Compared to March last year, the latest observations from the European Sentinel-5P satellite show a marked decrease in nitrogen dioxide concentrations in large European cities such as Madrid, Barcelona, Paris and Milan. Containment measures to curb the COVID-19 pandemic are producing this positive temporary effect.
The COVID-19 disease caused by the new coronavirus has spread rapidly across the planet, with nearly 725,000 confirmed cases. To stop the spread of this pandemic, strict measures are being applied around the world to contain it, closing cities and even entire countries.
This cessation of activity has been reflected in a significant reduction in concentrations of pollutants, especially in large cities. Coinciding with the adoption of quarantine measures, the European Sentinel-5P satellite of the Copernicus program has recently mapped pollution in Europe and China, confirming a significant decrease in nitrogen dioxide (NO2), one of the main harmful substances emitted by vehicles. and industry.
Scientists from the Royal Netherlands Meteorological Institute (KNMI) have used data from Sentinel-5P to monitor both weather and pollution in Europe. In this way, a strong reduction in NO2 concentrations has been confirmed in European cities such as Madrid, Barcelona, Milan and Paris.
Satellite images show nitrogen dioxide concentrations between March 14 and March 25, 2020 compared to the 2019 monthly mean concentration.Henk Eskes, from KNMI, explains why they chose those dates: “The concentrations of this pollutant vary from day to day due to weather changes. It is not possible to draw conclusions based solely on data from one day. The chemistry of our atmosphere is not linear”.
“Thus, he adds, the percentage drop in concentrations may differ slightly from the drop in emissions. Atmospheric chemistry models, which observe daily changes in meteorological weather, must be combined withreverse modeling techniques to quantify emissions from satellite observations. By combining data from a specific period, ten days in this case, the meteorological variability is partially averaged and we can begin to see the impact of changes due to human activity.”.
The KNMI team, in collaboration with scientists from around the world, has begun work on a more detailed analysis using ground data, atmospheric data, and reverse modeling to interpret observed concentrations and to better estimate the influence of confinement measurements.
New estimates underway
“To obtain quantitative estimates of changes in emissions due to transportation and industry, we have to combine data from the Tropomi instrument on the Copernicus Sentinel-5P satellite with atmospheric chemistry models, "explains Henk," some studies that have already begun, but they will still take time to complete”.
Other northern European countries, such as the Netherlands and the United Kingdom, are also being watched closely, but scientists have detected greater variability due to their unstable weather conditions, a factor that must also be taken into account. New measurements taken this month will help assess changes in nitrogen dioxide over the northwest of the continent.