Modeling sea-salt aerosols in the atmosphere 2. Atmospheric concentrations and fluxes

Abstract

Atmospheric sea-salt aerosol concentrations are studied using both long-term observations and model simulations of Na+ at seven stations around the globe. Good agreement is achieved between observations and model predictions in the northern hemisphere. A stronger seasonal variation occurs in the high-latitude North Atlantic than in regions close to the equator and in high-latitude southern hemisphere. Generally, concentrations are higher for both boreal and austral winters. With the model, the production flux and removal flux at the atmosphere-ocean interface was calculated and used to estimate the global sea-salt budget. The flux also shows seasonal variation similar to that of sea-salt concentration. Depending on the geographic location, the model predicts that dry deposition accounts for 60-70% of the total sea-salt removed from the atmosphere while in-cloud and below-cloud precipitation scavenging accounts for about 1% and 28-39% of the remainder, respectively. The total amount of sea-salt aerosols emitted from the world oceans to the atmosphere is estimated to be in the vicinity of 1.17 × 1016 g yr-1. Approximately 99% of the sea-salt aerosol mass generated by wind falls back to the sea with about 1-2% remaining in the atmosphere to be exported from the original grid square (300 × 300 km). Only a small portion of that exported (∼4%) is associated with submicron particles that are likely to undergo long-range transport.