Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 8 12 2008 10.5194/acp-8-3283-2008 http://www.atmos-chem-phys.net/8/3283/2008/ http://www.atmos-chem-phys.net/8/3283/2008/acp-8-3283-2008.html http://www.atmos-chem-phys.net/8/3283/2008/acp-8-3283-2008.pdf 3283 3289 2008-06-27 Comparison of total ozone and erythemal UV data from OMI with ground-based measurements at Rome station I. Ialongo iolanda.ialongo@uniroma1.it G. R. Casale A. M. Siani Physics Department, Sapienza, University of Rome, Italy Ground-based total ozone and surface UV irradiance measurements have been collected since 1992 using Brewer spectrophotometer at Rome station. Erythemal Dose Rates (EDRs) have been also determined by a broad-band radiometer (model YES UVB-1) operational since 2000. The methodology to retrieve the EDR and the Erythemal Daily Dose (EDD) from the radiometer observations is described. Ground-based measurements were compared with satellite-derived total ozone and UV data from the Ozone Monitoring Instrument (OMI). OMI, onboard the NASA EOS Aura spacecraft, is a nadir viewing spectrometer that provides total ozone and surface UV retrievals. The results of the validation exercise showed satisfactory agreement between OMI and Brewer total ozone data, for both OMI-TOMS and OMI-DOAS ozone algorithms (biases of −1.8% and −0.7%, respectively). Regarding UV data, OMI data overestimate ground based erythemally weighted UV irradiances retrieved from both Brewer and YES Radiometer (biases about 20%). The effect of aerosols on UV comparisons was investigated in terms of Aerosol Optical Depth (AOD), showing medium-large correlation at SZA larger than 55°. Further sources of uncertainty, such as the difference in the atmospheric conditions between local noon and OMI overpass time and the OMI spatial resolution, were also discussed. 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