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Discussion papers
https://doi.org/10.5194/acp-2019-955
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-955
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 06 Nov 2019

Submitted as: research article | 06 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Megacity and local contributions to regional air pollution: An aircraft case study over London

Kirsti Ashworth1,*, Silvia Bucci2,*, Peter J. Gallimore3,*, Junghwa Lee4,a,*, Beth S. Nelson5,*, Alberto Sanchez Marroquin6,*, Marina B. Schimpf7,b,*, Paul D. Smith8, Will S. Drysdale5,c, Jim R. Hopkins5,c, James D. Lee5,c, Joe R. Pitt9, Piero Di Carlo10,**, Radovan Krejci11,**, and James B. McQuaid6,** Kirsti Ashworth et al.
  • 1Lancaster Environment Centre, Lancaster University, LA1 4YQ, UK
  • 2Laboratoire de Météorologie Dynamique, UMR8539, IPSL, CNRS/PSL-ENS/Sorbonne Université/École Polytechnique, Paris, France
  • 3Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
  • 4Institute of Meteorology and Climatology, Leibniz Universität Hannover, Hannover, Germany
  • 5Wolfson Atmospheric Chemistry Laboratory, Department of Chemistry, University of York, YO10 5DD, UK
  • 6School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
  • 7Facility for Airborne Atmospheric Measurements (FAAM), Cranfield, MK43 0AL, UK
  • 8Swedish University of Agricultural Sciences, Svartberget Fieldstation, SE-92291 Vindeln, Sweden
  • 9School of Earth and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
  • 10Department of Psychological, Health & Territorial Sciences, University "G. d'Annunzio" of Chieti-Pescara, Chieti, Italy
  • 11Department of Environmental Science and Analytical Chemistry (ACES) & Bolin Centre for Climate Research, Stockholm University, S-10691 Stockholm, Sweden
  • anow at: Department of Modelling of Atmospheric Processes, Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
  • bnow at: German Aerospace Centre (DLR), Institute of Atmospheric Physics, Oberpfaffenhofen, Germany
  • cNational Centre for Atmospheric Science, University of York, York, YO10 5DD
  • *Participant of STANCO training school
  • **Co-PI of STANCO training school

Abstract. In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Aircraft Research). Measurements were made from the UK’s Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 Atmospheric Research Aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different airmass origins over the two days such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events.

The background air upwind of London was relatively clean during both days; concentrations of CO were 88–95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6–1.8 ppbv, and NOx were 0.7–0.8 ppbv. Downwind of London, we encountered elevations in all species with CO > 100 ppbv, VOCs 2.8–3.8 ppbv, CH4 > 2080 ppbv and NOx > 4 ppbv, and peak concentrations in individual pollution events higher still. Levels of O3 were inversely correlated with NOx during the first flight, with O3 concentrations of 37 ppbv upwind falling to ~ 26 ppbv in the well-defined London plume. Mass balance techniques were applied to estimate pollutant fluxes from London. Our calculated CO2 fluxes are within 10 % of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO.

On the second day, winds were lighter and downwind O3 concentrations were elevated to ~ 39–43 ppbv (from ~ 32–35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear spikes from local sources.

This series of flights demonstrated that megacity outflow, local fresh emissions and more distant UK sources of pollution all contribute to pollution events in the southeast of the UK. These sources must therefore all be well-characterised and constrained to understand air quality around London.

Kirsti Ashworth et al.
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Short summary
In July 2017 we flew 3 research flights around London during a European Facility for Airborne Research (EUFAR) training school. We made continuous measurements of concentrations of key pollutants (ozone, NOx, aerosol particles, CO, CO2 and methane) and meteorology, and collected periodic samples of air to analyse for volatile organic compounds. We saw evidence that plumes of pollution from the city, strong local emissions and pollution from distant sources all contribute to regional pollution.
In July 2017 we flew 3 research flights around London during a European Facility for Airborne...
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