wavelength values are oscillatory in nature resulting in non 

optimal phase matching angles, hence less optimal laser energy performance. 

3.2 Pulsed Valve Operation 

The performance of the pulsed valve system was expected to be a weakness in the whole 

REMPI-TOFMS system since (1) it cannot be heated above 200-210 o

C, (2) it would need 

frequent cleaning following exposure to “dirty” samples (e.g., high concentrations, high PM, 

“sticky” gases), and (3) it could be subject to fast wear and tear on the pulsating poppet made of 

Vespel material. Since most of the applications funded under SERDP were related to the 

detection of more volatile analytes, it was not necessary to heat the valve system continuously to 

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April 2010 

such high temperature. Good results were obtained at valve temperatures of 150-180 °C. Also, 

implementing a 10 μm inline filter prevents passage of ultrafine PM which otherwise can pass 

through standard fiber filters, reaching the poppet in the pulsed valve system. The swivel 

mounted double valve systems worked properly. However, the number of equipment connections 

to the inlet side of the valve makes switching from one valve to the other in case of failure more 

cumbersome. The swivel valve design was also modified during the funding period to avoid 

vacuum leaks under applied stress to the pulse valve unit when connections to sampling line and 

equipment were present. 

3.3 Data Acquisition Software 

Time of flight spectra are commonly recorded using a digital oscilloscope. The data acquisition 

during this project made use of a fast digitizer card inside a PC. Measurements performed on the 

large REMPI-TOFMS instrument used a 500 megahertz (MHz) digitizer card (Signatec) while 

the small REMPI-TOFMS instruments all include a PC with a 1 gigahertz (GHz) digitizer card 

from the same manufacturer. Laser control was performed using provided software (Continuum) 

or provided LabView virtual instruments (OPOTEK). A snapshot of the data acquisition 

software which was in part developed during this SERDP project by SRI International is shown 

in Figure 3-2. Data acquisition stores data files to the hard disk that include time, wavelength, 

ion signal, and multiplier detector voltage. Depending on the number of averaged laser shots, a 

data acquisition period as fast as 0.1 s, however, in reality 10 or 20 laser shots are typically 

averaged before data is written to hard disk. The data acquisition software has the capability to 

immediately calculate the integrated area under a time of flight ion peak. This works very well 

under controlled conditions such as time or wavelength dependence of an analyte in the presence 

of a limited number of nom-interfering analytes such as in multi-analyte calibrated gas mixtures. 

Under fluctuating emission conditions with a larger number of unknown analytes such as in the 

exhaust of a combustion system, it is more advantageous to record and store the whole mass 

spectrum (within set mass limits) and perform post-analysis processing in order to asses if 

interfering events such a changes in baseline signal occurred. Although this method of data 

acquisition is more demanding (large data files and post-data processing) it is much better for 

data quality assurance with the additional benefit that all data is saved. As part of the SERDP 

project, a custom macro was written for use with the data analysis software (Origin 6.1 and 

higher, OriginLab Corp.) which simplifies the post-data analysis processing. 

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April 2010 

Figure 3-2. Photo of data acquisition software in operation. 

3.4 Calibration of REMPI-TOFMS System 

External calibration of the detected ion signals was typically performed at the beginning and at 

the end of the day. This was accomplished by monitoring the response to a 100 ppb calibrated 

gas mixture in nitrogen containing 14 aromatic compounds (Scott Specialty Gases). The 

concentration of a target analyte is derived from the ratio between its ion signal intensity and that 

of the same analyte as present in the calibration gas mix, normalized for possible laser energy 

changes. Concentrations of those exhaust analytes not present in the calibration mix were derived 

from the ionization probability ratios between benzene and such analytes as found by Cool and 

coworkers (Velazquez et al., 1998). In the case of concentration calibration of compounds that 

are in their crystalline form at room temperature, such as PAHs, a diffusion-tube-based delivery 

system was designed and applied to generate a known concentration of a specific analyte in the 

gas phase. The absolute concentration of this delivery system was verified independently for 

each analyte of interest using external high resolution GC (HRGC) combined with low resolution 

MS (LRMS) analysis. 

System performance monitoring is provided by addition and measurement of fully deuterated 

benzene (C6D6) since it is unambiguously detected and is not an exhaust product. A linear 

REMPI-TOFMS response has been established over several orders of magnitude of 

concentration (ppt to ppm range) for all aromatic compounds of interest. Since the response to all 

compounds is linear with concentration, the measured response to the added C6D6 was used as an 

indicator for REMPI-TOFMS system performance. 

All recorded ion signals were corrected for possible changes in laser energy during post analysis 

processing of the experimental data. 

REMPI-TOFMS has the capability to individually identify a large set of aromatic compounds 

and this can be accomplished in real time with a 1 s resolution at a high pptv level concentration. 

No sample clean-up or extraction is needed and consequently, qualitative results are available 

instantaneously. 

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4. Sampling from DoD Sources 

This report presents the results obtained with REMPI-TOFMS, LIBS, ORS, online-GC and other 

standard EPA methods during the sampling from multiple sources. Table 4-1 summarizes the 

research efforts that were taken during this SERDP project to obtain emission factors for 

multiple relevant sources. 

Table 4-1. Source testing. 

Source 

Number Chapter Source Date Location Used REMPI-TOFMS 

System 

1 7,8 Diesel Generator 04/2004 EPA, RTP, NC Large 

2 9 Aircraft Ground 

Equipment 05/2004 EPA, RTP, NC Compact 

4 11 Municipal Waste 

Combustor (MWC) 12/2004 Portsmouth, VA Compact 

3 10 Boiler / ETV 09/2005 EPA, RTP, NC Compact (two systems) 

5 12 DoD vehicles 10/2006 Aberdeen, MA Compact 

4 11 MWC 12/2006 Portsmouth, VA Compact (two systems) 

6 13 Military Aircraft 10/2007 Tyndall AFB, FL Compact 

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5.	 Source 1: Validation of REMPI-TOFMS Measurements on a U.S. Marine 

Corps Diesel Generator 

REMPI-TOFMS has been applied to the exhaust of a diesel generator in order to provide 

extensive emission concentrations of aromatic compounds, both under steady state conditions as 

well as during transient events, such as a cold start. REMPI-TOFMS results were compared 

qualitatively and quantitatively with extractive sampling techniques utilizing GC/MS analyses, 

providing insights to the applicability and precision of the method. 

5.1 Experimental section 

The diesel generator tested was a 60 kW Tactical Utility (Class 2) Generator set provided by the 

United States Marine Corps (Figure 5-1). It was placed outside and the exhaust was ducted past 

the sampling ports into a point exhaust vent of the building. All ducts were thermally isolated 

and kept under negative pressure to prevent fugitive emissions from entering the building. The 

diesel generator exhaust was sampled sub-isokinetically through a 1⁄4" (6.35mm) stainless steel 

line at typical flow rates of 2 L/min [at standard temperature and pressure (STP)]. A micro fiber 

filter, kept at 150 °C, was placed in the sample line in order to avoid soot reaching the valve inlet 

system of the REMPI-TOFMS instrument. A flexible 9 m long, 1⁄2" (1.27 cm) diameter, silicon 

steel transfer line transferred the exhaust gas to the REMPI-TOFMS instrument. This line was 

maintained at 150 °C while sampling exhaust gases in order to avoid adsorption of the organic 

compounds to the walls. Upstream from the filter, 0.1 L/min of 1 ppm fully deuterated benzene 

(C6D6) in nitrogen was added as a dynamic spike to obtain typical concentrations of 60 ppb C6D6 

in the total exhaust stream. C6D6 was chosen as an internal calibration gas for REMPI-TOFMS 

since its mass of 84 m/z and ionization wavelength will not interfere with the detection of 

aromatic compounds. It is not present in the diesel exhaust gas itself, and has an ionization 

wavelength within the commonly used wavelength scanning range (250-360 nm). The 

concentration of C6D6 was also monitored to indicate the potential for adsorptive loss of VOC 

during soot loading on the filter surface (sampling bias). 

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April 2010 

Figure 5-1. U.S. Marine Corps tactical utility generator. 

Most of the steady state diesel generator exhaust measurements were recorded over three nonconsecutive days within a 7-day period. The purpose of the repetition was to (1) evaluate diesel 

generator exhaust emission levels at different days and (2) to verify the reproducibility of the 

REMPI-TOFMS results on a day-to-day basis. Emission data were collected and calibrated for a 

selected group of organic compounds using the method described previously. Multiple 

repetitions of this method provide information about how many samples should be taken to 

obtain representative and accurate emission factors using REMPI-TOFMS. Concurrently, colocated diesel generator exhaust samples were taken with two EPA established extractive 

analysis methods, being Method 0040 (EPA, 1996a) and Method 0010 (EPA, 1986a), in order to 

verify the accuracy of the concentrations as determined by REMPI-TOFMS. All steady state 

results were obtained during a 75% loading (“full load”) of the diesel generator. With the major 

exhaust analytes now established, the cold and warm starts of the diesel generator verified the 

ability of REMPI-TOFMS to perform fast, real time measurements of such transient events. 

5.2 Results and Discussion 

5.2.1 Steady State Diesel Generator Results 

A survey wavelength scan of the exhaust gas stream in Figure 5-2 illustrates the complexity of 

aromatic compounds in diesel generator exhaust. Each mass spectrum plotted is the average over 

10 single-shot mass spectra at a set laser wavelength. The wavelength was scanned in 0.01 nm 

steps. Traces of ion signals at mass 78, 92, 94, 104, 106, and 120 are identified as single aromatic 

ring compounds while the dominant traces at mass 128 and higher are methylated-PAHs. The 

single peak at mass 84 (λ=257.8 nm) is C6D6 as added to the diesel generator exhaust as an 

instrument monitor. With the diesel generator running at full load condition, the wavelength was 

tuned over the range where all BTEX compounds as well as many PAHs are ionized. No major 

ion signals, other than those due to minimal fragmentation, were detected below mass 78 

(benzene) for any wavelength within the 250 to 360 nm wavelength window. At low (less than 

m/z = 128) mass, the 3D graph shows contributions of all BTEX compounds as well as other 

compounds. At a wavelength optimized for benzene detection, numerous additional ion signals 

are detected as illustrated in the mass spectrum in Figure 5-3. The inset in (B) shows the lower 

part of the mass spectrum recorded. Methylated benzenes (◊) and methylated naphthalenes (×) 

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April 2010 

are indicated; the former group is not ionized at the higher wavelength. Major “ghost” mass 

peaks due to instrument anomaly are indicated ( | ) below the mass spectra. There appears to be a 

characteristic series of mass peaks with poor spectral resolution that can tentatively be assigned 

to methylated naphthalenes. Another series that can be identified are methylated benzenes. A 

more extensive analysis of the mass spectra recorded with this TOFMS for diesel generator 

exhaust and calibration standards revealed that the molecular ion peak of each individual target 

analyte is accompanied by a second peak of lower intensity which appears approximately 1.25 to 

2.75 mass units lower, depending on the mass of the target analyte. This is not an ion signal due 

to fragmentation but rather an anomaly of the TOFMS instrument. Since there was no clear 

dependence found with all applied voltages in the TOFMS, signal intensity, as well the position 

of the laser beam in the ion source, this anomaly is or may have been due to an impedance 

mismatch in the signal circuit that occurred during these experiments. It clutters the observed 

mass spectrum as in Figure 5-2; however, since most of these peaks do not line up at an integer 

mass unit, they can be ignored in the analysis. 

Figure 5-2. A 3D survey scan (mass, wavelength, ion signal) 

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April 2010 

Figure 5-3. 	 Time-of-flight mass spectrum recorded at (A) optimum styrene (287.7 nm) 

and (B) Benzene (259.0 nm) ionization wavelength in diesel generator exhaust. 

Before concentrations can be derived from the ion signals in the diesel generator exhaust, it is 

necessary to verify if the spectroscopy of the target analytes matches with that of a calibration 

standard taken under identical experimental conditions. Figure 5-4 shows as an example the 

spectrum of toluene to illustrate that there are no detectable spectral interferences at the 

concentration level present in the diesel generator exhaust. To verify if a steady state diesel 

generator condition results in stable emission concentrations the REMPI signals of the detected 

benzene in the exhaust, and C6D6, as added to the exhaust, were recorded over a one-hour period. 

Both REMPI signals were found to be nearly equal in stability; the average REMPI signal for 

benzene had a relative standard deviation (RSD) σ = 6.1% while for C6D6, σ = 5.2% as 

illustrated in Figure 5-5. This observed stability of diesel generator exhaust emissions under 

steady state conditions simplifies the subsequent determination of emission levels for other 

aromatic compounds. 

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April 2010 

Figure 5-4.	 	 Comparison of 1+1 REMPI wavelength spectrum recorded for toluene in 

diesel generator exhaust and from calibration gas standard (the latter scaled 

to equal intensity). 

0 10 20 30 40 50 60 

Time (min) 

Figure 5-5.	 	 Monitored REMPI-TOFMS signal for reference gas (C6D6) and benzene in 

exhaust diesel generator. 

0 

2 

4 

6 

8 

10 

12 

14

 Laser Energy correceted Ion Signal (arb units)

0 10 20 30 40 50 60 

0 

2 

4 

6 

8 

10 

12 

14 

16 

18 

20 

benzene from diesel generator exhaust 

deuterated benzene internal standard 

26 
 
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Concentrations were derived from approximately 1 min averages of recorded ion signals between 

changes over nine predetermined wavelengths for phenol, p-xylene, m-xylene, o-xylene, 1,2,4­

trimethylbenzene, toluene, naphthalene, benzene, and deuterated benzene. Figure 5-6 shows the 

raw data results for such a nine wavelength sequence that includes the above mentioned target 

analytes. For simplicity, only the parent ion signals for the target analyte within each 1 min 

interval are shown; traces for all individual masses (range m/z = 75 - 300) are recorded during 

the whole sequence and stored to a computer hard disk. As can be seen, all ion signals are 

constant within the 1-minute intervals, an additional indication of stable emission concentrations, 

even on this short time scale. The ion signals have not been corrected for pulsed laser energy 

fluctuations that are visible in the noise of the ion signal. Since the laser energy detector is not 

fast enough for single laser pulse energy detection, the 1 s average of the laser energy (i.e., 10 

laser pulses) was continuously recorded and stored for further normalization. On Day 1, the ninetarget analyte sequence was repeated eight times as shown in Figure 5-7, which shows the 

complete mass traces. The observed ion signals remained constant for each individual compound 

over the 1.5 h of data acquisition. RSD in the 1 min averages typically range between 5 and 12%. 

The variation in the 1 min averages of each of the nine selected analytes, after correction for 

laser energy differences, ranged from 2 to 9%, well within the standard deviation of the 1 min 

averaged ion signals. Similar results were obtained for the external calibration of the diesel 

generator exhaust REMPI-TOFMS ion signals. This demonstrates that over the 1.5- hr timeframe 

of data acquisition, variations in emission levels in the diesel generator exhaust are much smaller 

than the accuracy with which REMPI-TOFMS can measure the concentrations. It is also in 

agreement with the previously discussed constant benzene emissions over an extended period of 

time. Since the variation in the observed 8-fold repeat of ion signals is comparable with the RSD 

of a single 1 min average, the number of repeats can be reduced to three. The final repeat of the 

nine target analyte sequence was obtained after a clean filter substitution. No changes in ion 

signals were observed for all nine studied analytes indicating that over a time period of more 

than 1.5 h, no bias is detected towards absorption of these target analytes on the soot loaded filter 

surface. 

0 

2 

4 

6 

8 

10 

12 

14 

94, phenol 275.1 nm 

Ion Signal (arb units) 

106, p-xylene 272.3 nm

106, m-xylene 270.7 nm

106, o-xylene 268.1 nm

120, 1,2,4 trimethylbenzene267.9 nm 

92, toluene 266.8 nm

128, naphthalene 266 nm

78, benzene 259.0 nm

84, d-benzene 257.8 nm 

1 2 3 4 5 6 7 8 9 10 
 


time (min)
 


Figure 5-6. 	 On-line REMPI-TOFMS ion signal traces of nine individual target analytes, 

labeled with mass, chemical name and used, most favorable ionization 

wavelength. 

27 
Ion Signal (arb. units) 

24 

22 

20 

18 

16 

14 

12 

10 

8 

masses:

 78

 84

 92

 94

 106

 120 

0 10 20 30 40 50 60 70 80 

time (min) 

EPA/600/R-10/050 

April 2010 

Figure 5-7. Recorded ion signals during nine repeats of the analyte cycle. 

To verify if the diesel generator exhaust emission pattern is constant over several days and to 

assess if the response of the REMPI-TOFMS instrument changes from day to day, the nine 

wavelength sequence measurements were repeated over three non-consecutive days within a 

seven day period. Analyte exhaust concentration levels appeared relatively consistent with each 

other, indicative of steady state diesel generator emission conditions on a day-to-day comparison. 

Variances ranging from 9 to 30% exist, however, for the investigated target analytes as shown in 

Figure 5-8. An analysis showed that most of the variation in the daily comparison of the 

individual target analytes was already present in the daily variation of detected ion signals from 

the diesel generator exhaust (13-25%) while the calibrated gas mix ion signals were fairly 

constant (5-12%) over the course of the three days of experiments. This suggests that the largest 

changes in emission levels are due to daily changes in the steady state diesel generator emissions, 

the latter being larger than the intraday variation (1-10%). 

28 
 
EPA/600/R-10/050 

April 2010 

Concentration (ppb) 

200 

180 

160 

140 

120 

100 

80 

60 

40 

20 

0 

Day 1 Day 2 Day 3 

phenol

 p-xylene

 m-xylene

 o-xylene

 1,2,4 tmbz

 toluene

 naphthalene

 benzene

 styrene 

Figure 5-8. 	 Observed day to day variations in estimated concentrations of BTEX-like 

analytes in exhaust diesel generator. 

Information regarding the emission level of other observed analytes in the diesel generator 

exhaust was extracted from separate measurements. Styrene (m/z = 104) and ethylbenzene (m/z 

= 106) were detected and identified based on their agreement with literature spectra. On the other 

hand, aniline (m/z = 93) was noticeably absent in the diesel generator exhaust. An upper value of 

the aniline concentration is determined to be 0.3 ppb, based on the similar ionization probability 

of aniline in comparison to benzene, being only a factor 1.67 lower (Velazquez, 1998). Note that 

this is not the REMPI-TOFMS instrument detection limit for aniline but rather the minimum 

concentration that would have been detectable in the diesel generator exhaust without significant 

ion signal overload on the detector at other masses. In fact, all aromatic compounds detected and 

discussed so far have detection limits in the low parts per trillion (ppt) range using this REMPITOFMS instrument as observed prior to this study. 

The qualitative analysis of the PAHs as observed in the diesel generator exhaust is obscured by 

the presence of a multitude of methylated naphthalenes. The identification of m/z = 128 as 

naphthalene is based on the spectral agreement of the S1 ← S0 band near 301.6 nm with literature 

(Velazquez, 1998). Note that for naphthalene, this band around 301.6 nm has significantly lower 

intensity than the (SN ← S1; N>1) bands between 250 and 278 nm. This example illustrates that 

naphthalene, like many other PAHs, can be readily detected at 266 nm using a fixed wavelength 

laser system, but that for analyte verification a tunable laser system is necessary. Following the 

naphthalene assignment, it is provisional to assign the mass 142, 156, 170 and 184 ion signals to 

methylated naphthalenes up to tetra methylnaphthalene. Minor mass contributions were observed 

at 266 nm for mass 152 and 154 that could be attributed to acenaphthylene and acenaphthene. 

Fluorene (m/z = 166) in diesel generator exhaust was confirmed by the agreement with the 

spectral features around 296 nm (Zimmermann et al., 1994). Assignment of m/z = 178 was 

complicated by the fact that the individual identification of the most likely PAHs, namely 

anthracene or phenanthrene, requires a two-color ionization scheme (1+1′ REMPI) and was 

beyond the scope of this work. The extractive sampling GC/MS analysis showed that only 

29 
 
 

DG Exhaust concentration (ppb) 

250 

200 

 Extractive Sampling

 REMPI-TOFMS 

150 

100 

50 

0 

1 2 3 

benzene toluene 

1 2 3 

m+p xylene 

1 2 3 

EPA/600/R-10/050 

April 2010 

phenanthrene was detected and no anthracene. With this additional information available, the 

mass 178 peak was assigned to phenanthrene. A low intensity mass peak was detected at mass 

202 with no clear spectral features as recorded in an additional wavelength scan (250-360 nm) 

that can be attributed to either pyrene or fluoranthene. Without further 1+1′ REMPI experiments, 

a distinction can not be made as to which isomer is detected. The concentrations of the observed 

PAHs in diesel generator exhaust were obtained from a comparison between the established 

calibration curves for each PAH using the sample delivery system and the diesel generator 

exhaust ion signals. 

The diesel generator exhaust emission results obtained by REMPI-TOFMS were compared with 

those from standard extractive and GC/MS analyses, taken in parallel and at the same location in 

the exhaust gas flow. Since m- and p-xylene co-elute in the GC/MS analysis, the REMPITOFMS based concentrations for these isomers were added for comparison. Figure 5-9 shows 

the good agreement that is observed for the three day average benzene concentration (163 ± 14 

ppb with REMPI-TOFMS and 189 ± 24 ppb with GC/MS) with daily differences in measured 

concentrations varying between 1 and 25%. For toluene and the summed m- and p-xylene 

isomers, the agreement is only fair, as the REMPI-TOFMS results are up to 60% different from 

those determined using extractive sampling and GC/MS analyses. REMPI-TOFMS and GC/MS 

analyses measured, respectively, 83 ± 15 ppb and 120 ± 19 for toluene and 69 ± 16 ppb and 126 

± 10 ppb for the summed m- and p-xylene. The cause for this discrepancy is unknown. The 

extractive GC/MS analysis of the diesel generator emissions appears to have a similar level of 

variation in daily average concentration when observed in parallel with integrated, daily average 

REMPI-TOFMS measurements. 

Figure 5-9. 	 Comparison between extractive and REMPI-TOFMS concentrations for three 

exhaust analytes. 

30 
 
EPA/600/R-10/050 

April 2010 

5.2.2 Transient Diesel Generator Results 

So far, results have been presented revealing the constant emission levels under steady state 

diesel generator exhaust conditions. Since start-up of a cold engine includes a period of 

incomplete combustion, it was expected that emissions during start-up would not be constant. 

