held at the Cabauw Experimental Site for Atmospheric Research, the Netherlands, May – July 2005.

Meeting report

Prepared by

E.J. Brinksma, M. van Roozendael, T. Wagner, O. Ibrahim, A. Richter, F. Wittrock, H. Oetjen, G. Pinardi, C. Hermans, C. Fayt.

1. Aim of the Campaign

A 9-week campaign was held within the framework of the Dutch-nationally funded project DANDELIONS (Dutch Aerosol and Nitrogen Dioxide Experiments for vaLIdation of OMI and SCIAMACHY). The goal was to validate OMI and SCIAMACHY nitrogen dioxide measurements, OMI and AATSR aerosol measurements, and OMI and SCIAMACHY  column ozone measurements using groundbased and balloon observations, as well as models. A derived goal was to assess the accuracy of the used groundbased NO2 instrumentation. The campaign location was the Cabauw Experimental Site for Atmospheric Research (CESAR, 51.971 N, 4.927 E), but ozone observations were taken from De Bilt (35 km to the North east).

AT-2 funding was sought to extend this campaign significantly from what was originally planned; with AT-2 funding it became possible that three MaxDOAS groups participated with their instruments at the Cabauw location. These were the IFE-Bremen group (Andreas Richter et al.), IFE-Heidelberg group (T. Wagner et al.), and the BIRA group (M. van Roozendael et al.). These groups complemented the Dutch groups that were already taking part, namely KNMI (E. Brinksma et al., coordination, radio sondes, mini MaxDOAS, ozone sondes, Brewer, Sun Photometer, Globe handheld photometer), RIVM (D. Swart et al., nitrogen dioxide mobile lidar, groundbased in situ sampler, boundary layer lidar, aethalometer), and TNO The Hague (G. de Leeuw et al., various aerosol measurements), and the permanent meteorological, cloud, and radiation measurements at CESAR.


The campaign was opened with a kick-off meeting in Cabauw on May 10, 2005. Project goals were discussed and a website was launched, with a public as well as participant-restricted part at http://www.knmi.nl/omi/research/validation/dandelions/

2. Scientific Presentations

During the OMI Science Team meeting in De Bilt, on June 17, a session on the Dandelions campaign was organized, in which four presentations were given. At the wrap-up meeting on July 20, 2005, in Cabauw, each of the groups presented their results. Scientific results from each of the MaxDOAS groups are summarized in their individual reports, see Appendix 4.

3. Discussion Points

Primary topics of investigation with respect to NO2 were:

4. Conclusions and Recommendations

Preliminary results show that different MAX DOAS instruments give results within the expected error bars on a large number of days. We expect that the non-homogeneous distribution of NO2 combined with the different viewing directions of the instruments contribute largely to observed differences. A first comparison of surface mixing ratios retrieved from MAX DOAS data with the in-situ measurements on the site shows good agreement. Often, higher NO2 concentrations are viewed towards the south. The temporal variation of NO2 at the site was large over time periods less than an hour, highlighting the need for good matching of time and location in validation of tropospheric NO2 columns from satellite measurements. Preliminary comparisons to OMI and SCIAMACHY tropospheric and stratospheric NO2 columns over Cabauw are satisfactory.

We are planning to investigate the role of aerosols in the retrievals, and the importance and accuracy of the assumed NO2 altitude profiles. This document has focused on the AT-2 sponsored MAXDOAS participation, while the complete campaign includes NO2 lidar, balloon radiosondes, various aerosol and cloud instruments also.

5. Participants

Ellen Brinksma, Jacques Warmer, André Swinkels, Ed Worrell, and others, KNMI

Michel van Roozendael, Caroline Fayt, Gaia Pinardi, and Christian Hermans, BIRA/IASB

Andreas Richter, Folkard Wittrock, Hilke Oetjen, IUP Univ. Bremen

Thomas Wagner, Ossama Ibrahim, IUP Univ. Heidelberg



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