01 Nov 2022
01 Nov 2022
Status: this preprint is open for discussion.

Pandemic Restrictions in 2020 highlight the significance of non-road NOx sources in central London

Samuel J. Cliff1, Will Drysdale1, James D. Lee1, Carole Helfter2, Eiko Nemitz2, Stefan Metzger3,4, and Janet F. Barlow5 Samuel J. Cliff et al.
  • 1Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, YO10 5DD, UK
  • 2UK Centre for Ecology and Hydrology, Bush Estate, Penicuik, EH26 0QB, UK
  • 3Battelle, National Ecological Observatory Network. 1685 38th Street, Boulder, CO 80301, USA
  • 4Dept of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, 1225 W Dayton St, Madison, WI 53711 USA
  • 5Department of Meteorology, University of Reading, Reading, RG6 6BB, UK

Abstract. Fluxes of nitrogen oxides (NOx = NO + NO2) and carbon dioxide (CO2) were measured using eddy covariance at the BT Tower in central London during the coronavirus pandemic. Comparing fluxes to those measured in 2017 prior to the pandemic restrictions and the introduction of the Ultra-Low Emissions Zone (ULEZ) highlighted a 75 % reduction in NOx emissions between the two periods but only a 20 % reduction in CO2 emissions and a 32 % reduction in traffic load. Use of a footprint model and the London Atmospheric Emissions Inventory (LAEI) identified transport and heat and power generation to be the two dominant sources of NOx and CO2 but with significantly different relative contributions for each species. Application of external constraints on NOx and CO2 emissions allowed the reductions in the different sources to be untangled identifying that transport NOx emissions had reduced by > 75 % since 2017. This was attributed in part to the success of air quality policy in central London, but crucially due to the substantial reduction in congestion that resulted from pandemic reduced mobility. Spatial mapping of the fluxes suggests that central London was dominated by point source heat and power generation emissions during the period of reduced mobility. This will have important implications on future air quality policy for NO2 which until now, has been primarily focused on the emissions from diesel exhausts.

Samuel J. Cliff et al.

Status: open (until 13 Dec 2022)

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  • RC1: 'Comment on egusphere-2022-956', Anonymous Referee #2, 13 Nov 2022 reply

Samuel J. Cliff et al.

Samuel J. Cliff et al.


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Short summary
Emissions of nitrogen oxides (NOx) to the atmosphere are an ongoing air quality issue. This study directly measures emissions of NOx and carbon dioxide from a tall tower in central London during the coronavirus pandemic. It was found that transport NOx emissions had reduced by > 75 % since 2017 as a result of air quality policy and reduced congestion during coronavirus restrictions. During this period, central London was thought to be dominated by point source heat and power generation emissions.