FunNature & AnimalMario Molina:

Mario Molina:

Mario Molina was born in 1943 in Mexico, although he has American nationality. He studied chemical engineering and, after graduating, went to France and Germany to further his studies. In 1967 he began his research on the ozone layer in the United States.

 

 

His doctoral thesis dealt with the chemical reactions that produce laser light, but when he finished it in 1973, Mario Molina felt somewhat disoriented and wanted to dedicate himself to the study of phenomena of greater social interest. The same thing happened to his colleague and friend Sherwood Rowland, and both decided to reconvert their trajectory by choosing a field that was little traveled and, apparently, with few possibilities: it was a question of following the trail of some chemical compounds of industrial origin that were accumulating in the atmosphere.
Nobody bet much on them, since these compounds did not seem to produce significant effects, given their low concentration, but after a year they had published one of the scientific articles that have caused the most talk in recent decades. In it they affirmed that chlorofluorocarbons (CFCs), compounds used in refrigeration equipment, air conditioning, aerosols and other applications, could destroy the ozone layer that defends us from solar ultraviolet radiation. It was the announcement of a true terrestrial catastrophe that, thanks to them, has not come to pass.

Before his investigations, the atmosphere seemed like the great sink, capable of absorbing everything …
-In a certain way it is, since most of the gases that are emitted, both of natural and industrial origin, are eliminated by industrial processes. But there are some compounds that are stable, non-toxic, and highly diluted in the atmosphere, so it was thought that there should be no problem associated with them.

Among all the gases that we emit into the atmosphere, why did you choose CFCs?
-Precisely because, due to their great chemical stability and low concentration in the atmosphere, nobody paid much attention to them. It occurred to us to study them because they are of industrial origin, they are not produced by nature, and that meant that they were changing the chemical composition on a global level. The challenge was trying to predict what was going to happen to those molecules, follow their trail, and see if there were any consequences. We soon discovered that the CFCs ended up rising to the stratosphere, where they would find the ultraviolet radiation from the Sun to destroy them. In 1974 we published an article in Nature in which we hypothesized that CFCs would break down in the stratosphere and that decomposition elements, including atomic chlorine, could attack ozone through reactions in chain.

When they published it, nobody paid much attention to them …
-In the beginning, no. At that time no one outside the scientific world had heard of the ozone layer and ultraviolet rays. The article had repercussion only in the scientific community that worked with these things, but the first reactions were of skepticism. When the scientists examined it in more detail, they already reacted appropriately.

How did you feel when Shigeru Chubachi announced in 1984 that he had discovered a significant ozone depletion in Antarctica?
-At first I felt a bit of disbelief, because we had not predicted that it would happen at the poles. In general, we had a good understanding of the chemistry of the process, but the effect of polar clouds had not been clarified and it took us time to do so, both for us and the rest of the scientific community. We designed specific experiments to disprove our hypothesis, because at first many people thought that Antarctica was just a matter of meteorology. A couple of years later, I saw that the discovery was proof of our prediction.

How is ozone destroyed?
-Ozone (O3) is continuously being formed and destroyed naturally. Ultraviolet radiation breaks it down into atomic and molecular oxygen (O2), which combine again to form more ozone. Although ozone only accounts for a few parts per million in atmospheric composition, the amounts of solar energy it consumes are much greater than the energy our society uses. Therefore, in the stratosphere, the temperature increases with height and the layer is very stable. CFC molecules are broken down by ultraviolet light when they rise above the ozone layer. Then the chlorine atoms are free and combine with the atomic oxygen, preventing the formation of more ozone; Afterwards, they can react with another oxygen atom and O2 is formed and the chlorine atom is free again to continue preventing the formation of ozone. It is a chain reaction, as a single chlorine atom can perform this operation hundreds of thousands of times. Then, little by little it falls towards the troposphere, where the rain deposits it on the surface.

How long does it take to make that journey since the CFC is issued?
-The emission takes between three and seven years to reach the troposphere for it to decompose, which is when it has its maximum effect, and then it begins to decrease. But the half-life of chlorine in the stratosphere is about 50 years.

If these gases were to stop emitting now, how long would it take for the atmosphere to be free of CFCs and would the ozone layer recover?
-Considering that production stopped at the end of 1995 and not taking into account the small quantities that continue to be emitted, the maximum destruction will occur within two years, before the end of the century, but it will not be much greater the current effect. And so it will continue for 50 more years. In half a century, we can fix the ozone hole.

