Abstract
Abstract. Satellite observations of the high-resolution TROPOspheric Monitoring Instrument (TROPOMI) on Sentinel-5 Precursor can be used to observe nitrogen dioxide (NO2) at city scales to quantify short time variability of nitrogen oxide (NOx) emissions and lifetimes on a daily and seasonal basis. In this study, 2 years of TROPOMI tropospheric NO2 columns, having a spatial resolution of up to 3.5 km × 5.5 km, have been analyzed together with wind and ozone data. NOx lifetimes and emission fluxes are estimated for 50 different NOx sources comprising cities, isolated power plants, industrial regions, oil fields, and regions with a mix of sources distributed around the world. The retrieved NOx emissions are in agreement with other TROPOMI-based estimates and reproduce the variability seen in power plant stack measurements but are in general lower than the analyzed stack measurements and emission inventory results. Separation into seasons shows a clear seasonal dependence of NOx emissions with in general the highest emissions during winter, except for isolated power plants and especially sources in hot desert climates, where the opposite is found. The NOx lifetime shows a systematic latitudinal dependence with an increase in lifetime from 2 to 8 h with latitude but only a weak seasonal dependence. For most of the 50 sources including the city of Wuhan in China, a clear weekly pattern of NOx emissions is found, with weekend-to-weekday 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=nitrogen monoxide (NO) + NO2) play a key role in atmospheric chemistry, air quality, and climate
The exponentially modified Gaussian (EMG) method was applied to the mean TROPOspheric Monitoring Instrument (TROPOMI) NO2 column data of the selected regions, and nitrogen oxide (NOx) emissions and lifetimes were calculated for all available TROPOMI measurements of the 2-year period from 1 March 2018 to 29 February 2020 and separated into seasons, working days and weekends, and pre-Covid-19 times and the Covid19 pandemic
The NOx emission estimates from this study are first compared to results from other recent studies (Beirle et al, 2019; Goldberg et al, 2019; Lorente et al, 2019), which estimated NOx emissions with TROPOMI data
Summary
Nitrogen oxides (NOx=NO + NO2) play a key role in atmospheric chemistry, air quality, and climate. They are emitted into the atmosphere by both natural processes and human activity. Microbial processes in soils, and naturally occurring wildfires. The dominant source of NOx is fossil-fuel combustion from traffic, residential heating, cooking, and the industry and energy sectors. These sources are concentrated in cities and urban areas. Biomass burning and the use of fertilizers are significant sources of NOx (Jacob, 1999; Seinfeld and Pandis, 2006; Stocker, 2014)
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