Variability of nitrogen oxide lifetimes and emission fluxes estimated by Sentinel-5P observations

Satellite observations of the high-resolution instrument TROPOMI on Sentinel-5P make it possible to measure nitrogen dioxide (NO₂) at city level and even to quantify the variability of NO_x emissions and lifetimes on a seasonal and daily basis.
NO₂ is an air pollutant and especially in cities of particular importance due to the large number and strength of emission sources in combination with people living nearby exposing their health to the polluted air. To quantify nitrogen oxide emissions and lifetimes with their variability in space and time, satellite data is especially suited as it provides daily global coverage and large number of measurements. The TROPOspheric Monitoring Instrument (TROPOMI) on Sentinel-5P, launched in October 2017, provides, thanks to its higher spatial resolution when compared to previous satellite instruments, the possibility of detailed investigations on lifetimes and emissions of air pollutants.
Two years of TROPOMI NO₂ data with a spatial resolution of up to 3.5 km x 5.5 km together with ECMWF ERA5 wind data are analyzed. The NO₂ data around a source is linked to the ERA5 wind data and rotated to a uniform wind direction to get clear emission patterns. Out of these two-dimensional maps of the mean NO₂ distribution, one dimensional line densities are calculated by integration across wind direction. Lifetimes and emission fluxes are calculated for different NO_x sources such as cities and power plants distributed over the world. They are compared among each other and to bottom-up emission inventories. Seasonal variability and weekday versus weekend effects in lifetimes and emissions are discussed.