Emissions were recorded during the start-up of the diesel generator at the beginning of the day 

(“cold start”). As illustrated in Figure 5-10 (a), at t = 40 sec, the diesel generator was started and 

brought directly to the “full load” operational condition. With the laser wavelength optimized for 

benzene (λ = 259 nm) detection, an initial sharp spike of ~ 10 s in benzene concentration was 

detected, as well as in several other BTEX and PAH concentrations. The benzene peak intensity 

represents a transient maximum concentration of 14 ppm, which is 90 times larger than the 

steady state emission levels (1 min average) recorded after 5 minutes of diesel generator run 

time. Similar transients, but with significantly different durations, were observed for all detected 

PAHs and methyl-substituted PAHs of which naphthalene and two methylated naphthalenes are 

shown in the insert of Figure 5-10 (a). Again, the emission levels after 5 minutes are equal to the 

steady state emission levels reported previously for all detected compounds. Following cold start, 

the increase in ion signal, hence concentration, of these larger mass compounds is slower than 

for benzene due to the 150 °C temperature used for the sampling equipment. The maximum 

emission level of 1.5 ppm for naphthalene was found to be a factor of 14 higher than the steady 

state emission level that day (109 ppb). The high selectivity of REMPI-TOFMS prevents the 

study of all individual BTEX compounds during the same cold start so there is no complete 

information available about specific peak emissions for all BTEX compounds. Benzene peak 

emissions from cold starts of the diesel generator on other days were found to be in good 

agreement, with less than 20% variation in the peak emission concentration. The integrated area 

under the transient benzene ion signal following the cold start in Figure 5-10 (a) was calculated 

to be a factor of 28 higher than that of the steady state emissions during an equal time interval of 

15 seconds. Consequently, the amount of benzene emitted at a cold start (first 15 seconds) is 

equal to the amount emitted over a 7 min time period under steady state conditions. With the 

laser wavelength positioned where toluene is effectively ionized (λ ~ 265.8 nm), similar results 

were obtained for a different cold start. In this case, the toluene transient peak was found to be 

about a factor of 23 higher than the steady state emission concentration. Figure 5-10 (b) shows 

the normalized ion signals recorded in parallel for other masses during this cold start. The higher 

sampling temperature of 200 °C resulted in an equal incline (in 4-6 seconds) for all masses, 

excluding sampling bias of higher mass analytes. The tail end of the curve, however, appears to 

be different depending on the molecular structure. All single aromatic ring molecules decay 

faster to their respective steady state values while the two-ring methylated-naphthalenes show a 

slower decay. The figure has a bias towards this statement since the concentrations of the latter 

group of molecules remained higher than those for the former group, or, in other words, the 

sharp increase following a cold start is less intense for (methylated-) naphthalenes than for single 

aromatic ring molecules. Taking this into account by using the decay rate from the peak to half 

the value between peak and steady state level, the decay rates are still a factor of three slower. 

The explanation behind this observation can be attributed to the diesel generator combustion 

process where apparently the transition from a process of incomplete combustion (cold-start) to 

more or less complete combustion (steady state) is faster for single aromatic ring analytes than 

for double aromatic ring analytes. Similar “memory effects” have been observed for PAHs in 

31 
 
waste incinerators using REMPI-TOFMS (Heger et al., 1999). No evidence was found for 

significantly delayed (in terms of minutes) PAHs emissions. 

The sampling time of REMPI-TOFMS for each data point is 1 second (10 laser shots average ion 

signal). This is clearly sufficient to resolve the 7 sec (full width half maximum, FWHM) 

emission peak during cold startup. In contrast with that, the extractive sampling technique using 

Tedlar bags (EPA Method 0040) has to sample for several minutes to get sufficient information 

and the GC/MS analysis revealed no elevated emission values for the first 2-3 minutes that 

includes cold startup. Apparently, these short events go unnoticed in the extractive sampling 

technique. 

0 60 120 180 240 300 360 

0 

50 

100 

150 

200 

250 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

B

Normalized Ion Signal 

double ring aromatics 

single ring aromatics 

0 60 120 180 240 300 360 

× 20 

Diesel Generator ON time (sec) 

A

 naphthalene

 methylnaphthalene

 dimethylnaphthalene 

Ion Signal (arb. units) 

Benzene

Concentration (ppm) 

16 

14 

12 

10 

8 

6 

4 

2 

0 

0 30 60 90 120 150 

time (sec) 

EPA/600/R-10/050 

April 2010 

Figure 5-10 (a, b). (a) Real-time transient benzene emissions following a cold start. (b) 

Normalized ion signal traces for single aromatic ring (thin lines) and double 

aromatic ring (fat lines) analytes. 

Similar transient results were obtained for start-up events when the diesel generator was already 

at its operating temperature. Figure 5-11 shows benzene and naphthalene concentrations during a 

triple repeat of these warm restarts. The benzene emissions were found to be a factor of 2.3 

lower (6 ppm versus 14 ppm) in comparison to the cold start, while for naphthalene this ratio was 

a factor of 5-6 lower (250-300 ppb versus 1.5 ppm). This indicates that naphthalene (and 

probably all PAHs) is predominantly formed during a significant period of incomplete 

combustion, such as a cold start, in comparison to the shorter periods of incomplete combustion 

with a warm restart. Again, only a real time detection method, such as REMPI-TOFMS, can 

provide this information. 

32 
 
0 

1 

2 

3 

4 

5 

6 

7 

Benzene 

Concentration (ppm) Loading DG

OFF 

ZERO 

FULL 

300
 


Naphthalene 

Concentration (ppb) 250 

200 

150 

100 

50 

0 

time (min) 

0 5 10 15 20 25
 


EPA/600/R-10/050 

April 2010 

Figure 5-11. Transient REMPI-TOFMS results. 

Top frame: Loading profile during warm restart test schedule. Middle frame: Transient 

benzene emissions following three restarts as recorded at the wavelength for benzene 

detection. Bottom frame: Transient naphthalene emissions. 

Besides a sharp rise in emissions during a restart, the shutdowns of the diesel generator were also 

accompanied by transient, yet smaller, increases of benzene and naphthalene concentrations 

before dropping to zero. This is probably due to the additional emission of small amounts of 

unburned hydrocarbons in the final movement of the engine piston without combustion of the 

diesel fuel. Note that the relatively slow signal decay upon shutdown is due to the large duct 

volume from which REMPI-TOFMS continues to sample, even when the diesel generator was 

shutdown. For comparison, the signal decay time for the sampling of BTEX compounds at 2 

L/min including the 9 m transfer line at 150 °C was found to be 2-3 s while the decay time that 

includes sampling from the duct volume as shown in Figure 5-11 was 10-12 s. 

33 
 
EPA/600/R-10/050 

April 2010 

6.	 Source 1: U.S. Marine Corps Diesel Generator Air Toxic Emission 

Characterization 

This chapter continues the work described in Chapter 7 (Oudejans et al., 2004), by using 

REMPI-TOFMS to determine HAP emission factors for a diesel generator, both for steady state 

and transient operations, such as start-ups. Temporally-resolved and mode-relevant emission 

factors were determined for the most prevalent aromatic air toxics and compared to cumulative 

samples collected simultaneously via conventional EPA Methods. These measurements were 

compared to emission factors available in EPA databases to determine the efficacy of the 

REMPI-TOFMS method as well as the need for real time emission factors. Other online 

measurement techniques for VOC, fine particles, particle-bound PAHs, and O2, CO2, and CO 

were used in this study to complement the gaseous organic air toxics measurements and to 

highlight potential relationships. 

6.1 Experimental 

Air toxic emissions were characterized for a Tactical Utility Generator (Class 2, MEP6) provided 

by the United States Marine Corps. This is a Kurz & Root diesel-engine-driven, JP-8-fired, 

tactical, skid-mounted unit, Model MEP006A. The engine is a liquid-cooled, 6-cylinder, 4 

stroke, and turbo-charged diesel. The generator is a 50/60 kW, brushless, air cooled, rotating 

field generator. The maintenance records are dated June, 1973; presumptively this is its initial 

year of operation. The hours of operation are unknown. The load bank was a 100-kW, variable 

load, Avtron model. The diesel generator set was placed outside the research facility, and the 

exhaust was connected to a 25.4 cm diameter duct of 350 cm length with sampling ports 

connected to the various sampling equipment. The exhaust gas was drawn past the sampling 

ports, through a dilution tunnel, and connected to a point exhaust on the building. The sampling 

duct was thermally insulated and under negative pressure to prevent any fugitive emissions. 

Various operational loads on the generator were established via connection to a variable, pre-set, 

100-kW Avtron load bank. 

The organic air toxic emissions were characterized for cold and hot starts, different engine loads, 

and steady state operating conditions. Measurements were made using the REMPI-TOFMS, an 

on-line GC (OLGC) system (75 m RTX624 column), a photoelectric aerosol sensor (PAS 2000), 

an ELPI, and extractive EPA certified methods. Emission rates were determined for steady state 

conditions at a nominal load of 75% of the total load, or 45 kW power output, at least 30 minutes 

after start-ups. Data were taken for three consecutive days and reported as average daily 

concentrations and standard deviations thereof. 

The REMPI-TOFMS results were compared with reference data, obtained concurrently with the 

conventional EPA sampling/analytical methods listed in Table 6-1, as well as the OLGC. Steady 

state emission factors for the target organic pollutants obtained with the reference methods were 

compared to the integrated values obtained with the REMPI-TOFMS system. 

34 
 
 

 

 

EPA/600/R-10/050 

April 2010 

Table 6-1. EPA sampling methods. 

Class of 

Targets 

EPA 

Methods Reference and Web-Link 

VOCs M-0040 

M-8260b 

SW-846 “Test Methods For Evaluating Solid Wastes, Physical/Chemical Methods,” 

Office of Solid Waste, Method 0040 “Sampling Of Principal Organic Constituents From 

Combustion Sources Using TEDLAR Bags,” 1996. 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/0040.pdf 

Method 8260b “Volatile Organic compounds by Gas Chromatography/Mass 

Spectrometry (GC/MS),” 1996. 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/8260b.pdf 

Semi Volatile 

Organic 

Compounds 

(SVOC) 

M-0010 

M-8290a 

SW-846, Test Methods For Evaluating Solid Wastes, Physical/Chemical Methods, Office 

of Solid Waste, Method 0010 Modified Method 5 Sampling Train, 1986. 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/0010.pdf 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/8290a.pdf 

U.S. Environmental Protection Agency, Method 8290a “Semi volatile Organic 

Compounds by HRGC/High Resolution Mass Spectroscopy (HRMS),” 1998. 

Carbonyl M-0011 

M-8315a 

SW-846 “Test Methods For Evaluating Solid Wastes, Physical/Chemical Methods,” 

Office of Solid Waste, Method 0011 “Sampling for Selected Aldehydes and ketone 

Emissions from Stationary Sources,” 1996. 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/0011.pdf 

SW-846 “Test Methods For Evaluating Solid Wastes, Physical/Chemical Methods,” 

Office of Solid Waste, Method 8315a “Determination of Carbonyl Compounds by High 

Performance Liquid Chromatography (HPLC),” 1996. 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/8315a.pdf 

CO Method 10A 

Determination of Carbon Monoxide Emissions in Certifying Continuous Emission 

Monitoring Systems at Petroleum Refineries, http://www.epa.gov/ttn/emc/promgate/m10a.pdf 

O2 

Method 3A Determination of Oxygen and Carbon Dioxide Concentrations in Emissions from 

Stationary Sources http://www.epa.gov/ttn/emc/promgate/m-03a.pdf CO2 

Samples from the diesel generator exhaust were taken for the REMPI-TOFMS through a 0.64 cm 

stainless steel line at typical flow rates of 2 L/min (at STP). Since the REMPI-TOFMS measures 

vapor phase analytes only, the sample was collected under sub-isokinetic conditions and filtered 

through a micro-fiber filter (at 150 °C) to avoid PM reaching the valve inlet system of the 

REMPI-TOFMS instrument. The filter was a Unique Product International heated filter element 

(Model FLT-1584A) comprised of a glass/polytetrafluroethylene (PTFE) fluorocarbon microfiber composite, with a particulate efficiency of 99.9% at 1.0 μm. A flexible, 9 m long, 1.27 cm 

diameter, Silico-Steel transfer line conveyed the exhaust gas to the REMPI-TOFMS instrument. 

This line was kept at 150 °C while sampling exhaust gases in order to minimize adsorption to the 

line walls. 

An OLGC system (Ryan et al., 1998) was used for this project to aid in the identification of 

volatile organic and organo-chlorinated compounds. The OLGC system contains a heated sample 

delivery system, a purge and trap sample concentration system, and the GC analytical system. 

The sample concentration device is a Tekmar LSC-2000 thermal desorption unit, modified to 

accommodate the direct collection of combustion samples from the stack or from a Tedlar bag. 

35 
 
EPA/600/R-10/050 

April 2010 

The GC analytical system is an HP 5890 series II GC equipped with both a flame ionization 

detector (FID) and an electron capture detector (ECD). 

On-line monitoring of the diesel exhaust PM size distribution was performed using a Dekati Ltd. 

ELPI. Particles from the flue gas were sampled through a unipolar corona charger. The electric 

current carried by the charged particles into each impactor stage is measured in real time by a 

sensitive multi-channel electrometer. The particle collection into each impactor stage is 

dependent on the aerodynamic size of the particles. Measured current signals are converted to 

aerodynamic size distribution using particle size dependent relations describing the properties of 

the charger and the impactor stages. 

The particle-bound PAHs were monitored using a real-time PAS 2000 from EchoChem 

Analytics (Burtscher, 1992; Dunbar et al., 2001). This analyzer photoionizes PAHs on the 

surface of particles while the gas molecules and particles themselves remain neutral. The PAHladen particles from the sample flow pass through a quartz tube with an excimer lamp mounted 

around it. The lamp operates at high frequency and high voltage, ionizing the surface of the 

particles. The charged particles then flow through a short tube to remove all negatively charged 

particles. Subsequently, the charged particles are collected on a filter element which is mounted 

in a Faraday cage. An electrometer measures the ion current associated with the charged particles, 

which is proportional to the concentrations of the PAHs (three or more aromatic rings) bound on 

their surface. 

The steady state emission results obtained by REMPI-TOFMS for organic compounds were 

compared with those obtained via EPA standard Methods 0040 (volatiles), 0011 (carbonyls), and 

0010 (semi-volatile PAHs) and the OLGC technique. The method comparison used emission 

data obtained during nine sampling runs that occurred on three consecutive days. Since the 

reference methods are cumulative sampling techniques that provide a time-averaged 

concentration value, direct comparisons can only be made with the integrated values obtained 

with REMPI-TOFMS. Only compounds that had concentrations above the detection limit for all 

three measurements techniques were used. Since m- and p-xylene co-elute in the GC/MS 

analysis, the REMPI-TOFMS-based concentrations for these isomers were summed for 

comparison. Sub-isokinetic sampling for REMPI-TOFMS (to avoid particles in the detector) was 

equivalent to the isokinetic reference methods; even the semi-volatile PAH compounds were all 

found within the gas phase fraction, allowing direct comparison of the REMPI/TOFMS with the 

reference method measurements. 

The system performance of the REMPI-TOFMS was evaluated based on the relative accuracy 

(RA) measure (EPA, 2000a). The results presented here only provide a relative comparison of 

this technique with promulgated EPA techniques based on a limited number of parallel sampling 

tests (N = 5 and 3 for BTEX and naphthalene compounds, respectively). The RA is defined in 

this work as the absolute mean between the measured values of a specific compound determined 

by the REMPI-TOFMS system and the values determined by the reference method (RM) plus the 

2.5% error confidence coefficient of a series of tests divided by the mean of the reference 

method. 

36 
 
d + CC
 
 RA =
 
 ×100 

RM 

EPA/600/R-10/050 

April 2010 

(1) 

d

where is the absolute value of the mean of the difference between i pairs of data defined as 

d 

_ 

= 1 ∑

n 

di n i=1 CC in which n is the number of parallel data points, is the absolute value of the 

S 

t 0.975 

n confidence coefficient defined as 

d 

in which Sd is the standard deviation and t0.975 is the 

Student’s t distribution for 0.975, and RM is the average of the reference method samples. 

6.2 Results and Discussion 

6.2.1 Steady State Emissions 

Steady state emission measurements were compared between on-line REMPI-TOFMS, OLGC, 

and the standard reference methods that use extractive sampling and analysis for volatile and 

semi-volatile organic air toxic compounds (Table 6-2). Results were also compared with an 

emission factor for a related source (large stationary diesel) published in an EPA database (EPA, 

1993), albeit under a different test cycle. In general, the emission factors measured by REMPITOFMS versus the reference methods vary by less than a factor of 2, which demonstrates the 

accuracy of the REMPI-TOFMS as an organic air toxic emission monitor. Generally good 

agreement was observed for the REMPI-TOFMS benzene emission measurements when 

compared to the OLGC results and the corresponding EPA reference method (Table 6-3). 

While additional tests would likely have improved the RA, these values are still noteworthy; for 

the m- and p–xylene and toluene, the RA was determined to be around 60-80%. Higher 

naphthalene concentrations were observed with the REMPI-TOFMS compared with the 

reference method, resulting in a RA of more than 110%. 

In general, standard deviations of the REMPI-TOFMS-measured compounds are in agreement 

with the corresponding standard deviations of the respective compounds measured with the 

OLGC or the reference methods. This suggests that the precision of each method is relatively the 

same. 

6.2.2 Emissions during Startups 

Cold and hot startups of the diesel engine caused immediate, sharp emission peaks for benzene 

and other BTEX compounds, as well as for all gas-phase PAHs and methyl-substituted PAHs as 

measured by REMPI-TOFMS. The very short response time of the REMPI-TOFMS for each 

data point (1 s for a 10-laser-shot average ion signal) was sufficient to resolve the transient 

emissions for each individual target organic air toxic; results for benzene and naphthalene are 

illustrated in Figure 6-1. The cold start benzene peak intensity (~ 15 ppm), which represents the 

maximum benzene concentration measured, was found to be about 100 times larger than the 

steady state emission levels (~ 150 ppb, 1 min average) recorded after 5 minutes of diesel run 

time. Similarly, the cold start naphthalene concentration (~ 1.5 ppm) was 14 times larger than its 

steady state emission level (~ 110 ppb, 1 min average). This concentration behavior is consistent 

37 
 
15
 

12
 


 Benzene (ppm) 9
 


6
 


3
 


0
 


0 1 2 3 255 260 265 270 275 

Temperature Diesel Exhaust Concentration 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

1.2 

1.4 

1.6 

0 1 2 3 255 260 265 270 275 

 Naphthalene (ppb) 

6000 

5000 

3000 

4000 CO (ppm) 

2000 

1000 

0 

0 1 2 3 255 260 265 270 275 

6 

4 CO2 (%) 

2 

0 

0 1 2 3 255 260 265 270 275 

0 

50 

100 

150 

200 

250 

300 

350 

0 1 2 3 255 260 265 270 275 

 Temperature (oC) 

Cold Start

Hot Start

Engine Off

Hot Start

Engine Off 

Hot Start 

EPA/600/R-10/050 

April 2010 

with the presence of unburned fuel during the initial fuel-rich combustion reported in Boesl et 

al., (1998, 2000). The CO, CO2, and temperature traces (Figure 6-1) also reflect the changes in 

combustion conditions as the engine cylinders heat up and combustion efficiency improves. 

Figure 6-1. 	 Cold and hot start-up emissions of benzene, naphthalene, CO, and CO2 with 

exhaust temperature. 

The time duration from the peak concentration to the steady state concentration varied from 

seconds to several minutes and was a function of the specific compound. Benzene reached steady 

state concentration within a few seconds, whereas naphthalene took several minutes. The 

transient benzene emissions during a cold start (~ 10 s) were about 20 times those during the 

period of steady state operation, meaning that about 200 s of steady state benzene emissions were 

equivalent to those emitted during cold starts. For naphthalene, a longer transient period during a 

cold start of about 6 min resulted in a four-fold increase over the same-period steady state 

emissions. For CO, a 3 min transient period contained about three times as many emissions as 

during the same steady state period. 

38 
 
Table 6-2. Air toxic emission factors determined by jet REMPI-TOFMS, OLGC, and EPA reference met

AP-42. 

	


Compounds 

MW 

REMPI-TOFMS OLGC Reference Method 

Average Stdev Average Stdev Method Average 

(g/gmole) kg/kWh ppb % kg/kWh ppb % kg/kWh ppb 

Benzene 78 1.31E-06 156 9.3 1.28E-06 152 16.5 1.57E-06 187 

Toluene 92 7.93E-07 80 23.2 6.84E-06 142 15.0 1.18E-06 119 

Ethylbenzene 106 1.03E-06 90 d 6.66E-06 120 10.8 4.80E-07 42 

Xylenes 106 1.20E-06 106 23.2 a a 

m,p-xylenes 106 7.64E-07 67 27.6 1.17e-06 103 10.1 1.44E-06 126 

m-xylenes 106 6.48E-07 57 26.4 a M 0040 a 

p-xylenes 106 1.36E-07 12 36.5 a a 

o-xylenes 106 4.20E-07 37 15.1 a a 

Styrene 104 5.00E-07 44 12.9 b b 

Chlorobenzene 113 3.63E-08 3 <2.42E-09 <0.2 2.66E-08 2.2 

Hexane 86 a <1.85E-09 <0.2 9.25E-08 10.0 

Formaldehyde 30 4.58E-06 1384 

Acetaldehyde 44 a a M0011 8.60E-08 18 

Acrolein 56 3.86E-07 63 

Naphthalene 128 1.51E-06 110 25.2 1.10E-06 80 

Acenaphthylene 152 a 5.66E-08 3.4 

Acenaphthene 154 a 8.46E-09 0.5 

Fluorene 166 2.48E-07 14 c 1.43E-07 8.0 

Phenanthrene 178 6.38E-07 33 c 4.34E-07 22.6 

Anthracene 178 a <8.96E-09 <0.4 

Fluoranthene 202 a 1.22E-08 0.6 

Pyrene 202 a M0010 3.54E-08 1.6 

Benz(a)anthracene 228 Non-Detect (ND) 

a 

2.22E-09 0.1 

Chrysene 228 ND 2.47E-09 0.1 

Benzo(b)fluoranthene 252 ND <8.96E-09 <0.3 

Benzo(k)fluoranthene 252 ND <8.96E-09 <0.3 

Benzo(a)pyrene 252 ND <8.96E-09 <0.3 

Indenol(1,2,3-cd)pyrene 276 ND <8.96E-09 <0.3 

Dibenz(a,h)anthracene 278 ND <8.96E-09 <0.3 

Benzo(g,h,l)perylene 276 ND <8.96E-09 <0.3 

Notes: (a) immeasurable with this technique; (b) not attempted; (c) one data point; (d) EPA, 1993; ND = non-detect. 

39 
 

 

 

 

EPA/600/R-10/050 

April 2010 

Table 6-3. RA of the three measurement methods during parallel sampling. 

Method REMPI-TOFMS OLGC RMa RA 

Compounds Average Sd Average Sd Average Sd REMPI-TOFMS/RM OLGC/RM 

ppb % ppb % ppb % % RM 

benzene 156 9.3 165 16.5 182 19.0 36 36 

toluene 80 23.2 142 15.0 116 21.3 59 39 

m-,p-xylene 67 27.6 103 10.2 121 14.0 79 34 

naphthalene 110 25.2 NAb NAb 80 3.2 114 NAb 

a

RM = reference method+ 

b

Not available 

Similar transient concentration phenomena were obtained for hot start events. Figure 6-1 also 

illustrates the concentrations response of benzene and naphthalene during a triple repeat of the 

hot start-ups. However, peak concentrations were lower and durations to reach steady state 

concentrations were generally shorter than with the cold starts. The transient concentration 

responses to changes in operating conditions are a function of their mechanism of formation and 

their mass transfer properties to the detector. Concentration levels are a result of in situ formation 

processes and survival of unburned parent fuel. For pollutants whose concentrations are 

dependent predominantly on formation reactions inside the cylinder, transient concentrations 

may last only few seconds. Compounds that are present as a result of unburned fuel droplets are 

more closely related to the time for the engine block temperature to reach thermal equilibrium. 

This time is source dependent, could last hundred of seconds (Rakopoulos et al., 1998), and will 

be shorter for warm startups in which the combustion chamber walls already exceed ambient 

temperatures. 

