Sea-Salt Size Distributions from Breaking Waves: Implications for Marine Aerosol Production and Optical Extinction Measurements during SEAS

Abstract

The authors' participation in the Shoreline Environment Aerosol Study (SEAS) involved measurements focused on the coastal aerosol size distribution and related optical measurements, including aerosol light scattering, visibility, and remote sensing of aerosol using lidar backscatter. Aerosol production from shoreline breaking waves and the more distant reef (?1 km) was characterized for dry sizes between 0.01 and 10 ?m for both their contribution to the marine aerosol population and their influence on near-surface lidar extinction. Thermal volatility was used to extract the refractory sea-salt particles from the other constituents volatile at 360°C. At 7 m ASL and 20 m inland from the water's edge the production of sea-salt nuclei number was often in the range of 50?100 cm?3 above the open-ocean value of ?250 cm?3. This number peak was near 0.03-?m dry diameter, while light scattering was dominated by a few particles larger than 1 ?m. This indicates that production of sea salt from breaking waves contributes not only to aerosol mass and optical effects but also to nuclei mode particle number in remote regions. Separate studies of optical closure quantified links between the size distribution and optical scattering measurements, visibility, and extinction values for both nearshore breaking waves and open-ocean conditions. These data confirmed that extinction derived from coastal lidar measurements at 0.530 ?m was accurate to better than the 25% uncertainty claimed for the lidar inversion.