An improved tropospheric NO2 product for the GEMS instrument

Nitrogen oxides are among the most important pollutants in the troposphere. They are emitted in many anthropogenic activities such as fossil fuel use for energy production and transportation or agricultural burning. At high concentrations, nitrogen oxides are a health hazard. They also are involved in the formation of tropospheric ozone and acid rain.

There are many different ways to measure nitrogen oxides in the atmosphere. Satellite observations of NO₂ are one of the most powerful as they provide excellent coverage. However, the spatial resolution is limited and in the case of measurements from low-earth satellites, there is only one measurement per day. The latter problem can be overcome by using geostationary satellites, and the Korean GEMS instrument is the first to provide hourly NO₂ observations over Asia.

In this study, a full year of tropospheric NO₂ columns are retrieved from GEMS observations. Different retrieval settings are applied and the results compared with a particular emphasis on the analysis of the diurnal variation of NO₂. Sensitivity tests include correction for the polarisation sensitivity of the GEMS instrument, different stratospheric correction schemes, different surface reflectances and different a priori profiles. While all of these parameters affect the retrieved NO₂ columns, the pattern of the diurnal variation of the retrieved tropospheric columns appears to be robust, at least over regions with large pollution signals.