The rate at which pollutants retreat from the peak concentration to the steady state level may also 

be, in part, an artifact of their transfer time to the detector. Tests changing the sample line 

temperature from 150 °C to 200 °C resulted in a 1 to 3 s reduction of the cold startup peak width 

for benzene and toluene and a 35 s reduction (from 76 to 41 s) for naphthalene (the peak width 

duration is defined from cold startup until double the steady state concentration). This 

phenomenon is likely due to transfer line wall adsorption of the target analyte and, hence, is a 

function of the pollutant’s vapor pressure. 

REMPI-TOFMS was able to resolve emission concentrations during start-ups, as well as the 

differences between the two types of start-ups (cold and hot), because of its high sampling 

frequency. Standard sampling methods required extended sample collection time with Tedlar 

bags and were unable to resolve these transients. The OLGC showed elevated concentrations 

during start-ups, but since the sampling time was set at 5.6 min, this period was well in excess of 

the transient peak durations observed by REMPI-TOFMS. 

No solid-bound PAHs were observed by the PAS during the cold and hot startups (see Figure 

6-2). This may be misleading for two reasons. First, combustion-derived PM may be contained 

within a mist of small, re-condensed droplets of unburned fuels. These droplets are not easily 

40 
 
EPA/600/R-10/050 

April 2010 

photo-ionized and remain neutral, hence, undetectable by the PAS. Second, there also may be 

extensive dilution of the PAH mass due to the large number of particles present at startup. The 

solid-bound PAHs first appear after the transient peaks of the benzene (for example), and their 

concentrations steadily subside with run time. 

350 120

 Temperature 

 Solid-Phase PAHs 

0 200 400 600 800 2000 2250 2500 

Run Time (Seconds) 

300 100 

250 

80 

PAHs Concentration @ 14(%) O (μg/m3) 2

Temperature (oC) 

200 

60 

150 

40 

100 

20 50 

0 0 

Figure 6-2. 	 Temporal temperature and particle-bound PAH concentrations in the diesel 

exhaust. 

6.2.3 Emissions during Load Variation 

The modal (load change) characterization of the targeted air toxics, solid-bound PAHs, 

temperature, and CO/CO2 were determined by the REMPI-TOFMS, the PAS analyzer, duct 

thermocouples, and the continuous emission monitor (CEM) system, respectively. Seven 10 kW 

increments in load, from no load to 60 kW, resulted in benzene, naphthalene, CO, and CO2 

concentrations shown in Figure 6-3 while particle-bound PAH measurements are shown in 

Figure 6-4. The relatively higher concentrations observed during the no-load condition are likely 

due to the same cold startup phenomena observed earlier. The no-load conditions resulted in 

higher aromatic and CO concentration than the low-load (10 kW) condition. Further increases in 

load resulted in compound-specific concentration trends: benzene increased in concentration at 

higher loads, whereas naphthalene showed little apparent change. Methylated naphthalenes (not 

shown), determined only with REMPI-TOFMS, also increased. Increased pollutant 

concentrations are likely due to the higher fuel to air ratio at higher loads, also reflected by the 

increase of the concentrations of CO and CO2 (Figure 6-3) and the decrease in O2. When the 

emission concentrations are evaluated at a constant oxygen level at the stack, minimal variation 

between load levels (from 10 to 50 kW) is noted (about 12% Sd for CO and less than 0.6% Sd for 

CO2). The no-load and full load conditions had slightly higher CO emission rates that the other 

41 
 
EPA/600/R-10/050 

April 2010 

load conditions. The exhaust gas temperature at the sampling location increased linearly with the 

load due to an increase in the heat release rate and lower air/fuel ratio in the combustion 

chamber. 

Load 

300
 

250
 No Load 10 kW 20 kW 30 kW 40 kW 50 kW 60 kW

benzene (ppb) 200
 


150
 


100
 


50
 


0
 


Diesel Exhaust Concentrations200
 naphthalene (ppb)
 

160
 

120
 

80
 

40
 

0
 

500
 

400
 CO (ppm) 

300
 

200
 

100
 

0
 

8
 CO (%) 2
 

6
 

4
 

2
 

0 

400
 

350
 Temperature (erature ( o

C)
 

300
 

250
 

200
 

150
 

0 10 2 0 30 4 0 5 0 6 0 7 0 
 

Run Time (min) 

	 
 Temperature 

Figure 6-3. 	 Load change emissions of benzene, naphthalene, CO, and CO2 with exhaust 

temperature. 

42 
 
380 

140 360 

340 120

Temperature at the sampling location (oC) 

 Temperature

 Particle-bound PAHs 

0 10 20 30 40 50 60 70 

320 

100 

300 

280 80 

260 60 

240 

 Particle-bound PAHs (μg/m 3) 

220 

200 

40 

20 

180 

0 

Run Time (min) 

EPA/600/R-10/050 

April 2010 

Figure 6-4. Temperature distribution and particle-bound PAH concentrations under 

varying loads. 

43 
 
EPA/600/R-10/050 

April 2010 

7.	 Source 2: Real-Time Measurement of Trace Aromatics during Operation 

of Aircraft Ground Equipment 

This chapter describes work that extends the REMPI-TOFMS emission factor determinations to 

a U.S. Marine Corps gas turbine, contrasting the HAP concentration trends during startups, 

shutdowns, and load changes and demonstrating the ability to monitor these trace pollutants. 

Concentrations were compared to published emission factors available in EPA databases and the 

referenced literature to determine the efficacy of the REMPI-TOFMS method. 

Two gas turbine units using JP8 fuel, included in the general category of aerospace ground 

equipment (AGE), were previously characterized (Gerstle et al.,1999). The AGE classification 

system includes aircraft support equipment such as air compressors, floodlights, bomb lifts, 

turbines, generators, and heaters. Auxiliary power units (APUs) (GTCP85-180 and GTCP165-1) 

from C-130H and C-5A/B aircraft, respectively, were tested at constant power settings, or about 

120 kg fuel/h. Ambient air samples were taken to allow for background correction. The authors 

found from testing with these and aircraft engine sources that of the 120 or so compounds 

identified, only a few compounds were universally detected, suggesting that emission 

characterization is fairly engine or source specific. Benzene, toluene, and xylenes were prevalent 

and formaldehyde was over 90% of the aldehydes/ketone present. The authors mentioned the 

possibility of reducing the characterization effort by monitoring a few surrogate compounds, but 

were unable to test this theory due to an insufficient database (lack of replicates on a single 

source). 

7.1 Experimental 

7.1.1 AGE 

The exhaust of a turbine engine compressor, USAF type A/M32A-95 (Large Aircraft Starting 

unit), was sampled with the REMPI-TOFMS system. This AGE (Figure 7-1) is used to furnish 

pneumatic power for ground support of aircraft systems. Its primary mission is to start engines 

for a variety of aircraft. The turbine engine, fuel and electrical systems, as well as the air delivery 

system are enclosed inside a four-wheeled, towable cart. The cart contains a 300 L metal fuel 

tank which holds JP-8, a kerosene-based fuel (MIL-T-83133) used as the standard military fuel 

(U.S. Army, 2001). It is comprised of paraffins, olefins (≤ 5% by vol), and aromatics (≤ 25% by 

vol) with less than 0.3% sulfur (S) by mass and a minimum net heat content of 42,700 kJ/kg 

(Kimm et al., 1997). Annual fuel consumption per AGE unit is typically low (on the order of 750 

L/year) but the large number of units make AGE a high category of total usage. The JP-8 fuel 

headspace above the liquid layer of a nearly empty fuel barrel (at 25 °C) was sampled into the 

REMPI-TOFMS sampling line. Concentrations of target analytes were determined by calibrating 

the measured ion signals with those from a TO-14 Aromatics Subset (Supelco) gas standard 

cylinder mixture containing 100 ppb of aromatic analytes (BTEX). 

44 
 
EPA/600/R-10/050 

April 2010 

Figure 7-1. Aircraft ground equipment outside EPA facilities 

7.1.2 Operating and Sampling Procedures 

The AGE was operated for two days to characterize its emissions under idle and full load 

conditions as well as start up and shut down scenarios. The idle and full load operating periods 

ranged from 1 to 4 h duration, interspersed with refueling times. Consecutive, ~ 2 h cycles of 

start up and shut down were completed over a 6-7 h sampling day. 

REMPI-TOFMS sampling was conducted using 5 cm diameter ports located about 30 cm below 

the top of a 4.9 m high, 0.84 m x 0.28 m rectangular carbon-steel duct covered with 7.6 cm 

fiberglass insulation. This duct was built to convey the AGE exhaust away from building air 

intakes. A 2 L/min isokinetic sample was pulled through a 15 m, 0.95 cm (inner diameter) heated 

(150 °C) transfer line to a heated (150 °C), filter. Filters were exchanged at least three times per 

day (1 to 3 h sampling time) to minimize capture of the target analytes on the carbon-laden filter. 

Beyond the filter, a 3 m long, 1.25 cm diameter silico steel coated transfer line (at 150 °C) 

conveyed the sample to the REMPI-TOFMS instrument. A small quantity of 1 ppm C6D6 in N2 

calibration gas was added upstream of the filter as an internal calibrant. REMPI-TOFMS 

sampled directly from the 2 L/min exhaust with a slipstream of approximately 1 mL/min. 

Fourteen pre-determined wavelengths in the λ = 258 – 275 nm range were selected, based on 

established wavelength scan libraries, for their high probability of detecting discrete, individual 

(isomer selective) compounds. This wavelength changing sequence method was performed 

during steady state idle (low) and full load AGE operational modes where changes in 

concentration were expected to be gradual. The REMPI ion signal of a target analyte at its 

specific wavelength was recorded for 1 minute before switching to the next wavelength. This 15 

minute sequence was repeated multiple times within the sampling time period as defined by the 

conventional extractive sampling methods. In addition, cold/hot starts and shutdowns were 

followed in real time at the most effective wavelength for toluene ionization (267 nm) without 

additional wavelength changes in order to eliminate losses in data acquisition during wavelength 

switches (~ 2 s). 

45 
 
EPA/600/R-10/050 

April 2010 

Conventional extractive sampling techniques, based on EPA Methods, were used to validate the 

integrated REMPI/TOFMS measurements taken over the same sampling time. VOCs were 

sampled in parallel with the REMPI-TOFMS, using standard extractive sampling for volatiles 

from the duct into stainless-steel Summa canisters and analyzed by GC/MS (EPA 1999) for 60 

target compounds and for unknown VOCs as tentatively identified compounds (TICs) using the 

National Institute of Standards and Technology (NIST) spectral database (NIST, 2005). Nine 

samples from the turbine stack were taken during the two days of sampling, four at idle load and 

five at full load. All samples were extracted from a 0.65 cm (1/4 inch) port through a 0.65 cm 

(1/4 inch) Teflon tube. All summa canister samplings were started with an initial vacuum of 76.2 

cm (30 inches) Hg and ended with 1.2 to 0 cm Hg (3 to 0 inches of Hg) Two summa canisters 

were also used as a feed into the REMPI-TOFMS instrument as well as the GC/MS for further 

validation of the methods. 

PAHs were sampled using EPA Method 0010 (EPA, 1986a) and Method 5 (EPA, 1986b) 

sampling, and analyzed via a modified EPA Method 8270 (EPA 1996b) using a toluene 

extraction solvent and deuterated and fluorinated pre-sampling spikes. Formaldehydes and other 

carbonyl group compounds were sampled via EPA Method 0011 (EPA, 1996c). This method 

uses a sample train configuration adapted from EPA Method 5, wherein the sample gas is 

collected in an aqueous, acidic 2,4-dinitrophenyhydrazine (DNPH) solution, and analyzed via 

EPA Method 8315A (EPA, 1996d) using high performance liquid chromatography (HPLC). 

Results of the carbonyl groups were provided to develop additional emission factors for the AGE 

and not for the purpose of the REMPI/TOFMS validation. 

Emissions factors were calculated by dividing the concentration of the compound by the amount 

of fuel used, or g/kg of fuel. Graphical results are reported as the value ± 1 standard deviation, σ. 

Tabular results are reported as RSDs divided by the average value, or σ / average (AVG). 

Comparisons between measurement methods are made with matched pairs of each target analyte 

using a paired t test. 

7.2 Results and Discussion 

REMPI-TOFMS traces during AGE startups, low load, and high load operation show complex 

emissions of varying concentrations. Figure 7-2 shows a 3D time-resolved trace of the emissions 

during a cold start (commencing at 2 min, 20 s) followed by about 5 min of low load operation. 

The concentration is proportional to the ion signal strength and the mass values highlight the 

different compounds that are observed. The cold start results in a significant peak of toluene (m/z 

= 92) as well as a number of other methylated naphthalenes (m/z = 128 to 184). The trace shown 

is optimized for toluene detection at λ = 267.5 nm. At this wavelength, methylated naphthalenes 

are also efficiently ionized while benzene and other single ring aromatics are marginally 

detected. The initial concentrations decline within 1 min, then are mostly constant during the low 

load operation. At 6 min and 53 s a change to high load shows signal reduction across the whole 

mass range, indicating a large drop in the measured concentrations. The lower concentrations are 

expected due to dilution from the increased throughput air in the turbine and increased 

combustion efficiency. 

46 
 
 

 

 

At t = 2 min,20 s: 

Cold start to idle load 

At t = 6 min, 53 s: 

naphthalene 

C1 -

C2 -

C3 -

toluene 

benzene 

Idle to high load 

EPA/600/R-10/050 

April 2010 

Figure 7-2.	 	 REMPI-TOFMS time-resolved trace of cold startup, idle (low) load, and high 

load conditions. 

Note: λ = 267.5 nm, optimized for toluene detection, but not calibrated externally. 

A wavelength scan of the steady state, low load emissions (Figure 7-3) shows discrete spectra for 

a number of individual compounds including toluene, phenol, styrene, and individual xylenes 

isomers. When the wavelength spectra from two selected mass numbers (m/z 92 and 106) from 

Figure 7-3 are compared to those obtained with a calibrated gas mixture (Figure 7-4), no 

wavelength interferences are observed, allowing for unambiguous concentration determinations. 

Also note that isomer separation for xylenes is possible using the moderately broad spectral linewidth of the laser system. Larger PAH analytes, such as methylated naphthalenes, are visible in 

Figure 7-3 but their characteristically broad wavelength spectra obscures spectroscopic details 

that could otherwise have been used for individual isomer identification. The observed emission 

compounds have little overlap with a headspace analysis of the JP-8 fuel drum (not shown), 

suggesting that the majority of the operating emissions are due to secondary organic byproduct 

formation rather than emission of unburned fuel. The predominance of benzene, toluene, and 

phenol in the emissions are not noted in the fuel headspace, which is dominated by xylenes and 

trimethylbenzene concentrations. 

Analysis of the AGE emission traces enables determination of major compound concentrations. 

With the laser set to a wavelength specific for each compound, real time integrated 

concentrations were determined during idle and high load operation. These REMPI-TOFMSderived concentrations were compared to standard EPA sampling and analysis methods. REMPITOFMS results were first compared against a standard analysis of emission gases gathered into a 

common Summa canister during low load operation. Figure 7-5 shows two replicate tests of 

REMPI-TOFMS BTEX measurements and two tests via standard GC/MS, both from the Summa 

canisters. Good agreement is observed, validating the REMPI-TOFMS quantification with the 

standard methods. 

47 
 
EPA/600/R-10/050 

April 2010 

phenol, 94 

toluene, 92 

xylenes, 106 

styrene, 104 

trimethylbenzenes, 120 

methylated 

naphthalenes 

Figure 7-3. REMPI-TOFMS wavelength-resolved trace during idle (low) load condition. 

The REMPI-TOFMS on-line measurements were then compared against emissions sampled in 

parallel via EPA standard Method TO-15 (EPA, 1999). Figure 7-6 shows a comparison of idle 

(low) load emissions from two sequential testing phases, with the Phase I and II TO-15 analyses 

done by a commercial laboratory then an EPA laboratory, respectively. Duplicate Phase I 

REMPI-TOFMS measurements predominantly fall within the ± 1 standard deviation range of the 

two GC/MS analyses. No apparent explanation was found for the wide disparity of the 

commercial laboratory analyses. The REMPI-TOFMS results were reasonably precise suggesting 

the actual emission variations were minimal over the short sampling period (~ 30 min). In Phase 

II, duplicate REMPI-TOFMS results agree quite well with the TO-15 standard analysis provided 

by our in-house laboratory. 

Comparison of the time-resolved REMPI-TOFMS-determined concentrations at high and idle 

(low) load versus the CO and CO2 concentrations (Figure 7-7) shows no apparent time-resolved 

relationship between combustion efficiency and trace organic emissions. Post-startup REMPITOFMS results show benzene and toluene declining to about 30 to 20% of their original values 

over a 5 h period while other organics, CO, and CO2 appear relatively constant. These declines 

occur throughout several startup/high load cycles, showing progressively declining organic 

emissions with time. Here, however, changes in CO2 level appear to be inversely related to a few 

compounds, most notably benzene, toluene, and phenol. 

48 
 
 

1.0 

0.8 

0.6 

Normalized ion signal 0.4 

0.2 

0.0 

-0.2 

-0.4 

-0.6 

-0.8 

-1.0 

Reference Spectrum toluene 

Mass 92, toluene 

AGE 

266 268 270 272 274 276 

-1.0 

-0.8 

-0.6 

-0.4 

-0.2 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

Mass 106 

Normalized Ion Signal 

Reference Spectrum 

xylenes + ethylbenzene 

AGE 

p-xylene 

m-xylene o-xylene 

ethylbenzene 

266 268 270 272 274 276 

Wavelength (nm) 

EPA/600/R-10/050 

April 2010 

Figure 7-4. 	 Comparison of (selected) AGE wavelength spectra versus the TO-14 

calibrated gas standard. 

49 
 
250 

Concentration (ppb) 

200 

150 

100 

50 

0 

benzene 

toluene 

ethylbenzene 

m,p-xylenes 

styrene 

o-xylene GC/MS

REMPI

GC/MS

REMPI 

Measurement Technique 

EPA/600/R-10/050 

April 2010 

Figure 7-5. 	 Comparison between GC/MS and REMPI-TOFMS analysis of summa 

canister gases. 

0 

500 

1000 

1500 

2000 

Concentration (ppb) 

 REMPI Phase I

 TO-15 Phase I, commercial lab

 REMPI Phase II

 TO-15 Phase II, EPA lab 

Benzene Toluene Ethylbenzene o-Xylene m-,p-Xylene Styrene 

Target Compounds 

Figure 7-6. 	 Comparison between REMPI-TOFMS measurements at low load and TO15 

method analyses by two laboratories. 

NOTE: Ranges represent 1 σ values. REMPI range from three 1-min concentration estimates. 

50 
 Idle Concentration (ppb) CO Concentration (ppm) 

6 

8 

10 

4 

 benzene toluene

 phenol styrene

 p-xylene m-xylene

 o-xylene ethylbenzene

 1,2,4 trimethylbenzene

 1,3,5 trimethylbenzene

 naphthalene fluorene 

300 

400 

500 

200 

2 100 

0 0 

High 

Load 

High 

Load 

High 

Load Idle 

Concentration (ppb) 

CO2 Concentration (ppm) High Load 

Start

Shutdown

Start 

Shutdown

Start 

Shutdown 

Start 

20000 400 

CO2 16000 300 CO 

12000 

200 

8000 

100 4000
 


0
 
 0 

10:00	 11:00 12:00 13:00 14:00 15:00 16:00 17:00 

Time (h:min)

EPA/600/R-10/050 

April 2010 

Figure 7-7. REMPI-TOFMS and CO and CO2 CEM concentrations during a series of 

startups (the initial startup was a cold start) and shutdowns (for refueling), 

operating at high, high, then idle load. Range of data (barely visible) are 

shown for benzene. 

Emission factors determined by REMPI-TOFMS as well as standard methods TO-15 for BTEX 

compounds, 0010 for PAHs, and 0011 for aldehydes are shown in Tables 7-1, 7-2, and 7-3, 

respectively. Data are presented for both idle load and high load steady state emissions. 

Comparisons are also shown for published emission factors from related AGE sources operating 

under full (high) load. 

Idle load emission factors of BTEX compounds (Table 7-1) at 23 kg of fuel per hour are 

typically about two orders of magnitude higher than full load emission factors at 78 kg of fuel 

per hour. This suggests that emissions from operation of AGE units under idle conditions may be 

significantly underestimated if they are calculated simply from fuel consumption and the full 

load emission factors. 

51 
 
Table 7-1. Emission factors for BTEX compounds during idle and full load operation. Comparison with 

AGE Type A/M32A-95 (this work) GTCP85-18

Operating Condition Idle Full 

Sampling Technique TO-15 REMPI-TOFMS TO-15 REMPI-TOFMS 

VOCs g/kg of fuel g/kg of fuel g

Value RSD (%) Value RSD (%) Value RSD (%) Value RSD (%) Value 

Benzene 9.8E-01 70.1 7.0E-01 1.1 8.6E-03 88.6 3.3E-03 1.7 1.5E-02 

Toluene 4.1E-01 74.1 2.7E-01 0.8 5.0E-03 107 2.8E-03 1.0 4.4E-03 

Ethylbenzene 1.0E-01 81.6 1.2E-01 5.7 2.3E-03 135 7.1E-05 18.3 1.2E-04 

m-Xylenes a a 4.6E-02 1.4 a a 8.1E-05 6.2 a 

p-Xylene a a 1.1E-01 1.1 a a 1.8E-04 3.6 a o-Xylene 1.7E-01 45.4 8.3E-02 1.2 5.4E-04 97.8 7.5E-05 5.6 3.3E-04 

m,p-Xylenes 2.4E-01 84.1 1.6E-01 1.2 3.4E-03 120.0 2.6E-04 4.4 2.4E-03 

Xylenes 3.5E-01 82.8 2.4E-01 1.2 3.8E-03 105.0 3.4E-04 4.7 2.7E-03 

Styrene 2.1E-01 95.5 1.7E-01 1.4 3.8E-04 47.4 4.8E-04 4.5 1.9E-04 

1,3-Butadiene 2.0E+00 0.1 a a 2.6E-03 97.4 a a b 

(a): Immeasurable with this technique (b): Non-detect (c): Detected but not quantified due to potential wavelength overlap (d): Gerstle et al. (1999) 

52 
 
Table 7-2. Emission factors for PAH compounds during idle and full load operation. Comparison with p

AGE Type A/M32A-95 (this work) GTCP85-180d GTCP

Operating Condition Idle Full Full 

Sampling Technique M-0010 REMPI-TOFMS M-0010 REMPI-TOFMS M-0010 

g/kg of fuel g/kg of fuel g/kg of fuel 

PAH Compounds 

Value RSD (%) Value RSD (%) Value RSD (%) Value RSD (%) Value Va

Naphthalene 1.56E-01 3.9 7.97E-02 2.04 5.60E-04 16.1 2.05E-04 3.21 5.55

Acenaphthylene 6.07E-03 48.0 b b b 

b 

Acenaphthene b c b b 

Fluorene 1.66E-02 18.7 1.20E-02 0.06 2.96E-05 56.3 6.27E-05 4.69 

Phenanthrene 9.00E-03 15.4 5.24E-03 0.03 2.11E-05 66.7 1.13E-04 21.51 

Anthracene 5.10E-04 38.9 b b 

b 

Fluoranthene 1.47E-03 28.0 

c b 

Pyrene 2.22E-03 0.2 

Benzo(a)anthracene 1.48E-04 17.5 

b b 

Chrysene 2.19E-04 10.3 

Benzo(b+k)fluoranthene 3.02E-04 20.4 

Benzo(a)pyrene 9.00E-05 54.3 

Indeno(1,2,3-cd)pyrene 7.85E-05 8.2 

Dibenz(a,h)anthracene b b 

Benzo(ghi)perylene 1.15E-04 28.1 

(b): Non-detect (c): Detected but not quantified due to potential wavelength overlap (d): Gerstle et al. (1999) 

53 
 
Table 7-3. Emission factors for aldehydes compounds during idle and full load operation. Comparison w

Operating Condition Idle Full Full 

Sampling Technique M-0011 M-0011 M-0011 

Aldehydes Compounds Value RSD (%) Value RSD (%) Value Value 

Formaldehyde 1.63E+00 29.9 8.29E-03 43.2 2.03E-02 1.88E-02 

Acetaldehyde 4.10E-01 35.7 1.70E-03 50.8 2.09E-03 5.62E-03 

Acrolein 2.17E-01 21.4 1.86E-04 80.7 3.04E-04 b 

Propionaldehyde 8.00E-02 37.0 1.74E-04 35.4 b b 

(b): Non-detect 

54 
 
 

EPA/600/R-10/050 

April 2010 

Minimal differences (less than 2x) are observed between REMPI-TOFMS and TO-15 methods 

for determining emission factors of BTEX compounds during idle (low) load operation (Table 

7-1). The R2 values for the TO-15 and REMPI-TOFMS compound matched pairs are 0.99 and 

0.84 for idle and high load conditions, respectively. For the idle tests, two of seven paired 

compounds (benzene and ethylbenzene) were beyond the 95% confidence level for no 

differences between the methods. During high loads, the most abundant compounds, benzene 

and toluene, are within a factor of three. However, differences for some of the lower 

concentration compounds exceed 10x, with REMPI-TOFMS recording lower values. Three of 

the seven paired compounds (benzene, o-xylene, styrene) exceeded the criterion, indicating 

differences in the methods’ concentrations. The range of the TO-15 data (n=2) results in high 

RSDs (commercial laboratory analyses only). This variation does not show on the simultaneous 

REMPI-TOFMS results. 

