When heavy, lung-damaging smog descends on cities like Los Angeles and Milan, it's natural to raise our fists and curse ozone. Ozone molecules, simply three oxygen atoms bound together, are extremely reactive and can cause real damage at ground level. But higher up, ozone is a beneficial and crucial component of Earth's atmosphere.
The stratosphere -- the layer of our atmosphere just above the one we breathe -- includes only a thin layer of ozone. There are about three ozone (O3) molecules for every 10 million air molecules, and this layer is thicker over the poles than the equator [source: NOAA]. It might seem insignificant compared to the depth of the rest of the atmosphere, but it does a very important job. It prevents much of the sun's ultraviolet-B (UV-B) light, from reaching the Earth. This UV light can cause skin cancer, cataracts and other disorders.
Ozone protects us from the sun by interacting with light. It's created when ultraviolet light hits oxygen molecules (O2) in the stratosphere, splitting the molecules into two atoms of oxygen (O). When this atom encounters another oxygen molecule, the two combine to make ozone (O3). Ultraviolet light also breaks ozone back down into an oxygen molecule and an oxygen atom. Check out this animation from NASA to see how this works.
This process is called the ozone-oxygen cycle, and it converts UV radiation into heat, protecting the Earth. Other substances in the stratosphere, like chlorine, break the ozone back down into oxygen molecules and atoms. Usually, the building up and breaking down is a balanced process, but it can change according to seasons and because of natural events like volcanic eruptions.
But most scientists agree that human activity has caused an imbalance in the oxygen-ozone cycle that has led to a hole in the ozone layer over Antarctica. In this article, we'll find out what's causing the hole, whether we can create a patch, and what we can do to help stop the depletion of our critical UV protection.
So, how does ozone depletion happen in the first place?
The Ozone Hole
The ozone-oxygen cycle that keeps the ozone layer relatively stable has been derailed. The problem is that more ozone is breaking down than the sun can rebuild. This imbalance comes from the "hole," or thinning, in the ozone layer over Antarctica. Human-produced ozone-depleting compounds are doing most of the damage.
Ozone-depleting compounds contain bromine, chlorine, fluorine, carbon and/or hydrogen in different combinations. You've probably heard about one of the most common types of ozone-depleting compounds, known as chlorofluorocarbons (CFCs). CFCs contain only fluorine, carbon and chlorine, and traditionally have been used in refrigeration, air conditioning, aerosol cans and as industrial solvents. An over-abundance of these compounds, released into the air by human activities, has resulted in the Antarctic ozone hole.
Complex chemical reactions, which occur in Antarctica during the winter and spring, act to destroy ozone. In the winter, the sun doesn't reach the South Pole and a polar vortex forms. The polar vortex is an air current around the pole that isolates the air. The CFCs that arrive at the vortex can't get out, so they become concentrated there.
When sunlight returns to Antarctica in the spring, chemical reactions on the surface of these clouds break ozone-depleting compounds down into atoms of chlorine and bromine. These atoms are deadly to ozone. One chlorine atom can break apart 100,000 ozone molecules, and bromine is 40 times more destructive [source: EPA]. This happens naturally in the stratosphere, but the chlorine and bromine there isn't as concentrated as it becomes during the Antarctic spring. These atoms destroy much of the ozone over Antarctica, throwing off the balance of the rest of the ozone layer.
The polar vortex exists only over Antarctica, which is why the ozone "hole" exists only there. But the bigger the hole gets, the thinner the ozone layer will become over the rest of the Earth. This means more dangerous UV radiation will reach the Earth's surface.
An obvious solution, then, would be to pump more ozone up there to try to counteract the thinning. But creating an ozone patch is not a simple proposition.
Can We Patch The Ozone Hole?
If we could patch the hole over Antarctica, the natural ozone-oxygen cycle might fall back into balance. But unfortunately, we can't make more ozone to patch the hole. It takes a lot of energy to make ozone molecules -- in the atmosphere, the intense energy of the sun drives most of the work. But down at ground level, it's not a practical proposition. Plus, ozone is such a dangerous pollutant at ground level, it might not be wise to produce it even if it were easier to do.
To repair the ozone layer, then, we must stop releasing ozone-depleting compounds into the atmosphere. In 1987, more than 180 countries agreed to address the problem in the Montreal Protocol. In signing the protocol, those countries agreed to phase out ozone-depleting chemicals like CFCs, halons and carbon tetrachloride. In the United States, any products containing these compounds carry warning labels, and they can only be used if there is no suitable, non-ozone-depleting product available.
Scientists hope that, if these compounds are completely discontinued, the ozone layer will return to normal by 2050 [source: EPA].
In the meantime, wear sunscreen, immediately repair leaky cooling appliances, and be sure to only use HVAC repair services that are certified to properly deal with the refrigerant they remove.
For more information on the ozone hole, CFCs and related topics, look over the links on the next page.
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More Great Links
- Environmental Indicators: Ozone Depletion. EPA.http://www.epa.gov/ozone/science/indicat/
- Velasquez-Manoff, Moises. "The latest on hydrofluorocarbons." Christian Science Monitor. August 10, 2009.http://features.csmonitor.com/environment/2009/08/10/the-lastest-on-hydrofluorocarbons/
- Ozone: Good Up High, Bad Nearby. EPA.http://www.epa.gov/oar/oaqps/gooduphigh/
- Stratospheric Ozone. NOAA.http://www.ozonelayer.noaa.gov/science/basics.htm