Although Aura is one of the US-launched Earth Observing System satellites, it includes instruments made by scientists from around the world. An excellent example is the Ozone Monitoring Instrument -- OMI -- made by scientists in the Netherlands and used to watch the formation of air pollution over Europe. OMI can measure the level of nitrogen oxides (NOx) in a 10 km column of air above the surface; the presence of nitrogen oxides, particularly nitrogen dioxide (NO2) is a strong indicator of smog.
The gas - which comes from motor vehicle exhausts, power plants and industry - is an important precursor in the production of ground-level ozone, part of the photochemical smog that can blight city air, particularly in summer.
By following the development and spread of NO2, OMI can be used to help make forecasts of where problem air might develop. Long-term tracking of the gas can also identify emission hotspots.
The Dutch scientists use the OMI readings to generate daily maps of NO2 levels above Europe. To an extent the results aren't terribly surprising; the air above cities like London, Paris and Rotterdam is far dirtier than the air above rural and smaller urban areas. It is useful, however, to see how the NO2 moves, and -- as with many of the satellite studies -- the primary value comes from continued monitoring of changes, so as to better see the real-world effects of mitigation programs.
OMI measures more than just Europe, of course. Aura is on a polar orbit, so covers all of the Earth; the OMI team intends to expand their daily reports to more cities around the globe in the coming months and years.
(Thanks, Tim du Toit)
Interesting, how powerful computeres calculate such analysis and maps?