photoacoustic instrument: an ear for black carbon by pat arnott collaborators: hans moosmüller,...
TRANSCRIPT
PhotoAcoustic Instrument: An Ear for Black Carbon
By Pat Arnott
Collaborators: Hans Moosmüller, Fred Rogers, John Walker, Rick Purcell, Dan Wermers, Rich Raspet, Willie Slaton, James Mehl, Adel Sarofim, Kerry Kelly, Dave Wagner (Univ. Utah.)
Funding over the Years: EPA, NPS, ONR, NSF, DOE, DOD-SERDP, DRI
http://photoacoustic.dri.edu
My other great passion -- Cirrus Clouds
FIRE!!
Soot: 10 - 50 nm monomers chained together to form larger
aggregates. ‘Onion Shell’ structure of the monomers.
IMAGE CREDIT:http://7starm.asu.edu/Buseck2000%20/figure_10.htm
TEM images of soot.
A, B. Chain-like soot aggregates. (A--Phoenix, after Katrinak et al., 1993; B--Sagres, Portugal, ACE-2).
C. High-resolution TEM image of the arrowed soot aggregate showing the onion-like structure of soot spheres. (Southern Ocean, ACE-1; after Pósfai et al, 1999).
Atmospheric Aerosol Applications and Research•Radiation transfer, light scattering and absorption, emission.
•Climate simulation
•Visibility at the National Parks
•Military applications - sensor performance and plume visibility
•Cloud albedo (Twomey effect, more aerosol, more competition for water vapor, smaller droplets, ammonium sulfate aerosol)
•Cloud lifetime (Black carbon causes local heating from sunlight absorption, cloud dissipation).
•Health effects
•PM 2.5 levels are legislated
•Likely that PM will be further differentiated into E.C., O.C., etc.
•Source Level Combustion
•Engine performance
•Power plants
OUTLINE
• Atmospheric and combustion aerosol.• Aerosol optics and instrumentation.• Calibration of the photoacoustic instrument for light
absorption:• Nitrogen Dioxide gas• Kerosene-flame soot
• Photoacoustic IOP at the DOE-SGP, March 2000.• Light absorption as a function of RH• Instrument evaluation
• Conclusions and Questions
ATMOSPHERIC AEROSOL
•http://www.cmdl.noaa.gov/aerosol/
Visibility: Good for tourism, bad for military when engine plumes become visible.
•IMPROVE: (Interagency Monitoring of PROtected Visual Environments)
•Aerosols are a dominant influence on man-made visibility impairment.
•Aerosol optical properties are very important and are measured.
National Park Service, Forest Service, Fish and Wildlife Service, Bureau of Land Management, and Environmental Protection Agency
Subset of aerosols: Those that strongly absorb visible light.
• Typically formed from combustion of fuels in engines and from burning things.
• Appreciable elemental carbon component.
Source Elemental Carbon (g) / Fuel (kg)
Vehicles, diesel engine 2
Fireplace, softwood 1.3
Jet engine 1
Fireplace, hardwood 0.39
Vehicles, gasoline engines 0.02
Solid fossil fuel (briquettes, lignite) 0.001
Natural gas 0.0003
Approximate emission factors for different sources of elemental (black) carbon (from Ogren and Charlson, 1984).
Aerosol Optical Properties: Absorbing particles.For small optical depths,
and D < 0.1 µm:
I(L)/I(0) = e(- L),
(1/m) ≈ S.O.C (m2/g) x (g/m3),
L = path length,
= aerosol concentration by mass.
•Absorption dominates for D < 0.1 µm (Rayleigh scattering).
•Aside: For non-absorbing aerosols, Extinction=Scattering. Note the strong dependence of the scattering coefficient on diameter!
More Realistic Optical Model for Absorption by SootSoot AgglomerateGraphitic crystalites welded together at junctionsfrom high temperature generation during incomplete combustion of diesel fuel.
