ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-4593-2009 Spatial and temporal UV irradiance and aerosol variability within the area of an OMI satellite pixel Kazadzis S. 1 2 5 Bais A. 2 Balis D. 2 Kouremeti N. 2 Zempila M. 2 Arola A. 3 Giannakaki E. 2 Amiridis V. 4 Kazantzidis A. 2 Finnish Meteorological Institute, Climate Change Unit, Helsinki, Finland Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Greece Finnish Meteorological Institute, Kuopio Unit, Finland National Observatory of Athens, Institute of Space Applications and remote sensing, Athens, Greece National Observatory of Athens, Institute for Environmental Research and Sustainable Development, Athens, Greece 16 07 2009 9 14 4593 4601 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/4593/2009/acp-9-4593-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/4593/2009/acp-9-4593-2009.pdf

Results of an experimental campaign that took place in the greater Thessaloniki area were used to investigate temporal and spatial UV variability within an OMI satellite pixel. UV irradiance and aerosol optical depth measurements were performed for a one month period at three sites characterized as urban, rural and industrial, depending on their location and possible local aerosol sources. OMI showed a general UV irradiance overestimation compared to all three sites and for all atmospheric conditions. During the campaign the standard deviation calculated from the three sites for UV irradiance at 324 nm was of the order of 26%. For cloudless days with high spatial aerosol variability, UV differences reached ±20% within the OMI pixel. For cloudy days UV differences up to 100% were found at the three sites, a percentage that depends on the ground-based data integration time used for the comparison. Here we tried to focus on the limitations when trying to interpret results of UV irradiance comparisons between OMI satellite and ground based stations, taking into account the UV variability within an OMI pixel, due to such small scale spatial cloud and aerosol inhomogeneities.

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