Aerosol layers over Oklahoma as seen from Twin Otter on May 27, 2003 Photo courtesy of Roy Woods

1. How well can we measure the vertical profiles of aerosol extinction, scattering and absorption? 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. Smirnov A. Strawa, D. Turner, J. Wang, E. Welton Aerosol layers over Oklahoma as seen from Twin Otter on May 27, 2003 Photo courtesy of Roy Woods

2. 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°) Airborne in-situ measurement of Extinction = + For simple lab aerosol (RAOS, Sheridan et al., 2004) Accuracy: 11%Accuracy: 2% Accuracy: 7% (Anderson & Ogren, 1998)

3. ARM Aerosol IOP – May 2003 SGP Site CF, Oklahoma Photo from Roy Woods

4. ARM Aerosol IOP – May 2003 CIRPAS Twin Otter • 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

5. Regular Vertical Profiling • 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

6. Neph scattering comparisons during formation flights Difference in nephelometers can largely be explained by 1 mm diameter cut on Cessna

7. Twin Otter: Absorption comparison during level legs Photoacoustic

8. Raman Lidar SMART trailer Photo courtesy Yin-Nan Lee, BNL

9. NASA Ames Airborne Tracking SunphotometerAATS-14: 354-2139 nmAerosol Optical Depth and H2O columnAerosol Extinction and H2O density in suitable profiles

11. AOD: AERONET minus AATS-14 Observation #

24. Eastern Asia, 2001 C-130: Bias: +6% Redemann et al., 2003 Twin Otter: Bias -13% Schmid et al., 2003 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) U.S. East Coast, 2001, Bias -15% Magi et al. (2004) Aerosol IOP Southern Africa, 2000, Bias -4% (Magi et al., 2003) Oklahoma, 2003,Bias -14% How well did past campaigns do on AATS vs Neph+PSAP comparisons?

25. 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.