| OMI (Ozone Monitoring Instrument) NO2 satellite-data are compared with ground-based observations from Pandora spectrometer in Helsinki (Finland) during 2012. This provides information about satellite NO2 data quality at high latitude location. The Pandora NO2 total column values corresponding to the satellite overpass in Helsinki usually range between 0.2 DU and 0.5 DU. The difference between satellite- and ground-based NO2 column amounts is on average -0.03 DU and -0.008 DU for all skies and clear sky conditions, respectively. The clear sky overpasses mainly correspond to summer days and, thus, to smaller solar zenith angles.
The in situ NO2 surface concentrations in Helsinki are analysed together with the vertical column amounts. The seasonal and weekly cycles from satellite, Pandora and in situ data are compared. The different datasets show a similar wintertime peak and a lower signal during the weekend, as compared to the other weekdays. The changes in the NO2 levels over the last 10 years are also evaluated. |