NASA scientists reported that the Ozone Hole over Antarctica in September 2013 is slightly smaller and has slightly more ozone than recent year measurements. This is good news. Here is why.
Oxygen is the third most abundant element in the universe behind Hydrogen and Helium. It is the second most abundant element by volume in our atmosphere making up 20.8% of the air we breathe. It is normally found in a two molecule state in the air as that is colorless, odorless, and tasteless and the formula O2. Because it it highly reactive with other elements, it is also found in many other compounds. By mass, it makes up 49.2% of mass of Earth’s crust and 88.8% of the oceans.
Ozone is a form of Oxygen with three molecules instead of two with the formula O3. It is a pale blue gas and has a pungent smell. You might recall the smell if you have experienced electrical discharges and sparks. It is a much more active element chemically than the two molecule form of Oxygen. Near the Earth’s surface, Ozone damages mucous and respiratory tissue. It damages plants and causes damage to rubber. It is a biological hazard and strong pollutant at ground levels. It occurs in much smaller concentrations than the two molecule version. But, since it is highly reactive, small concentrations have a large impact.
High in the stratosphere, Ozone is a very beneficial and important substance. It interacts with ultraviolet-B radiation from the Sun and prevents it from reaching the surface. This is a protection to plant and animal life. So, Ozone is both helpful and harmful to living things depending on where it is found.
Scientists regularly measure the amount of Ozone in the stratosphere in order to know the concentrations around the Earth. They produce maps of the concentrations like this one from September of 2013. The blue and violet regions are where Ozone is less abundant. This map shows a large Ozone Hole in the atmosphere over the Antarctic and reaching into S. America. The areas on the ground in that hole are less protected from ultraviolet-B rays. This is not a good thing.
Dobson Units of Ozone Concentration
Monitoring of the ozone is carried out by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite and the Ozone Monitoring and Profiler Suite (OMPS) on the NASA-NOAA Suomi NPP satellite. Measurements from these satellites allow the scientists to calculate the area of the hole marked in blue above. And, the amount of ozone in the atmosphere is calculated in Dobson Units DU. What is a Dobson Unit of ozone? Without getting into the technical details, let me give you an example.
If you could get all of the ozone gas molecules to drop to the surface of the Earth at 0˚C and 1 atmosphere of air pressure and form a layer, it would be an average thickness of only 3 millimeters. That is two pennies deep. Scientists say Earth’s normal ozone concentration is 300 DU for that thickness. That is represented by the large green areas on the global image above. The Ozone Hole in blue and violet has less ozone concentration in the atmosphere. The value is down to about 100 DU. That is a third of what is found over the rest of the globe.
During the Antarctic winter, the ozone concentration there is about the same as everywhere else on Earth, 300 DU. As the Sun shines more and more during the Antarctic summer, the concentration decreases from the interactions between ultraviolet-B rays and the molecules. By September, the value has decreased to about 100 DU. This low value is referred to as a hole in the concentration map.
Here is a video of the 2013 year values. Watch the change from green to blue. Watch the small charts of concentration and area. Replay as needed. It only lasts 8 seconds. Switch to HD with the gear button at lower right of the video. Every year this cycle occurs.
Historical Changes in Ozone Since 1979
Some history of the study of ozone can be found in this link.
In 1973, scientists suspected a man-made link to the decrease of ozone in the atmosphere. It was believed that chlorofluorocarbons (CFCs) were accumulating in the atmosphere, interacting with sunlight, and releasing large quantities of chlorine. The chlorine reacted with the ozone to decrease it in turn. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) were also found to be responsible. As a result of this research, an international treaty was opened for signature on 16 September 1987 called the Montreal Protocol banning several ozone destroying substances.
It has been a long and slow process of recovery for Earth. Here are snapshots of the Ozone Hole from four different years. The size of the hole has increased. The concentration in Dobson Units has decreased. But, their changes have slowed. If you want to see a year to year animation of the hole from 1979 to 2013, follow this link.
I obtained a table of values from NASA of the areal extend of the hole as well as the concentration in Dobson Units for September 1979 – 2013. These were charted below. A trend curve was added to each plot. Both trends have reversed and show some improvement. The ozone concentration each year is slowly recovering. The areal extend of the hole is slightly smaller in recent years. Neither of these improvements is large. But, the trend is present. We need to continue to adhere to the Montreal Protocol and encourage all nations to do their best to restrict the use of these harmful chemicals in their growing populations. We have a long way to go.