Aerosol optical depth and burden from large sea salt particles

Sea-salt aerosol (SSA) particles are natural aerosols which exert a large impact on various geo-chemical and geophysical processes and on Earth's climate. Emissions of SSA are mainly influenced by the wind near ocean surface. Waves and whitecaps formed by the wind break and then inject sea drops into air. Because large SSA are removed quickly from the atmosphere due to gravitational deposition, most climate models do not consider SSA with radius larger than a few tens of micrometer. For example, the cut-off size of dry coarse SSA in the Community Earth System Model (CESM) is about 10 μm in radius. This study assesses the impact of large SSA on the aerosol optical depth and aerosol burden in the atmosphere by using the CESM with parameterization of larger SSA emissions. We found that despite the large deposition rate, SSA with radius larger than 10 μm contributes more than 8% to the total aerosol optical depth (AOD) over mid- and high-latitude oceans, particularly between 40° S and 65° S, and over 10% to the total global SSA mass burden. We also found that considering the large SSA in the model significantly improves the agreement of simulated AOD in CESM with the observation from MODIS (Moderate Resolution Imaging Spectroradiometer) and AERONET (Aerosol Robotic Network).