Satellites are the best available measuring instruments to detect man-made pollution worldwide. Atmospheric scientist Pieternel Levelt initiated OMI and TROPOMI, two of the most prestigious measuring instruments for the detailed mapping of harmful pollutants in the atmosphere.

TROPOMI, the latest of the two, is capable of identifying and studying sources of pollution with even greater precision. The recently launched satellite will also be monitoring the main greenhouse gas emissions. 

Air quality

Both satellite instruments are orbiting at a distance of hundreds of kilometres from the earth and play a leading role in monitoring various pollutants which are affecting air quality and climate. OMI, TROPOMI’s precursor, has been active since 2004 and is still producing important data. ‘OMI boasts the longest measurement series for nitrogen dioxide and sulphur dioxide in the atmosphere. After 13 years it is still in very good condition, which is rare for a satellite instrument,’ Levelt says.

The data produced by both instruments can tell scientists all sorts of thing, including the country’s main religion,’ Levelt explains. ‘Economic activities and other human interventions which impact on the atmosphere can be traced through the amount of nitrogen dioxide produced by a given country. On religious holidays the amount is much smaller. The data will tell you economic growth in Dubai has stopped, while nitrogen dioxide emissions in China have been growing since 2014, and are increasing in India and Africa.’


TROPOMI, which was launched on October 13, is different from OMI in a number of important ways. The instrument’s resolution is ten times greater – and this opens new doors for scientists. Levelt: ‘TROPOMI has a spatial resolution of 3.5 by 7 kilometres, which makes it possible to identify different sources of air pollution. In a city like Rotterdam, for example, we can distinguish between the emissions from the port area and those produced by the city centre. In that context it will be interesting to see whether or not measures to combat pollution are making a difference. The resolution is powerful enough to monitor a plume of smoke from the larger industrial areas in time, which will give us an idea of how such plumes, resulting from industry or forest fires, develop.

Greenhouse gases

TROPOMI is also capable of measuring two of the main greenhouse gases, i.e. methane and ozone which occur in the troposphere, the lower part of the earth’s atmosphere. After CO2 these are the greenhouse gases most instrumental in climate change, Levelt says. ‘Moreover, ozone is poisonous, a real threat to the troposphere. We have expressly designed TROPOMI to determine ozone concentrations more precisely. We also want to get a better idea about the role it plays in relation to climate change. The fact is that we don’t really know how much ozone there is in the troposphere, which is also true about the amount of dust particles in the atmosphere. TROPOMI can help us find out, although this will still be a bit of a challenge.’


There is only one way to tackle the problem, Levelt says, and that is by increasing the number of measurements and so build a bigger knowledge base. ‘Monitoring, carrying out solid and precise measurements, that is our most important role. TROPOMI may not be the only instrument in the field but it is a major data contributor.’

Satellite measurements are a reliable resource for monitoring air pollutants, Levelt concludes. At present the knowledge about the amount of air pollutants released into the atmosphere is based mainly on information provided by state services or companies. ‘Whereas a single satellite can monitor pollution all over the globe’, Levels says. ‘They make excellent verification instruments, not just to measure pollution in the Netherlands but worldwide.’


The TROPOMI project was commissioned by the Netherlands Space Office (NSO) and is financed by the ministries of Economic Affairs, Infrastructure and Environment and Education, Culture and Science, as well as the European Space Agency (ESA).

The TROPOMI instrument was designed and built on the instruction of the Dutch government and the European Space Agency (ESA). The principal investigator is provided by weather bureau KNMI while the co-principal investigator is provided by SRON. Airbus Defence and Space Nederland is the main contractor for TROPOMI. TNO is responsible for the optomechanical design. The development of TROPOMI data products is a joint project partnered by institutes from The Netherlands, Germany, Great Britain and Finland.

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Published: October 2017