Abstract
Abstract. A smoke plume, coming from an accidental fire in a textile warehouse in the north of Paris, covered a significant part of the Paris area on 17 April 2015 and seriously impacted the visibility over the megalopolis. This exceptional event was sampled with an automatic N2 Raman lidar, which operated 15 km south of Paris. The industrial pollution episode was concomitant with the long-range transport of dust aerosols originated from the Sahara, and with the presence of an extended stratus cloud cover. The analysis of the ground-based lidar profiles therefore required the development of an original inversion algorithm, using a top-down aerosol optical thickness matching (TDAM) approach. This study is, to the best of our knowledge, the first lidar measurement of a fresh smoke plume, emitted only a few hours after an accidental warehouse fire. Vertical profiles of the aerosol extinction coefficient, depolarization ratio, and lidar ratio are derived to optically characterize the aerosols that form the plume. We found a lidar ratio close to 50±10 sr for this fire smoke aerosol layer. The particle depolarization ratio is low, ∼1±0.1 %, suggesting the presence of either small particles or spherical hydrated aerosols in that layer. A Monte Carlo algorithm was used to assess the uncertainties on the optical parameters and to evaluate the TDAM algorithm.
Highlights
Accidental fires cause casualties and significant property damages
The uncertainties on aerosol optical properties retrieved from N2 Raman lidar measurements are mainly (i) bias linked to the effective vertical resolution, (ii) bias due to an inaccurate aerosol extinction coefficient (AEC) in the reference zone, (iii) bias due to the assumed model of the molecular contribution, (iv) bias due to the assumed Ångström exponent, and (v) random error associated with the signal noise characterized by the signalto-noise ratio (SNR)
We find that TDAM resolves the two peaks of AEC separated by six points, which is related to an effective vertical resolution of 270 m in this study
Summary
Accidental fires cause casualties and significant property damages. In France, one house fire occurs every 2 min, adding up to 263 000 domestic fires each year, causing about 100 deaths and 10 000 injuries (http://iaaifrance.fr/, last access: 3 December 2018). In particular, are becoming wellestablished tools that are used in the study of numerous areas of importance in the atmospheric sciences (Ansmann et al, 1992; Behrendt et al, 2007; Di Girolamo, 2004; Whiteman, 2003) The use of both Raman- and elastic-backscatter lidar signals allows the independent retrieval of the aerosol extinction and backscatter coefficients As an intermediate, Ansmann (2006) applied the two-layer approach of the Klett method to determine a pair of column lidar ratios for the boundary layer and for the lofted free tropospheric aerosol layer All these approaches are based on the premise that the elastic channel maximum range can reach an altitude where the backscattered signal is dominated by its molecular contribution (with pure Rayleigh scattering), so as to normalize the signal.
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