First Continuous Aerosol Measurements at Testa Grigia at 3480 m asl: Aerosol Populations and Transport Dynamics in the Southern European Alps

Abstract. High-elevation observatories are crucial for monitoring atmospheric aerosols, which play a key role in the climate system due to their effects on radiation, cloud, and snow albedo. We present the first measurements of aerosol size distribution and absorption coefficient at a 1-hour time resolution collected at the Testa Grigia Observatory (3,480 m asl) in the Italian Alps. This dataset spans from September 2021 to May 2023. We identified three distinct aerosol population types reaching the observatory, reflecting distinct transport pathways. The coarse particle population is indicative of long-range transport air masses from Sahara. Conversely, the fine particle population is linked to mesoscale circulations and boundary layer dynamics (from the Po Valley and local alpine valleys), and broader continental flows. Finally, periods of generally low particle number correspond to the influence of clean air from the free troposphere and the Mediterranean basin. The upper bound of the frequency of boundary layer influence is equal to 28 %. Conversely, Sahara Dust Events (SDE), identified as periods characterized by coarse aerosol population transported from the Sahara region, are observed for 6 % of the time. These events are predominantly recorded during spring and early summer and show strong correspondence with reanalysis data provided by CAMS (Copernicus Atmosphere Monitoring Service) ensemble model. The seasonal variability of PM10 concentration associated to SDE is explained by the variability to dust emission regions, dust mobilization over source region, and efficiency of dust transport mechanisms.