# Presentation: 666288

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

**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. Smirnov
- A. Strawa, D. Turner, J. Wang, E. Welton

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

## 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)

**Notes:**
How to get extinction from in-situ measurements. No need to explain corrections.

## ARM Aerosol IOP – May 2003

- Photo from Roy Woods

**ARM Aerosol IOP – May 2003**
**SGP Site CF, Oklahoma**

## ARM Aerosol IOP – May 2003

** ****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 Otter**

**ARM Aerosol IOP – May 2003**

## 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

**Regular Vertical Profiling**

## Neph scattering comparisons during formation flights

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

## Twin Otter: Absorption comparison during level legs

**Twin Otter: Absorption comparison during level legs**

**Photoacoustic**

## Photo courtesy Yin-Nan Lee, BNL

- SMART trailer

## NASA Ames Airborne Tracking SunphotometerAATS-14: 354-2139 nmAerosol Optical Depth and H2O columnAerosol Extinction and H2O density in suitable profiles

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## AOD: AERONET minus AATS-14

- Observation #

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

## 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.