Since 1996, satellite nadir measurements have provided tropospheric NO2 columns data on a global scale.These observations have been used for the quantification of regional air pollution, the estimation of pollution trend and the emission budget calculation.In the past ten years, a lot of papers have been published on the retrieval of tropospheric NO2 from satellites.However, there are still many important issues needing to be improved such as cloud, priori profile shape, and aerosol.Validation of NO2 columns from satellite is also essential, especially over polluted regions such as Beijing, but so far not many comparison studies have been performed over China.