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This paper presents a comparison of NO 2 data measured with the Ozone Monitoring Instrument (OMI) on board the EOS‐AURA satellite with ground‐based direct‐Sun Brewer measurement data. Since its deployment in July 2004, OMI has provided more than 2 years of daily high‐resolution (∼13 × 24 km 2 at nadir) NO 2 vertical column density maps. We describe the retrieval, which includes an estimation of the stratospheric and tropospheric fraction of total NO 2 columns, the air mass factor (AMF) correction based on detected tropospheric NO 2 enhancements, and the generation of the gridded data product. We present a validation study of the gridded NO 2 data set using data from a Brewer MK3 double monochromator in direct‐Sun mode located at NASA Goddard Space Flight Center in Greenbelt, Maryland, USA. Monthly averages of coinciding measurements correlate well (r = 0.9) but OMI data are about 25% lower than the Brewer measurement data (slope 0.75, intercept −0.38 × 10 15 molecules/cm 2 ). We present a detailed uncertainty analysis for both ground and satellite data and discuss the possible reasons for the observed differences.
Wenig et al. (Wed,) studied this question.