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GOME NO2
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VALIDATION

Tropospheric NO2 from GOME measurements  


Introduction    Data    FAQ   References    Links    Contact

Top Introduction:

Nitrogen dioxide plays an important role in both troposphere and stratosphere.  It is involved in catalytic ozone destruction and at the same time in the “buffering” of ozone destroying halogen oxides into more stable reservoir substances. In the troposphere, NO2 is one of the key players in the formation of photochemical smog during pollution episodes. Locally, it may also contribute to radiative forcing.

From GOME measurements, NO2 columns can be retrieved in the 425-450 nm region. NO2 columns are part of the GOME lv2-products provided by DLR, but at the IUP Bremen an offline scientific NO2 product is created. The GOME measurements contain both tropospheric and stratospheric contributions, and a separation algorithm has to be used if tropospheric columns are the quantity of interest. In the case of NO2, the most simple method is to use the Pacific sector as a clean background value and to assume that stratospheric NO2 is zonally homogeneous. The difference between the actual measurement and the reference sector interpreted as tropospheric excess.

As an example, the plot shows tropospheric excess NO2 from GOME for 1999. In addition to a general offset over the continents, strongly enhanced NO2 columns are detected over the industrialised parts of the world and in regions of intense biomass burning. There also is some indication of NO2 from lightning over Africa and for transport from the US, Asia and Africa to the Oceans.

Top Data:

Total columns of NO2 based on GOME Near Real Time data can be found on the GOME NRT page.

Monthly averaged tropospheric NO2 columns for the POET project can be downloaded here.

Stratospheric NO2 column data can be found on the QUILT page.

If you have any requests, please contact Andreas Richter.

Top FAQ:

  • Why are there only individual stripes of data?
    The stripes of data are the individual orbits of GOME measurements. There are 14 orbits per day, each of which has a swath width of 960 km. Together, they cover the globe within 3 days. Please note that it takes 35 days until the orbit pattern is repeated exactly (repeat cycle). Therefore, the measurements sample a given location on earth slightly differently over the course of a month which improves the spatial resolution in monthly averages over the resolution of an individual GOME measurement.
  • Why are the satellite swaths sometimes so much smaller?
    On some days (the 5th, the 10th, and the 25th of a month) GOME is operated in a special "narrow swath" mode. In this mode, the spatial resolution is improved to 80 x 40 km2 but the spatial coverage is reduced as result of the smaller swath (240 km instead of 960 km).

  • Why are there sometimes two orbits close to each other around 150° longitude while on other days there is a wider gap between orbits?
    The daily maps produced here are based on all orbits with their first measurement on the day of interest, where time is UT. However, the UT date change occurs somewhere in the middle of one of the orbits close to 150° longitude, and depending on where this change happens, one orbit more or less will be displayed for a given day. In those cases where two orbits are close to each other, the difference in time is nearly 24 hours which often can be seen as a mismatch of flow patterns.

  • Why are so many pixels missing?
    Most of the gaps in the time series are either times when the instrument or the complete satellite was down or cloudy scenes which were removed from the tropospheric columns.

  • Why are there negative values in the tropospheric columns?
    The quantity plotted is the tropospheric excess column of NO2, which is the surplus of NO2 as compared to a clean region. Therefore, the background of tropospheric NO2 is missing in the data, which is introducing a negative offset. In addition, the analysis is based on the assumption that the stratospheric NO2 field variation is correctly reproduced by the SLIMCAT model, and errors are introduced if this does not hold (for example in spring or close to the polar vortex).

  • What is the spatial resolution of GOME?
    The spatial resolution of GOME is 320 x 40 km2 in standard mode and 80 x 40 km2 for the narrow swath measurements (see above).

Top References:

Top Links:

Top Contact:

If you are interested in more information or GOME tropospheric NO2 data, please contact Andreas Richter.