Stratospheric NO2 data from GOME-2A
For validation purposes, a time series of daily GOME-2A NO2 columns (January 2007 - October 2017) within a 200 km radius has been created which can be downloaded in ASCII format for a number of validation stations.
This GOME-2A NO2 product produced at the University of Bremen is a simple total column data set assuming a purely stratospheric NO2 without tropospheric contribution. The retrieval settings are similar to those described in
with the exception of not including the empirical sand signature and the correction for GOME-2A polarisation sensitivity. To compensate for this, a higher degree polynomial is used.
In July 2013, the swath of GOME-2A was reduced by afactor of two reuslting in ground-pixels of 40x40 km2 but less daily coverage. This results in different sampling patterns in particular in low latitudes and can be noticed in teh time series.There is some indication for less stable NO2 retrievals in the years since 2014 leading to latitudinal dependent drifts in the data. This is currently under investigation and data from that period should be interpreted with care. As an alternative, data from the GOME-2B instrument can be used which is available from the GOME-2B stratospheric NO2 page.
Please also read the disclaimer.
The data format is plain ASCII with 29 header lines starting with a '*' character followed by the lines with the data organized in 12 columns separated by blanks:
column 1: fractional day of year 1993 UT
column 2: fractional day of year UT
column 3: solar zenith angle [°]
column 4: daily average slant column of NO2 [molec cm-2] in 200 km radius
column 5: daily average vertical column of NO2 [molec cm-2] in 200 km radius
column 6: daily minimum slant column of NO2 [molec cm-2] in 200 km radius
column 7: daily minimum vertical column of NO2 [molec cm-2] in 200 km radius
column 8: daily maximum slant column of NO2 [molec cm-2] in 200 km radius
column 9: daily maximum vertical column of NO2 [molec cm-2] in 200 km radius
column 10: rms of NO2 slant columns
column 11: rms of NO2 vertical columns
column 12: average chisquare of retrieval
The full data set with all individual overpasses can be downloaded as a zip-file (> 700 MBytes) here.
GOME-2A NO2 columns provided on this page are a scientific product created at the University of Bremen and based on the operational lv1-spectra provided by EUMETSAT. They are not related to the operational GOME-2A lv2-products distributed by DFD/DLR that also contain NO2 columns. Although the two GOME-2A NO2 data products agree qualitatively, the differences are significant, and thorough validation will have to be performed of both products.
Only the descending part of the orbit is used in this data set to avoid complications from averaging over measurements taken at different local time. However, at high latitudes, GOME-2A has several overpasses per day and systematic changes are expected from the diurnal profile of NO2. For detailed comparison with other data sets, the full overpass files have to be used (see link below table).
The NO2 columns in the files provided on this page are total columns assuming a stratospheric profile (US standard atmosphere with the troposphere set to 0). Wherever there is substantial NO2 in the troposphere (for example in polluted regions such as Germany), the columns will exceed the real stratospheric ones and are not very accurate.
If you have any questions, comments or data requests, please contact Andreas Richter.