Published BTEX emission factors (Gerstle et al., 1999) for similar-type AGE units at full load 

are predominantly higher than REMPI-TOFMS results (Table 7-1). Nonetheless, their matched 

pair compounds with REMPI-TOFMS are correlated at R2 = 0.85 and 0.95 for the GTCP85-180 

and the GTCP165-1 units, respectively. 

PAH emission factors show few differences between REMPI-TOFMS and Method 0010 

determinations (Table 7-2) both for idle and full load. 

As with the BTEX compounds, PAH emission factors are at least an order of magnitude higher 

for idle than for full load. The one published PAH emission factor (Gerstle et al. 1999) for 

naphthalene is about 30X the REMPI-TOFMS value at full load. Aldehydes emission factors 

(Table 7-3) by Method 0011 (Aldehydes are immeasurable by REMPI-TOFMS conditions 

employed here since their ionization energy exceeds 10.5 eV) again show two orders of 

magnitude higher emission factors for idle than full load; emission factors are generally 

comparable to published values (Gerstle et al., 1999). 

Finally, Figure 7-8 compares the benzene and naphthalene startup responses for the AGE and 

diesel generator. The AGE maintained fairly constant concentrations of benzene and 

naphthalene, while the generator showed rapid declines by about 1 min. The ability of REMPITOFMS to discern distinctive startup responses in these units makes it an important instrument 

for characterizing and distinguishing source emissions under varying conditions. 

55 
 
1.0 

0.8 

0.6
 

 benzene AGE emissions 

 naphthalene AGE emissions

 benzene DG emissions 0.4
 


 naphthalene DG emissions
 


0.2 

0.0 

Time (min) 

 Normalized Concentration, % of max 

-1 0 1 2 3 4 5 

 

EPA/600/R-10/050 

April 2010 

Figure 7-8. 	 Comparison of startup responses of benzene and naphthalene for the AGE 

and diesel generator. 

7.3 ORS Measurements during AGE sampling 

An ORS system was added to the AGE test plan to perform with an OP-FTIR spectrometer 

(manufactured by IMACC, Inc.). A second measurement using the IMACC OP-FTIR was 

operated in radiance mode to collect data from the gas turbine exhaust. 

7.3.1 Experimental Design 

One OP-FTIR with one retro reflector was used for data collection. The retro reflector was set up 

on scaffolding approximately 7 meters high, located adjacent to the engine exhaust stack. The 

retro reflector was placed on a tripod and elevated so that it is slightly higher than the top of the 

stack. The OP-FTIR instrument was mounted on a tripod on top of a vertical structure 

approximately 2 meters high. The instrument was located such that the physical path length 

between the instrument and the retro reflector was approximately 20 meters (see Figure 7-9). The 

spectra were measured as single beams (I) that were signal averaged for 30 seconds, and 

collected with a spectral resolution of 0.5 cm-1. The OP-FTIR operated in static scanning mode, 

collecting data for several hours over a two day period. The data is stored as interferograms on 

the data collection computer, and backed up to CD-ROM. The background spectra (Io) were 

created synthetically using OP-FTIR S/W. 

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Retroreflector 

Turbine 

Plume 

OP-FTIR 

Plume Width = 0.5 m 

Figure 7-9. ORS measurement configuration. 

7.3.2 ORS Instrument-Retro reflector Distance 

The physical distance between the OP-FTIR instrument and the retro reflector was measured 

using a Topcon, Inc. model GTS-211D theodolite. This distance is required for converting the 

products of incomplete combustion (PIC) data to path average concentration (PAC) values. PAC 

is equal to PIC divided by the optical path length. The optical path length is two times the 

physical distance, accounting for travel to and from the retro reflector. 

7.4 Data Processing 

The concentrations were determined by a regression fit to reference spectra using the Beers Law 

expression: 

I/Io = A = -Log10(αCL), 

where: 

I = single-beam measurement 

Io = background spectrum 

A = absorbance spectrum 

α = molecular absorptivity (extinction coefficient) 

C = concentration of the absorbing molecule 

L = total path-length of the infrared beam through the molecular plume 

The regression equation is written as: 

Af(ν) = ΣrAr(ν) + a + b ν + ε(ν) 

Data analysis was performed by the chemometric regression method that is referred to as 

classical least squares (CLS) and is written as: 

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April 2010 

Af(ν) = ΣrAr(ν) + a + b ν + ε(ν) 

Where: 

Af(ν)= measured field absorbance spectrum 

Ar(ν) = reference spectrum of chemical species, r 

a is a scalar that corrects for the baseline error 

b is a scalar that corrects for the baseline slope 

ε(ν) is the error or residual term 

The summation is over all species, r, that absorb in the region of analysis. 

7.4.1 ORS Results 

The 2-days of data gathering using the ORS equipment resulted in the measurements of criteria 

pollutants such as CO and CO2 as well as other compounds found in the absorption spectra such 

as formaldehyde, ethylene, and aliphatic mixture, the later which presumably originated from the 

fuel; n-octane is a major component of the aliphatic mixture and was used as a surrogate for the 

entire mixture. Other components include n-nonane, n-heptane, n-hexane and probably some 

bent-chain species. 

Data validation was performed by comparing the reference spectrum of a target species to the 

measured spectrum from the turbine plume. The trace emissions for formaldehyde, ethylene, and 

octane are presented in Figures 7-10, 7-11, and 7-12, respectively. 

The results of the ORS measurements were compared with stack measurements for CO and CO2, 

obtained using regular CEM instruments. The results were comparable for CO; however, the 

ORS results were not sensitive enough to differentiate between the high and low loads for CO2 as 

illustrated in Figure 7-13. Furthermore, drift of the ORS concentrations from those of the CEMs 

was observed throughout the day. This was due to an insufficient path length of the beam in the 

relatively small plume as well as effects of diurnal temperatures changes. The ORS system was 

not used for subsequent tests due to its limitations for measurement of point source emissions. 

58 
 
Relative Absorbance Relative Absorbance 

2850	 2900 2750	 2800
 

Wavenumber (cm-1) 

EPA/600/R-10/050 

April 2010 

Figure 7-10. Comparison of the reference spectrum of formaldehyde (blue trace) to a 

measured spectrum of the turbine plume (red trace) 

Figure 7-11. Comparison of the reference spectrum of ethylene (red trace) to a measured 

spectrum of the turbine plume (blue trace) 

59 
 
Relative Absorbance 

2800 2850 2900 2950 3000 

Wavenumber (cm-1) 

Figure 7-12. Comparison of the reference spectrum of n-octane (red trace) to a measured 

spectrum of the turbine plume (blue trace) 

12000 250

10000 200 

CO Concentration (ppm) 2 

8000 

150 

6000 

100 

4000 

Shutdown 

2000 

50 

Low Load Full Load 

09:36 

0 

10:48 12:00 13:12 14:24 15:36 16:48 18:00 

0 

CO2 (CEM)

 CO2

 (Open Path) 

Time (EDT)

 CO (CEM)

 CO (Open Path)

 CO Concentration (ppm0 

EPA/600/R-10/050 

April 2010 

Figure 7-13. Comparison between CEM and ORS measurements 

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8.	 Source 3: Verification Results of REMPI-TOFMS as a Real-Time 

PCDD/F Emission Monitor 

In 2005, REMPI with TOFMS was used in an international ETV test program monitoring levels 

of PCDD/F in a hazardous-waste-firing boiler (Cowen, 2006). Prediction of PCDD/F levels was 

based on prior determination of an indicator compound and intercorrelation of the indicator and 

PCDD/F concentrations. This chapter reports the determination of indicator compounds and the 

performance of REMPI-TOFMS during the ETV tests. 

8.1 Materials and Methods 

8.1.1 Boiler testing 

An 860 KW capacity, 3-pass fire-tube, marine package boiler (Superior Boiler Works, Inc.), 

firing #2 fuel oil was used as the combustion gas source (Figure 8-1). The flue gas from the 

boiler passes through an exhaust duct to a manifold and then on to an air pollution control system 

(APCS). The APCS consists of a natural-gas-fired secondary combustion chamber, a fabric filter, 

and an acid gas scrubber to ensure proper removal of pollutants. The fuel oil was doped at a 

constant ratio of a surrogate hazardous waste (1,2-dichlorobenzene, DCB) and a source of metal 

catalyst (copper naphthenate) to promote PCDD/F formation. Fuel flows were measured with a 

total liquid volume meter. The amount of injected copper was set to simulate that of a refusederived fuel (RDF) ash (100 mg per kg of ash), conditions in which PCDD/F formation is 

favorable. The feed-rate of the mixture was varied to achieve a high (200-500 ppm) and low (10­

50 ppm) target HCl concentration in the flue gas with the expectation of generating relatively 

high and low PCDD/F concentrations, respectively. Test runs of various durations were 

conducted under each set of operating conditions. Four 4-hours and two 8-hour sampling periods 

on successive days (i.e., totaling 16 hours per sample) were used to assess short-term and longterm accuracy of the measurements. 

The test campaigns sampled for PCDDs/Fs and semi-volatile PAHs using EPA methods 23 

(EPA, 1996d), and 0010 (EPA, 1996a), respectively. Both Method 23 and Method 0010 consist 

of a 125 °C heated probe, 125 °C heated box containing a filter, water-cooled condenser, watercooled XAD-2 resin cartridge, impinger train for water determination, vacuum line and pump, 

and a dry gas and orifice meter. 

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April 2010 

Figure 8-1. Marine package boiler at EPA facilities. 

The test campaigns sampled for PCDDs/Fs and semi-volatile PAHs using EPA methods 23 

(EPA, 1996d), and 0010 (EPA, 1996a), respectively. Both Method 23 and Method 0010 consist 

of a 125 °C heated probe, 125 °C heated box containing a filter, water-cooled condenser, watercooled XAD-2 resin cartridge, impinger train for water determination, vacuum line and pump, 

and a dry gas and orifice meter. 

All emission measurements for this work were taken prior to the APCS from a horizontal section 

of the exhaust duct (20 cm diameter steel pipe) sufficient in length and free of flow disturbances 

so that PM can be sampled in accordance with standard sampling requirements. Stoichiometric 

ratios were verified through monitored O2 and CO2 emission concentrations. Continuous 

emission monitors (CEMs) included four gas analyzers: high and low range CO (Rosemount 

Analytical Model 880 non-dispersive infrared analyzer (NDIR), Range = 0-500 ppm), O2 

(Rosemount Analytical Model 755 R, Range 0-25%, calibrated range 0-10%), and CO2 

(Rosemount Analytical Model 880 NDIR, Range 0-20%). 

8.1.2 REMPI-TOFMS Testing 

Samples for the REMPI-TOFMS were taken through a 0.95 cm outer diameter stainless steel line 

at typical flow rates of 2 L/min (all flows are reported at 101.325 kPa and 273.15 K). A flexible, 

9 m long, 1.27 cm diameter, Silico-steel transfer line conveyed the exhaust gas to the REMPITOFMS instrument. The line was kept at 150 °C while sampling exhaust gases in order to 

minimize adsorption to the line walls. The sample was collected under sub-isokinetic conditions 

62 
 
 

 

EPA/600/R-10/050 

April 2010 

and filtered through a micro-fiber filter (at 150 °C) to avoid PM reaching the valve inlet system 

of the REMPI-TOFMS instrument. The REMPI-TOFMS underwent an in-situ calibration at the 

start of each test using fully deuterated benzene, C6D6, added to the exhaust stream. Deuterated 

benzene can be readily detected without spectral or mass interferences and is not an exhaust gas 

component. 

8.1.3 Indicator Compounds 

The use of indicator compound measurements to predict PCDD/F values requires a predetermined correlation analysis to find the best indicator compound or compounds and to 

determine its mathematical relationship with the PCDD/F measure. These indicator correlations 

are likely to be source-specific, requiring an initial series of sampling tests for determining 

compound concentrations from which to run correlation analyses. Selection of the PCDD/F 

indicator compound was based on a “pre-ETV,” six-test measurement campaign of 31 

compounds (Table 8-1). These 31 compounds were selected, in part, based on the general 

understanding that lower chlorinated compounds are more readily detectable with REMPITOFMS than the higher chlorinated compounds (Zimmermann et al., 1999). These pre-ETV tests 

replicated the high and low dopant loads that would occur under the subsequent actual ETV 

study. A correlation analysis was run on the results between the PCDD/F TEQ and other semivolatile compounds sampled by EPA Method 0010 (EPA, 1996a). The highest correlation, R2

, 

between the REMPI-detectable compounds and the TEQ values, and one that has a positive (+) 

coefficient, provides an indicator candidate. 

Table 8-1. Candidate TEQ surrogate compounds from pre-ETV Method 0010 sampling. 

Compounds: 1-Methylnaphthalene 1,3-Dichlorobenzene 

2-MCDD 2-Chloronaphthalene 1,4-Dichlorobenzene

 2,7- + 2,8-DiCDD 1-Chloronaphthalene 1,2-Dichlorobenzene 

2,3-DiCDD Acenaphthylene 2-Chlorophenol 

2,3,7-TriCDD Dibenzofuran 3- + 4-Chlorophenol 

1-MCDF Fluorene 2,4-Dichlorophenol 

3-MCDF Phenanthrene 2,5-Dichlorophenol 

2-MCDF Fluoranthene 2,3-Dichlorophenol 

naphthalene Pyrene 2,6-Dichlorophenol 

2-Methylnaphthalene Chlorobenzene 3,4-Dichlorophenol 

Compound concentrations are determined by monitoring pre-determined, compound-specific 

optimal wavelengths. After measurement of the emissions, an external calibration of the detected 

ion signals was accomplished with a 100-ppb calibrated gas mixture in nitrogen containing 14 

aromatic compounds, including monochlorobenzene (MClBz). The concentration of a target 

analyte was derived from the ratio between its ion signal intensity and that of the same analyte 

present in the calibration gas mix, normalized for any laser energy changes. 

Time-integrated concentrations for the indicator compound, obtained with REMPI-TOFMS, are 

entered into the predictive correlation equation obtained from the pre-ETV tests to determine the 

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April 2010 

TEQ estimate. This value is then compared with the results from the cumulative M23 sampling 

methods. Sub-isokinetic sampling for REMPI-TOFMS to minimize particles reaching the filter 

in front of the detector was assumed equivalent to the isokinetic sampling reference methods: 

under lean firing conditions all of the volatile and semi-volatile compounds would be found 

within the gas phase fraction, allowing direct comparison of the REMPI/TOFMS with the 

reference method measurements. 

The accuracy of REMPI-TOFMS during the ETV tests was determined by comparing results 

from nine runs obtained with isokinetic sampling via Method 23 (EPA, 1996d). Simultaneous 

extractive Method 23 samples were taken before and after the REMPI-TOFMS sampling port. 

The correlation-derived TEQ estimation was compared with these EPA Method 23 results. 

8.2 Results and Discussion 

8.2.1 Pre-ETV results 

Sampling during the pre-ETV phase with EPA Method 0010 (M10) resulted in measurable 

concentrations for the compounds listed in Table 8-1. The PCDD/F TEQ value was derived from 

a predetermined correlative relationship with the best single predictor chosen from amongst over 

30 compounds consisting of chlorophenols, chlorobenzenes, and PAHs. A single-predictor 

regression model using these M10 concentrations versus the EPA Method 23 TEQ 

concentrations (ranging from 0.90 ng TEQ/Nm3

 to 25.50 ng TEQ/Nm3 resulted in a best-fit 

model (R2 = 0.7420) for TEQ using MClBz. MClBz was previously detected in the flue gas of an 

incinerator using REMPI-TOFMS (Thanner et al, 1998, Zimmermann et al., 1999) and by SPIIT-TOFMS (Kuribayashi et al., 2005). Figure 8-2 shows the fit of a linear regression model of 

TEQ on MClBz, based on the six lean-fire test runs with a 0.95 confidence belt for TEQ 

predicted from the fitted model, TEQ = 1.23 + 53.85 MClBz. 

8.2.2 ETV Results 

In the ETV field test, REMPI-TOFMS monitored MClBz in real time to derive a concentration 

for use in the predictor equation. The MClBz detection limit [signal/noise (S/N) = 3, 10 s signal 

averaging time] was 1 ppb which was on occasion higher than the encountered concentration in 

the exhaust gas. An extended time averaged mass spectrum at the optimal wavelength for MClBz 

detection as shown in Figure 8-3 makes quantification possible. The calculated MClBz 

concentration for this mass spectrum was 0.4 ppb. A total of nine tests with sampling durations 

between four to sixteen hours were conducted, resulting in standard method PCDD/F 

concentrations from 0.9 to 6.0 ng TEQ/m3

. 

64 
 
EPA/600/R-10/050 

April 2010 

0 

5 

10 

15 

20 

25 

PCDD/F TEQ (ng/m3 ) 

 Pre-ETV DataB 

Linear Fit of Data1_B 

Upper 95% Confidence Limit 

Lower 95% Confidence Limit 

0.0	 0.1 0.2 0.3 0.4 0.5 

MClBz (μg/m3) 

Figure 8-2. Pre-ETV phase determination of MClBz as a PCDD/F TEQ surrogate 

0.00 

0.02 

0.04 

0.06 

0.08 

0.10 

0.12 

0.14 

0.16 

0.18 

100 102 104 106 108 110 112 114 116 118 120 

0.000 

0.005 

0.010 

0.015 

0.020 

0.025 

REMPI Ion Signal (arb units) 

37ClBz 

35ClBz 

80 100 120 140 160 180 200 220
 


m/Z
 


Figure 8-3. REMPI-TOFMS mass spectrum of MClBz with inset of relevant mass range. 

0.1 ppb for a 4 min averaging period, S/N = 3. 

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EPA/600/R-10/050 

April 2010 

The comparison of PCDD/F TEQ determined by the standard EPA Method 23 (M-23) and that 

determined by the predictor equation using REMPI-TOFMS time-integrated measurements of 

MClBz is seen in Figure 8-4. For the high waste-firing-rate with a range of PCDD/F TEQ values 

between 3.9 and 6.0 ng TEQ/m3

, the REMPI-TOFMS-predicted TEQ values had a relative 

difference of 26% with the standard, EPA Method 23 results. At the low waste-firing-rate (0.9 to 

1.6 ng TEQ/m3

) the relative difference increased to 219%. This decrease in predictive capability 

was attributable to the chosen predictor, MClBz, being below its GC method detection limit for 

the lower firing rate. The uncertainty in the MClBz measurements was confirmed by evaluating 

the waste feed rate versus the MClBz concentrations: no correlative agreement was apparent at 

the lower concentrations, suggesting that the standard sampling and analytical methods for 

MClBz were unreliable at these concentrations. This is more easily seen in Figure 8-5 where M10 and REMPI measurements have similar predictions of PCDD/F TEQ, but depart from the M23 results when PCDD/F TEQ has lower values. Improvements in the selection of the model 

predictor and use of a second predictor in a multivariate, 2-predictor model would likely improve 

the correlation (e.g., adding 2-methylnaphthalene improves R2 from 0.74 to 0.93) and the ability 

of REMPI-TOFMS to determine PCDD/F TEQ. 


 

7 

6 

5 

4 

3 

2 

 Low DiClBz Rate 

1 

 High DiClBz Rate 

0 m/z 

Sampled PCDD/F: M23 (ng TEQ/m3)
 

Predicted PCDD/F: MClBz from Jet REMPI (ng TEQ/m3) 

0 1 2 3 4 5 6 7 

Figure 8-4. 	 ETV phase comparison of TEQ from Method 23 and MClBz prediction from 

REMPI-TOFMS measurements 

66 
 
8
 

6
 

4
 

2
 

0 

0 1 2 3 4 5 

ETV 2005 Run Number 

 % (REMPI Predicted Results)

 % (M-23 Results)

 % (M-10 Predicted Results) 

6 7 8 9 10 
 

PCDD/F TEQ (ng/m3) 

EPA/600/R-10/050 

April 2010 

Figure 8-5. 	 Comparison of M-10 and time-integrated REMPI predictions of PCDD/F 

TEQ with actual M-23 measurements. 

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April 2010 

9. Source 4: Sampling from MWC Flue Gas 

Two field measurement campaigns have been performed at the same MWC site using REMPITOFMS instruments to monitor pre-determined target compounds in real time in the flue gas 

prior to the air pollution cleaning system. These campaigns were conducted under challenging 

conditions due to the presence of dust and large ambient temperature changes. 

9.1 Portsmouth Naval Shipyard Waste Combustor 2004. 

The primary objective of the first MWC study was the field demonstration of the REMPITOFMS technology to measure target organic compounds identified as potential indicators for 

PCDD/F TEQ determinations. Prior to the field study, the REMPI-TOFMS was found to 

measure easily, reliably, and potentially online or through a short pre-concentration step, 

PCDD/F TEQ indicators include compounds such as low chlorinated PCDD/F compounds, 

chlorobenzenes, chlorophenols, and PAHs. The main objective of this first test at this MWC was 

to test and validate the REMPI-TOFMS instrument in the field using the results from an initial 

MWC sampling campaign that provided correlations for potential indicators. 

This initial campaign of this project focused primarily on extractive flue gas samplings prior to 

the air pollution control system (APCS), which consists of a spray dryer and baghouse, and to a 

lesser extent at the stack. The primary sampling locations were the spray dryer catwalk area 

(SDA) at the exit of boilers 1 and 2. These locations were chosen to provide concentrations of 

the target compounds of interest that were sampled in a relatively reasonable time, and analyzed 

by the EPA-RTP Organic Laboratory using HRGC/ LRMS. A potentially multivariate, nonlinear, 

time-variant model was developed based on the initial sampling campaign (in 2003). The model 

relates the gas-phase concentration of one or more indicator compounds from sub-isokinetic 

samples from SDA2 with the PCDD/F TEQ and PCDD/F total (from SDA2-iso). This model 

was used to develop a test matrix that would optimize field-sampling data collection in the first 

field demonstration of the REMPI-TOFMS instrument. Validation of the system was performed 

using extractive methods for dioxins and furans. The main classes of compounds that were 

targeted in this project were primarily mono- to octa-chlorinated dioxins and furans (PCDD/Fs), 

chlorinated phenols (ClPhs), chlorinated benzenes (ClBzs), and PAHs. 

