Credit: Kristian Pikner
The green in auroras is caused by the ionization of oxygen in the upper atmosphere.
On January 23, 1978, Sweden became the first country to ban the use of aerosol sprays which use chlorofluorocarbons (CFCs) as their propellants. The ban came after research done by Frank Rowland and Mario Molina demonstrated CFCs interacted with ultraviolet light in the upper atmosphere to break the bonds of ozone molecules.
Chlorofluorocarbons are hydrocarbon molecules that have one or more chlorine and/or fluorine atoms taking the place of the hydrogen. They often have boiling points near 0 °C which makes them ideal to use in refrigeration systems and as liquid propellants. At their height, CFC-boiling powered half the world’s aerosol cans. CFCs were also found in fire extinguishers, dry-cleaning fluids, solvents, and air conditioners. With all these great things, what could go wrong?
Ozone is the name for a molecule composed of three oxygen atoms. In the upper atmosphere, ozone is created in a two-step reaction involving ultraviolet radiation. The first step, O2 molecules are hit with ultraviolet radiation to break it into its component oxygen atoms. These two oxygen atoms use more ultraviolet energy to combine with O2 to form O3 ozone. Ozone then absorbs more UV and breaks apart into O2 and singlet oxygen. With all this UV being absorbed just to make and break ozone, why is the loss of ozone a problem?
UV is a range of energies. The UV energy required to break O2 into singlet oxygen is not as energetic as the UV energy needed to break ozone apart. The UV energies to break ozone is the shorter wavelength UV known as UV-B and UV-C wavelengths. These are the UV wavelengths that cause biological damage down on the surface. Ozone absorbs most the “bad” ultraviolet radiation before it even gets to us.
Chlorofluorocarbons are relatively stable molecules. They don’t naturally break down easily into their component parts and tend to stay in the atmosphere. As they mix with the air in the upper atmosphere, these molecules also interact with UV energy. This time, the UV energy breaks off a chlorine atom from the CFC. This chlorine atom the big problem for ozone. Chlorine and ozone easily react with each other. One chlorine atom pulls one of the oxygens from ozone to make ClO and O2. ClO also reacts with ozone to free up the chlorine atom again and make 2 oxygen atoms.
The sum total of these reactions is one chlorine atom turns 2 ozone molecules into 3 O2 molecules…and you get to keep your chlorine atom to repeat the process with more ozone. Over the years, we’ve pumped a lot of CFCs into the atmosphere and the chlorine reactions finally manifested themselves into a ‘hole’ over the polar regions. This hole allowed the higher-energy ultraviolet through to the surface and we began to see biological effects.
Sweden, being closer to a polar region, was the first to decide to not add to the problem by banning of CFCs in aerosols. Eventually, the United Nations would form an international treaty to phase out the use of CFCs and other ozone-depleting compounds. Some felt these bans came too late and the hole is here to stay. Data is showing that is not true. The ozone hole seems to be shrinking and ozone levels are starting to increase. The hole is still there, it’s just half the size of it used to be.
Notable Science History Events for January 23
1988 – Charles Glen King died.
King was an American biochemist who independently discovered and isolated ascorbic acid (vitamin C). He was attempting to discover the molecule responsible for preventing scurvy in lemon juice and found ascorbic acid. Albert Szent-Gyorgi also made the same discovery and would go on to receive the Nobel Prize for his role in the discovery. King would also make discoveries in nutritional chemistry involving vitamins, fats, and enzymes.
1978 – Aerosol Sprays Banned in Sweden
1918 – Gertrude Belle Elion was born.
Elion was an American biochemist who shares the 1988 Nobel Prize in Medicine with James Black and George Hitchings for their work in developing drugs for a multitude of diseases and pathogens. Elion and Hitchings designed pharmaceuticals that relied on subtle biochemical differences between healthy cells and the pathogens that affect these cells. The drugs would target the difference and stop or kill the pathogen without harming the healthy cells.
1907 – Hideki Yukawa was born.
Nobel Foundation
Yukawa was a Japanese theoretical physicist who was awarded the 1949 Nobel Prize in Physics for his prediction of the meson particles in explaining the forces that hold a nucleus together. He predicted the existence of a particle that functioned as a carrier for the strong nuclear force that holds together the positively charged nucleus.
The pion particle is an important particle in explaining the strong nuclear force and was first detected by César Lattes in 1947. This discovery verified Yukawa’s theories and advanced the understanding of nuclear physics.
1876 – Otto Paul Hermann Diels was born.
Diels was a German chemist who shares the 1950 Nobel Prize in Chemistry with Kurt Alder for their development of diene synthesis, otherwise known as the Diels-Alder reaction. A diene is a hydrocarbon with two double bonds. The Diels-Alder reaction converts dienes and alkenes into ring molecules. It is important in the synthesis of many polymers, steroids, and alkaloids.
1810 – Johann Wilhelm Ritter died.
Ritter was a German scientist who invented one of the first dry pile galvanic batteries. Early batteries used electrodes dipped in an acid solution where the energy is produced through oxidation reactions. A dry pile uses just enough moisture to function without the dangers of spilling acid solutions. Ritter’s pile used alternating pieces of silver and zinc foil separated by pieces of paper.
Ritter was also responsible for the discovery of the ultraviolet region of the electromagnetic spectrum. While investigating the discoloration of silver salt crystals exposed to sunlight, he discovered there was a part of sunlight beyond the violet range responsible for the discoloration. He initially called this part of the light spectrum ‘de-oxidizing rays’ because of their chemical reactivity.
1796 – Karl Ernst Klaus was born.
Klaus was a Russian chemist who discovered the element ruthenium. His work at the Saint Petersburg Mint gave him access to several platinum ores. He would isolate different metals from these ores like osmium, palladium, iridium, rhodium, and of course, platinum. One of his metals found in the waste material of the platinum refining process turned out to be something he had never seen before. He determined its atomic weight and several of its properties and announced he had discovered a new element. He named his new element after Ruthenia, the Latin name for the Rus’ area of Russia.
Klaus was also known for his disregard for laboratory safety. He would frequently add ‘taste’ to his observations of new compounds. His notes had the taste of osmium tetroxide as ‘astringent and pepper-like’. Modern chemistry knows this compound is highly poisonous, causing blindness and fluid collecting in the lungs, and death. Klaus was laid out for two weeks after testing it. He also tested acid strength by sticking his finger into the solution and touching his tongue.