SciTech

How Things Work: Ozone depletion

Above is an image produced from one of NASA’s satellites that monitors ozone thickness over the earth. The purple portion of the figure shows the ozone “hole” over Antarctica.  (credit: Courtesy of NASA) Above is an image produced from one of NASA’s satellites that monitors ozone thickness over the earth. The purple portion of the figure shows the ozone “hole” over Antarctica. (credit: Courtesy of NASA)

Climate change, global warming, and ozone depletion are issues that have been discussed time and time again in the past few years. These issues basically boil down to two main points — first, that we are harming the environment, and second, that our actions are ultimately harming us.
However, what exactly is happening to the environment that is so harmful for us? And more importantly, what is it that we are doing to harm the environment?
While the topic of environmental damage is very vast, this article will address the issue in terms of one of the many problems we are facing today — that of ozone depletion.
To understand what the problem we face is, it is important to have a little background information on the subject.
Earth’s atmosphere is divided into five main layers, starting from the nearest to the surface of the earth and going upward. These are, respectively, the troposphere, the stratosphere, the mesosphere, the thermosphere, and finally the exosphere.
The ozone layer is found in the second layer, the stratosphere. This layer is made up of ozone molecules, which are made up of oxygen.
While each molecule of the atmospheric oxygen that we breathe in is made up of two atoms of oxygen, ozone is made up of three. This change makes ozone vastly different from atmospheric oxygen.

For one thing, ozone is blue in color and has a characteristic odor, and for another, the ozone layer is able absorb radiation that comes from the sun.
As explained on www.nas.nasa.gov when an oxygen molecule absorbs a short wavelength photon of light, the energy causes the molecule to split into two atoms of oxygen. One of these atoms collides with another two-atom oxygen molecule, forming a molecule of three atoms of oxygen — ozone. A similar splitting process occurs with the ozone molecules when they are broken down.

Ozone formation and destruction thus goes on continuously, maintaining a constant ozone concentration. This cycle of ozone destruction and production is the reason behind the layer’s ability to absorb the radiation, especially the harmful ultraviolet radiation, coming from the sun.
A portion of ultraviolet light, called UVB, is especially harmful, as it can cause cataracts and a variety of skin cancers, damage crops, and also harm marine and wild life.

As long as the ozone layer continued to absorb this radiation, the Earth was safe.
However, with the thinning of the ozone layer, exposure to this radiation has become a serious concern.
This raises the question of why the ozone layer is thinning in the first place.
Elements like chlorine act as catalysts in the breakdown of ozone. This means that they speed up the process of ozone breakdown without altering or getting depleted.

According to an article on www.epa.gov, one molecule of chlorine can degrade more than 100,000 molecules of ozone before it is removed from the atmosphere. With atoms like chlorine present in the atmosphere, ozone gets depleted faster than it is recreated, and this results in the depletion of the ozone layer. Initially, chlorine was not much of a threat to the ozone layer as there was hardly any chlorine that high up in the atmosphere.
However, with the advancement of technology, this scenario changed. As the article explained, science came up with new so-called “miracle substances” — chlorofluorocarbons (CFCs). CFCs were not very toxic, not flammable, and very cheap to produce. Industries therefore flocked toward these substances and used them in a variety of applications — in hair sprays, as refrigerants, and in a variety of different solvents.

It was not until the 1970s that people began to realize the harmful effects of CFCs. CFCs contain chlorine, but unlike many other chlorine-containing agents, CFCs are very hard to destroy. Most chlorine-containing compounds dissolve in water and come back down to the earth through rain. CFCs, however, do not dissolve in water.

Hence, they cannot come down with rain and end up going higher and higher in the atmosphere. Ultimately, they reach the stratosphere, where the chlorine in them harms the ozone layer.

Although CFCs are not the only substances that harm the ozone layer, they make up the majority of ozone-harming substances. The result of all these CFC emissions is that there is now a “hole” in the ozone layer that centers on Antarctica. The thickness of the ozone layer over a particular region changes with the season. The ozone hole over Antarctica is not really an area with no ozone, but one with a very thin layer. NASA satellites have been keeping a tab on the thickness of the ozone layer over this area and send readings every day. However, it is not only Antarctica that has to worry about ozone depletion.

The U.S. Environmental Protection Agency cites a study in which it was discovered that ozone levels in the middle latitudes — where most populated nations lie — decreased by 10 percent during the winter and by 8 percent during the summer. From 1973 to 2001, ozone levels have decreased by 2.3 percent every 10 years.
Although these statistics are somewhat depressing, governments around the world have taken steps to protect the world from the harms of ozone depletion.
The Montreal protocol was signed in 1987. However, it was not until the year 1996 that the countries that had signed the protocol completely stopped the production of CFCs. Although no more CFCs were released into the atmosphere after this point, the harm that was done was already quite great.
However, pacts like the Montreal protocol were useful in curbing the subsequent damage to the environment.

Although harm has already been done to the environment, pacts like this have ensured that we do not harm the environment any more.