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Published April 2000 | Published
Journal Article Open

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


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.

Additional Information

This journal is published under the terms of the Creative Commons Attribution 4.0 International (CC-BY 4.0) License. (Manuscript received 28 December 1998; in final form 4 October 1999) This research was conducted as part of the second Aerosol Characterization Experiment (ACE-2), which is a contribution to the International Global Atmospheric Chemistry (IGAC) core project of the International Geosphere-Biosphere Programme (IGBP). Financial support for the measurements and analyses was provided by the US National Science Foundation, Office of Naval Research, National Oceanic and Atmospheric Administration, and National Aeronautics and Space Administration, the Max Planck Society, and the European Commission DG XII (Environment and Climate). Acknowledgment is given to the AERONET program for making available CIMEL sunphotometer aerosol optical depth measurements and to the Ozone Processing Team at NASA Goddard Space Flight Center for making available TOMS EP data. We also thank Q. Wang at the Naval Postgraduate School in Monterey, CA, for providing us with differentially corrected Global Positioning System data for the ACE-2 Pelican flights.

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