Measured Infrared Absorption and Extinction 

Cross Sections for a Variety of Chemically and 

Biologically Derived Aerosol Simulants 

by Kristan P. Gurton, Rachid Dahmani, 

David Ligon, and Burt Bronk 

ARL-TR-3253 June 2004 

Approved for public release; distribution unlimited. 
NOTICES 

Disclaimers 

The findings in this report are not to be construed as an official Department of the Army position unless 

so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of the 

use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Adelphi, MD 20783-1197 

ARL-TR-3253 June 2004 

Measured Infrared Absorption and Extinction 

Cross Sections for a Variety of Chemically and 

Biologically Derived Aerosol Simulants 

Kristan P. Gurton, Rachid Dahmani, David Ligon 

Computational and Information Sciences Directorate, ARL 

Burt Bronk 

Air Force Research Laboratory at ABCCOM 

Approved for public release; distribution unlimited. 
ii

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 

OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

June 2004 

2. REPORT TYPE 

Final 

3. DATES COVERED (From - To) 

September 2003 to January 2004 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

4. TITLE AND SUBTITLE 

Measured Infrared Absorption and Extinction Cross Sections for a Variety of 

Chemically and Biologically Derived Aerosol Simulants 

5c. PROGRAM ELEMENT NUMBER 

5d. PROJECT NUMBER 

3FEJ00 

5e. TASK NUMBER 

6. AUTHOR(S) 

Kristan P. Gurton, Rachid Dahmani, David Ligon, and Burt Bronk 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

U.S. Army Research Laboratory 

ATTN: AMSRD-ARL-CI-EE 

2800 Powder Mill Road 

Adelphi, MD 20783-1197

8. PERFORMING ORGANIZATION 

 REPORT NUMBER 

ARL-TR-3253 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) 

U.S. Army Research Laboratory 

2800 Powder Mill Road 

Adelphi, MD 20783-1197

11. SPONSOR/MONITOR'S REPORT 

 NUMBER(S) 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

Approved for public release, distribution unlimited. 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

In an effort to establish a more reliable set of optical cross sections for a variety of chemical and biological aerosol simulants, we have 

developed a flow-through photo-acoustic system capable of measuring the absolute, mass-normalized, extinction and absorption cross 

sections. By employing a flow-through design, we avoid issues associated with closed aerosol photo-acoustic systems and improve sensitivity. 

Although the results shown here were conducted over the tunable carbon dioxide laser waveband region (i.e., 9.20 to 10.80 μm), application to 

other wavelengths is easily achievable. Aerosols considered are categorized as biological, chemical, and inorganic in origin, i.e., bacillus 

subtilis endospores, dimethicone silicone oil (SF-96 grade 50), and Kaolin clay powder (alumina and silicate), respectively. Results compare 

well with previously measured spectral extinction using Fourier transform infrared spectroscopy. Comparison with Mie theory calculations 

based on previously published complex indices of refraction and measured size distributions is also presented. 

15. SUBJECT TERMS

Aerosol, photo-acoustic, absorption, infrared, extinction 

16. SECURITY CLASSIFICATION OF:

19a. NAME OF RESPONSIBLE PERSON

Kristan P. Gurton 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified 

c. THIS PAGE 

Unclassified 

17. LIMITATION

OF 

ABSTRACT 

Ul 

18. NUMBER 

OF PAGES 

23 

19b. TELEPHONE NUMBER (Include area code) 

(301) 394-2093 

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18
iii

Contents

List of Figures iv

Acknowledgment v

1. Introduction 1

2. Experiment 2

3. Results 7

4. Conclusion 10

5. References 11

Distribution 13
iv

List of Figures 

Figure 1. Schematic of flow-through photo-acoustic experiment used to measure in situ

extinction and absorption cross sections....................................................................................3 

Figure 2. Cross-sectional schematic of a top set of acoustic dampeners used to isolate the 

electret inner cavity....................................................................................................................5 

