Optical and Microphysical Properties of Aged Biomass Burning Aerosols and Mixtures, Based on 9-Year Multiwavelength Raman Lidar Observations in Athens, Greece

Abstract

Mean optical and microphysical aerosol properties of long-range transported biomass burning (BB) particles and mixtures are presented from a 9-year (2011–2019) data set of multiwavelength Raman lidar data, obtained by the EOLE lidar over the city of Athens (37.58° N, 23.47° E), Greece. We studied 34 aerosol layers characterized as: (1) smoke; (2) smoke + continental polluted, and (3) smoke + mixed dust. We found, mainly, small-sized aerosols with mean backscatter-related (355 nm/532 nm, 532 nm/1064 nm) values and Ångström exponent (AE) values in the range 1.4–1.7. The lidar ratio (LR) value at 355 nm was found to be 57 ± 10 sr, 51 ± 5 sr, and 38 ± 9 sr for the aerosol categories (1), (2), and (3), respectively; while at 532 nm, we observed LR values of 73 ± 11 sr, 59 ± 10 sr, and 62 ± 12 for the same categories. Regarding the retrieved microphysical properties, the effective radius (reff) ranged from 0.24 ± 0.11 to 0.24 ± 0.14 μm for all aerosol categories, while the volume density (vd) ranged from 8.6 ± 3.2 to 20.7 ± 14.1 μm−3cm−3 with the higher values linked to aerosol categories (1) and (2); the real part of the refractive index (mR) ranged between 1.49 and 1.53, while for the imaginary part (mI), we found values within 0.0108 i and 0.0126 i. Finally, the single scattering albedo (SSA) of the propped particles varied from 0.915 to 0.936 at all three wavelengths (355–532–1064 nm). The novelty of this study is the provision of typical values of BB aerosol properties from the UV to the near IR, which can be used in forecasting the aerosol climatic effects in the European region.

Optical and Microphysical Properties of the Aerosols during a Rare Event of Biomass-Burning Mixed with Polluted Dust

“…Furthermore, the AE varied from 1 to 2.01, from 1.01 to 1.21 (AEb355/532) (Figure 3b), and from 0.91 to 1.48 (AEb532/1064) (Figure 3e). The significantly low values of the color ratio along with the aforementioned AE values are indicative of the presence of mixed biomassburning and dust aerosols [84][85][86][87], which were found to originate from North Kazakhstan and South Russia, as determined via the FLEXPART simulations presented above (Figure 2).…”

“…The retrieved profiles of b aer (Figure 6a) and δ 532 (Figure 6b) on 23 May (20:30-21:45 UTC) showed the presence of four elevated layers, characterized by high aerosol backscatter coefficients (Figure S11) and values of δ 532 ranging from 19-27%, indicating the presence of mixed biomass-burning and dust aerosols [33,62,87,107]. In order to identify the various aerosol layers, we used the gradient method [108] by studying the slope of the backscatter coefficient.…”