Differential Photoacoustic (DPAS) Method for PM Absorption ...cires1.colorado.edu/jimenez-group/UsrMtgs/UsersMtg18/PKU_talk.pdfDifferential Photoacoustic (DPAS) Method for PM Absorption

1

Differential Photoacoustic (DPAS) Method

for PM Absorption Measurement

Zhenhong Yu

Aerodyne Research, Inc.

[email protected]

Peking University

5/09/2016

2

Outline

The Center for Aero-Thermodynamics

(CATD) in Aerodyne

Development of the DPAS technique

Instrument performance

Field measurement on aviation soot

Calibration

Summary

3

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

4

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

5

• 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

6

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

7

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

8

What is Photoacoustic effect?

l

cf

20

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

9

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

10

DPAS Detection Scheme

Sample Cell

Function

GeneratorDAQ

Laser

Microphone

Reference Cell

Microphone

FFT Analysis

11

Current Design

12

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

13

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.

14

Allan Analysis

15

Instrument Evaluation on Laboratory

Combustor

DPASMSS

16

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

17

Particle Size Distribution

18

Comparison between MSS and DPAS

~1ppm NO2

Zeroing

19

Differential Results

20

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

21

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.

22

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

19

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

25

Characterization of 130nm Au-NP

25

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

26

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.

27

28

Acknowledgement

Aerodyne Research, Inc.

Dr. Richard Miake-Lye

Dr. Paul Kebabian

Dr. Gregory Magoon

Dr. Jay Peck

James Assif

William Brown

William Rundgren

United Technologies

Research Center (UTRC)

David Liscinsky

Bruce True

Dr. Jacquelynn Garofano