A continuous-flow diffusion chamber for airborne measurements of ice nuclei

A continuous-flow thermal gradient diffusion chamber was developed for oper ating in an aircraft and detecting ice nucleating aerosol particles in real time. The chamber volume is the annular space between two vertically orien ted concentric cylinders. The surfaces of the chamber are coated with ice a nd held at different temperatures, thus creating a vapor supersaturation. U pstream of the chamber, all particles in the sample air larger than 2-mum d iameter are removed with inertial impactors. The air then flows vertically downward through the chamber, where ice crystals nucleate and grow on activ e ice nuclei to between similar to3- and 10-mum diameter in 3-10 s of resid ence time. At the outlet of the chamber, an optical particle counter detect s all particles larger than similar to0.8 mum. Those particles larger than 3 mum are assumed to be the newly formed ice crystals and comprise the ice nucleus count. This paper describes the principles of operation, hardware a nd construction, data system, calibration, operational procedures, and perf ormance. Limitations of the technique are presented, and examples of measur ements are shown.