In view of the agreements that have led to a ban on the manufacture of CFCs, it appears that politicians have responded to the scientists’ warning …
-It’s true, but it wasn’t easy. The international agreement was organized by the United Nations Environment Program (UNEP) with the support of all governments, but diplomatic efforts were very difficult. Industry was opposed to regulation, but since they are a relatively small number of large chemical industries, they were able to be talked to and shown that the scientific evidence was very clear. The largest of all, the Du Pont, had said years before that if the evidence was clear they would stop production, and although it took them some time, they ended up accepting the agreement. Industries were actively involved in the Montreal Protocol, making it easier for governments to support it. It is significant that there are technical solutions for all the important uses of these products, which allow industrial production to continue with compounds that are less bad for the atmosphere.

Are these products really less harmful?
-There are three important groups. HCFCs -hydrochlorofluorocarbons- still have chlorine and are considered a temporary solution, but the amount that reaches the stratosphere is less, because a good part of the emissions is oxidized in the lower atmosphere, since they are not as inert as CFCs. They are not perfect, but they allow for the development of better technologies in the coming years. Another solution is HFCs, chemically similar compounds but without chlorine and which are already being used in car air conditioning systems. The third solution is the use of different technologies. Thus, CFC 113, which is used in the microelectronics industry to clean the chips, has been eliminated and now they are washed with soap and water and other products, and a technology has even been developed that does not require cleaning these cards.

Greenpeace advocates the use of butane and other hydrocarbons as substitutes in refrigeration. Its viable?
-In certain cases, yes, as is also ammonia, which was used before CFCs and was left behind because it is toxic and caused accidents. Now there are circumstances that allow ammonia to be used in a safer way, especially in industrial processes. The problem with butane is that it is flammable, but it can be used in aerosol cans as a propellant.

The ozone layer has been the banner of many environmental organizations. Was it justified or has it been done excessive catastrophizing?
-It has been exaggerated, because it is presented as the end of the world. The problem is serious because of the amount of ozone that has disappeared, and there are effects that seem clear, such as the increase in the number of cases of skin cancer, but in other aspects its influence cannot be calculated exactly, because we do not have enough details. It should be understood that the severity of the problem depends on the amount of chlorine. If it has not been more important, it is because it has been resolved.

But, despite the ban on producing more CFCs, the use of those that exist has not been banned and it is said that a black market for these compounds has been created …
-It is one of the problems that the treaty tries to control. The important thing is that there are new technologies and that it is not necessary to produce refrigerators that use CFCs, so that black market is doomed to disappear.

Why is the biggest hole at the south pole, so far from the emission zones?
-The difference between the two hemispheres is a matter of the topology of the Earth. Antarctica is a continent surrounded by oceans and, on the other hand, in the Arctic there are many continental masses. This changes the circulation and stability of the polar vortex, a swirling, turbulent movement of air. In the southern hemisphere this vortex remains on the continent and the temperature drops much more, which is what determines the clear disappearance of ozone. In the north it also disappears, but it is not so localized, it is not concentrated. While in Antarctica more than 99% of ozone disappears, in a very specific area in the northern hemisphere it disappears much less, but in a larger area.

What decrease occurs in our hemisphere?
-It varies every year, as it depends on the temperatures and the places. Taking averages from different latitudes and years, the decrease is between 5 and 10 percent.

Why does the temperature influence?
-Because the condition for the greatest destruction of ozone to occur is that the cold lasts for several weeks, the time it takes for chlorine to attack ozone intensely. In the northern hemisphere, even if the temperature drops to similar values, it does so for only a couple of days, not two or three weeks, and that is the fundamental difference.

Apart from CFCs, what else attacks the ozone layer?
-Halons, which are used mainly in fire extinguishers and which are also controlled by the Montreal Protocol. The other harmful compound is methyl bromide, which is used as a fumigant in agriculture. Supersonic aircraft may also damage ozone by emitting nitrogen oxides, but that is a future problem, because there are still few fleets of supersonic aircraft.

Are you still working on the issue?
-Yes, but we do not only do chemistry studies of the stratosphere, but also of the lower atmosphere, the troposphere, where pollution problems, both urban and global, still require a lot of research.
Ignacio F. Bayo

This interview was published in December 1996, in number 187 of VERY Interesting

 


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