Abstract
Satellite observations of the high-resolution instrument TROPOMI on Sentinel-5 Precursor can be used to observe nitrogen dioxide (NO2) at city scales, to quantify short time variability of NOx emissions and lifetime on a seasonal and daily basis. In this study, two years of TROPOMI NO2 data, having a spatial resolution of 3.5 km x 5.5 km, together with ECMWF ERA5 wind data have been analyzed. NOx lifetimes and emission fluxes are calculated for 45 different NOx sources comprising cities and power plants, distributed around the world. The retrieved emissions are lower than the bottom-up emission inventories from EDGAR v5.0 but are in good agreement with other TROPOMI based estimates. Separation into seasons shows a clear seasonal dependence of emissions with in general the highest emissions during winter, except for cities in hot dessert climates, where the opposite is found. The NOx lifetime shows a systematic latitudinal dependence with an increase in lifetime from two to eight hours with latitude but only a weak seasonal dependence. For most of the 45 sources, a clear weekly pattern of emissions is found with weekend-to-week day ratios of up to 0.5, but with a high variability for the different locations. During the Covid-19 lockdown period in 2020 strong reductions in the NOx emissions were observed for New Delhi, Buenos Aires and Madrid.
Highlights
Nitrogen oxides (NOx) play a key role in atmospheric chemistry, air quality and climate
We present investigations of the variability of NOx emissions and lifetimes estimated from Sentinel-5P TROPOspheric Monitoring Instrument (TROPOMI) observations for selected urban areas around the world
As the operational TROPOMI tropospheric NO2 product has been reported to be low in comparison to independent measurements, part of the apparent overestimation by EDGAR could be related to a TROPOMI low bias
Summary
Nitrogen oxides (NOx) play a key role in atmospheric chemistry, air quality and climate. In the atmosphere NOx is defined 15 as the sum of nitrogen monoxide and nitrogen dioxide (NOx = NO + NO2). It is emitted into the atmosphere by both natural processes and anthropogenic activity. The dominant source of NOx is fossil-fuel combustion by anthropogenic activity, from traffic, residential heating, cooking and the industry and energy sectors. These sources are concentrated in cities and urban areas. NO2 is released in smaller amounts but is rapidly produced in the atmosphere where NO reacts with ozone (O3). During the day NO2 is photolyzed, reforming NO and producing an oxygen atom O, which forms O3 in a termolecular reaction
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