Airborne measurements of trace gases and aerosols over the London metropolitan region
Author:
McMeeking G. R.,Bart M.,Chazette P.,Haywood J. M.,Hopkins J. R.,McQuaid J. B.,Morgan W. T.,Raut J.-C.,Ryder C. L.,Savage N.,Turnbull K.,Coe H.
Abstract
Abstract. 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) 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 30% in the background aerosol), nitrate (24% plume; 18% background) and organic aerosol (30% plume; 30% background). 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 (15% mass increase on average). Black carbon mass was the major exception, which more than doubled in the urban plume and lead to a decrease in the single scattering albedo from 0.91 in the background aerosol to 0.86 in the London plume, on average. Our observations indicated that regional aerosol appeared to dominate urban sources, 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.
Publisher
Copernicus GmbH
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