Estimations of NOx emissions, NO2 lifetime and their temporal variation over three British urbanised regions in 2019 using TROPOMI NO2 observations

Abstract

Quantification of air pollutant emissions is crucial to accurately model their concentrations. Nitrogen oxides (NO_x: nitrogen dioxide NO₂ and nitric oxide NO) have adverse effects on health, agriculture and natural ecosystems both directly and due to their role in the formation of secondary pollutants. This work estimates annual total NO_x emissions, mean NO₂ lifetime, their seasonal variation and the weekday–weekend effect, over three selected British urban areas with NO₂ pollution (London, Manchester and Birmingham). The method combines an exponentially modified Gaussian fitting function and wind rotation technique, using TROPOMI tropospheric NO₂ observations together with reanalysis wind fields. The analysis for 2019 yields total emissions of 113 kT of NO_x over London, and 37 kT and 22 kT over Manchester and Birmingham, respectively. Compared to the UK National Atmospheric Emissions Inventory, this represents an increase of 6% for Manchester, 18% for London, and a decrease of 33% for Birmingham. These values are improved compared to a recent published study finding larger discrepancies with the same inventory (from 55% to 105% for the relevant cities), despite some overall consistencies. The weekday NO_x emissions are larger than at the weekend, by a factor of 1.54 for Manchester, 2.68 for London and 3.05 for Birmingham. Notably, it has been found Birmingham has a longer NO₂ mean lifetime for weekdays (∼6 h) than for the weekends (∼2 h) and Manchester presents a mean NO₂ lifetime almost 4 times higher in summer (6.13 h) than in autumn (1.64 h). More generally, the findings on emission, emission rate and lifetime suggest management of emissions might be needed for weekdays in London and Birmingham, and for weekends in Manchester.