Instrument Development - Cloud Condensation Nuclei Counter

Abstract: A cloud condensation nuclei counter (CCNC) is used to study the ability of aerosol particles to serve as cloud condensation nuclei (CCN) depending on their size, chemical composition and the ambient water super saturation. In this study, the new operation mode Scanning Flow CCN Analysis (SFCA) was evaluated for the Continuous-Flow Streamwise Thermal-Graident Cloud Condensation Nuclei Counter from Droplet Measurement Technologies (CCNC DMT-100). By continuously changing the flow rate through the instrument, while keeping the streamwise temperature gradient and pressure constant, the SFCA enables measurements of entire super saturation spectra with high temporal resolution. The SFCA was evaluated for three magnitudes of the streamwise thermal gradient (4, 10 and 18 K) using three types of calibration particles (sodium chloride, ammonium sulfate and sucrose). By examining the flow rates at which the particles activated into cloud droplets, the critical flow rates could be related to the critical super saturations found from Köhler theory. In this way, calibrations between the flow rates and super saturations of the CCNC were obtained. Nine calibration curves were obtained in total, one for each substance and streamwise temperature gradient. To verify the validity of the curves, 95% confidence intervals were calculated. The calibration curves were then compared with each other to evaluate the reability of the operation mode. The SFCA was found to be reliable for streamwise temperature gradients of 4 and 10 K, but somewhat less reliable for a temperature gradient of 18 K. The calibration curves were also found to be the least reliable at the ends.