Figure 3. Measured size distributions for silicone oil SF-96, BG, and Kaolin clay aerosol...........6 

Figure 4. Typical calibration curve for the photo-acoustic spectrophone with isopropanol 

vapor ..........................................................................................................................................7 

Figure 5. Comparison of the measured and calculated extinction and absorption cross 

sections for silicone oil SF-96, grade 50. (The individual data points seen in the figure 

represent the photo-acoustic measured cross sections. The solid [red] line represents 

previously measured spectral extinction with FTIR aerosol spectroscopy. The solid 

[blue] and dashed (green) lines represent Mie theory calculations based on the size 

distributions seen in figure 3 and the previously published complex indices of Querry 

(12).)...........................................................................................................................................8 

Figure 6. Comparison of the extinction and absorption cross sections for aerosolized BG 

endospores. (The individual points seen in the figure represent the photo-acoustic 

measured cross sections. The solid [red] line represents previously measured spectral 

extinction with FTIR aerosol spectroscopy. The remaining dashed [green] and solid 

[blue] lines represent Mie theory calculations based on the size distributions seen in 

figure 3 and the previously published complex indices of Querry (12).) ..................................8 

Figure 7. Comparison of the extinction and absorption cross sections for aerosolized Kaolin 

clay powder. (The individual points seen in the figure represent the photo-acoustic 

measured cross sections. The solid [red] line represents spectral extinction previously 

measured with FTIR aerosol spectroscopy. The remaining dashed [green] and solid 

[blue] lines are the corresponding Mie theory calculations based on the size distributions 

seen in figure 3 and the previously published complex indices of Querry (12).)......................9 
v

Acknowledgment 

We would like to thank Dr. Paul Pellegrino and Dr. Nicholas Fell of the U.S. Army Research 

Laboratory for their continued supportand technical expertice. 
vi

INTENTIONALLY LEFT BLANK. 
1

1. Introduction 

Currently, there is great interest in developing both point and stand-off detection instrumentation 

capable of identifying the presence of harmful chemical and/or biological aerosols. Presently, 

the majority of sensors deployed in the field represent point detection schemes that are often 

based on a form of antibody tagging and/or chemical analysis that is conducted on collected 

samples. As a result, these methods often require periods on the order of several minutes for the 

chemical reaction to occur. Such time periods may prove critical in actual operation. 

A more desirable approach would be a detection method based on optical interactions with the 

agent. Such an approach would allow for real-time detection/identification. In addition, by 

considering various tunable laser systems, one can envision a detection scheme based on a light 

detection and ranging (LIDAR) approach in which the detection of a chemical or biological 

release can be accomplished at great distances. 

In order to design such systems, scientists and engineers will require a reliable, wellcharacterized database of optical constants for a variety of chemically and biologically derived 

aerosols, e.g., extinction, absorption, and scattering cross sections. Attempts to calculate these 

parameters have proved problematic for several reasons. 

First, predictive calculations require that the real and imaginary indices of refraction for the 

aerosol be known with reasonable certainty. Unfortunately, such constants are woefully lacking. 

This is particularly true for biologically derived materials. When they do exist, issues of 

accuracy and applicability often arise (1). 

Second, calculations for a polydispersed aerosol usually assume a certain particle size 

distribution when one is computing optical cross sections. Minor variation in either the breadth 

or form of these distributions can result in great uncertainty in the calculated cross sections. 

Third, many of the computational techniques used to predict the electromagnetic interaction with 

small particles assume that the aerosol is of a particular simple shape, e.g., a perfect sphere. For 

most biologically derived agents, this is rarely the case. For example, assuming a complex 

particle to be an effective sphere becomes less valid as the dimensions of the particle approach 

the optical wavelength (2). Since many airborne bio-particles have sizes in the 0.8- to 12-μm 

range, optical techniques that rely on IR wavelengths operate where effective sphere calculations 

are prone to error (3). 

