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Discussion papers | Copyright
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Research article 09 Jul 2018

Research article | 09 Jul 2018

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

A study of long-range transported smoke aerosols in the Upper Troposphere/Lower Stratosphere

Qiaoyun Hu1, Philippe Goloub1, Igor Veselovskii2, Juan-Antonio Bravo-Aranda3, Ioana Popovici1,4, Thierry Podvin1, Martial Haeffelin3, Anton Lopatin5, Christophe Pietras3, Xin Huang5, Benjamin Torres1, and Cheng Chen1 Qiaoyun Hu et al.
  • 1Univ. Lille, CNRS, UMR8518 – LOA – Laboratoire d’Optique Atmosphérique, 59000 Lille, France
  • 2Physics Instrumentation Center of GPI, Troitsk, Moscow, 142190, Russia
  • 3Institut Pierre Simon Laplace, École Polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France
  • 4CIMEL Electronique, 75011 Paris, France
  • 5GRASP-SAS, Remote sensing developments, 59650 Villeneuve d’Ascq, France

Abstract. Long-range transported smoke aerosols in the UTLS (Upper Troposphere/Lower Stratosphere) over Europe were detected in Summer 2017. The measurements of ground-based instruments and satellite sensors indicate that the UTLS aerosol layers were originated from Canadian wildfires and were transported to Europe by UTLS advection. In this study, the observations of two multi-wavelength Raman Lidar systems in northern France (Lille and Palaiseau) are used to derive aerosol properties, such as optical depth of the UTLS layer, Lidar ratios at 355 and 532nm and particle linear depolarization ratios at 355, 532 and 1064nm. The optical depth of the UTLS layers at 532nm varies from 0.05 to above 0.20, with very weak spectral dependence between 355 and 532nm. Lidar ratios at 355nm are in 31±15sr to 45±9sr range and at 532nm, the Lidar ratios are in the range of 54±12sr to 58±9sr. Such spectral dependence of Lidar ratio is known to be a characteristic feature of aged smoke. The typical particle depolarization ratios in the UTLS smoke layer are 25±4% at 355nm, 19±3% at 532nm and 4.5±0.8% at 1064nm. The relatively high depolarization ratios and such spectral dependence are an indication of a complicated morphology of aged smoke particles. We found an increase of depolarization ratio versus transport time. The depolarization ratio at 532nm increases from below 2–5% for fresh smoke to over 20% for smoke aged more than 20 days. The 3β+2α observations of two cases at Palaiseau and Lille sites were inverted to the aerosol microphysical properties using regularization algorithm. The particles distribute in the 0.1–1.0μm range with effective radius of 0.33±0.10μm for both cases. The derived complex refractive indices are 1.520.05)+i0.0210.010) and 1.550.05)+i0.0280.014) for Palaiseau and Lille data. The retrieved aerosol properties were used to calculate the direct radiative forcing (DRF) effect specific to the UTLS aerosol layers. The simulations derive daily net DRF efficiency of −79.6Wm−2τ−1 at the bottom of the atmosphere for Lille observations. At the top of the atmosphere, the net DRF efficiency is −7.9Wm−2τ−1. The results indicate that the UTLS aerosols strongly reduce the radiation reaching the terrestrial surface by absorption. The heating rate of the UTLS layers is estimated to be 3.7Kday−1. The inversion of Palaiseau data leads to similar results. The heating rate predicts a temperature increase within the UTLS aerosol layer, which has been observed by the radiosonde temperature measurements.

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Short summary
Smoke plumes generated in the Canadian fire activities were lifted to the upper troposphere/lower stratosphere and transported across the Pacific from North America to Europe. It indicates that fire activities can be an important role in global air quality and radiation budget. Our results provide a comprehensive characterisation for smoke aerosols at such high altitude by using multi-wavelength Raman Lidars and a evaluation of the radiative effect of the smoke plumes.
Smoke plumes generated in the Canadian fire activities were lifted to the upper...