A laboratory facility to study gas-aerosol cloud interactions in a turbulent environment: The π chamber

We have developed a facility capable of generating cloud conditions in two ways. The first is by reducing the pressure in the chamber, thereby simulating an updraft in the atmosphere, and the second is by forcing a temperature difference between two parallel, water-coated plates, inducing moist Rayleigh-Bénard convection. The more traditional mode via expansion produces a cloud lifetime limited by how long the expansion can be maintained (on the order of 10 min). Cloud formation through mixing allows the cloud to be sustained as long as the temperature difference is maintained and cloud condensation nuclei are supplied; in practice, such cloud conditions have been maintained for many days during extended measurement studies. Operation using both modes simultaneously is also possible. Laboratory experiments have the advantage of allowing us to decouple the full complexity of the atmosphere. Often, model comparisons with field results, as important as these are, are confounded by the lack of steady conditions, poor characterization of initial and boundary conditions, relatively sparse measurements, and the sheer level of complexity for many days during extended measurement studies. Operation using both modes simultaneously is also possible. Laboratory experiments have the advantage of allowing us to decouple the full complexity of the atmosphere. Often, model comparisons with field results, as important as these are, are confounded by the lack of steady conditions, poor characterization of initial and boundary conditions, relatively sparse measurements, and the sheer level of complexity.