Cracking the chemical code on how iodine helps in forming clouds

Iodine is a highly reactive element. It forms radial species that undergo rapid chemical reactions in the atmosphere. Most of the iodine found in the atmosphere comes from the ocean. It exists as iodide in the oceans, also present in table salt. Atmospheric iodine is increasing on a global level. The current levels have reached three times more than those were in past 70 years. 

Keywords: Iodine, CLOUD, atmosphere, iodide, sea ice, cloud cover

New research published in the journal Nature Chemistry was conducted at the world's largest particle physics laboratory, the European Organization for Nuclear Research (CERN) was the first time that any experiment demonstrated the gas-phase form of iodine that is known as iodic acid. The research also suggests the catalytic role of iodine in atmospheric particle formation.

Researchers hope that this new knowledge on iodine's atmospheric interactions can apply to global atmospheric and climate models to help scientists for a better understanding of its environmental impacts such as increased cloud cover, which could exacerbate global warming-related thinning of Arctic sea ice.

An experiment known as  CLOUD (Cosmics Leaving Outdoor Droplets) has become the world's leading laboratory experiment for studying the remaining poorly understood aspects of aerosol and cloud formation.

Rainer Volkamer, co-lead author on the paper, professor of chemistry at CU Boulder, and fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES) said, "This is the only such experiment that exists in the world. It's an honor to be part of the collaboration and to be leading it in the context of a study like this one".

In the CLOUD chamber at CERN, the researchers accessed a laboratory environment with perfect control over conditions like temperature, pressure, humidity, ozone concentration, and iodine concentration. They also accessed different light sources resembling different aspects of the solar spectrum. By setting up this artificial, indoor atmosphere that has the possibility of certain reactions to happen or not. Through this, scientists could accurately gather data on iodine chemical reactions that lead to forming and growth of particles.

Theo Kurten, co-lead author of the study and professor of chemistry at the University of Helsinki said, "This is a great example of experiments and computations coming together to answer a question that neither of them could have answered on their own".

Iodine doesn't need the help of other molecules (known as "bases") to form atmospheric particles like other elements such as sulfur (or sulfuric acid). Researchers also found that it is quite efficient at this process compared to other elements. Thus, the formation of particles from iodic acid is not only limited to coastal iodine hot spots or locations where the chemical bases are available but also can occur throughout the atmosphere.

Henning Finkenzeller, the first author of the study, a part of his dissertation at CU Boulder said, "It's a global phenomenon, and the global significance of iodine in particle formation may be bigger than currently thought".