Scientists from the Royal Netherlands Meteorological Institute (KNMI) have been using data from the Copernicus Sentinel-5P satellite to monitor both weather and pollution over Europe. Recently, the Copernicus Sentinel-5P satellite mapped air pollution across Europe and China, revealing a significant drop in nitrogen dioxide concentrations. Researchers say this is correlated to the quarantines in effect due to COVID-19. The new images clearly illustrate a strong reduction of nitrogen dioxide concentrations over major cities across Europe, specifically Milan, Paris, and Madrid. These images, using data from the Copernicus Sentinel-5P satellite, show the average nitrogen dioxide concentrations from March 14 to 25, 2020, compared to the monthly average concentrations from 2019. Credit: Contains modified Copernicus Sentinel data (2019-20). Courtesy of KNMI/ESA The satellite images show nitrogen dioxide concentrations from March 14 to 25, 2020, compared to the monthly average of concentrations from 2019. “The nitrogen dioxide concentrations vary from day to day due to changes in the weather,” Henk Eskes, from KNMI, said. “Conclusions cannot be drawn based on just one day of data alone.” By combining data for a specific period of time, in this case 10 days, the meteorological variability partly averages out and shows the impact of changes due to human activity, he said. “The chemistry in our atmosphere is nonlinear,” Eskes continued. “Therefore, the percentage drop in concentrations may differ somewhat from the drop in emissions. Atmospheric chemistry models, which account for daily changes in weather, in combination with inverse modeling techniques are needed to quantify the emission based on the satellite observations.” The KNMI team, in collaboration with scientists worldwide, have started to work on a more detailed analysis using ground data, weather data, and inverse modeling to interpret the concentrations observed and to estimate the influence of the shutdown measures. “For quantitative estimates of the changes in the emissions due to transportation and industry, we need to combine the TROPOMI data from the Copernicus Sentinel-5P satellite with models of atmospheric chemistry. These studies have started but will take some time to complete,” Eskes said. Other countries in northern Europe are being closely monitored, including the Netherlands and the United Kingdom, but scientists have observed a larger variability owing to changing weather conditions. New measurements from this week will help to assess the changes in nitrogen dioxide over northwest Europe. “The special features of the Copernicus Sentinel-5P satellite, with its high spatial resolution and accurate ability to observe trace gases compared to other atmospheric satellite missions, allows for the generation of these unique nitrogen dioxide concentration measurements from space,” said Claus Zehner, ESA’s Copernicus Sentinel-5P mission manager. “The long-term cooperation between ESA and KNMI proves very valuable and shows the importance of complementary analyses by different partner organizations,” said Josef Aschbacher, ESA’s director of Earth observation programs. “As we can see, the Copernicus Sentinel-5P satellite is the best satellite equipped to monitor nitrogen dioxide concentrations on a global scale.”