Abstract

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.

Highlights

  • The second Aerosol Characterization Experiment (ACE-2) of the International Global Atmospheric Chemistry Project (IGAC) ran from 16 June to 25 July 1997

  • We report on CLEARCOLUMN results obtained by combining airborne sunphotometer and in-situ measurements taken aboard the Pelican aircraft, space-borne NOAA/Advanced Very High Resolution Radiometer (AVHRR) data and ground-based lidar and sunphotometer measurements

  • We use a vertical aerosol optical depth (AOD) profile obtained from a Micro Pulse Lidar (MPL) in conjunction with a Cimel sunphotometer (Smirnov et al, 1998), both operated at the Izana observatory (28.30°N, 16.50°W, 2367 m) on Tenerife

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Summary

Introduction

The second Aerosol Characterization Experiment (ACE-2) of the International Global Atmospheric Chemistry Project (IGAC) ran from 16 June to 25 July 1997. The results presented in this study are part of the ‘‘Clear-sky column closure experiment’’ (CLEARCOLUMN) activity, one of 7 ACE-2 activities (Raes et al, 2000). Clearsky column closure experiments call for characterization of aerosol layers by simultaneous measurements using different techniques that can be related using models (Quinn et al, 1996). In this study we report on Pelican flights tf and tf performed on 8 and 17 July 1997. On both days, 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

Airborne measurements
Space-borne measurements
Ground-based measurements
Flight tf15 — 8 July 1997
Flight tf20 — 17 July 1997
Findings
Summary and conclusions

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