As a result, we present a flow-through photo-acoustic technique (first proposed by Bruce et al.), 

which is designed to directly measure in situ the absolute mass normalized extinction, 

absorption, and total scatter cross sections for a variety of chemical, biological, and background 

aerosols (4,5,6). Previous attempts to apply photo-acoustic spectroscopy to aerosols used a 
2

closed sample volume and as a result, were subject to nonuniform aerosol concentrations because 

of particle settling (7). In addition, such techniques were limited in sensitivity because of 

residual absorption of the transmission windows that resulted in signals that were comparable or 

greater than the absorption of the aerosol in question. In order to avoid these problems, Bruce 

designed an acoustically isolated flow-through cell that allowed for in situ analysis of moderate 

and weakly absorbing aerosols. With this design, high system sensitivities on the order of 

0.001 km–1 are routinely achieved. 

The materials considered for this study include dimethicone silicone oil (SF-96 grade 50), 

bacillus subtilis endospores (BG), and Kaolin clay, which represent chemical, biological, and 

natural background aerosols, respectively. For comparison, we present Mie theory calculation 

based on measured size distributions and previously published complex indices of refraction. 

2. Experiment 

Consider a sample volume containing an optically absorbing aerosol. If a laser is passed through 

this volume, a portion of the light will be absorbed by the aerosol particles, resulting in particle 

heating (here we assume that the absorption attributable the surrounding gas is negligible 

compared to the resultant particle absorption). This particle heating will subsequently result in a 

pressure rise within the sample volume. If the laser is now modulated at some convenient 

acoustic frequency, say 1 kHz, a resultant pressure wave will result at that same 1-kHz 

modulation frequency. It is well established that the power of the resultant acoustic signal is 

directly proportional to the optical absorption cross section of the absorbing particles (8). The 

constant of proportionality that relates the actual absorption cross section to the acoustic signal is 

determined via an appropriate calibration gas. One of the more intriguing aspects of aerosol 

photo-acoustics is that, in principle, it only depends on the fraction of light absorbed by the 

media and thus requires no a priori knowledge of aerosol particle shape, size, or complex 

refractive index. By designing a system in which the probe laser also serves as a coincident 

short-pass transmissometer, we can obtain an independent determination of the optical extinction 

simultaneously with the absorption measurement. As a result, accurate values of the singlescatter albedo are also determined when we find the difference between the total extinction and 

absorption. 

The basic flow-through photo-acoustic measurement is shown in figure 1. As seen in the figure, 

the system consists of a small 0.6-m3

 aerosol chamber which is used to confine the dispersed 

aerosol. The chamber is flushed with dry air before each run in order to minimize any residual 

absorption attributable to water vapor. A small fan placed in the corner of the chamber is used to 

gently stir the aerosol to ensure that a uniform particle concentration is maintained. 
3

Figure 1. Schematic of flow-through photo-acoustic experiment used to measure in situ extinction and 

absorption cross sections. 

Situated at the bottom of the chamber is a cylindrical flow-through spectrophone where both the 

extinction and absorption measurements take place. Embedded in the wall of the spectrophone is 

a highly sensitive electret microphone that is positioned in the center of a hollow cylindrical 

column in which the aerosol flows. A small (6 mm in diameter) electret condenser microphone 

consists of a high voltage internal membrane, a metal electrode, and a field effect transistor 

(FET). The microphone is externally powered through a simple RC circuit by a DC power 

supply. The diaphragm of the electret is mounted flush with the flow column in order to 

properly match the longitudinal acoustic mode generated within the cylindrical region. The inner 

cavity where the electret is mounted represents a resonant subsystem (basically, a double openended resonator) which is intentionally designed to be nonresonant, i.e., low Q values on the 

order of 20 to 50 for continuous wave (cw) sources, to avoid fluctuations in the spectrophone 

responsivity because of changing aerosol concentrations. 

The dispersed aerosol is gently drawn from the chamber through the column that runs axially 

through the spectrophone. A modulated cw carbon dioxide (CO2) laser, tuned to a specific IR 

wavelength and operated at approximately 100 mW, is directed through a barium fluoride (BaF2) 

window, situated at the top of the chamber, and down through the center of the spectrophone. 

