Iodine, bromine, and chlorine in the Hawaiian marine atmosphere

Abstract

Approximately 200 samples of rainwater, aerosol, and gas were collected from the atmosphere in the zone of the northeast trade winds on the island of Hawaii west of Hilo and over the ocean east of Hilo during the summer of 1963. Analysis of these samples by neutron activation showed that: (1) The I/Cl and Br/Cl ratios in the rain samples increased with increasing altitude, and the I/Cl ratio was 500 to 1000 times higher than in sea water while the Br/Cl ratio was only slightly higher than the seawater value. (2) The I/Cl ratio in aerosol particles increased with increasing alitude and distance from the sea. On the shore the I/Cl ratio was 10 to 40 times greater than the seawater value, while a half mile inland the I/Cl ratio was over 200 times greater than the seawater ratio. (3) The Br/Cl ratio was greater than the seawater value for aerosol samples collected on land but was less than the seawater ratio for samples collected from an aircraft over the ocean. (4) There was a tendency for the I/Cl ratio to increase with decreasing particle size for the aerosol samples. (5) Approximately half of the Cl and Br present in the Hawaiian atmosphere was in a gaseous form, whereas a larger percentage of the I apparently existed as a gas. Some of the possible mechanisms which might cause the well-known atmospheric I enrichment, such as photochemical oxidation of iodide at the sea surface and the presence of an I-rich organic film on the sea surface, are correlated with the results of this investigation. A tentative explanation involving photochemical oxidation and possible Br contamination from automobile exhausts is offered for the surprising difference in the Br/Cl ratios over sea and land.