The maps shows 14 days averages of tropospheric Copernicus Sentinel-5 Precursor Nitrogen Dioxide measurements. Concentrations of short-lived pollutants, such as Nitrogen Dioxide, are indicators of changes in economic slowdowns and are comparable to changes in emissions. Using a 14 day average eliminates some effects which are caused by short term weather changes and clouds cover. The average gives a view over the whole time period and therefore reflects trends better than shorter time periods.
The image shows the concentration of nitrogen dioxide (NO2) in the lowest kilometers of the atmosphere. Nitrogen oxides are mainly produced by human activity and the combustion of (fossil) fuels, such as road traffic, ships, power plants and other industrial facilities. Burning activities and wildfires also contribute significantly to the NO2 concentrations observed. NO2 can have significant impacts on human health, both directly and indirectly through the formation of ozone and small particles.
The nitrogen dioxide map shown in this image is measured by the Tropomi instrument on the Sentinel 5 Precursor satellite. The Tropomi measurements are performed in the visible part of the spectrum. Because Tropomi cannot see through thick clouds, the concentrations near the surface can only be measured under cloud-free or partly cloudy conditions. More information on the Tropomi NO2 measurements and quality assessment can be found in the Product Readme file.
Nitrogen dioxide concentrations in our atmosphere, as well as the cloud cover, vary widely from day to day owing to the fluctuations of emissions, as well as variations in weather conditions. In order to visualise longer-term variations in NO2, for instance the impact of covid-19 lockdown measures on the NO2 concentrations, the image shows the concentration averaged over a period of two weeks (14 days), in steps of one week. Note that even after averaging over two weeks there are still remaining signatures of persistent weather situations. The quantification of changes in nitrogen oxide emissions requires more detailed analyses, combining the measurements with models that describe the day-to-day variability of air pollution.
The Copernicus Sentinel-5P NO2 measurements were first filtered for clouds according to the recommendation in the Product Readme file (only data with a qa_value > 0.75 was used). Then the two weeks of measurements are mapped on a fixed latitude-longitude grid of 8193 x 16385 pixels. The grid is turned into an EPSG:4326 geotiff file using the appropriate color scale, which is again turned into a EPSG:3857 tile map.
This service is provided as part of the Sentinel-5P Product Algorithm Laboratory (S5P-PAL) and contains modified Copernicus Sentinel data processed by S[&]T.
Questions regarding this service can be send to the ESA EO Support Helpdesk.