In order to predict the current state and future development of the Earth's climate system, detailed knowledge on how atmospheric aerosol particles from various sources interact with clouds is needed. In this article we present, based on continuous aerosol measurements in a remote continental location, direct observational evidence that aerosol particles formed in the atmosphere from gaseous precursors eventually participate into cloud droplet activation. By combining the measurement data with theoretical calculations, we further demonstrate that the albedo of clouds may be significantly influenced by atmospheric aerosol formation, and that this process needs to be taken into account when estimating the indirect climatic effects of aerosols in the global atmosphere.