Aerosol layers over Oklahoma as seen from Twin Otter on May 27, 2003

Photo courtesy of Roy Woods

B. Schmid, BAER Inst. & NASA Ames Res. Ctr.E. Andrews, P. Arnott, P. Colarco, D. Covert, J. Eilers, R. Elleman, R. Ferrare, C. Flynn, B. Holben, H. Jonsson, J. Ogren, J. Redemann, K. Ricci, J. Seinfeld, A. SmirnovA. Strawa, D. Turner, J. Wang, E. Welton

How well can we measure the vertical profiles of aerosol extinction, scattering and absorption?

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Aerosol Extinction (1/km)

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Neph+PSAP (453 nm) 18:34-18:52 UT

Airborne in-situ measurement of

Extinction =Absorption

• Particle Soot Absorption Photometer (PSAP)

=467, 530, 660 nm

• low RH• Corrections (Bond et al.,

1999, Virkkula et al, 2004)

– scattering contribution– loading correction

Scattering

• Nephelometers– TSI: = 450, 550, 700 nm,

low RH– RR: = 540 nm,

RH=20,60,85%

• Corrections (Anderson & Ogren, 1998)

– light source– angular truncation (7°-170°)

+

For simple lab aerosol (RAOS, Sheridan et al., 2004)

Accuracy: 11% Accuracy: 2%

Accuracy: 7% (Anderson & Ogren, 1998)

Photo from Roy Woods

ARM Aerosol IOP – May 2003SGP Site CF, Oklahoma

• Aerosol: extinction (Cadenza, AATS-14), scattering (4 nephs), absorption (PSAP, photoacoustic, Cadenza), aerosol optical depth (AATS-14), size

• Gases: Water vapor • Cloud: liquid water, droplet size distribution, CCN • Radiation: solar and IR, up and downwelling, broadband and spectral• Stabilized platform• Flew 60.6 flight hours during 16 flights on 15 days

CIRPAS Twin OtterARM Aerosol IOP – May 2003

• Cessna C-172N• 2-3 times/week• Level legs at altitudes between 500 m and 3500 m• Since March 2000 (PI J.Ogren)• Submicron aerosol: TSI Neph, PSAP, RR Neph humidified• 4 formation flights with Twin Otter during AIOP

Regular Vertical Profiling

Neph scattering comparisons during formation flights

Difference in nephelometers can largely be explained by 1 m diameter cut on Cessna

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0.0 0.5 1.0 1.5 2.0Ångström exponent (550/700 nm)

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Cessna/Otter@ 550 nm

AOS statisticssubum/total

Impactor on Twin Otter

Twin Otter: Absorption comparison during level legs

Photoacoustic

Photo courtesy Yin-Nan Lee, BNL

Raman Lidar

SMART trailer

NASA Ames Airborne Tracking SunphotometerAATS-14: 354-2139 nm

Aerosol Optical Depth and H2O columnAerosol Extinction and H2O density in suitable profiles

1 3 6 9 12 15 18-0.1

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340 nmbias= 0.022, 6%rms= 0.038, 10%

1 3 6 9 12 15 18-0.1

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380 nmbias= 0.022, 7%rms= 0.035, 11%

1 3 6 9 12 15 18-0.1

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440 nmbias= 0.022, 8%rms= 0.032, 12%

1 3 6 9 12 15 18-0.1

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501 nmbias= 0.016, 7%rms= 0.027, 11%

1 3 6 9 12 15 18-0.1

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675 nmbias= 0.008, 5%rms= 0.019, 11%

1 3 6 9 12 15 18-0.1

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870 nmbias= 0.002, 2%rms= 0.015, 12%

1 3 6 9 12 15 18-0.1

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1020 nmbias= 0.002, 2%rms= 0.015, 14%

1 3 6 9 12 15 18-0.1

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1638 nmbias= -0.006, -9%rms= 0.013, 20%

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Observation #

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AATS-14 AOD

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T A

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340 nm

n= 18 y = 0.930 x + 0.047rms= 0.038, 10.5%

0 0.1 0.2 0.3 0.4 0.50

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AATS-14 AOD

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T A

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500 nm

n= 18 y = 0.933 x + 0.031rms= 0.027, 11.1%

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AATS-14 AOD

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T A

OD

870 nm

n= 18 y = 0.940 x + 0.010rms= 0.015, 12.4%

0 0.05 0.1 0.15 0.2 0.250

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0.25

AATS-14 AOD

AE

RO

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T A

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1020 nm

n= 18 y = 0.923 x + 0.010rms= 0.015, 14.2%

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n= 6705 r2 = 0.958y = 1.021 x + -0.224rms= 0.628, 19.4 %

in-situ - H2O Density [g/m3]

AA

TS

-14

- H

2O D

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sity

[g/m

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x y # profiles # data pointsAATS-14 Neph+PSAP 26 3484AATS-14 Cadenza 26 2710

AATS-14 MPLNET 2.0 13 587AATS-14 MPLNET 3.0 17 689

AATS-14 Raman Lidar 12 537

AATS-14 in-situ H2O 35 6705

Aerosol Extinction

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Aerosol Extinction

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How well did past campaigns do on AATS vs Neph+PSAP comparisons?

U.S. East Coast, 1996, Bias -14% (Hegg et al., 1997, Hartley et al., 2000)

Canary Islands, 1997, Bias -20% (after inlet correction) (Schmid et al.,

2000)

Southern Africa, 2000, Bias -4% (Magi et al., 2003)

U.S. East Coast, 2001, Bias -15% Magi et al. (2004)

Eastern Asia, 2001

C-130: Bias: +6% Redemann et al., 2003

Twin Otter: Bias -13% Schmid et al., 2003

Oklahoma, 2003, Bias -14%

Aerosol IOP

Conclusions

• Aircraft in-situ measurements with 1µm size-cut account for ~50-100% of the total scattering (depending on particle sizes)

• When both aircraft equipped with 1µm size-cut, scattering agrees within ~10%.

• Inter- and intra-platform comparisons of absorption show discrepancies (~50%). New methods (photoacoustic, Cadenza) are promising.

• Accuracy of extinction measurement is best understood. New Cadenza instrument agrees within 3% with Neph+PSAP.

• When compared to airborne sunphotometer extinction, in-situ measurements are biased low (2 - 4 Mm-1, 12 - 45%), lidar measurements biased high (4 - 26 Mm-1,13 - 49%). We expect better agreement from a “healthier” Raman lidar.

• Looking at results from 6 field campaigns, airborne Neph+PSAP measurements of extinction tend to be biased slightly low (<15%) when compared to airborne sunphotometer extinction.