9.2 Experimental Approach 

The main objective of this test program was to develop potential organic indicator compounds 

that can mimic PCDD/F TEQ emissions, and test the validation of REMPI-TOFMS to produce 

sensitive, time resolved measurements of these target indicator compounds. 

To further examine REMPI-applicable indicator compounds, samples were taken from a MWC 

with multiple RDF fired boilers (>400 Mg/day) over a 9 day period for PCDD/F and other 

combustion by-products. Samples were drawn from the flue gas duct prior to the flue gas 

cleaning system; hence, concentrations do not represent stack emissions. Over the course of nine 

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days, 23 sampling periods were completed. Sampling for PCDD/F included 1 h Method 0023 

(M23) samples and three 5-min M23 samples taken throughout a 1 h sampling period. Sampling 

for semi-volatiles (e.g., monochlorobenzene, phenol) was accomplished with REMPI-TOFMS 

and by standard extractive sampling via Method 0010 (M10). These runs paralleled the M23 

sampling periods, and should be comparable. M10 samples were analyzed for semi-volatiles; in 

this case only the back half values are reported (in μg/m3, dry). These back half semi-volatile 

values should be directly comparable to the REMPI-TOFMS determinations, as they are both 

post-filter (akin to what the XAD “sees”) measurements. It should be noted that M10 samples 

were 1 h in duration whereas REMPI was on-line; hence many of the REMPI-detectable semivolatiles reported by M10 were not above the on-line concentration detection limits of REMPITOFMS. 

9.3 Test Matrix 

The test matrix presented here refers to the first campaign of testing with the REMPI-TOFMS 

system. The proposed time sequence of the initial data was based on a statistical analysis of the 

initial MWC data. The time sequence of those sampling events recorded on the same axis as the 

CO stream data showed some evidences that the largest PCDD/F TEQ values observed followed 

a period of identifiable CO instability reflected by an upsurge of CO spikes above a 600 ppm 

threshold level. The sampling strategy for this testing campaign was to capture and identify 

delayed effects of the critical CO period on the PCDD/F formation with a minimal loss of 

instantaneous PCDD/F TEQ and other surrogates compounds in the process of averaging over 

any particular sampling time. Six identifiable phases of boiler operation were proposed in this 

sampling campaign to be characterized experimentally: 

Phase 1. Normal operation: This testing phase will start after normal operations that would have 

lasted at least 6 hours after a startup without any sign of probable shutdown 

Phase 2. High frequency CO spiking without boiler shutdown: This sampling phase will 

correspond to an identifiable period of CO instability due probably to a plug in the feed 

system. This transitional period last in general less than 2 hours. 

Phase 3. Boiler leading to shut-down: This phase is expected to occur within 2 hours of phase 2 

conditions. The shutdowns can be unscheduled, and due to high CO hourly averages or 

initiated by the boiler. 

Phase 4. Actual boiler shutdown phase 

Phase 5. Boiler early startup: This sampling phase will start just after the boiler startup is 

initiated after a scheduled or unscheduled shutdown 

Phase 6. Boiler late startup: This phase will be performed about 3 hours after the startup, after 

the early startup phase is completed. 

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9.4 Results 

9.4.1 General On-site REMPI-TOFMS Instrument Performance 

The first field study of the first compact REMPI-TOFMS instrument (December 2004) was 

satisfactory based on the relative fast setup time (~ 6 hours) between arrival onsite and the first 

detection of flue gas constituents and the near 90% coverage of real time (2s sampling period) 

REMPI-TOFMS data during parallel conventional Method 0010 and Method 0023 sampling. In 

one occasion, the sampling periods were delayed in order to have REMPI-TOFMS available for 

parallel sampling after a system shutdown. This occurred after ultrafine fly-ash passed through 

the inline filter (or was pulled into the system during a swap of filters) and got trapped in the 

pulsed valve inlet system hereby obstructing the pulsed sample flow. The exchange of filter 

elements using a single housing unit resulted in a temporary loss in PAH signal intensity most 

likely due to the initial low temperature of the new filter element. Preheating a clean new 

element did resolve this issue and was implemented later in the sampling campaign. 

9.4.2 REMPI-TOFMS results 

The focus of REMPI-TOFMS during this sampling campaign was on the real time detection of 

PAHs and monochlorobenzene, if possible in real time. Over the course of a seven day period, 

the flue gas of the MWC was sampled with REMPI-TOFMS for a total of 58 hours. In parallel, 

23 EPA Method 0010 (semi-volatiles) and 0023 (PCDD/Fs) samples were taken. After day 2, all 

sampling equipment was relocated to a different boiler (“B”) area due to unscheduled extended 

maintenance on the first boiler (“A”). This provided an opportunity to compare boiler 

performances under normal, “steady state” conditions. As illustrated in Figure 9-1, there are 

large differences in emissions of especially naphthalene over the course of a 4 hour time period. 

PAH emissions for boiler “B” were generally much higher during the shutdown of a boiler as 

shown in Figure 9-2. The observed transient naphthalene spikes are most likely due to residual 

smoldering waste with flare-ups. It should be pointed out that PAH concentrations are elevated 

under conditions of lower flow velocity in the duct from which the sample is taken which tend to 

enhance the concentration but not the actual emissions at that time. 

More dramatic changes in PAH concentrations occur during the period leading up to a shutdown 

of a boiler (B) as well as during the startup. An example of emissions during the startup of the 

boiler is shown in Figure 9-3. 

A similar transient response was observed during another startup of the same boiler. In that case, 

the REMPI-TOFMS wavelength was toggled between detection of PAHs and 

monochlorobenzene providing partial real time data for both as shown in Figure 9-4. 

70 
 
300 30 

250 

Concentration (ppb) 200
 

150
 Boiler A 

25 

100
 10 

50
 5 

0
 0 

Boiler B

 naphthalene

 fluorene

 phenanthrene/anthracene

 pyrene/fluoranthene 

15:00 16:00 17:00 18:00 19:00	 11:00 12:00 13:00 14:00 15:00 

Plant Time (h:min), Day 2 Plant time (h:min), Day 5 

20 

15 

EPA/600/R-10/050 

April 2010 

Figure 9-1. 	 Comparison between real time results for PAHs acquired with REMPITOFMS at identical Boiler A and Boiler B for two 4-h intervals that were 

typical of the normal (steady state) operation. 

25

20 

19:45 20:00 20:15 20:30 20:45 21:00 

10 

15 

 naphthalene

 fluorene

 phenanthrene/anthracene

 pyrene/fluoranthrene 

Concentration (ppb) 

BOILER OFF LINE 

SHUTDOWN 

5 

0 

Plant Time (h:min) 

Figure 9-2. 	 Emissions of PAHs during shutdown of boiler. Break in data during filter 

change. 

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EPA/600/R-10/050 

April 2010 

Figure 9-3. A 3-dimensional qualitative depiction PAH emissions during the startup of a 

boiler (at ~ t=10 min). 

Figure 9-4. Emissions of selected PAHs and monochlorobenzene during startup of boiler. 

The parallel sampling of REMPI-TOFMS with conventional Method 0010 provide the 

possibility to compare (time-averaged) concentrations during these time intervals. Figure 9-5 

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EPA/600/R-10/050 

April 2010 

shows such comparison in the case for naphthalene which was readily detected with the REMPITOFMS instrument. 

What is also clear from all results is that flue gas contains multiple PAH-like compounds as 

visible in a typical mass spectrum recorded at the wavelength for monochlorobenzene detection 

(Figure 9-6). 

Since the single color REMPI-TOFMS ionization method is more efficient for PAHs than for 

chlorinated aromatics, it is extremely difficult, if not impossible, to efficiently detect higher 

chlorinated aromatics such as trichlorobenzene in the presence of more abundant analytes with 

equal mass. 

9.4.3 Method 0023 and Method 0010 Results 

An analysis of M23 PCDD/F TEQ values with simultaneously-sampled M10 results in 

significant correlations for multiple semi-volatile compounds (Table 9-1). The best 5-min 

sampling duration predictors for this facility, based on Table 9-1 results in combination with 

typically greater spectral resolution and sensitivity for trichlorobenzenes versus 

tetrachlorobenzenes, appear to be 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, and 1,3,5­

trichlorobenzene. The detection limit for 1,2,4 trichlorobenzene with 2-color REMPI (established 

post first MWI test) was about 1 ppb, a value commonly found in incinerators. An additional 

analysis examined these correlations under the assumption of a 20 and 40 minute time lag 

between the concentration of the indicator and that of the PCDD/F TEQ. As can be seen in Table 

9-1, no convincing improvement in correlation is found with the time-lagged indicators, 

suggesting that the increase in the indicator compound is due to a parallel or related mechanism 

to the formation of the PCDD/F TEQ compounds. These results suggest that indicators are likely 

system-specific, requiring final selection by testing at each plant, albeit from a list of fairly likely 

and common candidates. 

9.5 Portsmouth Naval Shipyard Waste Combustor 2006 

The introduction of a two color REMPI approach towards ionization of an analyte increased the 

accessibility of higher chlorinated aromatics for real time measurement. This enhancement, 

among others, resulted in a second sampling campaign at the same MWC (December 2006) with 

the objective of sampling 1,2,4-trichlorobenzene (124-TrClBz), preferably in real time, as the 

dioxin toxicity indicator compound. REMPI-TOFMS sampled 124-TrClBz using a two color 

ionization method. 

Work reported here shows the first REMPI-TOFMS measurements for a specific PCDD/F 

indicator compound (1,2,4-trichlorobenzene) along with simultaneous conventional sampling for 

PCDD/F TEQ values. 

73 
 
 

 1 hour extractive Method 0010 

1 hour averaged jet REMPI-TOFMS 

Concentration (ppb) 

120 

100 

80 

60 

40 

20 

0 

shutdown 

[at start 1h] 

startup [at start 1h]

shutdown [at start 1h]

high CO

normal, steady

high CO 

startup [in middle 1h]

late startup

normal, steady

after high CO

shutdown [at end 1h] 

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 

BOILER A BOILER B
 


Sample Number
 

Figure 9-5. 	 Comparison between REMPI-TOFMS time averaged concentrations and 

those from conventional Method 0010 sampling during the course of the 

sampling campaign. 

2.0 

1.8 

1.6 

Ion Signal (arb units) 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

80 100 120 140 160 180 200 220 240 260 

mass (amu) 

EPA/600/R-10/050 

April 2010 

Figure 9-6. Mass spectrum recorded at monochlorobenzene wavelength (~ 270.8 nm). 

74 
 

 

 

EPA/600/R-10/050 

April 2010 

Table 9-1. R2 for PCDD/F TEQ based on 36, 5-min samples at the MWI. 

TEQ TEQ TEQ 

 Lag=0 n=36 Lag=20 

n=24 

Lag=40 

n=12 

12DiClBz 0.482 0.516 0.594 

13DiClBz 0.551 0.499 0.215 

14DiClBz 0.074 0.355 0.010 

123TrClBz 0.558 0.520 0.642 

124TrClBz 0.709 0.414 0.195 

135TrClBz 0.703 0.444 0.116 

1234TeClBz 0.727 0.518 0.559 

1235TeClBz 0.642 0.529 0.655 

1245TeClBz 0.702 0.398 0.132 

PeClBz 0.619 0.604 0.586 

HxClBz 0.391 0.557 0.599 

The 0.95 critical values for testing the null hypothesis of “no significant correlation” for n= 36, 24 and 12 are 0.108, 0.164, 

and 0.332, respectively. Lag = time duration in min between event and concentration correlation. 

9.6 Materials and Methods 

REMPI-TOFMS was employed at an MWC with multiple refuse-derived-fuel (RDF) fired 

boilers to sample flue gas concentrations after the boiler chamber and prior to the air cleaning 

devices. The boiler was operated under steady state conditions, shutdowns, and startups. Boiler 

shutdowns would normally occur with operating problems such as jams in the fuel feeding 

system or for routine maintenance but were initiated for these tests to observe the pollutant 

response during transient operating conditions. Flue gas sampling for REMPI-TOFMS was 

accomplished with a glass-lined, stainless steel sampling probe coupled to a heated (T = 170 °C) 

line. A heated filter (T = 150 °C) prior to the REMPI inlet prevented PM from clogging the 

pulsed inlet valve. The filter was changed daily to minimize adsorption or desorption phase bias 

of target analytes. Sampling was sub-isokinetic to minimize particle collection. REMPI was 

operated in a 2-color, 2-photon mode. The wavelength of the first laser, 284 nm, was set in 

resonance with the origin of the S1← S0 transition for 1,2,4-trichlorobenzene (TrClBz), a 

suspected PCDD/F indicator compound. A fixed 213 nm wavelength completed the ionization 

process. Continuous CO, O2, and CO2 measurements were taken from the plant’s post-boiler, 

pre-stack monitors. The possible presence of concentration gradients within MWC ducts were 

evaluated for their potential detrimental effects on establishing concentration correlations. 

Simultaneous measurements were taken at 30% and 50% of the cross-duct width to check for 

stratification of PCDD/F concentrations. In parallel to the REMPI-TOFMS measurements, 74 

PCDD/F samples (modified EPA Method 23) were taken over a four day period. Typically, three 

5-min duration samples were collected over 1-h periods during steady-state, shutdown, and 

startup conditions. There was approximately 15 min between samples. The samples were 

analyzed by HRGC/LRMS for all three TrClBz (1,2,3-; 1,2,4-; and 1,3,5-TrClBz) compounds 

75 
 
EPA/600/R-10/050 

April 2010 

and by HRGC/HRMS for the 17 toxic equivalency factor (TEF) weighted compounds that 

comprise the PCDD/F TEQ measure. A field blank and an XADTM sorbent blank showed 

minimal levels of 1,2,4-trichlorobenzene compared to the lowest measured sample level. The 

choice of units from which to compare compound concentrations depends on the purpose of the 

comparison. The various operational modes at the facility result in different RDF feed-rates, 

boiler temperatures, and flue gas flowrates. For example, comparison in units of mass per waste 

feed of steady state emissions versus those during facility shutdowns could make the latter 

exceptionally high if pollutant production is more related to mass of waste on the grate or the 

amount of deposits on the boiler. In this paper, concentrations are compared on a time basis to 

understand how different process options at the plant affect the rate of PCDD/F production. 

9.7 Results 

Pre-APCS PCDD/F TEQ concentrations are reported in Table 9-2. Transient operating 

conditions resulted in higher average PCDD/F TEQ values and RSDs by almost 4-fold. Peak 

concentrations of PCDD/F TEQ exhibit at least a 10-fold increase during startups over those of 

the average steady state values. Integrating the mass concentration rate curve suggests that the 

TEQ levels during a combined shutdown and startup period are ~ 25 percent of the plant’s 

projected daily PCDD/F TEQ concentrations. The effect on plant stack emissions, however, 

remains to be determined. 

Table 9-2. PCDD/F TEQ emission rates from HRGC/HRMS analyses. 

Operating Condition Four Day Averages (μg TEQ/min) 

High Low Average RSD 

Steady State (SSTS#) 208 109 154 23% 

Shutdown (SSHD#) 349 98 203 64% 

Startup (SSUP#) 1262 181 529 86% 

Simultaneous M23 samples taken across the duct showed less than 10% RSD between the 

values, confirming that measurements of PCDD/F indicator compounds are amenable to 

correlation analyses. GC-measured di- and tri-chlorinated benzene isomers showed excellent 

correlation with PCDD/F TEQ. Two of the three diClBz isomers showed an average correlation 

(R2) with PCDD/F TEQ of 0.85. All three of the triClBz isomers, including target 1,2,4-triClBz, 

had an average R2

 of 0.90 with PCDD/F TEQ. These results suggest that any one or combination 

of these target ClBz isomers would make excellent indicators. Figure 9-7 summarizes the 5­

minute average concentrations of PCDD/F TEQ, 1,2,4-triClBz using GC/MS and 1,2,4-triClBz 

values using REMPI-TOFMS. 

76 
 
SSTS 1 

SSTS 2 

SSTS 3 

SSTS 4 

SSTS 5 

SSTS 6 

SSTS 7 

SSHD 1 SSHD 2

SSHD 3 SSHD 4

SSUP 1 

SSUP 2 

SSUP 3 SSUP 4 

SSUP 5 

SSTS1

SSTS2

SSTS3SSTS4

SSTS5 

SSHD1 SSHD2

SSHD4 

SSHD5

SSUP1 

SSUP2 

SSUP3 

SSUP4 SSUP5 

SSTS1

SSTS2 

SSTS3

SSTS4SSTS5 

SSHD1 

SSHD2 

SSHD3 SSHD4 

SSHD5

SSUP1 SSUP2 

SSUP3

SSUP4SSUP5 

SSTS1 SSTS2 

SSTS3 SSTS4 

SSHD1 

SSHD2 

SSHD3 

SSHD4 

SSHD5 

SSUP1 SSUP2 

SSUP3 SSUP4 

0 

250 

500 

750 

1 000 

1 250 

1 500 

0 

4 

8 

12 

16 

Day 1 20

/min ), M a ss 18 0 (a rb .u nits )

 P CD D/F T E Q

 1, 2, 4-T r i C l B z

 R E M P I M a ss 1 8 0

 O 2 

Day 2 

n ( % ) 

lBz(mg 

entratio 

PCDD /F TEQ ( μg / min) , 1 , 2 , 4 -TriC 

O x y g en C o n c 

20 00 

10 00 

Day 3 

8 

4 

0 

Day 4 

0 

20 

16 

12 

Boiler Operation Status 	 	 Boiler Operation Status 

EPA/600/R-10/050 

April 2010 

Figure 9-7. 	 PCDD/F TEQ, conventional 1,2,4 triClBz and mass 18- REMPI-TOFMS ion 

signal over the course of the four day sampling campaign. 

The blue triangles represent the average oxygen concentration during the 5 minute sampling 

interval. 

The REMPI-TOFMS analysis of 1,2,4-triClBz concentration at the MWC was hindered by the 

presence of additional compounds of masses 180/182/184 that also ionized at 284 nm, obscuring 

the discrete 1,2,4-triClBz spectrum. Also, discrete changes in the relative abundance of the mass 

180/182/184 intensities were observed during shutdown and startup that cannot be explained by 

relative ion abundances of trichlorobenzene(s) only as illustrated in Figure 9-8. GC/MS analyses 

suggest that these compounds are substituted PAHs, such as trans-1,2-diphenylethylene (C14H12, 

stilbene) or methylfluorene (C14H12) for mass 180. The presence of the mass 180 interferents 

highlights the hazard in locating indicator compounds by a dissimilar technique (GC/MS) to that 

of the monitoring method (REMPI-TOFMS, in this case). Nonetheless, the mass 180 compounds 

predict PCDD/F TEQ values well on two of the four days, with R2

 of 0.76 and 0.79. Predictions 

on the other two days result in an R2 of 0.79 and 0.80 when the PCDD/F TEQ values are allowed 

to lag the REMPI-TOFMS mass 180 measurement by one sampling period (~ 15 min). PAHs are 

known to be early indicators of combustion upsets and appear to have compound-specific lag 

77 
 
times. Since all combustion shutdown/startup operations do not necessarily occur under the same 

conditions, and our sampling intervals would not necessarily have been at the same exact onset 

of the process changes, consideration of a single sampling period lag seems reasonable. These 

results demonstrate the ability of REMPI-TOFMS to provide real time feedback on correlative 

PCDD/F levels and offer promise for operational feedback to minimize emissions. 

 

 

140
 

M23 sampling times

 Startup 120 

100 

80 

60 

40 

20 

0 

 mass 180

 mass 182

 mass 184 

M23 sampling times 

Steady State 

M23 sampling times 

Shutdown 

Int. Ion Signal (arb units) 

17:00	 18:00 19:00 20:00 21:00 22:00 23:00 

Time (h:min) 

EPA/600/R-10/050 

April 2010 

Figure 9-8. Recorded REMPI-TOFMS ion signals for mass 180/182/184. 

The vertical bars indicate the shutdown (black) and startup (blue) events. 

78 
 
EPA/600/R-10/050 

April 2010 

10. Source 5: Emission Responses from HMMWVs, the M1 Abrams Tank, 

and the Bradley Infantry Fighting Vehicle 

Real time emission measurements of criteria pollutants, organic air toxics, and particles were 

made on two U.S. Army High Mobility Multi-purpose Wheeled Vehicles (HMMWVs), a 

Bradley Infantry Fighting Vehicle (IFV), and an Abrams M1 battle tank. The HMMWV 

emissions were measured while running on a dynamometer-based roadway simulator under the 

West Virginia and EPA Federal Highway Economy Test (HWFET) cycles, and under steady 

state, constant velocity conditions. REMPI-TOFMS emissions from cold and warm starts of the 

HMMWVs, the Bradley, and Abrams were recorded. 

The U.S. Army currently has over 99,000 tactical High Mobility Multi-purpose Wheeled 

Vehicles (HMMWVs) and over 12,000 tracked vehicles such as the M1 Abrams tank and 

Bradley IFV (https://www.osmisweb.army.mil/, 2008) that account for approximately half of the 

DoD vehicle fleet (http://www.globalsecurity.org/military/systems/ground/hmmwv-recap.htm). 

Some emissions data are available for the HMMWVs, primarily criteria pollutants, but none are 

known for the tracked vehicles. 

10.1 Experimental 

10.1.1 Platforms Tested 

Criteria and organic pollutant emissions were characterized during transient operation of four 

U.S. Army weapon platforms at the U.S. Army Aberdeen Test Center, Roadway Simulator 

(RWS). The RWS is the world's largest dynamometer, supporting vehicles ranging from 2,300 

kg (5,000 lb), 2-axle light vehicles (up to 192 km/h or 120 mph) to 27,300 kg (60,000 lb), 

tandem-axle tractor trailers (Schultz et al., 2005). Two versions of HMMWVs were tested for 

emissions on the RWS. These included a heavy HMMWV (M1097 A1) and a turbine engine, uparmored HMMWV (M1114). The HMMWV is currently the main transport vehicle for the DoD. 

These 6.2 L, General Motors vehicles consume almost 15 million gallons of JP-8 each year, 

making it the top-consuming vehicle type (17%) in the DoD inventory (Kemme et al., 2006). The 

6.5 liter Turbo Diesel 142 kW (190 hp) up-armored M1114 version has a higher payload 

capacity (1,043 kg) for a gross vehicle weight of 5,489 kg (GlobalSecurity.org, 2008a) and is 

equipped with a heavy armor protection package instituted during the Iraq war. Both of these 

vehicles were tested with two driving cycle protocols (described later) and stepped 

velocity/gradient cycle. 

Two additional weapons platforms, an M1 Abrams tank and a Bradley IFV, were tested at the 

facility but not on the RWS due to weight and track restrictions. The 62 metric ton M1 Abrams 

main battle tank is manufactured by General Dynamics Land Systems and powered by a 

Honeywell AGT 1118 kW (1500 hp) gas turbine. The Allison hydrokenetic transmission has four 

forward and two reverse gears. The Bradley is powered by a 447 kW (600 hp) Cummins VTA903T water-cooled 4 cycle diesel engine. It is a fully armored, fully tracked vehicle designed to 

79 
 
EPA/600/R-10/050 

April 2010 

carry mechanized infantry into close contact with the enemy (GlobalSecurity.org, 2008b). Both 

vehicles were fueled with JP-8, a standard military fuel (U.S. Army, 2001). 

