Atmospheric aerosol particles play a crucial role in cloud formation by acting as cloud condensation nuclei (CCN), influencing the Earth's radiative balance and hydrological cycle. The ability of aerosols to serve as CCN depends not only on their number concentration but also on their physical and chemical properties, as well as their mixing state. Hygroscopicity, which describes a particle’s ability to absorb water, is a fundamental property that governs aerosol behavior in the atmosphere. Since aerosol hygroscopic properties evolve throughout their atmospheric lifetime, understanding these changes is essential for assessing their role in cloud activation. This study presents a comprehensive analysis of aerosol physical, chemical, and activation properties measured at the ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure, http://www.actris.eu/) background site in Košetice (NAOK), Czech Republic. Our primary objective is to improve the understanding of aerosol activation processes and ambient hygroscopic properties, with a particular focus on how chemical composition influences CCN activity.