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Communication Dans Un Congrès Année : 2009

Lidar observations by circling the London orbital motorway

Résumé

A field campaign was conducted in London between 15 and 23 June 2009 in order to study the influence of emissions from within the London orbital motorway (M25) in terms of aerosol concentrations within the planetary boundary layer (PBL). The instrumental set-up involves a compact aerosol backscatter lidar, onboard a mobile van, developed by the CEA/LSCE and commercialized by LEOSPHERE Company and in situ instrumentation onboard the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 research aircraft devoted to aerosol and gas measurements. For this experiment, the eye-safe lidar has been working at the wavelength of 355 nm. These observations represent the first application of this lidar around the London area. Thanks to the excellent manoeuvrability of the van, we monitored the particulate emissions from vehicles on the M25 by circling the M25. Coordinated FAAM flights and lidar-van circuits were carried out around the M25. The possibility for the aircraft to perform vertical profiles into and out of airports gave us the opportunity to compare in situ measurements with lidar vertical profiles in terms of aerosol extinction coefficient. The aerosol extinction coefficient values shows spatial heterogeneities around the M25 and strong discrepancies were noticed between nephelometer and lidar measurements at 760 m. Such a severe discrepancy needs further investigation: the impact of clouds might be stronger and the correction of nephelometer values from relative humidity may be different, as suggested by lidar polarization observations showing higher values when relative humidity is lower. This work presents the first results of the spatiotemporal variability of aerosol concentrations in the London area. The future work particularly focuses on the link between the height of the different aerosol layers (convective PBL, nocturnal layer, residual layers...) and the aerosol loading in the low tropospheric column. The research aircraft enables a more accurate characterization of the detected plumes in terms of aerosol microphysical and optical properties. The coupling between active remote sensing and in situ measurements will allow the retrieval of vertical profiles of mass concentrations (PM10) in this urban environment with a very high vertical resolution (30 m).
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Dates et versions

hal-00667078 , version 1 (06-02-2012)

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Jean-Christophe Raut, Patrick Chazette, J. M. Haywood, P. Royer. Lidar observations by circling the London orbital motorway. 2009 AGU Fall Meeting, Dec 2009, San Francisco, United States. ⟨hal-00667078⟩
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