References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-12-5163-2012

Airborne measurements of trace gases and aerosols over the London metropolitan region

McMeeking

G. R.

¹ ⁹ Bart

² ¹⁰ Chazette

³ Haywood

J. M.

⁴ ⁵ Hopkins

J. R.

⁶ McQuaid

J. B.

² Morgan

W. T.

¹ Raut

J.-C.

⁷ Ryder

C. L.

⁸ Savage

⁴ Turnbull

⁴ Coe

Centre for Atmospheric Science, University of Manchester, Manchester, UK

School of Earth and Environment, University of Leeds, Leeds, UK

Laboratoire des Sciences du Climat et de l'Environnement, Laboratoire mixte CEA-CNRS-UVSQ, CEA Saclay, Gif-sur-Yvette, France

Observation Based Research, Met Office, Exeter, UK

College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK

Department of Chemistry, University of York, York, UK

Laboratoire Atmosphères, Milieux et Observations Spatiales, Laboratoire mixte CNRS-UVSQ-UPMC, Université Paris, Paris, France

Department of Meteorology, University of Reading, Reading, UK

now at: Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

now at: Aeroqual, 109 Valley Road, Auckland 1024, New Zealand

13 06 2012

12 11 5163 5187

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/5163/2012/acp-12-5163-2012.pdf

The Emissions around the M25 motorway (EM25) campaign took place over the megacity of London in the United Kingdom in June 2009 with the aim of characterising trace gas and aerosol composition and properties entering and emitted from the urban region. It featured two mobile platforms, the UK BAe-146 Facility for Airborne Atmospheric Measurements (FAAM) research aircraft and a ground-based mobile lidar van, both travelling in circuits around London, roughly following the path of the M25 motorway circling the city. We present an overview of findings from the project, which took place during typical UK summertime pollution conditions. Emission ratios of volatile organic compounds (VOCs) to acetylene and carbon monoxide emitted from the London region were consistent with measurements in and downwind of other large urban areas and indicated traffic and associated fuel evaporation were major sources. Sub-micron aerosol composition was dominated by secondary species including sulphate (24% of sub-micron mass in the London plume and 29% in the non-plume regional aerosol), nitrate (24% plume; 20% regional) and organic aerosol (29% plume; 31% regional). The primary sub-micron aerosol emissions from London were minor compared to the larger regional background, with only limited increases in aerosol mass in the urban plume compared to the background (~12% mass increase on average). Black carbon mass was the major exception and more than doubled in the urban plume, leading to a decrease in the single scattering albedo from 0.91 in the regional aerosol to 0.86 in the London plume, on average. Our observations indicated that regional aerosol plays a major role on aerosol concentrations around London, at least during typical summertime conditions, meaning future efforts to reduce PM levels in London must account for regional as well as local aerosol sources.

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