10.1.2 Test Protocols 

Two standardized driving cycles and one combined velocity and gradient cycle were used to test 

both HMMWVs. The West Virginia highway driving cycle (WV) was developed originally from 

local delivery tractor-trailer activity logged by West Virginia University (Nine et al., 2000) and 

described elsewhere (Clark et al., 1999). The WV cycle represents the travel on four-lane 

highways of trucks to and from distribution depots located outside the city delivery areas [see 

bottom panel, Figure 10-1 (A)]. The EPA Highway Fuel Economy Test (HWFET) driving 

schedule [U.S. Department of Energy (DOE)/EPA, 2008] represents a mixture of rural and 

interstate highway driving with a warmed-up engine, typical of longer trips in free-flowing 

traffic [see bottom panel, Figure 10-1 (B)]. The M1097 HMMWV was run once on both the WV 

and HWFET cycles while the M1114 had triplicate runs on both cycles. Both HMMWV types 

were run once on the stepped velocity and gradient cycle. Transient emissions of the M1 Abrams 

and the Bradley IFV were sampled directly from the exhaust during startup, stationary idle, 

increased idle, and shutdown without actual movement of the vehicles. 

Black: M1097; Red: M1114 HMMWV Black: M1097; Red: M1114 HMMWV 

60 

40 

20 

0

6 

4 

2 

0 

4 

2 

0 

1800 

1200 

0 

40 

80 

120 

0 

2 

4 

6 

0 

4 

8 

12 

Benzene 

CO2 

CO 

N 

Naphthalene 

Methylnaphthalene 

0 

2x105 

4x105 

0 

60 

120 

0 

100 

200 

0 

600 

1200 

1800

 Conc. (ppb) 

Benzene 

0 

5 

10

 Conc. (%)

CO2 

0 

300 

600

 Conc. (ppm)

CO 

0 

100

 Horsepower 

0 

30 

60 

90

 Velocity (km/h) 

N 

Naphthalene 

Methylnaphthalene 

600 

 Velocity (km/h) Conc. (ppm) Conc. (ppb) Horsepower 100 

0 

80 

40 

0 200 

100 

0 

9 

6 

3 

0 600 Conc. (%) 300 

0 5x105 

3x105 

0 

0 

90 

60 

30 

0 

0 5 10 15 20 25 0 2 4 6 8 10 12 14 

 Time (min) Time (min) 

Figure 10-1. Emission transients for the M1097 and M1114 HMMWVs. A: West Virginia 

and B: Highway HWFET cycles. 

10.1.3 Sampling Approach 

A 15.2 cm (6 in.) I.D. stainless steel sampling pipe was attached to the HMMWV tailpipes via a 

high temperature rubber adaptor to convey the emissions to the analyzers. The exhaust 

80 
 
EPA/600/R-10/050 

April 2010 

temperature was measured at or below about 273 °C and the gas pipe was heat traced to about 

200 °C. No dilution air was added, and the flow was monitored with an annubar pitot tube. 

Exhaust for the REMPI-TOFMS system, the particle measurement systems, and the continuous 

emissions monitors (CEMs) was sampled using separate heated lines maintained at about 125­

150 °C. 

The Bradley and Abrams idle, cold start, and warm start emissions were sampled at a rate of 1 

L/min by means of a 0.6 cm (1⁄4-inch) diameter stainless probe inserted inside their exhaust line. 

In all studies, a slip stream of the sample exhaust was sampled through the pulsed valve of the 

REMPI-TOFMS system at a rate of 1 mL/min. 

The exhaust gas criteria pollutants were analyzed using a self-contained CEM bench that 

included two analyzers using EPA promulgated Method 10A (EPA, 2000b) for CO [low CO: 

Rosemount NGA 2000, high CO: California Analytical Instrument and two analyzers using EPA 

Method 3A (EPA, 2006), one for oxygen (O2: Rosemount NGA 2000) and one for CO2 

(California Analytical Instrument)]. Each analyzer had a daily, 3-point calibration and a 3-point 

bias check before the start of the test, followed by a 3-point system calibration and bias check at 

the end of the test. Gas standards were introduced via the bias check port at the sample line inlets 

during pre-sampling CEM performance checks. The CEM is linked to a data acquisition system 

set for a sampling frequency of 10 s-1. 

The REMPI-TOFMS instrument measured aromatic organic air pollutants in real-time, parallel 

to the standard CEMs. BTEX, styrene, and gaseous PAHs, are among the non-exclusive list that 

were targeted for measurement. An approximately 1 L/min slipstream was pulled from the main 

sampling pipe through a 15 m long, 0.95 cm (3/8 in.) diameter Silico-Steel coated line at 150 °C 

towards the REMPI-TOFMS inlet. A glass microfiber filter (Unique Heated products) mounted 

directly downstream from the main sampling pipe prevents PM from reaching the REMPITOFMS instrument. Two filter housings were operated in parallel in order to have the capability 

to replace a filter element on an hourly basis without interruption of the sampling. The pulsed 

inlet valve (modified General Valve Series 99) of the REMPI-TOFMS instrument pulls 

approximately 1 mL/min into the ionization chamber of the TOFMS. 

Real time particle size distributions were measured with a Dakati ELPI. The ELPI is a 12-stage 

impactor with a single pre-stage knockout, measuring particle size distributions ranging from 30 

nm to 10 μm at a frequency of 1 Hz. The ELPI generates a particle size distribution by charging 

the particles based on geometrical diameter prior to them entering into a cascade impactor. The 

charged particles land on the impactor stages based upon their inertia and their charge is 

converted into a particle number and mass, given a known density. The sample was conveyed via 

a non-static, conductive tubing, diluted with two 10:1 VKL (Palas) venturi-based dilutors in 

series (for a 100:1 dilution), totaling 10 L/min at ambient temperature and pressure. Dilution 

ratios are verified by using measurements of pre- and post-diluted CO and CO2. Daily quality 

control checks on the ELPI were performed by zeroing the electrometer using a flush of high 

efficiency particulate arresting (HEPA) purified air and by monitoring the current profiles of the 

ELPI while it samples room air and HEPA purified room air. 

81 
 
 

EPA/600/R-10/050 

April 2010 

Longitudinal and lateral vehicle velocities and forces as well as engine rotation and vehicle speed 

data were provided by the RWS control system. 

Cold start emissions were evaluated in this study using a regression model (Heeb, 2001; as in 

Heeb and Weilenmann et al., 2005) which consists of a linear extrapolation to the ordinate of the 

idle state portion of the cumulative target compound (CO, CO2, benzene, naphthalene, 

methylnaphthalene, and others) evolution. The ordinate value is the target compound mass 

amount emitted from a single cold start event. 

The repeatability of the RWS facility operations and pollutant measurements were evaluated 

using the t-test statistical approach. RA is used to compare differences in the means of the target 

measurements between two cycles. All cycles within one type of driving profile (HWFET or 

WV) are compared with respect to the first cycle. The RA (%) is defined as follows: 

 

⎛ Sd ⎞ ⎜

⎜ d + t ⎟

⎟ 0.975 ⎝ n ⎠ RA = ×100 

RM (2) 

where: 

d = the mean of the absolute values of the differences between measurements taken at the 

same time during a complete cycle 
 

t = the t-value, 0.975 

Sd = the standard deviation of the differences between measurements taken at the same time 

during a complete cycle 

RM = the mean of the reference cycle 

n = number of measurements taken with a rolling average of 10 s during a complete cycle 

10.2 Results and Discussion 

REMPI -TOFMS and conventional CEMs were used to compare emissions from the dieselpowered heavy M1097 HMMWV with the armored-upfitted, turbine-driven M1114 HMMWV. 

Concentration values of benzene, naphthalene, methylnaphthalene, CO2, and CO as well as the 

total particle density (N), applied power (HP) and velocity (v) are shown for both vehicles on the 

WV and HWFET protocols, in Figure 10-1 (A) and Figure 10-1 (B), respectively. 

The RWS facility operations had excellent velocity repeatability between cycles for each driving 

cycle tested. The relative velocity accuracy for the HMMWV M1114 vehicle was 0.04% and 

0.44% HWFET cycles, and 0.2% and 0.5% for the WV cycles. The RA for both HWFET and 

WV triplicate cycles, for the criteria compounds measured using conventional CEMs varied from 

2.4% to 8.1% for CO2, and 7.4% to 31% for CO. The RA for the trace compounds concentrations 

measured by the REMPI-TOFMS system varied from 15% to 79% for benzene, 31% to 109% for 

naphthalene, and 47 to 214% for methylnaphthalene. The lower reproducibility of the emissions 

for naphthalene and methylnaphthalene are due to the compounding effect of their relatively low 

82 
 
EPA/600/R-10/050 

April 2010 

concentration (sometimes just above the detection limit of the REMPI-TOFMS system) and the 

variance in the engine performance. It should be noted that the first two of the triplicate tests 

were run successively while the third test was performed later (4-5 h) on the same day with the 

lower reproducibility always between the non-successive runs. 

10.2.1 WV Cycle 

REMPI PAH measurements for the armored (M1114) HMMWV (red traces) on the WV cycle 

showed benzene peaks of about 120 ppb with a median value of 20 ppb [Figure 10-1 (A)]. 

Naphthalene and methylnaphthalene peaks of 6 and 12 ppb, respectively, were accompanied by 

median values of < 1 ppb. The average emission factors for benzene, naphthalene, and 

methylnaphthalene for the WV cycle were 325, 14, and 29 μg/km (see Table 10-1). 

83 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EPA/600/R-10/050 

April 2010 

Table 10-1. Emission factors of M1097 and M1114 HMMWVs. 

Type of Engine M1097 HMMWV (CO/CO2 g/km), Others Air Toxics (μg/km) 

Vehicle Speed 32 

km/h 

48 

km/h 

64 

km/h 

80 

km/h 

80 km/h - 80 km/h - 80 km/h - 

HWFET WV 1.0% 

grade 

1.5% 

grade 

2.5% 

grade 

CO2 231 206 268 356 398 418 419 361 380 

CO 0.38 0.75 1.07 0.84 1.64 1.74 1.73 1.23 0.74 

benzene 246 1163 3228 3248 5271 7732 

NA 

5096 3482 

naphthalene 64 244 673 727 1133 1197 1001 564 

methylnaphthalene 128 386 1573 1658 1726 1463 2072 1184 

styrene 54 160 785 718 2165 1055 592 

NA 

phenol 60 116 421 428 1536 978 577 

1,2,4trimethylbz. 64 145 627 526 587 400 231 

p-xylenes 27 66 196 218 412 289 158 

m-xylenes 71 195 791 265 739 466 482 

1,3,5 trimethylbz 61 145 540 641 749 428 367 

o-xylene 38 127 501 476 354 337 

toluene 97 302 1132 1641 1376 1735 NA

ethylbenzene 24 70 329 526 70 221 

Type of Engine M1114 HMMWV (CO/CO2 g/km), Others Air Toxics (μg/km) 

Vehicle Speed 32 

km/h 

48 

km/h 

64 

km/h 

80 

km/h 

80 km/h - 80 km/h - 80 km/h - 

HWFET WV 1.0% 

grade 

1.5% 

grade 

2.5% 

grade 

CO2 383 354 350 421 522 581 647 493 435 

CO 0.61 0.37 0.28 0.21 0.20 0.19 0.18 0.42 0.55 

benzene 177.3 110.5 116.1 28.8 129.1 161.3 225.5 275.1 324.5 

naphthalene 23.2 9.1 5.4 3.0 2.0 2.0 2.0 12.7 13.6 

methylnaphthalene 21.8 4.2 6.8 6.5 3.7 2.7 2.3 19.8 28.8 

styrene 3.5 2.6 0.9 1.4 

NA 

phenol 7.7 6.4 6.8 9.8 

1,2,4 trimethylbz. 3.9 2.6 1.8 2.7 

p-xylenes 5.4 3.3 1.7 1.1 

m-xylenes 19.4 15.7 6.3 2.6 

1,3,5 trimethylbz. 8.8 5.2 4.0 2.8 

o-xylene 10.6 7.2 5.7 1.6 

toluene 37.8 30.3 20.9 3.2 

ethylbenzene 15.5 2.9 0.6 0.6 

84 
 
 

EPA/600/R-10/050 

April 2010 

The presence of naphthalene is expected; its presence in diesel fuel emissions is due to 

incomplete fuel combustion (24%) as well as pyrosynthetic processes (76%) from compounds 

such as methylnaphthalene (Rhead and Pemberton, 1996) or small unsaturated hydrocarbons 

(Badger and Novotny, 1963). Approximately 0.5% of the naphthalene in diesel fuel has been 

observed to have survived combustion (Rhead and Pemberton, 1996). Clearly, the emission 

factors for most of the BTEX compounds and PAHs found in the exhaust system are dependent 

on multiple factors such as their initial concentration in the parent fuel, their survivability in the 

combustion chamber, combustion efficiency of the engine, potential reformation in the cooling 

zones, and load. CO and CO2 were found to correlate poorly with benzene, naphthalene, and 

methylnaphthalene emissions for the M1114 (R2 always less than 0.30), eliminating their use as a 

correlative indicator of air toxics levels. 

The M1097 had much higher emissions than the M1114, reflecting the turbine adoption in the 

latter (see Table 10-1). The diesel M1097 exhibited significant quenching of the fuel combustion 

on the cold cylinder walls, resulting in considerable emissions. For example, the benzene peak 

value for the M1097 was about 1600 ppb versus about 120 ppb for the M1114. CO emissions 

similarly were higher with the M1097. The two vehicles also had distinct, pollutant-specific 

responses to the WV cycle. For example, the 15-25 min trace of the M1097 showed relatively 

high, sustained naphthalene and methylnaphthalene emissions that were not evident during the 

same period with the M1114. The average emission factors for benzene, naphthalene, and 

methylnaphthalene for the WV cycle reflect a 1-2 orders of magnitude higher emissions than the 

emissions from the M1114 engine. Correlations between REMPI-TOFMS detected analytes and 

CO, CO2 were found to be only marginally better for the M1097 (R2

 up to 0.59) than the M1114. 

10.2.2 HWFET Cycle 

As with the WV cycle, tests of the M1097 and M1114 on the HWFET cycle showed the M1097 

to have significantly higher overall air toxic emissions. The emission factors, presented in Table 

10-1, for both vehicles show dependence with the driving cycle; however, the results are within 

the accuracy of the cycle reproducibility. Again, CO and CO2 were found to correlate poorly 

with benzene, naphthalene, and methylnaphthalene emissions for the M1114 (R2

 always less than 

0.34). Correlations were slightly better for the M1097 (R2 up to 0.48). 

10.2.3 Velocity/Gradient Cycle 

Steady state emissions from a prescribed protocol of velocity and gradient changes show 

distinctive trace emissions from the M1114 and M1097 (Figure 10-2). 

With higher velocity, the M1097 produces higher CO and trace emissions, while gradient 

increases (at 80 km/h) appear to have no effect. The M1114 shows minimal effect of velocity 

and gradient increases. Trace organic emissions and CO tend to decrease with increased velocity 

but this is believed to be due to increased load and engine warm up. As already observed during 

the WV and HWFET cycles, observed concentrations with REMPI-TOFMS for trace analytes 

were found to be much lower in the M1114 exhaust when compared to the M1097 results. In 

fact, the highest emissions for the M1114 were temporary peaks after speed changes, especially 

from idle to 32 km/h. 

85 
 
 

 

 

M1097 200 M1114 2000 5 240 

1600 200 4 150 

 Benzene Napthalene 

Methylnaphthalene

 CO2 

CO 

0 10 20 30 40 50 60 70 140 150 160 170 180 

100 

 Benzene

 Conc. (ppb)

 Napthalene 

Methylnaphthalene 

CO2

 CO 

0 10 20 30 40 50 60 70 80 

 Incline (%) CO Conc. (ppm) Conc. (ppb) 

Velocity (km/h) CO Conc. (%) Conc. (ppb) 2 

160 1200 

 Conc. (ppb) 

3 

2 

120 

800 

80 

50 400 1 40 

0 0 0 0 

8 600 12 120 

80 

 CO Conc. (ppm) 

CO Conc. (%) 2 

6 

400 8 

4 

200 4 40 2 

0 0 0 0 100 4 100 4 Velocity (km/h)

80 80 3 3 

2 

 Incline (%) 

60 60

40 

20 

2 

1 

40 

1 20 

0 0 0 0 

Time (min) Time (min) 

EPA/600/R-10/050 

April 2010 

Figure 10-2. Steady-state benzene, naphthalene, methylnaphthalene, CO, and CO2 

emissions from the M1097 and M1114 HMMWVs during a velocity and 

gradient stepped cycle. 

10.2.4 Startups 

The fast time response of REMPI-TOFMS allows for documentation of trace emissions during 

startups. Figure 10-3 shows pollutant-specific responses for the M1097 and M1114. 

The M1097 cold startup shows benzene at ~ 230 ppb which rapidly (within 60 s) tails off to a 

steady state level around 50 ppb. This highlights the responsiveness of the REMPI system as 

well as the characteristics of the cold start emissions. The other trace pollutants, naphthalene and 

methylnaphthalene, show distinctive traces from that of the benzene, increasing over 60 to 120 s 

only to decline slightly to a steady state value. A similar benzene spike is observed for the 

M1114, although its period is less than 15 s, suggesting that benzene peaks are indicative of fuel 

benzene vaporization during cold engine fuel starts. Calculation of the cold start benzene 

emissions for the M1097 and M1114 HMMWVs indicate, respectively, that a 2.5 min and 5.5 

min period of steady state emissions are equivalent to those of a single cold start. Similar time 

equivalents were found for naphthalene to be 0.9 min and 7.5 min for the M1097 and M1114 

HMMWVs, respectively. 

86 
 
 

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April 2010 

-1 0 1 2 3 4 5 6 

0 

2 

4 

50 

150 

250 

0 

50 

100 

150 

200 

250 

0 

2 

4 

6 

8 

10 

12 

14 

16

CO 2 Conc. (%)

 Time (min)

 CO2

 CO 

Benzene Conc. (ppb)

 Benzene Napthalene 

Methylnaphthalene 

0 1 2 3 4 

0 

2 

4 

50 

150 

250 

0 

100 

200 

300 

400 

500 

0 

20 

40 

60 

80 

100

 CO2 

Time (min)

 CO 

CO Conc. (ppm) 

Benzene Napthalene 

Methylnaphthalene 

(M-)Naphthalene Conc. (ppb) 

Figure 10-3. Cold start emissions of benzene, naphthalene, methylnaphthalene, CO, and 

CO2 and PM size distribution for the M1097 (left) and M1114 (right) 

HMMWVs. 

10.2.5 Bradley and Abrams 

Figure 10-4 shows the 30 s average, steady state idle emissions from the Abrams and Bradley, 

respectively, of twelve organic compounds analyzed by REMPI. REMPI was sequentially set to 

each compound’s specific ionization wavelength throughout a 15 min period. Two types of idle 

measurements are reported for the Abrams (low and high idle) as well as the Bradley (“idle 0” 

and “idle 2” settings). The Bradley’s concentrations are about 100-1000-fold higher than those of 

the Abrams. The Bradley’s emissions are most abundant for the substituted naphthalenes and 

benzenes while the Abrams shows its highest concentrations in the lighter phenol, toluene, and 

benzene compounds. This may be due to a higher percentage of unburnt fuel in the Bradley 

exhaust versus the Abrams exhaust. 

87 
 
Benzene 

Naphthalene 

Methylnaphthalene 

Toluene 

Phenol 

Styrene 

p-Xylene 

m-Xylene 

o-Xylene 

Ethylbenzene 

124 trimethylbenzene 

135 trimethylbenzene 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

800 

700 

600 

500 

400 

300 

200 

100 

0 

Conc. (ppb) Conc. (ppb) 

 Low Idle

 High Idle
 

800 1,2,4 trimethylbenzene m-Xylene 

600 

 Idle 0 400 Idle 2
 1,3,5 trimethylbenzene 200 p-Xylene 

Phenol 

0 

10:42 10:43 10:44 10:45 10:46 

 Time (h:min) 

EPA/600/R-10/050 

April 2010 

Figure 10-4. Steady state organic emissions at analyte-specific wavelengths, A: M1 Abrams, 

low and high idle conditions, and B: Bradley IFV, idle 0 and 2 trials. Inset: 

real-time variance of organics at low idle. 

The Bradley and Abrams cold starts had quite dissimilar peak benzene concentrations at 600 and 

35 ppb, respectively (Figure 10-5). These peaks did not persist more than about 30 s and, like the 

M1097 and M1114, are derived from the unburnt fuel. The naphthalene and methylnaphthalene 

traces don’t exhibit such sharp startup peaks, perhaps reflecting an origin from combustion 

byproducts rather than as unburnt fuel. The Bradley’s methylnaphthalene concentrations were 

high, at almost 500 ppb even 6 min past the cold start. The naphthalene and methylnaphthalene 

emissions on the Abrams were very low, less than 2 ppb. The warm start on the Bradley showed 

similar pollutant-specific trends to its respective cold start. The Abrams appeared to have higher 

methylnaphthalene emissions on the warm start than during the cold start This observation is 

biased since the response was observed in addition to residual methylnaphthalene (at much 

higher concentration) in the sampling line after the shutdown preceding the warm start. 

The Abrams tank exhibits an interesting and repeatable emission profile during shutdowns. 

Figure 10-6 show that the Abrams undergoes a 3 min process to shut down in which the 

concentration of benzene undergoes a double peak followed in time by methylnaphthalene and, 

to a lesser extent, naphthalene. 

88 
 
1400 

1200 Benzene Conc. (ppb) 

Cold Start Warm Start 

600 

500 

1000 400 

800 

300 

600 

200 400 

100 200 

0 0 

0 2 4 6 0 2 4 6
 

40
 4 

(methyl)Napthalene Conc. (ppb) (methyl)Napthalene Conc. (ppb) 

15 

10 

 Benzene

 Napthalene

 Methylnapthalene 

Cold Start Warm Start 

1 

5 

0 0 

0 2 4 6 0 2 4 6 

Time (min) Time (min) 

3 

2 

35 

30

Benzene Conc. (ppb) 

25 

20 

 

EPA/600/R-10/050 

April 2010 

Figure 10-5. Cold and warm start emissions of benzene, naphthalene, and 

methylnaphthalene for the Bradley IFV and M1 Abrams. 

0 

5 

10 

15 

20 

25 

0 

5 

10 

15 

20 

25 

Methylnaphthalene

 Napthalene 

Methylnaphthalene

 Napthalene 

Benzene

Concnetration (ppb) 

Benzene 

0 1 2 3 4 0 1 2 3 4 

time (min) time (min) 

Figure 10-6. Benzene, naphthalene, and methylnaphthalene emissions during a shutdown 

of the M1 Abrams. 

