In this study we have attempted to quantify ozone uptake rates by aerosol and cloud droplets over the city of Athens. We find that in the upper Planetary Boundary Layer (PBL) the ozone uptake rates are high due to a preponderance of large cloud droplets and this is reflected in the fall of ozone concentration in this region over Athens. This is perhaps the first attempt at quantifying ozone uptake rates over Athens (which is typical of the Mediterranean region) including the effects of both collisional and diffusional contributions and the strength of our calculations lies in the accurate description and calculation of the diffusion coefficient of ozone at varying levels in the PBL. The diffusional contribution to the ozone uptake rate increases with increasing droplet size.