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Sentinel-5P data map nitrogen dioxide in Finland

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Large urban areas are often marred by nitrogen dioxide pollution, caused mainly by traffic and industrial burning of fossil fuels. Data delivered by Copernicus Sentinel-5P have recently enabled scientists to estimate surface-level nitrogen dioxide concentrations in Finland.

The problem of air pollution has been an increasing cause of concern worldwide. Since early 2018, the TROPOspheric Monitoring Instrument (TROPOMI) on-board the Copernicus Sentinel-5 Precursor satellite has been delivering images of air pollution, helping globally map pollutants, such as nitrogen dioxide, methane, carbon monoxide and aerosols.

A recent study – published in the scientific journal Atmospheric Environment – describes how data from Sentinel-5P of the European Union’s Copernicus Programme, were used to estimate surface-level nitrogen dioxide in the specific conditions of Finland [1]. The results complement the Finnish ground-based measurement network, to provide invaluable information for national environmental authorities in air quality assessment and reporting.


Location of Finnish in situ air quality stations

Copyright:ESA, Virta et al [1]

Several studies have established a connection between ambient nitrogen dioxide levels and increased mortality [2]. Consequently, many countries have enacted air quality (AQ) legislation to limit these levels, with monitoring achieved using ground-based AQ stations. There are existing methods to convert satellite-borne data to surface concentrations, to complement these in situ measurements from AQ stations. This study tested and adapted these methods to the specific scenario of Finland, with its relatively low concentrations of nitrogen dioxide and its high latitude.

Surface-level nitrogen dioxide concentrations were estimated in Finland over a two-year period, between May 2018 and May 2020, by using the reprocessed Sentinel-5P Product Algorithm Laboratory nitrogen dioxide dataset and the GEOS-Chem chemical transport model. These estimates were compared with surface-level nitrogen dioxide measurements from 44 Finnish in situ AQ stations, all having a minimum measurement coverage of 80 % during the study period. This allowed for the estimation of annual mean concentrations in areas between the different AQ monitoring stations in Finland.


Estimated mean surface-level nitrogen dioxide concentrations

Copyright:ESA, Virta et al [1]

The study evaluated the performance of two methods for estimating surface-level concentration and both methods were found to have good correlation with in situ measurements. A detailed analysis of the estimations showed that they are likely affected by the relatively large size of the satellite footprint, compared to in situ stations.

Significant overestimation in areas such as residential and parkland in Helsinki may be due to the inclusion of higher concentrations from the surrounding urban areas, whereas underestimation in highly trafficked areas may be due to the inclusion of lower concentrations from their surroundings. The study concluded that while the two methods may produce differing estimates, the overall distribution of concentrations is similar for both methods.

"Prior to this study, satellite-based surface concentration estimation techniques have mostly been validated against in situ measurements in North America, or other highly polluted regions. Our results show that these established methods, using data from Sentinel-5P, also perform similarly in Finland. We hope that these results will contribute to future Finnish air quality reporting to the European Union", explains researcher Henrik Virta, from the Finnish Meteorological Institute, who led the work.

A precursor to this study was earlier research supported by ESA, where satellite-based Sentinel-5P nitrogen dioxide products were compared with ground-based reference observations in Finland’s capital city, Helsinki [3]. This research showed that overall, levels of nitrogen dioxide during weekends were 30% lower than those observed during weekdays, and that spatial distribution was partially affected by systematic wind patterns.


Urban Helsinki shows a drop in pollutants during weekends

Copyright:ESA, Ialongo et al [3]

About the Copernicus Sentinels

The Copernicus Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to the European Union's Copernicus environmental programme.

The European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites on behalf of the European Union and ensuring the flow of data for the Copernicus services, while the operations of the Copernicus Sentinels have been entrusted to ESA and EUMETSAT.

Did you know that?

Earth observation data from the Copernicus Sentinel satellites are fed into the Copernicus Services. First launched in 2012 with the Land Monitoring and Emergency Management services, these services provide free and open support, in six different thematic areas.

For instance, the Copernicus Atmosphere Monitoring Service (CAMS) (implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Commission) provides continuous data and information on atmospheric composition. It supports many applications in a variety of domains including health, environmental monitoring, renewable energies, meteorology and climatology.



[1] Virta et al. Estimating surface-level nitrogen dioxide concentrations from Sentinel-5P/TROPOMI observations in Finland. Atmospheric Environment Volume 312, 1 November 2023, 11998. 10.1016/j.atmosenv.2023.119989

[2] Huangfu et al. Long-term exposure to NO2 and O3 and all-cause and respiratory mortality: A systematic review and meta-analysis. Environment International, 144 (2020), Article 105998, 10.1016/j.envint.2020.105998

[3] Ialongo et al. Comparison of TROPOMI/Sentinel-5 Precursor NO2 observations with ground-based measurements in Helsinki. Atmospheric Measurement Techniques, 13, 205–218.