IR detector

Dosimetric 

measurement 

Vacuum 

pump 

Flow 

meter 

chopper 

laser 

Aerosol 

chamber 

spectrophone 

Aerosol 

flow out 

Electret 

microphone

Acoustic 

dampeners 

Aerosol filter 

holder/substrate 

Inner cavity 

IR window with 

fresh air flush 
4

The beam exits through a windowless port at the bottom of the spectrophone. We measure 

attenuation of the laser caused by the aerosol by placing an IR calorimetric power meter at the 

outlet of the spectrophone. This arrangement effectively creates a short-path transmissometer 

which extends from the top of the aerosol chamber to the bottom of the spectrophone. We 

established a well-defined aerosol path length caused by gently drawing the aerosol out of the 

spectrophone at a point just above the exit port. The path length used here was 1.22 m. 

The modulated beam propagates through the center of spectrophone and a portion of its optical 

energy is absorbed by the aerosol. A rapid heating and subsequent cooling of the aerosol/air 

mixture occurs. This in turn produces an acoustic signal at the exact same frequency of the 

modulated laser beam. The acoustic wave signal is detected and amplified by the electret 

microphone via a “lock-in” amplifier tuned to the modulation frequency of the laser. 

Shown in figure 1 is the aerosol dosimetry portion of the measurement which is used to 

determine the mass concentration at any point in time. We periodically take mass samples 

during the photo-acoustic measurement by drawing known volumes of the aerosol/air mixture 

through a filter substrate that is inserted into the chamber. The resultant mass is collected on preweighed polycarbonate filters, nominal pore size 0.20 μm, and is weighed with a high precision 

analytical balance. Resultant aerosol mass densities (g/m3

) are then used to convert pathintegrated extinction/absorption coefficients (1/m) into mass normalized cross sections, (i.e., 

meters2/gram). 

Ambient acoustic noise resulting from movements within the laboratory is suppressed by a series 

of dampeners above and below the electret. The principle behind these acoustic dampeners is 

fairly straightforward (see figure 2). Shown in the figure is a cross-sectional schematic of a top 

set of three cylindrical dampeners. These dampeners fit snuggly together in the region 

surrounding the inner electret cavity and dissipate the acoustic noise that enters the spectrophone 

from either opening. 

Both aerosol and acoustic “noise” from the laboratory flow freely through the center cylindrical 

region of the spectrophone. Acoustic noise enters the spectrophone in the form of pressure 

fluctuations that are initially distributed over the area of the inlet nozzle shown as point A in 

figure 2. For purposes of our example, let us define the area at point A to be 1.0 cm2

. As the 

pressure wave propagates down toward the inner electret cavity, it encounters several small 

spaces at point B in the figure. At these points, the pressure wave is effectively redistributed 

over a much larger area, say 30.0 cm2, resulting in a reduction of the net pressure. The 

attenuation of the noise signal is repeated at each slit B until the desired noise suppression is 

achieved. We have found that a series of three or four dampeners placed above and below the 

electret cavity is sufficient to suppress typical noise levels encountered in the laboratory by 

approximately 20 dB at 1 kHz. Additionally, we isolate by machining the spectrophone 

enclosure from very dense materials, e.g., stainless steel or high density polyurethane. 
5

Figure 2. Cross-sectional schematic of a top 

set of acoustic dampeners used to 

isolate the electret inner cavity. 

Simulants are dispersed in one of two ways. For small particulates such as powders, the aerosol 

is injected into the chamber via a dispersion nozzle and compressed dry air. The dispersion 

nozzle has a counter-rotating spiral array of stainless steel brushes that effectively separates the 

particles during dispersion. 

If the simulant is a liquid, a pharmaceutical nebulizer is used. Approximately 20 psi of dry air 

are used to pump the nebulizer during dispersion, which produces a distribution, with a modal 

diameter in the 4- to 6-μm range. 

