Abstract. Atmospheric aerosols play a crucial role in the Earth's system,
but their role is not completely understood, partly because of the large
variability in their properties resulting from a large number of possible
aerosol sources. Recently developed lidar-based techniques were able to
retrieve the height distributions of optical and microphysical properties of
fine-mode and coarse-mode particles, providing the types of the aerosols. One
such technique is based on artificial neural networks (ANNs). In this
article, a Neural Network Aerosol Typing Algorithm Based on Lidar Data
(NATALI) was developed to estimate the most probable aerosol type from a set
of multispectral lidar data. The algorithm was adjusted to run on
the EARLINET 3β+2α(+1δ) profiles. The NATALI algorithm is
based on the ability of specialized ANNs to resolve the overlapping values of
the intensive optical parameters, calculated for each identified layer in the
multiwavelength Raman lidar profiles. The ANNs were trained using synthetic
data, for which a new aerosol model was developed. Two parallel typing
schemes were implemented in order to accommodate data sets containing (or not)
the measured linear particle depolarization ratios (LPDRs): (a) identification
of 14 aerosol mixtures (high-resolution typing) if the LPDR is available in
the input data files, and (b) identification of five predominant aerosol types
(low-resolution typing) if the LPDR is not provided. For each scheme, three
ANNs were run simultaneously, and a voting procedure selects the most
probable aerosol type. The whole algorithm has been integrated into a Python
application. The limitation of NATALI is that the results are strongly
dependent on the input data, and thus the outputs should be understood
accordingly. Additional applications of NATALI are feasible, e.g. testing the quality of
the optical data and identifying incorrect calibration or insufficient cloud
screening. Blind tests on EARLINET data samples showed the
capability of NATALI to retrieve the aerosol type from a large variety of
data, with different levels of quality and physical content.