An improved NO2 retrieval for the GOME-2 satellite instrument
Other literature type
Burrows, J. P.
Satellite observations of nitrogen dioxide (NO<sub>2</sub>) provide valuable
information on both stratospheric and tropospheric composition. Nadir
measurements from GOME, SCIAMACHY, OMI, and GOME-2 have been used in many
studies on tropospheric NO<sub>2</sub> burdens, the importance of different NO<sub>x</sub>
emissions sources and their change over time. The observations made by the
three GOME-2 instruments will extend the existing data set by more than a
decade, and a high quality of the data as well as their good consistency
with existing time series is of particular importance.
In this paper, an improved GOME-2 NO<sub>2</sub> retrieval is described which
reduces the scatter of the individual NO<sub>2</sub> columns globally but in
particular in the region of the Southern Atlantic Anomaly. This is achieved
by using a larger fitting window including more spectral points, and by
applying a two step spike removal algorithm in the fit. The new GOME-2 data
set is shown to have good consistency with SCIAMACHY NO<sub>2</sub> columns.
Remaining small differences are shown to be linked to changes in the daily
solar irradiance measurements used in both GOME-2 and SCIAMACHY retrievals.
In the large retrieval window, a not previously identified spectral
signature was found which is linked to deserts and other regions with bare
soil. Inclusion of this empirically derived pseudo cross-section
significantly improves the retrievals and potentially provides information
on surface properties and desert aerosols.
Using the new GOME-2 NO<sub>2</sub> data set, a long-term average of tropospheric
columns was computed and high-pass filtered. The resulting map shows
evidence for pollution from several additional shipping lanes, not
previously identified in satellite observations. This illustrates the
excellent signal to noise ratio achievable with the improved GOME-2