B

A

Aerosol

Flow in

Aerosol flow into the 

electret inner cavity 
6

Particle size distributions are measured in situ with an aerodynamic particle sizer (APS) (model 

3321, manufactured by TSI, Inc.). Because the APS uses a “time-of-flight” method to predict an 

aerodynamic diameter, accurate values for the “bulk” density of the aerosol particle are required. 

Bulk densities used for BG, SF-96, and Kaolin were 1.45, 0.97, and 2.64 g/cm3

, respectively. 

The measured size distributions for the three simulants considered are shown in figure 3. 

Figure 3. Measured size distributions for silicone oil SF-96, BG, and Kaolin clay aerosol. 

We calibrate the system before and after each run by inserting an appropriate absorbing gas into 

the spectrophone cell. For CO2 laser wavelengths, isopropyl alcohol or methanol vapor is used 

and provides adequate absorption and extinction of the IR laser over the tunable range of 9.2 to 

10.8 μm. As the vapor is drawn through the system, a portion of the laser energy is absorbed, 

resulting in an acoustic signal that is detected by the spectrophone. This absorbed energy is seen 

as a reduction in the overall laser power as measured by the calorimetric meter and is converted 

to an absolute extinction coefficient via the Beer’s law relation. Because the attenuating media is 

a gas, no scattering is present (we have assumed that attenuation by molecular scatting is 

negligible). In this situation, the path-integrated total extinction (1/m) of the CO2 laser is equal

to the measured absorption or, more precisely, to the acoustic response of the spectrophone. A 

typical calibration based on isopropanol vapor is shown in figure 4. 

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

0.1 1 10 100

Aerodynamic Diameter (um) 

Particle

 Count 

(au) 

SF-96

Bacillus subtilis (new)

Kaolin
7

Figure 4. Typical calibration curve for the photo-acoustic spectrophone with isopropanol vapor. 

3. Results 

Figures 5 through 7 show the mass normalized extinction and absorption for aerosolized SF-96 

oil, BG, and Kaolin clay, respectively. 

Each of the three graphs shows a comparison between two separate and independent 

measurements, i.e., the spectral extinction measured with photo-acoustics or a previous in situ

FTIR measurement conducted by the authors (9). Identical methods for dissemination were 

applied in both cases in an attempt to generate similar size distributions. In addition to the 

comparison between the two spectroscopic methods, measured cross sections are compared with 

a series of Mie theory calculations based on previously published complex indices of refraction 

and the actual size distributions shown in figure 3 (10,11,12). 

Because great effort was taken to duplicate conditions between the photo-acoustic and FTIR 

studies, we would expect the spectral extinction to compare well between the photo-acoustic (red 

data points) and the FTIR results (red solid line). As one can see in figures 5 through 7, 

agreement between the two independent measurements appears quite good. However, 

comparison between the measured quantities and the Mie calculated values does not track quite 

as well. One possible reason for the apparent disagreement may lie in the choice of refractive 

indices used in our calculations. 

1

10

100

1000

10000

012345678

Electret Signal (mV)

Absorption 

(1/km)
8

0.001

0.01

0.1

1

9 10 11

wavelength (um)

mass

normalized

coefficient

(m2

/gram)

Extinction (FTIR measured) 

Extinction (Mie theory)

Absorption (Mie theory)

Ext (photoacoustic meas.)

Abs (photoacoustic meas.)

Figure 5. Comparison of the measured and calculated extinction and absorption cross 

sections for silicone oil SF-96, grade 50. (The individual data points seen in the 

figure represent the photo-acoustic measured cross sections. The solid [red] line 

represents previously measured spectral extinction with FTIR aerosol spectroscopy. 

The solid [blue] and dashed [green] lines represent Mie theory calculations based on 

the size distributions seen in figure 3 and the previously published complex indices 

of Querry (12).) 

