Chemical characterization and source apportionment of aerosols at a high-altitude site (3106 m asl) in the Austrian Alps

The aim of the work was to determine the seasonal variability of particulate matter (PM) sources at the summit of Mt. Sonnblick in the Austrian Alps (3106 m asl, 12°57’E, 47°03’N) based on the chemical analysis of the PM₁₀ fraction. The Sonnblick Observatory is situated on the main alpine ridge and represents a high-altitude remote sampling site. The observatory is part of the Global Atmosphere Watch (GAW) and Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS) monitoring networks. Results obtained at remote monitoring stations enable seeing long-range air mass influences and could be treated as a reference source for other studies. A total of 244 weekly PM₁₀ samples were collected from 17 January 2019 to 28 December 2023.

Comprehensive chemical analyses were conducted to obtain concentrations of (i) carbohydrates and their derivatives and selected ions (by ion chromatography), (ii) organic and elemental carbon (by thermal-optical analysis) and (iii) selected elements (by inductively coupled plasma optical emission spectroscopy). In total, 36 components of PM in collected samples were measured. The obtained results were then used to identify the emission sources during the study period and to determine their seasonal variability and contributions. For this purpose, Positive Matrix Factorization (PMF) by U.S. Environmental Protection Agency was used. The analysis resolved four major source factors connected with: 1) Saharan dust events, 2) biomass burning, 3) anthropogenic-related emissions, and 4) sugars and sugar-related compounds. Each emission source was characterized with individual temporal pattern through the whole measurement period, e.g. the strong seasonal pattern was confirmed for sugars and sugar-related factor, with increased concentration during the vegetation season. Additionally, more than 15 Saharan dust events were identified and confirmed by numerical models and backward trajectory analyses. The overall results revealed that the Saharan dust events were confirmed as the dominant factor during the study period, with an approximately 40 % contribution to the PMF-related mass, while the average contribution of sugars and sugar-related compounds as well as that of the factor connected with anthropogenic-related emissions was around 25 %. The smallest contribution was found for the factor related to biomass burning ~10 %.

Acknowledgements
This work was financially supported by the Excellence Initiative – Research University program at the AGH University of Krakow (ID: 13958).