Observation of Sea Spray Aerosol Size Distribution in Hawai’i

Sea spray aerosol (SSA) play a significant role in the local climatology of coastal areas by acting as giant cloud condensation nuclei (GCCN), which can accelerate warm rain initiation due to their hygroscopicity. However, there is large uncertainty in SSA size and quantity in the atmosphere. In-situ observations of GCCN are particularly limited because of their low concentration and relatively large sizes. At NCAR, the giant nucleus impactor (GNI) was developed to observe giant aerosol particles. Deliquesced salt particles impact onto polycarbonate slides exposed to the free air flow and these slides are analyzed in a humidified environment under a laboratory microscope. With the GNI in mind, we developed a new, low-cost, and accessible method for sampling large SSA in the marine boundary layer. Using 3D printing and Arduino microcontrollers and sensors, we designed and built a SSA sampler named the “mini-GNI” that can expose polycarbonate slides to capture large SSA. The mini-GNI can be attached to a kite string, allowing for sampling at multiple altitudes simultaneously. We've also attached the mini-GNI to a drone, allowing for offshore to onshore SSA comparison. We've found that SSA in the boundary layer is relatively well mixed, but larger SSA are more prevalent at low altitudes. We've also found a stronger relationship of SSA number concentration to wave activity than to wind speed in our coastal measurements. The ultimate goal is a more complete understanding of the GCCN size distribution in the coastal marine boundary layer.