Abstract. We present spectrally resolved optical and microphysical properties of
western Canadian wildfire smoke observed in a tropospheric layer from
5–6.5 km height and in a stratospheric layer from 15–16 km height during
a record-breaking smoke event on 22 August 2017. Three polarization/Raman
lidars were run at the European Aerosol Research Lidar Network (EARLINET)
station of Leipzig, Germany, after sunset on 22 August. For the first time,
the linear depolarization ratio and extinction-to-backscatter ratio (lidar
ratio) of aged smoke particles were measured at all three important lidar
wavelengths of 355, 532, and 1064 nm. Very different particle depolarization
ratios were found in the troposphere and in the stratosphere. The obviously
compact and spherical tropospheric smoke particles caused almost no
depolarization of backscattered laser radiation at all three wavelengths
(<3 %), whereas the dry irregularly shaped soot particles in the
stratosphere lead to high depolarization ratios of 22 % at 355 nm and
18 % at 532 nm and a comparably low value of 4 % at 1064 nm. The lidar
ratios were 40–45 sr (355 nm), 65–80 sr (532 nm), and 80–95 sr
(1064 nm) in both the tropospheric and stratospheric smoke layers
indicating similar scattering and absorption properties. The strong
wavelength dependence of the stratospheric depolarization ratio was probably
caused by the absence of a particle coarse mode (particle mode consisting of
particles with radius >500 nm). The stratospheric smoke particles
formed a pronounced accumulation mode (in terms of particle volume or mass)
centered at a particle radius of 350–400 nm. The effective particle radius
was 0.32 µm. The tropospheric smoke particles were much smaller
(effective radius of 0.17 µm). Mass concentrations were of the
order of 5.5 µg m−3 (tropospheric layer) and
40 µg m−3 (stratospheric layer) in the night of
22 August 2017. The single scattering albedo of the stratospheric particles
was estimated to be 0.74, 0.8, and 0.83 at 355, 532, and 1064 nm,
respectively.
Depolarization and lidar ratios at 355, 532, and 1064 nm and microphysical properties of aged tropospheric and stratospheric Canadian wildfire smoke