Np = # of primary spherules (e.g. 10 - 400)Dp = Diameter of spherules (e.g. 30 nm ± 6 nm)
p = (=1.85-2.26 / )Spherule Density g cc
€
ΛabsAreamass
⎛ ⎝
⎞ ⎠ =
36πλρp
nk
n2 −k2 +2( )2+4n2k2
COMPLEXINDEXOF REFRACTIONm=n+ik
ValidforDp <<λ
Wavelengthof light=λ
See: Lee, K O., R. Cole, R. Sekar, M. Choi, J. Zhu, J. Kang, and C. Bae, 2001. Detailed characterization of morphology and dimensions of diesel particulates
via thermophoretic sampling. SAE Paper 2001-01-3572.
Rough Estimate of Aerosol Radiative Forcing: Clear Sky - Aerosol Loaded Sky, top of atmos.
Aerosol Single scattering albedo = Scattering / (Scattering + Absorption)
Humidity Influence on Light Scattering
•http://www.cmdl.noaa.gov/aerosol/
Nephelometers Measure Light Scattering
•These instruments operate by illuminating a fixed sample volume from the side, and observing the amount of light that is scattered by particles and gas molecules in the direction of a photomultiplier tubes. The instruments integrate over scattering angles of 7-170°
Simplified description of filter methods for light absorption. PSAP and AETHALOMETER
• Aerosol are deposited on the light-diffusing filter, multiple scattering substrate.
• Light absorbing aerosol reduce the light power at the photodetector.
• Light scattering aerosol don't reduce power in principle.• Calibration and effects of aerosol loading (blocking)??• We have noted Giant RH induced artifacts (PSAP).
Light(550 nm)
Air Inletto pumpPhoto-detector
Light diffusing
aerosol filter
PSAP: Particle Soot Absorption PhotometerA filter-based measure of light absorption.
•Reference filter on the right. Aerosol-loaded filter on the left. Compare light transmission through these filters as a measure of light absorption.
Airborne Data Example from the PSAP
Field data showing the high variability of aerosol light-absorption (Mm-1) with altitude, measured by NOAA/CMDL scientists aboard the C-130 research aircraft during the INDOEX field campaign. Profile was measured over the Indian Ocean at approximately 6 degrees north latitude on February 16, 2000. (Courtesy of P. Sheridan and J. Ogren, NOAA/CMDL.)
http://www.ogp.noaa.gov/aboutogp/spotlight/aerosols/aero9_00.htm
Data likely potential light absorption, relevant to a parcel at sea level and 273 K.
Aethalometer Data: Jumps on Filter Position Change: Data from Mark Green, DAS.
Aethalometer Data: Continued. Data from Mark Green, DAS, DRI.
Wavelength -> 370 470 520 590 660 880 950
Average before 620 496 469 438 443 421 418
Average after 821 577 522 519 482 456 454
Average increase 201 81 53 80 38 35 36
Average % increase
32.4 16.4 11.2 18.3 8.7 8.2 8.6
Aethalometer B.C. increase when new filter spot is used:
Hypothesis: The multiple scattering filter substrate evolves in time as aerosol are deposited on it. The ‘amount’ of multiple scattering decreases as aerosol are added, causing the instrument calibration to actually vary with time.
Solution: Don’t use filters!
Photoacoustic Instruments For Light Absorption Measurements
• Basic principles:• Laser light is power modulated by the chopper. • Light absorbing aerosols convert light to heat - a sound wave is
produced. • Microphone signal is a measure of the light absorption.• Light scattering aerosols don't generate heat.
Light(532 nm)
Air Inletto pumpPhoto-detectorMicrophoneChopper
FASCODE Babs for a horizontal path at 1 atm pressure, 1976 US Standard Atmos. gas composition. (Aid choice of laser wavelength).
Photoacoustic Instrument: What it looks like.
National Instrument’s Labview is used for data acquisition and signal processing.
Latest PA, internal workings...
Sketch of the Photoacoustic Instrument
Sample InletSample OutletWindowWindowPiezoelectric Transducer
Microphone and Surrounds
RESONATOR SECTION
COUPLINGSECTIONCOUPLINGSECTION
1047 nm LASERPhotodetector
Photoacoustic Instrument Details: Equation to Obtain Light Absorption Coefficient.
