Characterization of forest fire smoke event near Washington, DC in summer 2013 with multi-wavelength lidar

摘要

The multi-wavelength lidar technique was applied to the study of a smokeevent near Washington, DC on 26–28 August 2013. Satellite observationscombined with transport model predictions imply that the smoke plumeoriginated mainly from Wyoming/Idaho forest fires and its transportation toWashington, DC took approximately 5 days. The NASA Goddard Space Flight Center (GSFC) multi-wavelengthMie–Raman lidar was used to measure the smoke particle intensive parameterssuch as extinction and backscatter Ångström exponents together withlidar ratios at 355 and 532 nm wavelengths. For interpretation of theobserved vertical profiles of the backscatter Ångström exponentsγ at 355–532 and 532–1064 nm, numerical simulation wasperformed. The results indicate that, for fine-mode dominant aerosols, theÅngström exponents γ(355–532) and γ(532–1064) have essentially different dependence on the particlesize and refractive index. Inversion of 3 β + 2 α lidarobservations on 27–28 August provided vertical variation of the particlevolume, effective radius and the real part of the refractive index throughthe planetary boundary layer (PBL) and the smoke layer. The particle effective radius decreased withheight from approximately 0.27 μm inside the PBL to 0.15 μm inthe smoke layer, which was situated above the PBL. Simultaneously the realpart of the refractive index in the smoke layer increased to ≈ 1.5. The retrievals demonstrate also that the fine mode ispredominant in the particle size distribution, and that the decrease of theeffective radius with height is due to a shift of the fine mode towardsmaller radii.