Development of an experimental method to investigate the mechanism of bromoform formation on the sea

Abstract

Bromine atoms are known as substances that reduce tropospheric ozone. One of the substances that supply bromine atoms to the atmosphere is bromoform, a volatile organic bromine. High concentrations of bromoform have been found on the surface of sea ice in the polar regions, and photochemical reactions and oxidation of Br- by ozone are thought to be factors. The vertical distribution of bromoform concentration in snowpack and sea ice in Lake Saroma, a brackish lake on the coast of the Sea of Okhotsk in Hokkaido, Japan, revealed high concentrations of the organic iodine iodoethane on the sea ice surface, but low concentrations of bromoform. We focused on the temperature difference between the polar regions and Lake Saroma as the cause of this difference, and hypothesized that the reaction between I- and Br- on the sea ice surface is temperature dependent, and developed an experimental method for the reaction between ozone and sea ice to test this hypothesis. To confirm the formation of bromoform by the reaction of Br- and ozone in sea ice in the laboratory, we created artificial sea ice and supplied ozone to the sea ice surface. As a result, high concentrations of bromoform were detected on the sea ice surface.