False-color view of total ozone over the Antarctic pole. The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone. Credit: NASA Ozone Watch

A ship-based study shows that iodine is the second most important contributor to surface ozone loss in the Arctic atmosphere.

Near-complete ozone loss was observed between March and May 2020, indicating that ozone depletion in the Arctic is widespread during the sunlit period.

A previous survey in Antarctica linked elevated levels of iodine compounds to ozone destruction during the sunlit period in the upper atmosphere. But, it remains unclear whether iodine chemistry depletes ozone in the Arctic.

An international research team launched a ship-based Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition that measured the levels of halogen oxides during the sunlit period from March to October 2020. They also measured the levels of particulate iodine, iodic acid, and other related trace gases.

The team, which included Anoop Mahajan  from the Indian Institute of Tropical Meteorology in Pune, observed that iodine chemistry played a crucial role during some periods of extremely low ozone. Model-based simulations showed that an increase in iodine monoxide concentration enhanced ozone destruction by two- to three-fold during spring.

The highest iodine monoxide values were observed on the days with the lowest ozone. The maximum individual daily contribution of iodine to ozone loss surpassed that of bromine. This could become worse as melting ice sheets will create large ice-free areas in the Arctic, increasing the flux of ocean-emitted iodine compounds to the polar atmosphere, the researchers say.