The ozone hole is not formally a “hole” where no ozone is actually present, but is really a region of exceptionally depleted ozone in the stratosphere over the Antarctic that occurs at the start of Southern Hemisphere spring (August October). Satellite instruments supply us with daily pictures of ozone over the Antarctic region. The ozone hole image below shows the really low values (blue and purple colored area) centered over Antarctica on four October 2004. From the historical record we are aware that total column ozone values of a bit less than 220 Dobson Units weren’t observed prior to 1979. From an aircraft field mission over Antarctica we also understand that a full column ozone amount of under 220 Dobson Units is actually a consequence of catalyzed ozone loss from chlorine and bromine compounds. For these reasons, we utilize 220 Dobson Units as the boundary of the region representing ozone loss. Using the day snapshots of total column ozone, we are able to compute the part on the Earth which is actually enclosed by a line with values of 220 Dobson Units (the white line in the figure below).
Map of total ozone over the antarctic on October four, 2004 with the region under 200 Dobson Units highlighted The ozone hole is actually the region over Antarctica with total ozone of 220 Dobson Units or even lower. This map shows the ozone hole on October four, 2004. The information had been acquired by the Ozone Monitoring Instrument on NASA’s Aura satellite.
Chlorofluorocarbons as well as ozone Lots of people have read that the ozone hole is actually brought on by chemical substances called CFCs, light for chlorofluorocarbons. CFCs escape into the ambiance from refrigeration as well as propellant equipment and processes. In the low atmosphere, they’re very steady they persist for many years, possibly years. This long lifetime allows several of the CFCs to finally reach the stratosphere. In the stratosphere, ultraviolet light breaks the bond holding chlorine atoms (Cl) to the CFC molecule. A totally free chlorine atom moves on to take part in a number of chemical reactions that both equally destroy ozone and return the free chlorine atom to the environment unchanged, exactly where it is able to kill far more and more ozone molecules. For people that understand the story of ozone and CFCs, that’s the element of the tale that’s possibly familiar.
The element of the story that less individuals understand is actually that while the chlorine atoms freed from CFCs do ultimately destroy ozone, the damage does not occur instantly. The majority of the roaming chlorine that will get separated from CFCs actually becomes part of 2 chemicals which – under normalatmospheric things – are very stable that scientists think about them to be extended reservoirs for chlorine. So just how does the chlorine get out of the tank each spring?
Polar stratospheric clouds (Ozone and pscs) Under normal atmospheric conditions, the 2 chemical substances which store most atmospheric chlorine (hydrochloric acid, and chlorine nitrate) are actually healthy. But in the very long weeks of polar darkness over Antarctica in the winter season, atmospheric conditions are actually unusual. An endlessly circling whirlpool of stratospheric winds called the polar vortex isolates the air flow in the middle. Because it’s absolutely black, the environment in the vortex gets extremely cool that clouds form, although the Antarctic air is very slim and dried out. Chemical reactions take put that couldn’t take place elsewhere in the environment. These unusual reactions are able to happen just on the surface area of polar stratospheric cloud particles, which might be nitric acid, ice, or water, based on the temperature.
Photograph of a polar stratospheric cloud The frozen crytals which make up polar stratospheric clouds offer a surface area for the reactions that free chlorine atoms in the Antarctic stratosphere.
These reactions convert the inactive chlorine reservoir chemicals into much more active forms, particularly chlorine gas (Cl2). When the sunlight returns to the South Pole in October, UV light rapidly breaks the bond between the 2 chlorine atoms, releasing free chlorine into the stratosphere, exactly where it takes part in reactions that destroy ozone molecules while regenerating the chlorine (known as a catalytic reaction). A catalytic reaction permits an one-time chlorine atom to eliminate thousands of ozone molecules. Bromine is engaged in a minute catalytic reaction with chlorine which contributes a big portion of ozone loss. The ozone hole grows throughout the first spring until temperatures warm and the polar vortex weakens, ending the isolation of the atmosphere in the polar vortex. As air flow from the surrounding latitudes mixes into the polar region, the ozone destroying forms of chlorine disperse. The ozone layer stabilizes until the following spring