Circulation of Na, Cl, and Br in the tropical marine atmosphere

Abstract

Concentrations of Na, Cl, Br, and I in aerosols and Cl, Br, and I in inorganic gases were measured in the marine atmosphere off the west African coast (∼0°N, ∼0°W) in June 1977 and used to estimate their mean lifetimes and rates of production. Mean concentrations (in micrograms per cubic meter) during an 8‐day, stable, rain‐free period of the voyage follows: for paniculate Na 4.0, Cl 5.3, Br 0.017, and 1 0.004; for inorganic gas Cl 1.0, Br 0.012, and 1 0.013. The results of a steady state analysis suggest a ∼3‐day mean residence time for the marine aerosol during the period of our observations, a ∼667 μg m −2 d −1 loss rate of Cl (probably as HCl) from the marine aerosol, and a subsequent ‐day mean residence time in the marine atmosphere. A similar analysis for gaseous inorganic Br gave a μg m −2 d −1 mean loss rate from the marine aerosol and a ∼7‐day mean residence time. Computed dry deposition coefficients were (in centimeters per second) ∼0.4 for the marine aerosol, ∼0.77 for gaseous inorganic Cl, and ∼0.24 for gaseous inorganic Br.