Aerosol type classification analysis using EARLINET multiwavelength and depolarization lidar observations

Abstract

Abstract. We introduce an automated aerosol type classification method, called Source Classification Analysis (SCAN). SCAN is based on predefined and characterized aerosol source regions, the time that the air parcel spends above each geographical region, and a number of additional criteria. The output of SCAN is compared with two independent aerosol classification methods, which use the intensive optical parameters from lidar data: (1) the Mahalanobis distance automatic aerosol type classification (MD) and (2) a neural network aerosol typing algorithm (NATALI). In this paper, data from the European Aerosol Research Lidar Network (EARLINET) have been used. A total of 97 free tropospheric aerosol layers from four typical EARLINET stations (i.e., Bucharest, Kuopio, Leipzig, and Potenza) in the period 2014–2018 were classified based on a 3β+2α+1δ lidar configuration. We found that SCAN, as a method independent of optical properties, is not affected by overlapping optical values of different aerosol types. Furthermore, SCAN has no limitations concerning its ability to classify different aerosol mixtures. Additionally, it is a valuable tool to classify aerosol layers based on even single (elastic) lidar signals in the case of lidar stations that cannot provide a full data set (3β+2α+1δ) of aerosol optical properties; therefore, it can work independently of the capabilities of a lidar system. Finally, our results show that NATALI has a lower percentage of unclassified layers (4 %), while MD has a higher percentage of unclassified layers (50 %) and a lower percentage of cases classified as aerosol mixtures (5 %).

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

“…Finally, all the calculated mean values of aerosol optical properties were found to be consistent with those reported in the literature for the s [24,28,31,34,38,39] and s+md [33,41] particle categories.…”

“…The SCAN algorithm was then used to classify the aerosol layers, as described in [38]. SCAN is an important contributor in classifying aerosol layers and especially those of smoke origin, because it applies strict rules concerning classification including the one that concerns the variable "confidence" of the fire product of MODIS, and only the fire dots with confidence levels higher than 80% are used.…”

“…The classification algorithm used in this study, which is described in [38], was also able to retrieve the resident time (i.e., number of hours) of a HYSPLIT backward trajectory above a burned area. This information versus the variable LR532/LR355 for each aerosol layer of s and s+cp categories is presented in Figure 3.…”

“…The vertical profiles of the aerosol optical properties were retrieved using the single calculus chain (SCC) tool [39,40] in a homogeneous and quality-assured manner providing the values of LR at 355 and 532 nm, the AE extinction-related 355/532 coefficients as well as the AE backscatter-related 355/532 and 532/1064 coefficients. The aerosol characterization was based on a recently published study [38]. Finally, the aerosol microphysical properties reff, mR and mI, the vd, and the SSA at 355 nm, 532 nm, and 1064 nm of the BB layers were calculated according to [41].…”

Aerosol Characterization during the Summer 2017 Huge Fire Event on Mount Vesuvius (Italy) by Remote Sensing and In Situ Observations

“…Moreover, calibrated particle linear depolarization profiles (δ a (z)) were derived at 532 nm from the backscattered light components polarized along the direction perpendicular and parallel to the laser beam polarization, following the inversion procedure reported by Biele [32] and Freudenthaler. The LR and δ a are both key parameters for the classification of the aerosol type as they depend on aerosol microphysical properties and geometry [33]. Besides these aerosol properties, a recently published method can also be used for aerosol typing [34].…”