Rapid Scan Dynamic Humidity Particle Spectrometer

The Continuous-Flow Streamwise Thermal-Gradient CCN Counter (CFSTGC) ommercialized by Droplet Measurement Technologies has proven to be reliable, robust, and relatively simple to operate for ground-based and airborne measurements. Supersaturation changes are made by varying the temperature gradient between the top and bottom of the column. This provides a reliable supersaturation, but changing supersaturation requires 30-60 seconds, and the data is not valid during this time. A new mode of CCN instrument operation, called Scanning Flow CCN Analysis, or, SFCA addresses these issues. SFCA involves changing the flow rate in the instrument over time, while maintaining a constant temperature gradient; this causes supersaturation to continuously change, allowing the measurement of a supersaturation spectrum over a flow cycle, which can be as short as 10 seconds and without loss of data continuity. The CCN column can also be used as a subsaturated hygroscopic growth chamber by applying a reverse temperature gradient on the column. Very few instruments to date can operate at these high RH levels, which are crucial for understanding the water uptake properties of aerosol during their transition from cloud-free to cloudy conditions. In this proposal, the SFCA and subsaturated operational modes of the CCN will be expanded to improve the particle counting capability with a more sensitive optical particle counter. Software will also be developed to simplify the data analysis