0.001

0.01

0.1

1

9 10 11

wavelength (um)

mass 

normalized 

coeffcient 

(m2

/gr) Absorption (Mie theory)

Extinction (Mie theory)

Extinction (FTIR measured)

Ext (photoacoustic meas.)

Abs (photoacoustic meas.)

Figure 6. Comparison of the extinction and absorption cross sections for aerosolized BG 

endospores. (The individual points seen in the figure represent the photo-acoustic 

measured cross sections. The solid [red] line represents previously measured spectral 

extinction with FTIR aerosol spectroscopy. The remaining dashed [green] and 

solid [blue] lines represent Mie theory calculations based on the size distributions 

seen in figure 3 and the previously published complex indices of Querry (12).) 
9

0.001

0.01

0.1

1

9 10 11

wavelength (um)

mass 

normalized

coefficient

(m2

/gram)

Extinction (FTIR measured)

Extinction (Mie theory)

Absorption (Mie theory)

Ext (photoacoustic meas.)

Abs (photoacoustic meas.)

Figure 7. Comparison of the extinction and absorption cross sections for aerosolized Kaolin 

clay powder. (The individual points seen in the figure represent the photo-acoustic 

measured cross sections. The solid [red] line represents spectral extinction previously 

measured with FTIR aerosol spectroscopy. The remaining dashed [green] and solid 

[blue] lines are the corresponding Mie theory calculations based on the size distributions 

seen in figure 3 and the previously published complex indices of Querry (12).) 

Often, researchers must rely on optical constants derived from much earlier work when they are 

calculating certain coefficients. In cases when there is a high degree of standardization for the 

material in question, the optical constants determined from a particular sample most probably 

represent the material as a whole, e.g., commercially manufactured chemicals or powders. 

However, for substances that are created by a natural process, samples of a particular material 

may vary greatly. 

For example, the best overall agreement appears to be with the chemical simulant SF-96. The 

reason for this originates in the standard form in which the material is manufactured, i.e., 

produced by one vendor with a high degree of quality control. As a result, we believe the SF-96 

indices measured by Querry are the most accurate of the three simulants considered. 

In addition to issues of standardization between samples, great uncertainties can arise in 

reflective/transmissive techniques used to determine complex indices of refraction when 

conducted on powdered bulk materials, i.e., BG and Kaolin (13). Such methods are more 

accurate when conducted on liquids since they avoid problems with multiple scattering often 

seen in bulk sample “pellets”. Figures 6 and 7 highlight the magnitude of the uncertainty one 

might expect when computing certain cross sections based on indices of refraction derived from 

previous studies. 
10

Figure 6 shows the measured and calculated extinction and absorption for aerosolized BG 

endospores. Seen in the figure is the noticeable divergence that takes place between the 

measured absorption (green data points) and the calculated values based on Mie theory. We 

believe the primary reason for the disagreement stems from the fact that our endospore samples 

underwent a certain preparation in order to facilitate efficient dispersion and may not represent 

the spectroscopic grade bacillus subtilis used by Querry. Ion chromatography performed on both 

washed and unwashed endospore suspensions show small quantities of SO4

–2 with lesser 

amounts of PO4

–3, F–

, and Cl– ions, which have been attributed to small quantities of either a 

surfactant or residual growth media (14). Figure 7 shows a similar comparison for a Kaolin clay 

aerosol. Since Kaolin is mined throughout the globe and prepared by many different vendors, it 

was uncertain how “standard” our samples were. Again, we had to rely on previously measured 

indices of refraction. As one can see in figure 7, the agreement is reasonable, considering the 

number of unknown variables involved among the naturally occurring substances such as BG 

and/or Kaolin. 

4. Conclusion 

We have successfully developed an in situ flow-through photo-acoustic technique that is capable 

of directly measuring the absolute mass normalized extinction and absorption for a variety of 

biologically and chemically based aerosols. The flow-through design avoids problems that have 

plagued previous attempts at applying photo-acoustics to an aerosol medium. Although the 

results presented here were conducted at selected CO2 laser wavelengths, any convenient laser 

source capable of tens of milliwatts of power would suffice. Photo-acoustic results compare well 

with prior FTIR measured spectral extinction. 

