Clear-sky closure studies of lower tropospheric aerosol and water vapor during ACE-2 using airborne sunphotometer, airborne in-situ, space-borne, and ground-based measurements

• Published in: Tellus. Series B, Chemical and physical meteorology Chemical and physical meteorology, 2000-01, Vol.52 (2), p.568-593
• Main Authors: Schmid, Beat, Livingston, John M., Russell, Philip B., Durkee, Philip A., Jonsson, Haflidi H., Collins, Donald R., Flagan, Richard C., Seinfeld, John H., Gassó, Santiago, Hegg, Dean A., Öström, Elisabeth, Noone, Kevin J., Welton, Ellsworth J., Voss, Kenneth J., Gordon, Howard R., Formenti, Paola, Andreae, Meinrat O.
• Format: Article
• Language: English
• ISSN: 0280-6509; 1600-0889
• DOI: 10.3402/tellusb.v52i2.16659

We report on clear-sky column closure experiments (CLEARCOLUMN) performed in the Canary Islands during the second Aerosol Characterization Experiment (ACE-2) in June/July 1997. We present CLEARCOLUMN results obtained by combining airborne sunphotometer and in-situ (optical particle counter, nephelometer, and absorption photometer) measurements taken aboard the Pelican aircraft, space-borne NOAA/AVHRR data and ground-based lidar and sunphotometer measurements. During both days discussed here, vertical profiles flown in cloud-free air masses revealed 3 distinctly different layers: a marine boundary layer (MBL) with varying pollution levels, an elevated dust layer, and a very clean layer between the MBL and the dust layer. A key result of this study is the achievement of closure between extinction or layer aerosol optical depth (AOD) computed from continuous in-situ aerosol size-distributions and composition and those measured with the airborne sunphotometer. In the dust, the agreement in layer AOD (λ=380−1060 nm) is 3−8%. In the MBL there is a tendency for the in-situ results to be slightly lower than the sunphotometer measurements (10−17% at λ=525 nm), but these differences are within the combined error bars of the measurements and computations.