Light Absorption in Dimensions of Inverse Distance = Babs
B
abs
=
Pm
P
L
Ares
γ − 1
π2
f
0
Q
,
f0=Resonan ceFrequency.Q=ResonatorQualityFactor.Pm=Pea k AcousticPressurea t f0.γ=Ratio of Isobarican dIsochoricSpecificHeatsF orAir.PL=Pea k Laser Bea mPower at f0.Q=resonatorqual ity facto .rAres=Resonato r Cro ss Sectional Area.
Instrument Calibration Using NO2 and 532 nm Laser
pumpexhaustNO2
rotometer NO2 in N2
gas cylinder
volumephotoacousticinstrument
airrotometer
High resolution spectrum of NO2 and the photoacoustic measurement
130000
140000
150000
160000
170000
180000
190000
531.95 531.975 532 532.025 532.05Wavelength (nm)
846.1 mb, T = 21.5 C509 ppm ± 25 ppm NO
2 in N
2
•Uncertainty in laser wavelength and spectrum, and gas concentration.
Simultaneously measure extinction and absorption
micpiezo disk L power
modulatedlaser beam
p.a.p.a.p.a.p.n.p.n. x pd 1 D = L + 2h hhpd 2bs
•This calibration method reduces the uncertainty in laser wavelength and spectrum.
Extinction ≈ Absorption for large dose of NO2
150000
152000
154000
156000
158000
160000
1 3 5 7 9 11 13 15 17 19Measurement number
846 mb, T = 21.5 C509 ppm ± 25 ppm NO
2 in N
2
•Photacoustic measurement is the dashed line. Extinction and its uncertainty range are the solid lines.
Kerosene Soot Optical Properties and Calibration
1047 nm photoacoustic
instrument
532 nm photoacoustic
instrument
pumpkerosenelamp
inletfiltervalve
Response with a particle filter before inlets
-20
0
20
40
60
80
100
120
140
22:00 22:10 22:20Time (hh:mm)
1047 nm
532 nm
NO2 from Kerosene Lamp
lampadjusted
•Kerosene flame produces NO2. The 532 nm instrument responds to NO2, but the 1047 nm instrument does not. Concentration ≈ 3 ppb NO2 per 1/Mm.
Kerosene flame soot optical properties
-50000
0
50000
100000
150000
200000
250000
0
0.1
0.2
0.3
0.4
0.5
-25000
0
25000
50000
75000
100000
125000
0
0.1
0.2
0.3
0.4
0.5
Time (mm:ss)
Bext
Bext
Babs
Babs
ωo
ωo
)B
1047nm
)A
532nm
•Key Points:
•Babs(532 nm) ≈ 2 Babs(1047 nm), as expected for soot, Babs( ) 1/ .
•Single scatter albedo is less at 1047 nm than at 532 nm. Scattering is less at 1047 nm, proportionally less so than absorption.
•The single scatter albedo at 532 nm is similar to published values for similar fuel burns.
•Paper on calibration has been published (Rev. Sci. Instrum.)
Photoacoustic Data at 532 and 1047 nm
Message: Babs correlates well with elemental carbon mass. Theoretical dependence of Babs on wavelength predicts about a factor of 2 difference
in the absorption efficiency.
QuickTime™ and aGraphics decompressorare needed to see this picture.
0
0.5
1
1.5
2
0 0.1 0.2 0.3
Elemental Carbon (mg/m3)
Hill AFB 99, SERDP 99
Babs (1/km) = 5.5 E.C. (mg/m3) - 0.063
R2 = 0.93
QuickTime™ and aGraphics decompressorare needed to see this picture.
0
5
10
15
20
0 0.5 1 1.5 2
Elemental Carbon (mg/m3)
DOE CARAT 99FTP 10 - 11 (1 Ford 1 Dodge)
Babs (1/km) = 10.6 E.C. (mg/m3) + 0.37
R2 = 0.93
Photoacoustic Lower Limit:
0
100
200
300
400
500
600
BC (ng/m3)Zero Air
2 min. ave. time, 20 min. rezero
PARTICLE FREE AIR: 2 minutes average time, 200 mW 1047 nm laser.
Background usually below 30 ng/m3.