Finally, for comparison we have provided several Mie theory calculations that used the best 

available values for the complex indices of refraction and measured size distributions. 

Comparison of measured and Mie theory computed cross sections highlights the typical 

uncertainties one might expect when conducting similar predictive calculations. 
11

5. References 

1. Wieliczka, D.; Querry, M. Four Techniques to measure complex refractive indices of liquids 

and solids at carbon dioxide laser wavelengths in the infrared spectral region; CRDEC-CR062; U.S. Army Chemical Research, Development & Engineering Center, Jan. 1990. 

2. Bohren, C.; Huffman, D. Absorption and Scattering of Light by Small Particles, WileyInterscience Press 1983, New York, NY. 

3. Wick, C.; Edmonds, R.; Blew, J. Rapid detection and identification of background levels of 

airborne biological particles; ERDEC-TR-155; Edgewood Research, Development & 

Engineering Center, Jan. 1995. 

4. Bruce, C.W.; Pinnick, R.G. In-situ measurements of aerosol absorption with a resonate cw 

laser spectrophone. Appl. Opt. 1977, 16 (7), 1762–1765. 

5. Bruce, C.W.; Richardson, N.M. Propagation at 10 μm through smoke produced by 

atmospheric combustion of diesel fuel. Appl. Opt. 1983, 22 (7), 1051–1056. 

6. Bruce, C.W.; Stromberg, T.F.; Gurton, K.P. Trans-Spectral Absorption and Scattering of 

Electromagnetic Radiation by Diesel Soot. Appl. Opt. 1991, 30 (12), 1537–1546. 

7. Roessler, D.M.; Faxvog, F.R. Optoacoustic measurement of optical absorption in acetylene 

smoke. J. Opt. Soc. Am. 1979, 69 (12), 1699–1704. 

8. Rosencwag, A. Photoacoustics and Photoacoustic Spectroscopy, Krieger Pub., New York 

(1990). 

9. A detailed description of our FTIR measurements conducted on a variety of chemical and 

biological aerosols are at the time of this writing being considered for future publication in 

Appl. Opt. 

10. Gurton, Kristan, P.; Ligon, D.; Kvavilashvili, R.; Kvavilashvili, Measured infrared spectral 

extinction for aerosolized Bacillus subtilis var. niger endospores from 3 to 13um. Appl. Opt.

2001, 40 (25), 4443–4448. 

11. Gurton, Kristan P.; Ligon, David; Dahmani, Rachid. In situ measurement of the infrared 

spectral extinction for various chemical, biological, and background aerosols; ARL-TR3071; U.S. Army Research Laboratory: Adelphi, MD, Sept. 2003. 

12. Querry, Marvin R. Optical constants of minerals and other materials from the millimeter to 

the ultraviolet; CRDEC-CR88009; Chemical Research, Development and Engineering 

Center, November 1987. 
12

13. Wieliczka; Querry, M. Four techniques to measure complex refractive indices of liquid and 

solids at carbon dioxide laser wavelengths in the infrared spectral region; CRDEC-CR-062; 

Chemical Research, Development & Engineering Center, Jan. 1990. 

14. Pellegrino, P.M.; Fell, N.F., Bacterial endospore detection using terbium dipicolinate 

photoluminescence in the presence of chemical and biological materials. Anal. Chem., 1998, 

70, 1755–1760. 
13

Distribution

ADMNSTR 

DEFNS TECHL INFO CTR 

ATTN DTIC-OCP (ELECTRONIC COPY) 

8725 JOHN J KINGMAN RD STE 0944 

FT BELVOIR VA 22060-6218 

DARPA 

ATTN IXO S WELBY 

3701 N FAIRFAX DR 

ARLINGTON VA 22203-1714 

OFC OF THE SECY OF DEFNS 

ATTN ODDRE (R&AT) 

