To study the involvement of iodine in cloud formation, an international team led by CU Boulder researchers visited the European Organization for Nuclear Research (CERN), a research institute in Geneva, Switzerland that supplies the most ideal conditions for the study. CERN is home to the CLOUD chamber, an artificial enclosure that stands for Cosmics Leaving Outdoor Droplets. CLOUD is used to study aerosol and cloud formation—how particles in our atmosphere are created.
In the CLOUD chamber, the researchers could access a laboratory environment that could control conditions such as the temperature, colors of light, pressure, humidity, ozone concentration, and iodine concentration in the space.
Having conducted their experiments and formed some theories, the scientists then tested their findings in the real world by running more experiments. To do so, they chose the Maïdo observatory on Réunion Island, an area with little to no human activity—just right for conducting experiments where the slightest environmental change can produce dramatically different data.
How Does Iodine Form Clouds?
In order to understand how iodine is involved in creating clouds, a few facts about atoms and molecules must be known. An atom has three components: protons, neutrons, and electrons. Protons and neutrons make up the center of the atom, and the electrons surround the nucleus in a space called the electron cloud. In the electron cloud, electrons tend to form pairs with each other. So, when an odd number of electrons is present in an atom, one remains unpaired. Such atoms are radicals.
Iodine, number 53 on the Periodic Table of Elements, is commonly found in the ocean, the atmosphere, or the soil and is highly reactive. In the ocean, iodine is found as “normal” iodide, which is also in table salt. Under atmospheric conditions, it easily turns into radicals that are involved in quick chemical reactions, which can last anywhere from a few seconds to minutes. In the atmosphere, it is found in its gas form, iodic acid. Over the last seventy years, atmospheric iodine has been rapidly increasing; today, levels of it are triple those of seventy years ago. With the increased involvement of iodine, scientists have found, comes an increase in cloud cover, the fraction of the sky that is covered by clouds. Unfortunately, cloud cover has an inverse relationship with the amount of Arctic sea ice: a greater number of clouds yields an ever-decreasing amount of Arctic ice. Thus, atmospheric iodine levels likely drastically contribute to global warming.
Iodine oxide radicals, the product of atmospheric iodine’s reaction with the ozone layer of the Earth’s atmosphere, which rests above the troposphere (the layer closest to us), first form chemical bonds with themselves. Chemical bonds are made when the electrons that surround the nuclei of two or more atoms are shared or exchanged with each other. Afterward, they react with ozone and water and produce iodic acid, oxygen, and hypoiodous acid. Iodic acid is what contributes to cloud formation, as well as the formation of other particles.
Iodine is unusually efficient, compared to other elements, at forming atmospheric particles like clouds because it does not need other molecules to help it create a chemical reaction: it only needs a spot in the atmosphere. So, unlike many other atmospheric particles, atmospheric iodine is in great abundance. The efficiency of iodine at creating such particles is further increased by the fact that just one atom of iodine can catalyze, or kick-start, multiple reactions. Imagine a long, rectangular room with the back wall stretching on forever. Inside the room is a countless number of printers, neatly laid out in rows that continue on towards the unseeable back of the room. Each printer is continuously printing copies of a piece of paper. As you can imagine, the total number of printed copies increases to an unimaginable amount as time goes on. Just like how the copies are incalculably increasing, the amount of atmospheric particles in the atmosphere is too. That is the global significance of iodine in particle formation.
What Else did the Researchers Find?
In addition to confirming iodine’s role in forming particles in our atmosphere, the research team found that human activity has largely influenced the drastic increase in atmospheric iodine levels.
Unfortunately, human activity greatly decreases air quality worldwide and contributes an exigent amount to global warming. As Arctic sea ice melts and storms everywhere (especially those in the tropics) multiply with the ever-heightening temperature, an increased amount of iodine enters the atmosphere (melted ice becomes part of the ocean, which releases iodine into the atmosphere and tropical storms send iodine high into the atmosphere). Once it finds itself in the atmosphere, iodine contributes to one of two things: cloud cover or the elimination of the ozone layer. The atmospheric iodine molecules that slowly deplete molecules in the ozone layer are removing that which protects our planet from most of the sun’s ultraviolet rays, which warm up the Earth. Therefore, it makes sense that with an increase in iodine in the atmosphere, there is an increase in global warming.
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