Mass concentration estimates of long-range-transported Canadian biomass burning aerosols from a multi-wavelength Raman polarization lidar and a ceilometer in Finland
Authors: Shang Xiaoxia , Mielonen Tero , Lipponen Antti , Giannakaki Elina , Leskinen Ari , Buchard Virginie , Darmenov Anton S. , Kukkurainen Antti , Arola Antti , O'Connor Ewan , Hirsikko Anne , Komppula Mika 
Published: September 2021

Abstract. A quantitative comparison study for Raman lidar and
ceilometer observations, and for model simulations of mass concentration
estimates of smoke particles is presented. Layers of biomass burning aerosol
particles were observed in the lower troposphere, at 2 to 5 km height on 4
to 6 June 2019, over Kuopio, Finland. These long-range-transported smoke
particles originated from a Canadian wildfire event. The most pronounced
smoke plume detected on 5 June was intensively investigated. Optical
properties were retrieved from the multi-wavelength Raman polarization lidar
PollyXT. Particle linear depolarization ratios (PDRs) of this plume were
measured to be 0.08±0.02 at 355 nm and 0.05±0.01 at 532 nm,
suggesting the presence of partly coated soot particles or particles that
have mixed with a small amount of dust or other non-spherical aerosol type.
The layer-mean PDR at 355 nm (532 nm) decreased during the day from
∼0.11 (0.06) in the morning to ∼0.05 (0.04) in
the evening; this decrease with time could be linked to the particle aging
and related changes in the smoke particle shape properties. Lidar ratios
were derived as 47±5 sr at 355 nm and 71±5 sr at 532 nm. A
complete ceilometer data processing for a Vaisala CL51 ceilometer is presented from
a sensor-provided attenuated backscatter coefficient to particle mass
concentration (including the water vapor correction for high latitude for
the first time). Aerosol backscatter coefficients (BSCs) were measured at
four wavelengths (355, 532, 1064 nm from PollyXT and 910 nm from
CL51). Two methods, based on a combined lidar and sun-photometer approach,
are applied for mass concentration estimations from both PollyXT and
the ceilometer CL51 observations. In the first method, no. 1, we used
converted BSCs at 532 nm (from measured BSCs) by corresponding measured
backscatter-related Ångström exponents, whereas in the second method, no. 2, we used measured BSCs at each wavelength independently. A difference
of ∼12 % or ∼36 % was found between
PollyXT and CL51 estimated mass concentrations using method no. 1 or
no. 2, showing the potential of mass concentration estimates from a ceilometer. Ceilometer estimations have an uncertainty of ∼50 % in the mass retrieval, but the potential of the data lies in the great
spatial coverage of these instruments. The mass retrievals were compared
with the Modern-Era Retrospective analysis for Research and Applications,
version 2 (MERRA-2) meteorological and aerosol reanalysis. The inclusion of
dust (as indicated by MERRA-2 data) in the retrieved mass concentration is
negligible considering the uncertainties, which also shows that ceilometer
observations for mass retrievals can be used even without exact knowledge of the composition of the smoke-dominated aerosol plume in the troposphere.