THE PENTAGON 

WASHINGTON DC 20301-3080 

US ARMY TRADOC 

BATTLE LAB INTEGRATION & TECHL DIRCTRT 

ATTN ATCD-B 

10 WHISTLER LANE 

FT MONROE VA 23651-5850 

DIR FOR MANPRINT OFC OF THE 

DEPUTY CHIEF OF STAFF FOR PRSNNL 

ATTN J HILLER 

THE PENTAGON RM 2C733 

WASHINGTON DC 20301-0300 

EDGEWOOD CHEMICAL BIOLOGICAL CTR 

ATTN AMSSB-RRT-DP A C SAMUELS 

ATTN AMSSB-RRT-DP R VANDERBEEK 

5183 BLACKHAWK RD BLDG E-5554 

ABERDEEN PROVING GROUND MD 21010-5424 

SMC/GPA 

2420 VELA WAY STE 1866 

EL SEGUNDO CA 90245-4659 

US ARMY ARDEC 

ATTN AMSTA-AR-TD 

BLDG 1 

PICATINNY ARSENAL NJ 07806-5000 

US ARMY AVIATION & MIS LAB 

ATTN AMSAM-RD-MG-IP H F ANDERSON 

REDSTONE ARSENAL AL 35809 

US ARMY AVN & MIS CMND 

ATTN AMSMI-RD W C MCCORKLE 

REDSTONE ARSENAL AL 35898-5240 

US ARMY CECOM RDEC NVESD 

ATTN J HOWE 

10221 BURBECH RD STE 430 

FT BELVOIR VA 22060-5806 

US ARMY ECBC 

ATTN AMSSB-RRT BOTTIGER 

ATTN AMSSB-RRT E STUEBING 

5183 BLACKHAWK RD BLDG E-5951 

ABERDEEN PROVING GROUND MD 21010-5424 

US ARMY INFO SYS ENGRG CMND 

ATTN AMSEL-IE-TD F JENIA 

FT HUACHUCA AZ 85613-5300 

US ARMY NATICK RDEC 

ACTING TECHL DIR 

ATTN SBCN-TP P BRANDLER 

KANSAS STREET BLDG78 

NATICK MA 01760-5056 

US ARMY SIMULATION TRAIN & 

INSTRMNTN CMND 

ATTN AMSTI-CG M MACEDONIA 

12350 RESEARCH PARKWAY 

ORLANDO FL 32826-3726 

USAF ARMSTRONG LAB EDGEWOOD RDEC 

ATTN AMSSB-RRT B BRONK 

BLDG E-5951 

ABERDEEN PROVING GROUND MD 21010 

NAV RSRCH LAB 

ATTN J D EVERSOLE 

4555 OVERLOOK AVE 

WASHINGTON DC 20375 

HICKS & ASSOC INC 

ATTN G SINGLEY III 

1710 GOODRICH DR STE 1300 

MCLEAN VA 22102 

DIRECTOR 

US ARMY RSRCH LAB 

ATTN AMSRD-ARL-RO-D JCI CHANG 

PO BOX 12211 

RESEARCH TRIANGLE PARK NC 27709 
14

US ARMY RSRCH LAB 

ATTN AMSRD-ARL-CI-EE K GURTON 

(10 COPIES) 

ATTN AMSRD-ARL-CI-IS MAIL & RECORDS 

MGMT 

ATTN AMSRD-ARL-CI-OK-T TECHL PUB 

(2 COPIES) 

ATTN AMSRD-ARL-CI-OK-TL TECHL LIB 

(2 COPIES) 

US ARMY RSRCH LAB (cont’d) 

ATTN AMSRD-ARL-D J M MILLER 

ATTN AMSRD-ARL-SE-EE A GOLDBERG 

ATTN AMSRD-ARL-SE-EM D BEEKMAN 

ATTN AMSRL-SE-PO P PELLEGRINO 

ADELPHI MD 20783-1197