89 
EPA/600/R-10/050 

April 2010 

10.2.6 Number Size Distributions (NSDs) 

Figure 10-7 reports steady state NSDs for the M1097 and M1114 HMMWVs through the 

stepped velocity and gradient cycle of Figure 10-2. The cold start and the lower velocities on the 

M1097 tended to result in high particle numbers for all six median particle diameters between 39 

and 484 nm as compared to the higher velocities. The NSD showed little shift in particle 

diameter for all velocities, showing a maximum particle diameter at around 100 nm. Timeresolved (every 15 s) NSDs for the M1097 showed no size shifts from 0 to 90 s, although the 

maximum particle diameter decreased 50% (not shown). The M1114 showed somewhat lower 

particle counts than the M1097 but had about the same maximum particle diameter. Its response 

to velocity and gradient changes were quite different than the M1097, with higher particle 

emissions with velocity increases and a distribution shift to higher particle diameters at higher 

roadway gradients. This is seen more easily in Figure 10-8, which shows number concentrations 

versus speed and gradient changes, as well as CO, CO2, and organics. 

Both vehicles’ PM size distributions are in the range of ultra-fine inhalable particles peaking at 

around 100 nm diameter typical of diesel emissions found in other studies. Although particle 

number density is not regulated in the U.S. and is proposed in Europe, its significance is very 

important because of the pulmonary response to respiratory infections as well as adverse 

cardiovascular events. The particle number densities per km found in both vehicles are in the 

order of 1014. These are 100-1000 times higher than proposed European particle number 

emission standard for diesels of 5 x 1011 per km (Good, 2007). 

10.3 Emission Correlations 

Correlations between organic compounds, vehicle parameters [engine revolutions per minute 

(RPM), power (hp)], criteria pollutants (CO, CO2), O2, and NSDs by stage were analyzed across 

the various operating cycles to provide insights into pollutant mechanisms, surrogates for 

emission predictions, and operational modes to minimize pollutant generation. This method was 

used by Schulz et al. (1999) to gain insights into combustion mechanisms of pollutant formation. 

Highlights of these correlations are discussed below. 

The M1097 concentrations of toluene, benzene, naphthalene, and methylnaphthalene were the 

most closely correlated of the 12 organics with RPM, hp, CO, CO2, and O2. Across the range of 

steady state test conditions, these four compounds had an average R2

 of 0.82. The M1114, 

however, was poorly correlated for these four compounds with R2 = 0.40. The o-, m-, p-xylenes 

for the M1114, however, had an average correlation of R2 = 0.82. Benzene provides an 

illustrative example; the average correlation for benzene with vehicle parameters and criteria 

pollutants for the M1097 is 0.82. For the M1114, these R2

 values are 0.04 and 0.23 for two days 

of testing. 

For the M1097, the 12 organics had an average intra-correlation of R2 

= 0.60. This was highest 

for naphthalene at R2 = 0.89 and lowest for ethylbenzene, with R2 = 0.22. The M1114’s organic 

intra-correlation was lower than the M1097’s at R2

 = 0.57; the lowest was for benzene at R2 = 

0.04 (ethylbenzene was 0.58) and the highest at R2

= 0.85 for o- and m-xylenes. 

90 
 
 

 

 

 

 

 

dN/dLogD p (Part./km) 2.0x1014

1.5x1014 

1.0x1014 

5.0x1013 

0.0 

 32 km/h

 48 km/h

 64 km/h

 80 km/h 

80 km/h + 1.0 % 

80 km/h + 1.5 % 

80 km/h + 2.5 % 

M1097 

10 100 1000 10000 

Particle Diameter (nm) 

0.0 

5.0x1013 

1.0x1014 

1.5x1014 

M1114 

dN/dLogD p (Part./km) 

 32 km/h

 48 km/h

 64 km/h

 80 km/h 

80 km/h + 1.0% 

80 km/h + 1.5% 

80 km/h + 2.0% 

10 100 1000 10000 

Particle Diameter (nm) 

EPA/600/R-10/050 

April 2010 

Figure 10-7. Steady state PM size distribution for the M1097 HMMWV (top) and M1114 

HMMWV (bottom) during a stepped velocity and gradient cycle. 

For the M1097 and M1114, the NSDs by stage had an average intra-correlation R2 of 0.84 and 

0.88, respectively, for stages 3 (0.1193 μm) and larger. This suggests that particle NSDs were 

similarly altered (if at all) by changes in velocity, cycle type, and incline gradient. The fine 

particle stages on the M1097, but not on the M1114, were highly correlated with the other stages. 

From this limited dataset, it appears that good correlations between pollutants and operating 

conditions do not always exist. Use of these correlations would significantly aid vehicle emission 

characterizations by allowing one to predict levels of unmeasured pollutants from more easily 

measured pollutants. However, these correlations must be established beforehand on a sourceand pollutant-specific basis. 

91 
 
0.0 

0 

500 

1000 

1500 

2000 

2500 

2.0x10 4000 4 

1.8x104 

3500 

1.6x104 

1.4x104 

3000 

2500 

 Styrene o-xylene

 toluene

 124 trmbz ethylbenzene

 benzene

 naphthalene

 Methylnaphthalene

 m-xylene

 Phenol

 p-xylene

 135 trmbz 

39

 71

 119

 202

 316

 484

 CO2

 CO 

500 2.0x103 

2.0x1015 0 

1.2x1015

 o-xylene

 toluene

 ethylbenzene

 benzene

 naphthalene

 methylnaphthalene

 Styrene

 phenol

 124 trmbz

 p-xylene

 m-xylene

 135 trmbz 

CO2

 CO 

39

 71

 119

 202

 316

 484

 762

 dN/dLogDp (Part./hp-hr) Concentration (μg/hp-hr) 

Concentration (μg/hp-hr) 

1.2x104 

1.0x104 2000 

8.0x103 

1500 

6.0x103 

1000 

4.0x103 

1.5x1015 

 CO Concentration (g/hp-hr)

 dN/dLogDp (Part./hp-hr) 8.0x1014 

1.0x1015 

4.0x1014 

5.0x1014 

3000 0.0 6 7000 0.0 

14 

6000 5 12 

CO2 Concentration (g/hp-hr) 

CO Concentration (g/hp-hr) 

2

 CO Concentration (g/hp-hr) 

5000 

4 10 

4000 8 3 

3000 6 

2 

2000 4 

1 1000 2 

0 0 0 

20304050

50+1%

50+1.5%50+2.5% 

2030405060

50+1%

50+1.5%50+2.0%50+3.0% 

velocity (MPH) and incline velocity (MPH) and incline 

EPA/600/R-10/050 

April 2010 

Figure 10-8. Steady state REMPI, ELPI, and CEM data for the M1097 (left) and M1114 

(right). 

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April 2010 

11. Source 6: F-15 and F-22 Aircraft Engine Emissions 

This chapter describes the results of a field study using multiple extractive sampling techniques 

as well as real time detection techniques to measure gaseous emissions from F-15 and F-22 

fighter aircraft. Tests were performed between October 12 and 18, 2007 on the trim pad facility 

at Tyndall AFB in Panama City, Florida. Measurements were made on two different F100 

engines, and eight different F119 engines mounted on in-use aircraft. 54 test runs were 

performed at engine power levels that ranged from idle to full “military power”, with additional 

test runs at full augmented power (afterburner). The approach adopted for these tests involved 

extractive sampling at a distance of approximately 20-25 nozzle diameters downstream of the 

engine exit plane with real-time measurements using REMPI-TOFMS and a PTRMS (Battelle). 

Integrated air samples were also collected and analyzed for VOC. 

11.1 Experimental Method 

11.1.1 Aircraft/Engine 

The engines tested included the F100 engine associated with the F-15 Eagle and the F-16 Falcon 

aircraft and the F119 engine associated with the F-22 aircraft. The Pratt & Whitney F100 engine 

is the primary engine in the worldwide F-15 fleet and has gained overwhelming use with more 

than 85% of the world's air forces that fly the F-16. With more than 6,800 active installed 

engines worldwide and over 16 million flight hours, the F100 series represents a large proportion 

of the current fighter aircraft inventory. The F100 is an axial-flow turbofan produced in four 

variations: F-100-PE-100, F-100-PW-200, F-100-PW-220, and F-100-PW-229. The engines 

tested during this measurement campaign were F-100-PW-100 engines with normal thrust of 

12,420 pounds, rising to a maximum thrust of 14,670 pounds at full military power. Maximum 

afterburning thrust is 23,830 pounds. 

The F-22 aircraft incorporates a pair of new, higher thrust engines, the Pratt & Whitney F119­

PW-100, which is designed for efficient supersonic operation without afterburner. The F119 

engine develops more than twice the thrust of current engines under supersonic conditions, and 

more thrust without afterburner than conventional engines with afterburner. Each F-22 is 

powered by two of these 35,000-pound-thrust-class engines. 

The experimental design called for duplicate test cycles to be performed on each test engine with 

individual test runs conducted at each of the engine power settings shown in Table 11-1 (nominal 

percentage of maximum thrust in parentheses). Due to the extreme conditions encountered in 

sampling the exhaust at afterburner power levels, these tests were performed only on the final 

day of testing. 

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Table 11-1. Engine power settings tested. 

F-15 F-22 

Ground idle (65-70%) Idle (10%) 

Low intermediate (80%) Approach (20%) 

High intermediate (85%) Intermediate (70%) 

Full/Military (91-93%) Sub-military (80%) 

Afterburner (150%) 

11.1.2 Testing Venue 

The engines were tested at Tyndall AFB in Panama City, Florida. Tyndall is home to both the 

Air Force Research Laboratory Airbase Technologies Division and the 325th Tactical Fighter 

Wing. The 325th Operations Group of the 325th TFW is the focal point for all F-15 and F-22 

initial pilot training. Operations Group maintenance personnel service and prepare aircraft for 

flight. They also troubleshoot all mechanical problems that could prevent the aircraft from 

sustaining the mission. As part of their maintenance role they operate and use two noisesuppressing, “hush” houses and a trim pad for testing engines preflight. Their schedule typically 

involves testing 25–30 engines or aircraft per month and their facilities including the trim pad 

have recently been upgraded to handle the extreme requirements of the new, high thrust F-22 

aircraft. The engines that were tested were mounted in their associated aircraft, and the aircraft 

were tied down using existing anchors at the trim pad. The aircraft that were tested were 

representative F-22 or F-15 planes rotated out of the training program at Tyndall AFB. 

The trim pad (Figure 11-1) is an outdoor facility consisting of a circular concrete pad 

approximately 35 meters in diameter. A concrete wall approximately 4 meters high encloses the 

circumference of the trim pad with the exception of approximately 30 meters of the southeastern 

face. During testing the aircraft were tied down using a tail hook at the center of the trim pad 

with the nose of the aircraft facing the opening in the wall. An instrumented trailer housing the 

extractive measurement equipment was positioned on the trim pad approximately 20 meters off 

the right wing tip. A 16-foot van truck was situated near instrumented trailer, and housed the 

REMPI-TOFMS and supporting equipment. 

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April 2010 

Figure 11-1. Trimpad and location of probe and instrument trailers with respect to 

aircraft 

11.1.3 Exhaust Sampling 

Extractive sampling from the exhaust plume was conducted using a stainless steel probe located 

downstream on the engine exit plane (see Figure 11-1). The extractive sampling probe was 

positioned 23 meters behind the exhaust exit plane for tests at idle through military power, and at 

38 meters for afterburner tests. The probe inlet height was 3 meters above ground level. The base 

of the probe was secured to the trim pad with several concrete anchoring bolts to prevent 

movement of the probe during engine operation. Heavy duty chain was used to stabilize the top 

of the probe and was anchored to the trim pad in front of and approximately 45o

 on each side of 

the probe axis. 

The extracted sample was continuously transferred through heated, electrostatically protected 

Teflon tubing to a heated sampling manifold inside the instrumented laboratory. Exhaust was 

drawn from the manifold to a set of real-time monitoring instruments for continuous 

measurement of CO2, CO, nitric oxide (NO), nitrogen dioxide (NO2), total organic carbon, and 

individual VOC. Integrated samples (adsorbent cartridges and canisters) also were collected for 

laboratory analysis to determine carbonyl compounds and VOCs. 

11.1.4 REMPI-TOFMS Sampling Approach 

A 25’ heated line (150 °C) with a 1/8” SS insert was connected to the main sampling manifold 

inside the Battelle instrument trailer. An approximately 1.5 L per min flow was pulled through 

this line. The flow rate was verified visually by monitoring the pressure drop upstream from the 

REMPI-TOFMS pulsed valve. Marginal changes in flow rate do not affect recorded ion signals 

but are important during pre and post test calibration using dynamic spiking with calibration gas 

standards. Real time instrument performance was monitored using deuterated benzene that was 

added to the main exhaust gas stream at ~ 5 ppb concentration. Ion signal for deuterated benzene 

95 
 
EPA/600/R-10/050 

April 2010 

was verified at least once every hour for a 30s period. At the start and end of each day, a small 

amount of TO-14 calibration gas was added to the pulled gas stream (no aircraft engine running 

at such times) as a dynamic spike. This calibration gas was used for absolute calibration of the 

TO-14 analytes (as far as included in the sampling procedure) and verification of predetermined 

REMPI transition wavelengths. Calibration of the mass spectrum was performed and verified 

daily using afore mentioned TO-14 calibration gas standard. The exhaust flow was also used to 

measure CO and CO2 concentrations in the exhaust of the tested jet engines, independently from 

Battelle’s measurements. The sampling procedure as established by Battelle prior to the field 

sampling campaign did not allow for detection of exhaust gases during the startup and shutdown 

of any jet engine. In fact, a reverse flow purge was applied during such events to minimize the 

possibility of unburned jet fuel being sampled (and trapped) inside the sampling line. 

REMPI-TOFMS signals were recorded using the following approach: Based on the test plan, 

each jet engine was tested twice for each thrust level. Therefore, the first time around, the laser 

wavelength was tuned to the optimal wavelength for detection of benzene. This wavelength is 

also suitable for detection of PAHs and is useful for real time detection of transients without loss 

of data during wavelength switches. During the second sampling of the same thrust level, the 

wavelength was changed over a pre-determined set of nine wavelengths, including the benzene 

wavelength in order to collect data for (at least) nine analytes. 

In general, mass spectra from 75 to 180 m/z were recorded for every 20 laser shots resulting in a 

~ 2 s sampling period. The high-mass detection level was established to reduce the total amount 

of data collected and was determined by the lack of ion signals at higher mass number under 

conditions where real time low mass responses were clearly visible. Although this approach 

results in large datasets (more than 200 MB after 30 minutes), it also ensures the capability to 

verify if recorded ion signals are true ion signals or signals recorded due to changes in baseline 

signals as a consequence of changing ambient conditions inside the 16 foot truck enclosure 

where the REMPI-TOFMS instrument was positioned. 

A daily time synchronization of all equipment ensured the accuracy of all sampling periods. 

11.1.5 REMPI-TOFMS Data Analysis Procedure 

Under sampling conditions with ion signals well above the real time detection limit of ~ 1 ppb, 

the integrated area under a mass peak relates directly to the concentration by comparison of this 

integrated area with that of a calibrated gas mixture integrated area recorded under the same 

experimental condition. Across this jet engine exhaust sampling study, recorded ion signals at a 

2 s sampling period were frequently found to be near or below the 2 s detection limit of many of 

the target analytes. Therefore, time averaging was utilized to enhance the signal to noise ratio by 

reduction of the (random) noise. Time (30 s or 60 s average) mass spectra were obtained in postdata collection processing that represent the average mass spectrum at a specific wavelength per 

30 or 60 s time interval. 

Changes in the baseline signal will cause a bias in the results. To eliminate such bias, the average 

integrated area of two adjacent masses with no visually verified ion signal was subtracted from 

the integrated area for the mass of interest. The average concentration was than obtained through 

direct comparison with the integrated area under a dynamically spiked air sample with TO-14 

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EPA/600/R-10/050 

April 2010 

calibration gas. The presented REMPI-TOFMS results are focused on the sampling times with 

conventionally sampled (Summa) canisters. 

11.2 Results 

11.2.1 F-15 Tests 

Table 11-2 (obtained from Battelle) describes the followed sequence in sampling. Note that the 

ground idles (tests No. 1-A-1 and 1-B-1) were not performed since the exhaust plume did not 

reach the probe due to strong crosswinds that morning. 

Table 11-2. Summary of F-15 engine tests. 

Date Test No. Tail No. Engine Nominal 

Thrust % 

Start 

canister 

sampling 

Stop 

canister 

Sampling 

Probe 

Location 

10-12-07 1-A-2 031 2 80 9:00:52 9:10:52 Near 

10-12-07 1-A-3 031 2 85 9:16:45 9:26:45 Near 

10-12-07 1-A-4 031 2 92 9:31:43 9:41:43 Near 

10-12-07 1-B-2 031 2 80 10:19:16 10:49:16 Near 

10-12-07 1-B-3 031 2 85 10:54:19 11:04:19 Near 

10-12-07 1-B-4 031 2 92 11:09:14 11:34:14 Near 

10-12-07 2-A-1 031 1 70 13:05:35 13:15:35 Near 

10-12-07 2-A-2 031 1 80 13:20:23 13:30:23 Near 

10-12-07 2-A-3 031 1 85 13:36:54 13:46:54 Near 

10-12-07 2-A-4 031 1 92 13:51:26 14:01:26 Near 

10-12-07 2-B-1 031 1 70 14:13:15 14:43:15 Near 

10-12-07 2-B-2 031 1 80 15:25:10 15:35:19 Near 

10-12-07 2-B-3 031 1 85 15:40:40 15:50:40 Near 

10-12-07 2-B-4 031 1 92 15:55:09 16:20:09 Near 

Figures 11-2 through 11-5 show the concentration profiles during the one day of testing on an F15 airplane. The 1A and 1B series in Figure 11-2 show very minimal response for benzene, 

naphthalene, and methylnaphthalene. Figure 11-3 shows the results for the 2A series. In the early 

afternoon, the wind conditions were more favorable than in the morning to detect the exhaust 

plume, even at the idle conditions. This resulted in more favorable detection of both REMPI 

analytes as well as CO2. A clear correlation is visible between the observation of benzene, and 

CO2, due to the occasional interference of cross winds. Note that the large benzene transient 

between 2A2 and 2A3 sampling occurred when the jet engine was changing thrust levels 

confirming that fast changes in engine conditions (revving up and down in rpm) result in 

transient emissions. In comparison with the first data set shown in Figure 11-2, the CO2 emission 

levels are considerably larger due to more favorable detection of the plume. 

Figure 11-4 also shows data (inside blue box) for other BTEX-like target analytes (styrene, 

phenol, p-xylenes, m-xylenes, o-xylenes, toluene) collected during a sequence of pre-determined 

changes in REMPI laser wavelength. Detection of these analytes occurs only when the plume 

reaches the probe as indicated by the relative high CO2 concentration. Clearly there is a high 

correlation between any REMPI-TOFMS detected analyte and the CO2 concentration due to the 

fact that the exhaust plume does not always reach the probe. 

97 
 
F-15 exhaust Test 1A and 1B series 

3 3000 

2 

1A2 1A3 1A4 1B2 1B3 

09:00 09:30 10:00 10:30 11:00 11:30 

 Benzene

 Naphthalene

 Methylnaphthalene

 Canister sampling periods 

(16 ppb) 

2000 

1 1000 

0 0 

Time (h:min) 

CO Concentration (ppm)

2

Concentration (ppb) 

Figure 11-2. Concentration profiles during F-15 engines testing. 

F-15 exhaust Test 2A series 

14
 

12
 


3000 

2A1 2A2 2A3 2A4 

 Benzene

 Naphthalene

 Methylnaphthalene

 Canister sampling periods 

13:00 13:10 13:20 13:30 13:40 13:50 14:00 

10 

8 

CO Concentration (ppm) 

2

Concentration (ppb) 

2000 

6 

4 1000 

2 

0 0 

Time (h:min) 

EPA/600/R-10/050 

April 2010 

Figure 11-3. Concentration profiles during second sequence of F-15 engine testing. 

98 
 
 

F-15 exhaust Test 2B1 series 

3000 

Concentration (ppb) 

10

8 

2000 

6 

4 

1000 

2 

0 0

2B1 

 Benzene

 Naphthalene

 Toluene

 Methylnaphthalene

 Canister sampling period

 Styrene

 Phenol

 p- m- o- Xylenes 

14:10 14:20 14:30 14:40 14:50 

Time (h:min) 

CO Concentration (ppm) 

2

Figure 11-4. Concentration profiles during the 30 minute test 2B1. 

F-15 exhaust Test 2B series 

4000 

2B1 2B2 2B3 2B4 

 Benzene

 Naphthalene

 Methylnaphthalene

 Canister sampling period 

14:20 14:40 15:00 15:20 15:40 16:00 16:20 

10 

3000 8 

6 

CO Concentration (ppm) 

2

Concentration (ppb) 

2000 

4 

1000 

2 

0 0 

Time (h:min) 

EPA/600/R-10/050 

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Figure 11-5. Complete 2B series. 

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11.2.2 F-22 Tests 

Table 11-3 shows the test schedule for the F-22 engine tests. 

Figure 11-6 shows the CO2 and REMPI-TOFMS concentration data with the REMPI wavelength 

set to detection of benzene and PAHs. Data for other analytes at other wavelengths recorded 

during the 3B series resulted in non-detects for a 2s sampling period except for the low thrust 

levels. The largest transient benzene concentration was recorded immediately after the switch 

from sampling the back-flushed air to sampling of the aircraft exhaust. On this occasion, this 

happened shortly (less than 1 minute) after the restart of the jet engine. The transient benzene is 

therefore likely due to residual unburned fuel fumes that reached the sampling port. Changes in 

thrust level happen well before and after each sampling period and were accompanied by 

transient emissions that were not captured in the conventional samples. 

Figure 11-7 shows the REMPI-TOFMS data for the 4A and 4B series. The interesting 

observation here is the sharp increase in benzene concentration to a constant value between the 

4A3 and 4A4 as well as after the 4A4 conventional samples. During this time, the aircraft engine 

speed was reduced to a (unknown) low thrust level which agrees with the observed drop in CO2 

concentration. However, the observed benzene concentrations with REMPI-TOFMS were much 

higher than expected based on the observed CO2 concentration for lower thrust levels that were 

recorded earlier in the sequence. Figure 11-8 complements Figure 11-7 with data for other 

analytes that were sampled in the 4B series which are a replicate of the 4A series. 

Here again, some analytes are non-detects when considering a 2 s sampling time, especially for 

the higher thrust levels. Similar data responses were recorded during Test 5A and 5B and the 

results are tabulated in Table 11-4. 

For the 6A and 6B series, a comparison has been made with the PTR-MS data as measured by 

Battelle and provided for comparison. Figure 11-9 has such comparison for the benzene and 

naphthalene trace. For benzene, the agreement is very good, both in time response as well as 

absolute intensity. In the case of naphthalene (as well as other BTEX-like analytes; not shown) 

the quantitative comparison is fair at best with a consistently lower concentration measured with 

REMPI-TOFMS than with PTR-MS. 

A comparison between REMPI-TOFMS, PTR-MS, and (Summa) canister data as tabulated in 

Table 11-4 is possible for only a limited number of points since (1) the canister data is 

sometimes below the detection limit (2) no canister data is available for the 7A1 series and (3) 

naphthalene is not analyzed using canisters. 

If the canister data is considered to be the reference standard then there are seven data points in 

Table 11-4 where the PTR-MS has a concentration value above the detection limit of the canister 

as opposed to 0 data points for REMPI-TOFMS. This would suggest (independently from the 

REMPI-TOFMS results) that the PTR-MS results are in general too high. A comparison between 

REMPI-TOFMS and PTR-MS for of the obtained benzene concentration is good; others (where 

available) fair with up to a factor 20 difference in average concentrations recorded for 

naphthalene. 

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Table 11-3. Test schedule for the F-22 engine tests. 

