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

Samuel J. Cliff*, Will Drysdale, James D. Lee, Carole Helfter, Eiko Nemitz, Stefan Metzger, Janet F. Barlow

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Fluxes of nitrogen oxides (NOxCombining double low lineNO+NO2) and carbon dioxide (CO2) were measured using eddy covariance at the British Telecommunications (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 73 % 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 >73 % 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.

Original languageEnglish
Pages (from-to)2315-2330
Number of pages16
JournalAtmospheric Chemistry and Physics
Issue number4
Publication statusPublished - 17 Feb 2023

Bibliographical note

Funding Information:
The authors thank the National Ecological Observatory Network, a programme sponsored by the National Science Foundation and operated under cooperative agreement by Battelle. This material is based in part upon work supported by the National Science Foundation through the NEON Programme. The authors also thank Neil Mullinger and Karen Yeung (UK Centre for Ecology and Hydrology) for instrument and sample line maintenance; Ally Lewis and Rhianna Evans for help in paper preparation; and British Telecom (BT) for granting use of the tall tower for research purposes, particularly Karen Ahern and Guille Parada for arranging work permits and facilitating access to the site.

Funding Information:
This research has been supported by the UK Natural Environment Research Council and the Integrated Research Observation System for Clean Air project (grant nos. NE/T001917/1, NE/T001798/2) as well as through UKCEH's UK-SCAPE programme delivering National Capability (grant no. NE/R016429/1). Samuel Cliff was supported by the Panorama Natural Environment Research Council (NERC) Doctoral Training Partnership (DTP) (grant no. NE/S007458/1).

Publisher Copyright:
© Author(s) 2023

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