Differential Photoacoustic (DPAS) Method for PM Absorption ...cires1.colorado.edu/jimenez-group/UsrMtgs/UsersMtg18/PKU_talk.pdfDifferential Photoacoustic (DPAS) Method for PM Absorption
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Differential Photoacoustic (DPAS) Method
for PM Absorption Measurement
Zhenhong Yu
Aerodyne Research, Inc.
zyu@aerodyne.com
Peking University
5/09/2016
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Outline
The Center for Aero-Thermodynamics
(CATD) in Aerodyne
Development of the DPAS technique
Instrument performance
Field measurement on aviation soot
Calibration
Summary
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What does the CATD group do?
Contracting Research:
• Developing a sampling and measurement methodology for ICAO regulation on PM emissions (FAA)
• Evaluating emissions of in-service aircraft (ACRP)
• Characterize volatile PM from aircraft engines (SERDP)
• Investigating emission reduction due to alternative fuels (NASA)
• Working with industrial partners for engine certification (FAA)
Instrument Development:
• Measuring light absorption (UV to near-IR) of PM from either engine emissions or biomass burning for NASA’s Airborne Measurement Program
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Why working on emissions of aircraft engines
• Global aircraft fleet has a market value of $5.2 trillion in 2013
Unit cost: ~$50 million
Unit cost: 13.9 million
COMAC C919
CFM International LEAP-1C engine
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• Aviation consumes 3% of the world’s fossil fuel, of which more than 50% in stratosphere (cruise altitude).
• Current ICAO regulation on emissions only focuses on impact on local air quality via calculating emissions inventory in Landing – Takeoff (LTO) cycle (from ground up to 900 meter).
It is difficult to evaluate emissions of
aircraft engines
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Motivation
Prediction of direct radiative forcing require
parameterization of the optical properties of
light-absorbing carbon emissions with
respect to wavelength
Current parameterizations do not address
the range of variability within sources
Elemental carbon is not a good surrogate
for light absorbing carbon at wavelength
shorter than 800nm.
The light absorbing capacity of
carbonaceous aerosol is not a conservative
property from the point of emissions to
atmosphere
A light absorption measurement technique
at various wavelengths from UV to near-IR
is necessary
A. Laskin et al. Chem. Rev. 2015.
Absorption Ångströgm exponent (AAE) of
black carbon is normally assumed to be -1.0
in the global radiation balance models
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Current Technologies
Filter-based techniques:
• Multi-angle absorption photometer (MAAP)
• Particle soot absorption photometer (PSAP)
• Aethalometer
In situ techniques:
• Micro soot sensor (MSS) (single-cell photoacoustic at 880nm)
• Photo-Acoustic soot spectrometer (PASS-1 at 785nm)
• Single particle soot photometer (SP2)
• Cavity-attenuated phase shift (CAPS) PM SSA monitor
• Cavity ring-down spectroscopy (CRDS)+ scattering measurement
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What is Photoacoustic effect?
l
cf
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One-dimensional
Acoustic Resonators Frequency Quality Factor
~30
Laser radiation
Absorption
Excitation
Non-radiative
relaxation
Heating
Acoustic wave
Expansion
Microphone
Detection
𝐼 = 𝐼0𝜎𝑐𝑙
𝐼 = 𝑄
𝑄 = 𝑊 = ∆𝑃 × 𝑉 = ∆𝑃 × 𝑙 × 𝜋𝑟2
∆𝑃 =𝐼
𝑉=𝐼0𝜎𝑐
𝜋𝑟2
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Why is the correction for absorption of
gas species important?
Light absorption of
gaseous species could
be significant in the UV-
visible region when
evaluating PM
emissions from IC
engines
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DPAS Detection Scheme
Sample Cell
Function
GeneratorDAQ
Laser
Microphone
Reference Cell
Microphone
FFT Analysis
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Major Improvements
Reducing diameter of acoustic cell
Utilizing home-made MEMS
microphone array detectors (x4)
Modulating the 532nm laser via
direct electrical power control
Integrating bandpass filters and
preamplifiers with microphone
array detectors
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Calibration with NO2
Absorption cross section of
(1.45±0.06)10-19 cm2 for NO2 at
532nm from
Osthoff et al. J. Geophys. Res. 2006.
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Sampling & Measurement System
N2 diluted
sample
V3/NO
spill
valve
Dekati
DI-1000V2/NO
Control
valve
Aerodyne
DPAS PM
absorption
monitor
AVL Micro
Soot Sensor
(MSS)
AVL MSS pump
N2
SUPPLY
V4/NO
Isolation
valve
HEPA
Filtered
Shop Air
CA CO2
(0-5000 ppm)
HEPA
Pancake
filter
ExhaustP1 T1
P3 T3
2 bar MAX
AVL
Particle
Counter
(APC)
4 Way
Cal Gas + N2
Metal
Filter
N2
heater
P2 T2
Dilution N2
30psig
•½”
Room Air
V9
•¼”
V6
V7Zero
air
HEPA
•3/8”
V5/NC
V1/NC
Supply
valve
•¼”
Gas
measurements
•½”
P4
T4
cyclone
N2 purge
TSI
EEPS
Combustor
exhaust
Compliant with SAE Aerospace
Information Report (AIR) 6241
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Linear Correlation
The expected MAC (532nm) = 7.6±0.6 m2/g according to MAC (633nm) = 6.4±0.5 m2/g
Mulholland & Choi, Proc. 27th Symposium on Combustion 1998
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Under Development
A two-color brown carbon/black carbon
monitor operating at 360nm and 1064nm for
biomass burning studies.
A RGB DPAS instrument that measures
aerosol light absorption at 671nm, 532nm,
and 473nm simultaneously.
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Photoacoustic Signal Calibration
Gas-based methods:
• NO2 at 532nm – W.P. Arnott et al. 2000.
• O3 at 404, 532, and 659 nm – D. Lack et al. 2012.
• O2 at 762nm – G. Tian et al. 2009.
PM-based methods:
• Dried nigrosine dye at 532nm – D. Lack et al. 2006.
• Absorbing polystyrene sphere at 532nm – D. Lack et al. 2012.
Potential Calibration with Metal NPs
• Metal NPs strongly absorb UV-visible light
• Metal NPs can be manufactured uniformly
• Optical properties of metal NPs can be calculated from Mie theory
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2424
Optical Properties of Au-NP
Calculation results validated
against aqueous phase UV-VIS
spectra
Medium effects are important
to consider
Au nanospheres with dp = 130 nm
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Characterization of 130nm Au-NP
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Mono-dispersed particle
size distribution after
removing capping agent
with centrifuging
Good agreement between
extinction measurements and
Mie theory calculations in air
Density=19.6±0.4 g/cm3
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Imaging of Au-NP (130nm)
HRTEM imaging shows that the Au-NPs are uniform
in size with a diameter of 130 nm
D=130.2±1.0nm
Summary
DPAS instrument at 532nm was developed and tested
– The measurement is a turn-key and continuous
operation
– It is capable of providing information on
concentration, mass absorption coefficient (MAC),
absorption Ångströgm exponent (AAE), single
scatter albedo (SSA) in combination with other
measurements.
– The interference from absorption of gaseous
species is subtracted.
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