Gaseous and particulate bromine in the marine atmosphere

Sixty gaseous bromine samples collected from a 20-meter tower on the windward shore of Oahu, Hawaii, showed an average gaseous bromine concentration of approximately 50 ng/m3 as determined by neutron activation analysis. Particulate bromine samples collected simultaneously with the gaseous samples indicated that the gaseous bromine concentration in marine air is 4–10 times the particulate bromine concentration. Thermodynamic calculations indicate that, at the concentrations of gaseous and particulate bromine found in this work, sea salt particles should be the source of gaseous bromine in the marine atmosphere. Thermodynamic calculations also suggest that the Br/Cl ratio normally measured in oceanic rain can be explained by the dissolution of gaseous bromine in rain and cloud water and that it is not necessary to use some type of enrichment mechanism at the sea-air interface to explain bromine concentrations normally measured in the marine environment. The U-shaped dependence of bromine concentration on particle size normally observed in the marine atmosphere may possibly be explained by the existence of nonmarine bromine-containing particles and by the fact that in relation to particle lifetimes in the atmosphere the volatilization of bromine from sea salt particles proceeds slowly. Calculations indicate that gaseous bromine will have a residence time in the marine atmosphere of a few weeks, or approximately 7 times that of particulate bromine.