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Left behind after these subtractions is the desired 'signal' of narrower trace gas spectral absorption patterns, to be identified against sample cross sections. Applied to SCIAMACHY results, this technique is sufficiently sensitive to retrieve columns lower than a few parts of nitrogen dioxide per billion parts of air. To give an idea of scale, above highly polluted conurbations such as London, NO2 mixing ratios can reach values as high as a hundred parts per billion.

Nitrogen dioxide maps like that shown here have been produced using nadir-sounding data: while NO2 vary widely across the troposphere they are evenly spread across the upper atmosphere, the stratosphere. So nitrogen dioxide levels measured above the remotest parts of the Pacific were used to determine a general column for stratospheric nitrogen dioxide, which could be subtracted from the global data to determine tropospheric vertical column values.

"Results from this and other similar sensors could be used for chemical weather and air quality prediction in future," Beirle added. "For now we are focused on using the SCIAMACHY results to quantify the contributions of the different sources of nitrogen oxides such as fossil fuel combustion, biomass burning, lightning especially as the value of the latter is still highly uncertain."

About SCIAMACHY

SCIAMACHY is a spectrometer that maps the air over a very wide wavelength range, which allows detection of trace gases, ozone and related gases, clouds and dust particles throughout the atmosphere. It works by measuring sunlight, transmitted, reflected and scattered by the earth's atmosphere or surface in the ultraviolet, visible and near infrared waveleng
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Contact: Mariangela D'Acunto
mariangela.d'acunto@esa.int
39-069-418-0856
European Space Agency
11-Oct-2004