Preprints
https://doi.org/10.5194/acp-2021-180
https://doi.org/10.5194/acp-2021-180

  24 Mar 2021

24 Mar 2021

Review status: this preprint is currently under review for the journal ACP.

Spatially and temporally resolved measurements of NOx fluxes by airborne eddy-covariance over Greater London

Adam R. Vaughan1, James D. Lee1,2, Stefan Metzger3,4, David Durden3, Alastair C. Lewis1,2, Marvin D. Shaw1,2, Will S. Drysdale1,2, Ruth M. Purvis1,2, Brian Davison5, and C. Nicholas Hewitt5 Adam R. Vaughan et al.
  • 1Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, YO10 5DD, UK
  • 2National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK
  • 3National Ecological Observatory Network Program, Battelle, 1685 38th Street, Boulder, CO 80301, USA
  • 4Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, 1225 West Dayton Street, Madison, WI 53706, USA
  • 5Lancaster Environment Centre, Lancaster University, Lancaster, UK

Abstract. Flux measurements of nitrogen oxides (NOx) were made over London using airborne eddy-covariance from a low flying aircraft. Seven low altitude flights were conducted over Greater London performing multiple over-passes across the city during eight days in July 2014. NOx fluxes across the Greater London region exhibited high heterogeneity and strong diurnal variability, with central areas responsible for the highest emission rates (20–30 mg m−2 h−1). Other high emission areas included the M25 orbital motorway. The complexity of London’s emission characteristics makes it challenging to pinpoint single emission sources definitively using airborne measurements. Multiple sources, including road transport and residential, commercial and industrial combustion sources are all likely to contribute to measured fluxes. Measured flux estimates were compared to scaled National Atmospheric Emissions Inventory (NAEI) estimates, accounting for; monthly, daily and hourly variability. Significant differences were found between the flux-driven emissions and the NAEI estimates across Greater London, with measured values up to two times higher in Central London than those predicted by the inventory. To overcome the limitations of using the national inventory to contextualise measured fluxes, we used physics-guided flux data fusion to train environmental response functions (ERF) between measured flux and environmental drivers (meteorological and surface). The aim was to generate time-of-day emission surfaces using calculated ERF relationships for the entire Greater London region (GLR). 98 % spatial coverage was achieved across GLR at 400 m2 spatial resolution. All flight leg projections showed substantial heterogeneity across the domain, with high emissions emanating from Central London and major road infrastructure. The diurnal emission structure of the GLR was also investigated, through ERF, with the morning rush-hour distinguished from lower emissions during the early afternoon. Overall, the integration of airborne fluxes with an ERF-driven strategy enabled the first independent generation of surface NOx emissions, at high resolution using an eddy-covariance approach, for an entire city region.

Adam R. Vaughan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-180', Anonymous Referee #2, 26 May 2021
  • RC2: 'Comment on acp-2021-180', Anonymous Referee #1, 04 Jun 2021

Adam R. Vaughan et al.

Adam R. Vaughan et al.

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Short summary
Validating emissions estimates of atmospheric pollutants is a vital pathway towards reducing urban concentrations of air pollution and ensuring effective legislative controls are implemented. The work presented here highlights a strategy capable of quantifying and spatially disaggregating NOx emissions over challenging urban terrain. This work shows great scope as a tool for emission inventory validation and independent generation of high-resolution surface emissions on a city-wide scale.
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