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LIDAR DETECTION OF PARTICULATE MATTER:OVERVIEW AND APPLICATION TO AUTOMOTIVE EMISSIONS

Hans Moosmüllerhansm@dri.edu

Desert Research InstituteUniversity of Nevada System

Reno, NV 89512

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LIDAR Principle

LaserTransmitter

Time ResolvedReceiver

Distributed Backreflection

Transmission

S(r ) C T (r ) (r )

Spatially Resolved Measurement Along Line (1-D)r = c/2 tScanning => 2-D or 3-D Measurements

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S(r ) C T (r ) (r )LIDAR Equation

• For each distance r, there are two unknownsT(r) and (r), but only one measurement S(r)

• If extinction and backscatter can be related, and C is known, equation may be solved (Klett Inversion)

• If either T(r) or (r) are well known, the other quantity can be determined

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Distributed Backreflection• Particle Scattering

Particle Concentration, Shape , Size(?), Wind Velocity

• Rayleigh ScatteringAtmospheric Density, Temperature, Wind Velocity

• Raman ScatteringGas Density, Temperature

• Fluorescence (Quenching!)Atoms, Molecules, Biological Material?

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Distributed Return• Terra-Watt Femtosecond Laser

1012W, 10 - 100 fs = 10-13- 10-15 s

• Nonlinear Effects in Atmosphere1 - 20 km distance

• Plasma Channel (several 100 m)Self-Focusing, Filamenting

• White Light SourceDOAS in the Sky

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Transmission

• Atmospheric ExtinctionVisibility, Radiative Transfer, Aerosol Size Distribution, Concentration

• Differential Absorption Lidar Gas Concentrations: e.g., O3, NO2, SO2, Hg, H2OTemperaturePressure

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Automotive Emissions• Dynamometer Testing

Few vehicles under a large range of operating conditionsApplications: I&M, Emission Factors for Inventories and Modeling (e.g., MOBILE, EMFAC)Missing: Real Time PM Measurements

• Remote Sensing Large (10,000/day) number of vehicles under a limited number of operating conditionsApplications: I&M (Clean Screening & Gross Emitter Identification), Emission Factors for Inventories and Modeling (e.g., MOBILE, EMFAC)Missing: PM Measurements

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Gaseous Remote Sensing• Pioneered by Stedman & Bishop (DU)• Commercially Available• Measures Gaseous Column Content across

Road behind Vehicle• CO2, CO, NO, HC by IR, UV Absorption• Ratio to CO2 (& CO, HC) to Obtain Fuel-

Based Emission Factor (i.e., g/kg fuel)• Ancillary Measurements: Speed,

Acceleration, License Plate

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PM Emissions• PM Mass Nearly Exclusively Elemental

(EC) & Organic (OC) Carbon• EC: Strongly Light Absorbing

(i.e., Black Smoke)• OC: No Light Absorption

(i.e., White Smoke) • Mass Mean Diameter 0.1-0.2m• Not Covered by I&M Programs

(Exceptions: no visible emissions, Diesel opacity)Why is there no PM I&M?

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Visible PM Emissions?

0

1

2

3

4

5

6

7

8

9

10

0.01 0.1 1 10

Particle Diameter (µm)

White SmokeBlack Smoke

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Remote Sensing of PM

• IR Extinction: Insensitive Measure of EC• UV Backscatter: Sensitive to both EC & OC

Assume Transmission = 1• UV Extinction: Insensitive Measure of both

EC & OC• Lidar System helps to discriminate against

Road Dust and Beam Terminus Signal

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LORAXLidar On-Road Aerosol eXperiment

Bob Keislar (Operation)Claudio Mazzoleni (Grad. Student)Peter Barber (Theory)Hampden Kuhns (CEO)John Watson (PI)

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LORAXLidar On-Road Aerosol eXperiment

• Transmitter: 266-nm Passively Q-Switched, All Solid-State Nd:YAG Laser (6 kHz PRF)

• Receiver: 2” Telescope with Compact PMT• Data Acquisition: 8 GS/s, 1.5 GHz

Oscilloscope, IEEE 488 Interface to PC Running LabView

• Spatial Resolution: 20 cm

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SCHEMATICRear Plate

RSD3000Conventional Gas

Remote Sensor

IR Opacity, CO2,CO, & HC (NOx)