PHOTOACOUSTIC INSTRUMENT DYNAMIC RANGE: Ratio of lowest to highest detected signals.
30 ng/m3 for 2 minutes averaging time.
30 mg/m3, demonstrated as fast as 2 Hz rep. Rate.
€
106
Ambient Measurements in Reno: BC and PM
0
0.5
1
1.5
2
2.5
3
0
5
10
15
20
25
30
35
40
45
Local Date
BC ug/m3
DT PM ug/m3
Some Images of the Photoacoustic
Instrument in Operation
Mobile sampling from an RV. (Dave Campbell left, and Eric Fujita right.)
Sampling a vehicle (dyno) during a ‘unified’ driving cycle.
PA and dusttrak installed in the Univ. West Virginia trailer for sampling from their dilution tunnel.
BC During the Modified UC Test
1
10
100
1000
10000
100000
0:00 6:00 12:00 18:00 24:00 30:00 36:00 42:00 48:00 54:00 0:00Elapsed Time (mm:ss)
'Common' Gasoline Vehicle, Run 6-27, Toyota Corolla Wagon
Smoker, gasoline vehicle, Run 10-53, Mazda B2200
Diesel Automobile, Run 11-59, Mercedes 300D Turbo
Jet Exhaust: SERDP 2002, North Island CA
Continuous Measurements of Black Carbon …
• Are very helpful in validating your sampling system.
• Provide immediate feedback to average and instantaneous response of sources.
• Draft data can be delivered minutes after a sampling period ends.
• Not labor intensive.
• Can be sliced and diced 100,000 different ways to find out the conditions that give rise to maximal or minimal emissions, etc.
Photoacoustic IOP, MARCH 2000, DOE-ARM SGP Site
GOALS:
•Compare performance and calibration of filter-based instruments routinely used at the SGP with the photoacoustic
method.
•Evaluate the dependence of light absorption on relative humidity.
•Hoped for, and had the following conditions…–Clean air for background level comparisons (after rain).
–Air mass from long range transport of aerosol (moderately dirty air).
–Dirty air mass from local farmers burning their fields.
Images from the SGP
Block Diagram of the SGP measurementsHumidifierImpactors
(1 µm and 10 µm inlets)
ReferenceNephelometerPSAP #1InletPhotoacousticInstrumentPSAP #2PumpsHumidifiedNephelometer
Heater(get 40%RH)
New instruments: PSAP #2 and Photoacoustic instrument, downstream of the humidified nephelometer.
Humidity and inlet settings during a typical hourQuickTime™ and aGraphics decompressorare needed to see this picture.
40
50
60
70
80
90
975
980
985
0:00 10:00 20:00 30:00 40:00 50:00 0:0012 March 2000, 03:00 to 04:00
Zero Air
1 µm inlet
10 µm inlet
Quick-look light absorption at the SGP
•Photoacoustic measurements are in red, PSAP in black. The PSAP filter was overloaded during the smoke events.
Linear correlations of PSAP#1 and PAQuickTime™ and aGraphics decompressorare needed to see this picture.
X
XXXXXXXXXXXXX
XX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XX
XX
XXXXXXXXX
XXXXX
XX
XXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXX
XXXX
XXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXX
XXXXXXXXX
XXXXXX
XXXX X
XX
XX
XXXXX
XXXX
XXXXXX
XXXXXXXXXX
XX
XXXXXX
XXXXXXXX
XXXXXXXXXX
XXXXXXXXXXX
XXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXX
XXX
XXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXX
XXXXXXXXXXXXXXX
XXXXXXXXX
XX
XX
X
X
X
XXXX
XX
XX
XXXXXX
XXXXXX
XX
X
XX
XX
XX
X XX
XXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
0
10
20
30
40
50
0 10 20 30 40 50
PA Babs, 1 µm cut (Mm-1)
f(x) = (1.69 ± 0.03)x + 0.11 ± 0.12
R2 = 0.96 N = 3414
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXX
XX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
X
XXXX
XXXXXXXXX
XXXXXX
XXXXXXX
XXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXX
XXXX
XXXX
XXXXXXX
XX
XX
X
XXXXXXXXXXX
XXXXXX X
XXXXXXXXXXXXXXX
XXXXXXXXXXX
XXXXXXXX
XXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXX
XXXX
XX
XXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXX
XX
XXX
XXXXXXXXXXXXXXXXX
XXXXXXXX
XX
X
XX
X
XXXX
X XXX
XXXXXXXXXXXXXX
XXX
X
XX
XX
XX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
0
10
20
30
40
50
0 10 20 30 40 50
PA Babs, 10 µm cut (Mm-1)
f(x) = (1.61 ± 0.03)x + 0.30 ± 0.12
R2 = 0.96 N = 3414
•Very strong correlation. Slope indicates PSAP values are larger. Preliminary results, more evaluation in progress this summer at DRI.
