Lately, there is considerable climate-related interest in the so-called indirect aerosol effects related to boundary layer dynamics. The impact of aerosol-cloud interaction on cloud albedo and its efficiency to produce rain has a very low level of understanding (e.g. IPCC, 2007). The major goal of this research project is to relate in a meaningful way the cloud droplet formation at the top of the PBL to an elevated aerosol loading. The remote sensing techniques would allow the vertical profiling of aerosol loads within PBL. In-situ measurements would be used for the characterization of aerosols on the ground surface which may be representative for the PBL in the afternoon, when PBL is well mixed. Aerosol properties will be retrieved right before or right after cloud formation. The focus of this research is on low level clouds (i.e., stratocumulus, cumulus). The quantification analysis of cloud droplet formation and the cloud albedo estimation will be approached through space-borne remote sensing techniques by retrieving cloud properties such as the cloud droplets number concentration (CDNC) and cloud droplet effective radius (r_eff). These synergetic observations over the urban environment of Athens megacity will potentially reduce uncertainties on the impact of cloud-aerosol interaction on climate change.