Determination of NOx Sources by Combination of Satellite Images with Transport Modelling

Tropospheric nitrogen oxides (NO_X) play a key role in tropospheric photochemistry, being a limiting factor of tropospheric ozone production. NO_X have various sources with highly uncertain magnitudes. Therefore, the main task of our work is to combine GOME satellite image sequences with Lagrangian transport models to determine tropospheric NO_X sources. We focussed on case studies on different NO_X sources. So far we investigated biomass burning, NO_X industrial, NO_X and lightning NO_X. To simulate the atmospheric transport of these emissions we used the Lagrangian particle dispersion model FLEXPART (see http://www.fw.tum.de/EXT/LST/METEO/stohl).Firstly, we investigated transport of NO_X emissions from Canadian forest fires during August 1998 (Spichtinger et al. 2001), using a dispersion model calculations, Total Ozone Mapping Spectrometer (TOMS) aerosol index data, and tropospheric NO₂ columns derived from the GOME satellite data. We tracked an NO_X plume from forest fire hot spots, via the Atlantic Ocean, to the west coast of Europe. An NO₂ plume, comparable in magnitude to values over major anthropogenic emission regions, was found in the GOME data over the largest fire. This plume could be traced to Greenland on subsequent days. A weaker signal, very likely also due to the forest fires, was detected over the Atlantic Ocean and even close to Europe.Secondly, we studied intercontinental transport of nitrogen oxides from South African power plants to Australia in May 1998. This episode was also simulated with FLEXPART, which used NO_X emissions from the Global Emissions Inventory Activity (GEIA). Emission densities of the highly industrialised Highveld are among the highest in the world. Additionally, lightning emissions were added by utilising LIS data. Lightning NO_X amounted to around 10% of the simulated concentrations. Recently, the forest fire analysis was extended to a climatology of the fire seasons 1997 and 1998 with a focus on Siberian forest fire emissions. The fire season (May to October) of 1998 was, in contrast to 1997, very intense and dominated by very high fire activity in both Canada and Siberia. Transport of forest fire emissions was simulated with FLEXPART over the whole burning season 1998. NO_X was emitted from Siberian and Canadian forest fires according to the fire information from ATSR. The FLEXPART simulation shows that the strong boreal forest fires in 1998 enhanced both the TOMS aerosol index as well as GOME tropospheric column densities.Due to considerable uncertainties in the satellite data, in the chemical partitioning of NO_y, and wet and dry removal thereof, and unknown variations in fire intensity the results are rather qualitative. Climatalogical investigations and the quantification of NO_X emissions are our main future tasks.