f(RH) = PhotoacousticBabs(RH) / DryPSAPBabs
QuickTime™ and aGraphics decompressorare needed to see this picture.
J
J
JJJ
J
J
JJ
0.5
0.6
0.7
40 60 80 100RH (%)
J J
JJ
J
J
J
J
J
0.5
0.6
0.7
40 60 80 100RH (%)
•Interpretation: Photoacoustic instrument shows lower Babs as RH increases.
•Aerosol optics may change upon humidification (collapse chain aggregates)
•Sample line or humidifier particle losses may increase with RH
•Photoacoustic measurement may be influenced by RH via mass transfer.
PSAP # 2, humidified instrument, Quick Look
QuickTime™ and aGIF decompressor
are needed to see this picture.
•Babs (1/Mm) vs Julian Day. Ramps coincide with humidification ramps. Suggests caution when interpreting PSAP measurements done at high RH.
•Cellulose backing of filters is very hygroscopic. Fibers swell when they take up moisture, causing apparent light absorption.
7 Wavelength Photoacoustic Instrument Sketch.
L1L2L3L4L5L6OpticalChopperMotorized MirrorsPhoto-
acousticInstrument
OpticalMulti-meter
Laptop ComputerData Acquisition
and Control
L7SampleInlet
SampleOutlet
PumpNO2 DenuderParticle FilterMotorizedInlet Switcher
355 nm to 1047 nm. Gas calibration by oxygen at 760 nm on each measurement cycle.
Conclusions and Questions•Photoacoustic measurement of light absorption…
•Provides a fundamental measurement based on energy balance
•Calibration can be evaluated with absorbing gas and kerosene soot
•Has a very large dynamic range (120 dB)
•Is more demanding than filter-based methods
•Filter-based methods may be erroneous at high RH due to water deposition on the filter substrate.
•While aerosol light scattering does increase with RH due to particle swelling, light absorption does not increase with RH. Jury still out.
•Sample lines losses as a function of RH?? (Experience says yes)
•Are light absorbing aerosols hygroscopic?? (Literature says yes)
•Does the aerosol morphology change upon humidification?? (Lit. says yes)
•Does mass transfer (condensation and evaporation) affect the photoacoustic measurement??
Future Directions
1. Develop a multi-wavelength instrument for aerosol light absorption from the UV to the IR. (For quantifying absorption of sunlight by aerosol. Of importance to radiation transfer in the atmosphere, and satellite remote sensing of aerosol, as well as correction of satellite imagery for atmospheric effects.
2. Shink the instrument down to the point where it can be used on aircraft for ambient sampling, or directly on vehicles for source sampling applications.
3. Theoretical analysis of mass transfer contribution to the acoustic signal for soot (have solved the limiting case of a water droplet).
DRI Nephelometer with < 1 deg. truncation error.
Based on integrating sphere detection scheme.
Ravi Varma, UNR student in our ATMS program is working on the instrument.
Has been used in a road dust aerosol optics project.
DRI Extinction Instrument (few 1/Mm to 1000 1/Mm)
Lens Tube Lens Tube
NanoGreen Laser
Spacer
Optical Bench
3.12 in
LaserBeam
1 m
AlignmentStage
Clean AirPurge Inlets
IR Filter(Blocking)
Mode MatchingLens
PMT
DRI Extinction Instrument based on Cavity Ringdown Spectroscopy
Thanks for your attention…