Observing Sea Salt Aerosol Size Distribution with a Kite-Based Platform

Sea-salt aerosols, also known as Giant Cloud Condensation Nuclei (GCCN), act as extremely efficient cloud nuclei. They are large and hygroscopic and have been shown to rapidly grow by condensation. GCCN help to broaden the droplet spectrum, and can accelerate precipitation initiation in warm clouds. For this reason, the GCCN size distribution is important to quantify, but observing it is difficult. In ambient conditions at typical marine relative humidities, GCCN are always wetted and exist in the size range of large aerosols and tiny cloud droplets, often in the outer limits of both aerosol-observing and cloud-observing instruments. The salt amount (size and mass) inside the wetted droplet is even more difficult to quantify. Currently the best way to measure the GCCN size distribution is the Giant Nucleus Impactor (GNI) onboard the NSF/NCAR GV or C-130 aircrafts. With the miniaturization of technology, kites can also be used for observing sea-salt aerosols in the lower troposphere. We designed a 3D printed Arduino-based mini-GNI for observing sea-salt aerosols in the lower boundary layer near the coast with a kite platform.

The mini-GNI is attached to a kite string and lofted to 50-500 m altitude on strong trade-wind days from the windward coast of Oahu. Multiple mini-GNI units can be deployed along the same kite string for simultaneous observing at multiple altitudes. A long range radio transceiver is used to remotely control the exposure of a polycarbonate slide for sea-salt aerosol impaction. The slides are retrieved and analyzed in a lab after impaction. Atmospheric observations are also collected in-situ along the kite string to place the GCCN measurements in context. Additional testing and calibration are needed but early results suggest that the mini-GNI is promising for sea-salt aerosol measurement, especially at larger (>5 microns) sea-salt aerosol sizes and high wind (>10 m/s) environments.