Aerosol particles suspended in the atmosphere originate from a variety of natural and anthropogenic sources, with their optical, physical, and chemical properties often serving as indicators of their origin. However, long-range aerosol transport, ageing processes, and the mixing (external and internal) of various types in the atmosphere render aerosol-type identification a real challenge. Nevertheless, several techniques and classification matrices have been established for the better classification of aerosols into groups representative of their specific or dominant sources.

In this context, this study focuses on the first attempt at aerosol-type classification using in situ measurements from an aethalometer and a nephelometer at a continental background site in NW Greece (Kozani; 40.27 ^oN, 21.76 ^oE, 768 m). The classification matrix was based on the combined analysis of the Absorption Ångström Exponent (AAE) and the Scattering Ångström Exponent (SAE) values over a one-year period (2023).

Using appropriate threshold values, seven key aerosol types were identified and analyzed in terms of their seasonal, monthly and diurnal variations. The Black Carbon (BC)-dominated type was the most frequent, indicative of a regional background atmosphere influenced by fossil fuel combustion. A mixed Brown Carbon (BrC)–BC type was also frequently observed in winter, along with occasional occurrences of a pure BrC type, both of which are associated with biomass burning for residential heating in nearby villages. Another common category was a mix of large aerosols and BC, present throughout the year, while dust was detected episodically, primarily during Saharan dust transport events. Two types of aerosol, characterized by AAE values below 1 for fine (SAE>1) and coarse (SAE<1), were of lower frequency, indicating a possible mixing of carbonaceous aerosols with inorganic species of weaker spectral absorption. We analyzed the spectral absorption and scattering coefficients of each type of aerosol, as well as their single scattering albedo and PM_2.5 levels, which exhibit substantial seasonal variations.