Cloud Condensation Nuclei Counter (CCN)

It is being used in laboratories to measure how different materials form cloud droplets, in urban environments to study how pollution affects cloud and precipitation formation, and in weather modification to determine when and where to seed clouds. The CCN Counter is a continuous-flow thermal-gradient diffusion chamber for measuring aerosols that can act as cloud condensation nuclei. The CCN-100 draws an aerosol sample into 50-cm tall column, while the CCN-200 features two identical such columns. Inside the column(s), a thermodynamically unstable, supersaturated water vapour condition is created by taking advantage of the difference in diffusion rates between water vapour and heat. Water vapour diffuses from the warm, wet column walls toward the centreline at a faster rate than the heat. The wall temperature along the column gradually increases to create a well-controlled and quasi-uniform centreline super saturation. Through software controls, the user can modify the temperature gradient and flow rate to change super saturations and obtain the CCN spectra.