Droplet nucleation in a rapid expansion cloud chamber*

We present experiments conduced in a new aerosol-cloud chamber at Princeton University. Experiments are performed with precise control over the thermodynamic properties (humidity, temperature, pressure) and air quality (aerosol concentration) to study nucleation processes relevant to cloud microphysics. Rapid expansions allow for the nucleation of water droplets either in an homogeneous way, or on submicron aerosol particles. We characterize the time evolution of the pressure and temperature during the experiments, and compare the temperature evolution with classic adiabatic expansion in dry and moist environment. We employ optical diagnostics to track droplet nucleation and growth and characterize the size and total number of droplets being formed as a function of initial relative humidity and aerosol particles concentration and compare our experimental results to various theoretical prediction from the cloud microphysics literature.