"[These findings] have important consequences for the chemistry of the lower Antarctic atmosphere," Alfonso Saiz-Lopez, formerly of the University of Leeds and University of East Anglia, UK, and now at NASA Jet Propulsion Laboratory, told environmentalresearchweb. "The springtime iodine oxide levels are the highest reported anywhere in the atmosphere, and the apparent synergy between iodine oxide and bromine oxide suggests a hitherto unrecognized iodine emission mechanism."
Saiz-Lopez and colleagues from the University of Leeds, University of East Anglia, and British Antarctic Survey, UK, took measurements from the Halley Station on the Brunt Ice Shelf near the Antarctic coast from January 2004 to February 2005. They used the long-path differential optical absorption spectroscopy (LP-DOAS) technique. Until now, factors such as the logistical challenges of setting up scientific instrumentation in such a remote location had prevented such data collection.
The concentration of both iodine oxide and bromine oxide peaked in October during the austral spring at around 20 parts per trillion by volume. Similar levels of bromine oxide occur in the Arctic in springtime, but the Antarctic levels of iodine oxide were an order of magnitude larger than those seen in the Arctic.
According to the researchers, the study demonstrates for the first time that iodine greatly increases the rate of ozone destruction – by up to four times – in the Antarctic boundary layer chemistry.
"The presence of high concentrations of iodine oxide in the atmosphere points to the possibility of iodine aerosol formation," said Saiz-Lopez. "These particles could then provide condensation nuclei for other condensable vapours and grow to the point of becoming cloud condensation nuclei, and hence have an impact on climate."
The team also found that the halogens dominate HOx (OH + HO2) and NOx (NO and NO2) chemistry. As a result, they control the oxidizing capacity of this region of the Antarctic atmosphere. "The measurements also have major implications for the oxidation of dimethyl sulphide, which may form clouds, and mercury which is a toxic pollutant for the Antarctic biota," said Saiz-Lopez.
"More importantly, all of these interactions have so far remained virtually unconsidered in the Antarctic troposphere and therefore this work is of interest for a diverse community of marine/atmospheric chemists and biologists," he added.
The researchers, who reported their work in Science, are now trying to find the source of such a high burden of iodine oxide in the Antarctic atmosphere. Possible candidates include phytoplankton on the underside of sea ice that produce iodocarbons, and sea salt.
• Saiz-Lopez and colleagues have also measured iodine oxide from space for the first time, which they reported in Geophysical Research Letters. The satellite observations indicated that the presence of reactive iodine species is widespread over sea-ice covered areas in the Southern Hemisphere.