Earlier this year, the first data from the new Earth observation satellite Sentinel‑5P were released, providing a wealth of information about air quality. The results of quality checks carried out at ECMWF on ozone and nitrogen dioxide data from Sentinel‑5P are very promising.
Sentinel‑5P – the precursor to Sentinel‑5 – is the first satellite mission in Europe’s Copernicus Earth observation programme to be dedicated to monitoring atmospheric composition. Data from the mission will help to address global issues such as air quality, climate change and the ozone layer. Information from Sentinel‑5P will be used for air quality forecasting by the Copernicus Atmosphere Monitoring Service (CAMS), which is implemented by ECMWF on behalf of the European Commission. Processed data products will better equip Europe to address some of the challenges affecting citizens in their daily lives.
Sentinel‑5P hosts the state-of-the-art TROPOMI (Tropospheric Monitoring Instrument) spectrometer, which maps trace gases that affect our health and the climate. TROPOMI can also identify the location of significant emissions and their impact on atmospheric concentrations of key pollutants. This will help to better mitigate air quality problems and to provide better air quality forecasts.
Data evaluation
After its launch in October 2017, Sentinel‑5P data were evaluated and instruments were calibrated during a nine-month commissioning phase. Early data were compared with the CAMS global forecasting system, which is based on ECMWF’s Integrated Forecasting System (IFS). This made it possible to detect and solve teething problems.
Near-real-time (NRT) TROPOMI total column ozone and nitrogen dioxide retrievals were included passively in the CAMS system in July 2018 on the day they were officially released by the European Space Agency (ESA). Since then the data have been routinely monitored by ECMWF and plots can be found on the CAMS website (https://atmosphere.copernicus.eu/). ‘Monitoring’ in this case means that differences between the forecast model and the TROPOMI observations are calculated, allowing us to assess the quality of the data. However, at this early stage the data are not actively assimilated, hence they do not yet influence the CAMS forecasts.
Early impressions for ozone and nitrogen dioxide are that the data look very promising, and assimilation tests with the data are now beginning in parallel to the routine monitoring. If these tests are successful, assimilation of the data will be activated in the CAMS NRT system in the near future. Other retrievals from TROPOMI, including carbon monoxide, sulphur dioxide, formaldehyde and methane, will also be included in the CAMS system once the data become available later this year.
Outlook
We expect that Sentinel-5P will soon become one of the most important data sources underpinning the quality of CAMS information products. If all goes well, Sentinel-5P data will soon feed into daily global and European air-quality forecasts, ensuring that CAMS will be able to provide users with an improved reliable and quality-assured service.