VerticalTransferMirror

UV Laser LightIR & UV RSD300 LightBackscattered UV Laser Light

TransmitterSubsystem

ReceiverSubsystem

LORAX

LORAXBeam

Terminus

DataAcquisitionSubsystem

Exhaust Plume

LEGEND

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Main System & Beam TerminusAC Power

PTM

Opticalgate 1

Opticalgate 2

BeamsplitterAndPINPhtodiode

LASER

SPATIAL FILTER

MIRROR 1

MIRROR 2

IRIS

Laser BeamTo the beamterminus plate

PIN

B.P.F

LASERPOWERSUPPLY

Pointerpower supply

TELESCOPE

IRIS

CO2-Ref.Amplifier

B A T T E R Y

F O R

CO2-Ref.

Shutter

PIN triggersignal (BNC)

PIN extinctionsignal (BNC)

Red DiodeLaser(pointer)

CO2 and Ref.signal (BNC)

PMT signal (SMA)

Chopper

Em it te r

Parabolicmirror

CO2 & Ref.detector

cal.

cell

Laser Pointer 1 Laser Pointer 2

Optical gate retroreflector 1 Optical gate retroreflector 2

CO2-Ref.Corner Cube

Iris

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Main System

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Beam Terminus

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On-Road Operation

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Lidar Calibration (1)

• 6-m Calibration Tube Filled with Filtered Air (25.5 Mm-1/sr) or CO2 (75.5 Mm-1/sr)

• Calibration Similar to Nephelometer Calibration for each Range Gate

• Results in Absolute Calibration Including Lidar Overlap Correction

• Calibrates LORAX for Measuring PM Backscatter in Units of Rayleigh (1 Rayleigh = 25.5 Mm-1/sr)

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Example Gas Calibration

-155

-135

-115

-95

-75

-55

-35

-15

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0 1 2 3 4 5 6Range (m)

PMT

Sign

al (m

v)

CleanAirCO2R134a

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Lidar Calibration (2)

• Convert from PM Backscatter (Rayleigh) to PM Mass Density (g/m3)

• Define Calibration PMLogNormal Size Distribution, Density = 1250 kg/m3,(Mass Mean Diameter = 0.1m, Geometric Standard Deviation = 1.5 m)Refractive Index: nOC = 1.5, nEC = 1.5 + i 0.5PMSI: OC Sphere, PMDiesel: Sphere with EC Core & OC Shell of Equal Volume

• Calibration CoefficientsCSI = 0.16 mg/(m3 Rayleigh)CDiesel = 0.18 mg/(m3 Rayleigh)

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LORAX Use

• Initial Small Scale Use for Instrument Testing and Debugging

• First Large Scale Use During Summer 2002 in Las Vegas

• Measurement of 150,000 Vehicles• Southern Nevada Air Quality Study (SNAQS)

(Sponsored by Federal Transit Administration)

• Clark County Remote Sensing Study(Sponsored by Clark County Division of Air Quality Management and Department of Comprehensive Planning)

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Some High PM Emitters (>500 mg/mi)

Las Vegas, May 2002

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Example:CO2 and Backscatter Signals

0 100 200 300 400 500Time (ms)

Sign

al (a

rbitr

ary

units

) Integrated backscatteringCO2 extinction

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Example Correlation:CO2 and Backscatter

R = 0.98Slope = 20300 +/- 640P-value = 7.36E-34

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.05 0.1 0.15 0.2CO2 Extinction

Inte

grat

ed B

acks

catte

ring

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Future Work• Full Analysis of Las Vegas Study• Dissemination of Results (Papers &

Conferences)• Use for Off-Road Military Diesel Vehicles• Build Next Generation Instrument:

Higher SensitivityIntegrated PM & Gas MeasurementsEasier Use

• Commercialization

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Conclusions• Lidar used to add PM channel to on-road

remote sensing system• Measure PM emissions for large number

(104-106) of vehicles under a limited number of operating conditions

• Get PM emission statistics for SIPs in PM non-attainment areas

• Use for PM I&M (Clean Screening & Gross Emitter Identification)

• Lots of interest from ARB, BAR, and CRC