Date Test No. Tail No. Engine Nominal 

Thrust % 

Start 

canister 

sampling 

Stop 

canister 

sampling 

Probe 

Location 

10-15-07 3-A-1 045 2 10 9:53:23 10:03:23 Near 

10-15-07 3-A-2 045 2 20 10:07:44 10:17:44 Near 

10-15-07 3-A-3 045 2 70 10:22:30 10:29:55 Near 

10-15-07 3-A-4 045 2 80 10:39:32 10:49:32 Near 

10-15-07 3-B-4 045 2 80 12:00:08 12:23:40 Near 

10-15-07 3-B-3 045 2 70 13:29:32 13:39:32 Near 

10-15-07 3-B-2 045 2 20 14:36:40 14:46:40 Near 

10-15-07 3-B-1 045 2 10 14:52:03 15:18:15 Near 

10-16-07 4-A-1 43 FS 1 10 9:08:18 9:18:18 Near 

10-16-07 4-A-2 43 FS 1 20 9:22:40 9:32:41 Near 

10-16-07 4-A-3 43 FS 1 70 9:38:12 9:48:13 Near 

10-16-07 4-A-4 43 FS 1 80 9:57:29 10:07:29 Near 

10-16-07 4-B-1 43 FS 1 10 10:17:39 10:27:39 Near 

10-16-07 4-B-2 43 FS 1 20 10:33:23 10:43:23 Near 

10-16-07 4-B-3 43 FS 1 70 10:48:44 10:58:44 Near 

10-16-07 4-B-4 43 FS 1 80 12:40:50 12:50:50 Near 

10-16-07 5-A-4 43 FS 2 80 13:02:49 13:12:49 Near 

10-16-07 5-A-3 43 FS 2 70 13:19:10 13:29:10 Near 

10-16-07 5-A-2 43 FS 2 20 13:36:43 13:42:40 Near 

10-16-07 5-A-1 43 FS 2 10 14:22:00 14:32:02 Near 

10-16-07 5-B-4 43 FS 2 80 14:38:46 14:48:46 Near 

10-16-07 5-B-3 43 FS 2 70 14:54:28 15:04:28 Near 

10-16-07 5-B-2 43 FS 2 20 15:09:55 15:19:55 Near 

10-16-07 5-B-1 43 FS 2 10 15:23:19 15:31:05 Near 

10-17-07 6-A-4 041 2 80 9:15:29 9:25:32 Near 

10-17-07 6-A-3 041 2 70 9:29:44 9:32:49 Near 

10-17-07 6-B-4 041 2 80 9:54:09 9:55:20 Near 

10-17-07 6-A-1 041 2 10 10:16:47 10:26:47 Near 

10-17-07 6-A-2 041 2 20 10:32:47 10:40:08 Near 

10-17-07 6-B-3 041 2 70 12:06:59 12:16:59 Near 

10-17-07 6-B-2 041 2 20 12:20:32 12:30:32 Near 

10-17-07 6-B-1 041 2 10 12:35:54 12:45:54 Near 

10-17-07 7-A-1 041 1 10 12:51:28 12:54:40 Near 

10-18-07 8-A-3* 035 1 30 10:10:30 10:18:00 Far 

10-18-07 8-A-A/B 035 1 150 10:18:00 10:19:00 Far 

10-18-07 9-A-3 035 2 70 12:16:09 12:26:09 Far 

10-18-07 9-A-A/B 035 2 150 12:28:44 12:29:50 Far 

10-18-07 9-B-3 035 2 70 14:40:22 14:50:22 Far 

10-18-07 9-B-A/B 035 2 150 14:52:33 14:53:29 Far 

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Table 11-4. A comparison between Summa canister, REMPI-TOFMS and PTR-MS data 

with the PTR-MS average calculated from provided Battelle data and canister 

sampling time. 

Test Number Analyte REMPI PTR-MS Canister 

(ppb) (ppb) (ppb) 

benzene 0.05 0.25 < 0.36 

toluene 0.03 0.57 < 0.29 

6B3 styrene ND 0.46 Not available* 

m- + p- xylenes 0.11 0.46 < 0.53 

ethylbenzene 0.02 0.73 < 0.23 

naphthalene 0.02 0.41 No data 

benzene 0.34 0.82 0.89 

toluene 0.04 0.88 < 0.29 

6B2 styrene 0.06 0.55 Not available* 

m- + p- xylenes ND 0.64 < 0.53 

ethylbenzene ND 0.83 < 0.23 

naphthalene 0.03 0.52 No data 

benzene 1.67 3.07 3.84 

toluene 0.35 1.96 0.92 

6B1 styrene 0.15 1.48 Not available* 

m- + p- xylenes 0.15 2.01 < 0.35 

ethylbenzene 0.10 1.59 < 0.15 

naphthalene 0.09 0.88 No data 

benzene 0.55 0.98 Not available 

toluene Not sampled 1.16 Not available* 

7A1 styrene ND 0.43 Not available* 

m- + p- xylenes Not sampled 1.08 Not available 

ethylbenzene Not sampled 1.34 Not available 

naphthalene 0.06 0.61 No data 

* No styrene data received from Battelle; should have been analyzed from Summa canister 

102 
 
 Benzene 

0 

10 

20 

30 

40 

50 

60 

0 

1000 

2000 

3000 

4000 

5000 

6000 

3A13A23A33A43B43B33B23B1

 Naphthalene

 Methylnaphthalene

 Canister sampling 

Concentration (ppb) 

CO2 Concentration (ppm) 

10:00 11:00 12:00 13:00 14:00 15:00 

Time (h: min) 

Figure 11-6. Concentration during first sampling of F-22 engine. 

60 

50 

09:00 09:20 09:40 10:00 10:20 10:40 11:00 

0 

1000 

2000 

3000 

4A1 4A2 4A3 4A4 4B1 4B2 4B3 

Time (h: min)

 Benzene

 Naphthalene

 Methylnaphthalene 

Concentration (ppb) 

40 

CO Concentration (ppm) 2 

30 

20 

10 

0 

EPA/600/R-10/050 

April 2010 

Figure 11-7. Concentrations during 4A and 4B sampling of F-22 engine. 

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1 

2 

3 

4 

5 

6 

 Toluene

 Phenol

 Styrene

 Mass 106 

4B1 4B2 4B3 

0 0 

Concentration (ppb) 

3000 

2000 

1000 

CO Concentration (ppm) 2 

10:00 10:10 10:20 10:30 10:40 10:50 11:00 

Time (h: min) 

Figure 11-8. Concentrations for other REMPI-TOFMS detectable analytes. 

After movement of the (Battelle) sampling equipment to the location further from the engine 

nozzle, three afterburner tests were performed. Figure 11-10 shows the REMPI-TOFMS trace 

during the third afterburner test. REMPI-TOFMS data is available for the first and second 

afterburner test, however, the CO2 CEM trace is only complete for the last afterburner test. All 

three afterburner tests are similar in response. 

0 

5 

10 

15 

20 

25 

30 

35 

0 

3 

6 

9 

6B3 6B2 6B1 7A1

 REMPI Benzene

 PTR-MS Benzene 

Concentration (ppb)

 REMPI Naphthalene

 PTR-MS Naphthalene

11:50 12:00 12:10 12:20 12:30 12:40 12:50 13:00 

 Time (h:min) 

Figure 11-9. Comparison between REMPI-TOFMS and PTR-MS. 

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0 

5 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

0 

1000 

2000 

3000 

4000 

5000 

6000 

7000 

Concentration (ppb)

 Benzene

 Naphthalene

 Methylnaphthalene

 CO2 

CO 2 Concentration (ppm) 

14:51 14:52 14:53 14:54 14:55 14:56 

Time (h:min) 

Figure 11-10. Benzene and PAHs response during afterburner test. 

Figure 11-11 shows the comparison between REMPI-TOFMS and PTR-MS. In order to make 

such comparison, the REMPI-TOFMS data was revised to reflect a 10s sampling period to match 

the PTR-MS data. Here again, the comparison for the benzene data is very good while the 

naphthalene data is good in time dependence but fair in absolute concentration value. 

Average benzene concentrations as obtained with REMPI-TOFMS (see Table 11-3) were found 

to compare very well with the canister data as shown in Figure 11-12. The linear fit is to the 

black square data only. One outlier, namely the 9B AB (afterburner) value (red square in Figure 

11-12) had a 6 ppb concentration according to the summa can data and was non-detect for 

REMPI. This outlier can be explained by a slight (2-4 sec) difference in actual sampling times of 

the canister and REMPI during which a strong transient benzene spike may have occurred during 

the afterburner-to-idle transition (see Figure 11-10). When such a shift is included, the REMPI 

average concentration during this test becomes 6 ppb, in accord with the summa can data. 

Figure 11-13 shows the average benzene concentrations measured with REMPI-TOFMS during 

the canister sampling at the four thrust levels and four engines with duplicates. When corrected 

for average CO2 concentration, the emission factor in g/g carbon burned can be derived as shown 

in Figure 11-14. 

The observed trend of lower emissions with higher thrust levels is consistent across the data set. 

However, emissions for the lowest thrust level are not very reproducible, even for the same 

engine. This could suggest that the runtime history of the engine prior to sampling at the lowest 

nominal thrust level changes the emission level. 

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April 2010 

14:50 14:52 14:54 14:56 14:58 

0 

5 

10 

15 

20 

25 

30 

35 

40

 Benzene REMPI

 Naphthalene REMPI

 Benzene PTR-MS

 Naphthalene PTR-MS 

Concentration (ppb) 

Time (h:min) 

Figure 11-11. Comparison REMPI-TOFMS with PTR-MS for benzene and naphthalene. 

0 1 2 3 4 5 6 7 8 

0 

1 

2 

3 

4 

5 

6 

7 

8 

Summa Concentration (ppb) 

 Experimental data

 Linear Fit

 95% Confidence Limits 

REMPI Benzene concentration (ppb) 

Figure 11-12. Comparison between time averaged REMPI-TOFMS benzene data and 

Summa canister results. 

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-0.5 

0.0 

0.5 

1.0 

1.5 

2.0 

2.5 

3.0 

3.5 

4.0 

4.5 

5.0 

5.5 

6.0 

6.5 

7.0 

Benzene Concentration (ppb) 

 Plane 1 Engine 1

 Plane 1 Engine 1 repeat

 Plane 2 Engine 1

 Plane 2 Engine 1 repeat

 Plane 2 Engine 2

 Plane 2 Engine 2 repeat

 Plane 3 Engine 1

 Plane 3 Engine 1 repeat 

1 2 3 4
 

Thrust Level (% of max)
 

Figure 11-13. Benzene concentrations as function of thrust level F-22 engine. 

0 

5 

10 

15 

20 

25 

30 

35 

40

 Plane 1 Engine 1

 Plane 1 Engine 1 repeat

 Plane 2 Engine 1

 Plane 2 Engine 1 repeat

 Plane 2 Engine 2

 Plane 2 Engine 2 repeat

 Plane 3 Engine 1

 Plane 3 Engine 1 repeat 

Emission Factor Benzene (ug/g-carbon burned) 

0 10 20 30 40 50 60 70 80 90 100 
 

Nominal Thrust Level (%)
 

Figure 11-14. Benzene emission factor (μg/g carbon burned) for F-22 engines. 

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12. Conclusions 

This project has developed a technology termed REMPI-TOFMS for real time detection of trace 

aromatic organic compounds in complex (combustion exhaust) matrices. During this project the 

REMPI-TOFMS technology was transformed from a laboratory type, large frame research 

instrument to a compact system that was taken into the field and used to characterize trace 

aromatic air toxics. The REMPI-TOFMS system versatility was demonstrated by sampling on a 

broad range of sources from an MWC to an M1 Abrams battle tank. The system also proved 

portable, functional in harsh environments, reproducible, sensitive, and quick to respond, making 

it ideal for characterization of multiple source types and compound types. 

Operation of the LIBS system for detection of metals showed that its use was limited by the 

presence of carbonaceous soot. An LTA procedure prior to analysis looked promising but was 

not pursued due to the departure from the project of the LIBS cooperator, the U.S. Army 

Research Laboratory. Testing with ORS instrumentation did not prove fruitful, as daily drift of 

the criteria pollutant readings (compared to on-line CEMs) lent doubt to the value of these 

measurements for point source measurement. 

The low ppbv detection limit of REMPI-TOFMS is sufficient for detection of BTEX and small 

PAHs in exhaust gas streams from vehicles in real time. This is a capability not previously 

accomplished on such a wide variety of sources and to such an extent. Only in cases of 

significant exhaust dilution (high load AGE and higher thrust levels of jet engines) were the real 

time detection limits of the instrument insufficient to provide real time results. Variation of the 

system procedures allowed collection of an averaged response up to 1 minute in duration to 

greatly enhance the sensitivity of the instrument, resulting in minimal species non-detects. 

Emission factors for many small organic aromatic compounds in exhausts from a diesel 

generator, aircraft ground equipment, waste combustor, two HMMWVs, Abrams and Bradley 

vehicles, and F-15 and F-22 aircraft engines have been reported for the first time. Strong and 

significant transient emissions appear during changes in engine conditions, including shutdown 

and restarts. Steady state conditions were, in general, found to be constant over an extended 

period of time. REMPI-TOFMS was able to clearly distinguish effects of engine type (diesel, 

turbine) on emission characteristics. 

In critical operations, the REMPI-TOFMS instrument can be used to provide operational 

feedback, improving efficiency and reducing emissions. The speed and sensitivity of the REMPI 

instrument allows transient and steady state characterization of target pollutants emissions that 

can be used in assessing or developing new exhaust gas treatment systems for mobile sources or 

in developing emission factors by use-mode. For reasonably high ambient levels of air toxics, 

REMPI-TOFMS can also be used as an ambient air monitor. Its recent application to a near-road, 

highway emissions study proved its usefulness in open source sampling. Both of these 

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April 2010 

applications, point source or area source, are appropriate for REMPI-TOFMS and, thus, the 

technology could prove useful in a diagnostic and characterization capacity. 

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Rakopoulos, C.;Mavropoulos, G., Hountalas, D., 1998. Modeling the Structural Thermal 

Response of An Air-Cooled Diesel Engine Under Transient Operation Including a Detailed 

Thermodynamic Description of Boundary Conditions. Society of Automotive Engineers, SAE 

Technical Paper Series No. 981024. 

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Rhead, M. and Pemberton, R. Sources of Naphthalene in Diesel Exhaust Emissions. Energy & 

Fuels 10, 837-843, 1996. 

Ryan, J., Lemieux, P., Preston, W., 1998. Near-real-time measurement of trace volatile organic 

compounds from combustion processes using an on-line gas chromatograph. Waste Management 

18, 403–410. 

Schultz, G., Tong, I., Kefauver, K. and Ishibashi, J., 2006. Steering and Handling Testing Using 

Roadway Simulator Technology. International Journal of Vehicle Systems Modeling and 

Testing, Vol. 1, No. 1/2/3, pp. 32-47. 

Schulz, H., De Melo, B., and Ousmanov, F., 1999. Volatile Organic Compounds and Particulates 

as Components of Diesel Engine Exhaust Gas. Combustion and Flame 118, 179-190. 

Thanner R., Oser H., Grotheer H.-H., 1998. Time-resolved monitoring of aromatic compounds in 

an experimental incinerator using an improved jet-resonance-enhanced multi-photon ionization 

system jet-REMPI. European Mass Spectrometry 4, 215–222 

U.S. Army, JP-8, The Single Fuel Forward, Armaments Command Research, Development, and 

Engineering Center, MI, 2001. http://www.mfp.usmc.mil/TeamApp/G4/, “JP-8 Single Fuel Info 

Compendium 

U.S. Environmental Protection Agency, SW-846 On-line, Test methods for evaluating solid 

wastes, Physical/Chemical methods, Office of Solid Waste, Method 0010 Modified Method 5 

Sampling Train, 1986a, at URL http://www.epa.gov/epaoswer/hazwaste/test/pdfs/0010.pdf, 

accessed on November 12, 2003. 

U.S. EPA Method 5 “Determination of Particulate Matter Emissions from Stationary Sources,” 

found in 40 CFR part 60, appendix A, 1986b. http://www.epa.gov/ttn/emc/promgate/m-05.pdf 

(accessed January 2009) 

U.S. Environmental Protection Agency, 1993. Emission factor documentation for AP-42 section 

3.4, large stationary diesel & all stationary dual fuel engines. 

http://www.epa.gov/ttn/chief/ap42/ch03/bgdocs/b03s04.pdf (accessed January 2009). 

U.S. Environmental Protection Agency, SW-846 On-line, Test methods for evaluating solid 

wastes, Physical/Chemical methods, Office of Solid Waste, Method 0040 Sampling of Principal 

Organic Constituents from Combustion Sources using TEDLAR Bags, 1996a, at URL 

http://www.epa.gov/epaoswer/hazwaste/test/pdfs/0040.pdf, (accessed January 2009). 

U.S. EPA Method 8270 in SW-846 Test Methods for Evaluating Solid Waste, Physical/Chemical 

Methods, Office of Solid Waste, 1996b. 

http://www.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/8270d.pdf (accessed January 

2009) 

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U.S. EPA Method 0011 in SW-846 Test methods for evaluating solid wastes, Physical/Chemical 

methods, Office of Solid Waste, 1996c. 

http://www.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/0011.pdf (accessed January 2009) 

U.S. EPA Method 8315a in SW-846 Test methods for evaluating solid wastes, Physical/Chemical 

methods, Office of Solid Waste, 1996d. 

http://www.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/8315a.pdf (accessed January 

2009) 

U.S. EPA M-23A, Test Method 23A, Sampling method for polychlorinated dibenzo-p dioxins 

and polychlorinated dibenzofuran emissions from stationary sources. EPA-SW 846 On-Line, 3rd 

ed., 1996d. Available at: 

http://www.epa.gov/epawaste/hazard/testmethods/sw846/pdfs/0023a.pdf. 

U.S. EPA Method TO-15 “Determination of Volatile Organic Compounds (VOCs) in Air 

collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass 

Spectrometry (GC/MS)”, 1999. http://www.epa.gov/ttn/amtic/files/ambient/airtox/to-15r.pdf 

(accessed January 2009) 

U.S. Environmental Protection Agency, 2000a. Performance specification 2 specifications and 

test procedures for SO2 and NOX continuous monitoring systems in stationary sources. 40 CFR 

Ch.1 Pt.60, App. B, Spec.2. http://www.epa.gov/ttn/emc/specs/prompspec2.html (accessed 

January 2009). 

U.S. EPA, 2000b, Method 10A: “Determination Of Carbon Monoxide Emissions In Certifying 

Continuous Emission Monitoring Systems At Petroleum Refineries,” 

http://www.epa.gov/ttn/emc/promgate/m-10a.pdf. 

U.S. Environmental Protection Agency, 2004. EPA original list hazardous pollutants 

http://www.epa.gov/ttn/atw/188polls.html (accessed March 2005). 

U.S. EPA, 2006, Method 3A, “Determination of Oxygen and Carbon Dioxide Concentrations in 

Emissions from Stationary Sources (Instrumental Analyzer Procedure),” 

http://www.epa.gov/ttn/emc/promgate/m-03a.pdf 

Velazquez, J.; Voloboueva, L. A.; Cool, T. A., Selective Detection of Dibenzodioxin, 

Dibenzofuran and Some Small Polycyclic Aromatics. Combustion Science Technology 134, 

139-163. 

Weickhardt, C.; Boesl, U., 1993. Time resolved trace analysis of exhaust gas by means of laser 

mass spectrometry. Ber. Bunsenges. Phys. Chem. 97, 1716-19. 

Zimmermann, R.; Boesl, U.; Weickhardt, C.; Lenoir, D.; Schramm, K.-W.; Kettrup, A.; Schlag, 

E.W., 1994. Isomer-selective ionization of chlorinated aromatics with lasers for analytical timeof-flight mass spectrometry: First results for polychlorinated dibenzo-p-dioxins (PCDD), 

biphenyls (PCB) and benzenes (PCBz). Chemosphere 29, 1877-88. 

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Zimmermann R., Heger H., Blumenstock M., Dorfner R., Schramm K.-W., Boesl U., Kettrup A., 

1999. On-line measurement of chlorobenzene in wast incineration fl ue gas as a surrogate for the 

emission of polychlorinated dibenzo-p-dioxins/Furans (I-TEQ) using mobile resonance laser 

ionization time-of-flight mass spectrometry. Rapid Communications Mass Spectrometry 13, 

307–314. 

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14. Appendix A: List of Scientific/Technical Publications 

14.1.1 Journal Articles 

•	 L. Oudejans, A. Touati, and B.K. Gullett, “Real-Time, On-Line Characterization of 

Diesel Generator Air Toxic Emissions by REMPI-TOFMS”, Anal Chem., 76, 2517-2524 

(2004) 

•	 Brian K. Gullett, Abderrahmane Touati, Lukas Oudejans, and Shawn P. Ryan, “Real-time 

emission characterization of organic air toxic pollutants during steady state and 

transient operation of a medium duty diesel engine”, Atmosph. Envir., 40, 4037–4047 

(2006) 

•	 Brian Gullett, Abderrahmane Touati, and Lukas Oudejans, “Use of REMPI–TOFMS for 

real-time measurement of trace aromatics during operation of aircraft ground 

equipment”, Atmosph. Envir., 42, 2117–2128 (2008) 

•	 	 Brian Gullett, Lukas Oudejans, Abderrahmane Touati, Shawn Ryan, and Dennis Tabor, 

“Verification results of jet resonance-enhanced multiphoton ionization as a real-time 

PCDD/F emission monitor”, J. Mater. Cycles Waste Manag., 10, (2008) 32–37 

•	 submitted to Environmental Science & Technology, entitled “Transient PAH, PM, CO, 

and CO2 Emission Responses from HMMWVs, the M1 Abrams tank, and the Bradley 

Infantry Fighting Vehicle” by Brian Gullett, Lukas Oudejans, and Abderrahmane Touati 

(2009). 

14.2 Oral and Poster Presentations 

Results obtained during this project were presented to (international) audiences at the following 

conferences: 

•	 	 Annual conferences: 

o	 	 Partners in Environmental Technology Technical Symposium & Workshop, 

Washington, DC, annual, 2000-2007 (Posters) 

o	 	International Karasek Conference, annual, 2001-2008 (oral and/or poster) 

•	 	 Individual conferences: 

o	 	 Seventh International Congress on Toxic Combustion By-Products, NIEHS, 

Research Triangle Park, NC (2001) (Oral) 

o	 	 26th Annual EPA-Air & Waste Management Association Information Exchange 

EPA, RTP (2001) (Oral) 

o	 	 22nd International Symposium on Halogenated Environmental Organic Pollutants 

and POPs (Dioxin 2002), Barcelona, Spain (2002) (Oral) 

o	 	 27th Annual EPA-Air & Waste Management Association Information Exchange 

EPA, RTP (2002) (Oral) 

o	 	Eighth International Congress on Toxic Combustion By-Products, NIEHS, at 

University of Arizona, Tucson, AZ (2003) (Poster) 

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o	 	Laser Applications to Chemical and Environmental Analysis (LACEA) conference, 

Annapolis (2004) (Poster) 

o	 	 3rd International Conference on Combustion, Incineration/Pyrolysis and Emission 

Control (3rd i-CIPEC), Hangzhou, China, (2004). (Oral) 

o	 	 Air and Waste Management Association (AWMA) Symposium on Air Quality 

Measurements and Technology, Durham, NC (2006) (Oral) 

o	 	 10th International Congress on Combustion By-Products and their Health Effects, 

Ischia, Italy (2007) (Oral) 

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