The Ozone how has been growing since the 1990s, The hole is pictured in dark blue, with red indicating areas of recovery (high ozone). (Source: KNMI/ESA)
This graph shows the area of the hole over the course of each year for the last decade. (Source: KNMI/ESA)
This year there was more active chlorine particles from CFC pollution, thanks in part to weather patterns. These particles helped destroy extra ozone, increasing the size of the hole. (Source: KNMI/ESA)
We're back in the hole
Last year brought some seemingly good news -- the ozone hole shrunk for the first time in years. While it’s illogical to try to glean too many conclusions from an event so dependent on yearly weather variations, nonetheless many chimed in that the decrease was a sign that environmental-protection efforts were working.
Unfortunately, the news for this year is decidedly mixed. Again, like those who became over-excited last year, many may become overly gloomy at this latest report -- but it’s important to bear in mind that ultimately only long term trends paint the true picture.
In 2008 the European Space Agency (ESA) reported that the ozone hole over the Antarctic grew in both size and amount of ozone lost from 2007. While still not as large as the hole in 2006, the hole marks the reverse of a year of gains.
Ozone, O3, is a special chemical that exists in a thin layer found 25 km above the Earth in the upper atmosphere. This chemical blocks ultraviolet radiation, helping protect marine life, and protecting humans against skin cancer and cataracts. Unfortunately, this protective layer is being broken down by volatile halogens, such as chlorofluorocarbons (CFCs). While most of these compounds have been banned for decades by the 1987 Montreal Protocols, they remain in the atmosphere for decades, destroying massive amounts of ozone. This exacerbates yearly natural losses due to cold temperatures.
The ozone hole for 2008 reached a maximum size of 27 million km2, compared to 25 million km2 in 2007, and 29 million km2 in 2006 (approximately the size of North America). The overall CFC picture has remained relatively unchanged in the last several years, rather, the key difference in the hole size has been the weather. During the Southern Hemisphere's winter, the air over Antarctica is cut off from warmer airflow by the polar vortex. This leads to the formation of stratospheric clouds (PSCs). These clouds contain halogen pollution, which is energy by sunlight, forming radicals. These radicals go on to breakdown ozone, leading to the formation of an ozone hole.
Julian Meyer-Arnek of the German Aerospace Centre (DLR), who participated in the ESA's data analysis, commented on the 2007-2008 shift, stating, "In 2007 a less concentric and larger polar vortex led to an early onset of the ozone destruction in the sunlit parts of the polar vortex. Therefore, we saw an ozone hole formation in the beginning of September 2007 which corresponded to the average behaviour of the years 1995-2006."
He continues, "In 2008 a more concentric polar vortex led to a delay of the onset of the ozone destruction of about one week. The preconditioning of the polar chemistry was about the same for both years, although in 2008 the temperatures were slightly below the 2007 temperatures leading to slightly improved formation of PSCs. Since the polar vortex remained undisturbed for a long period, the 2008 ozone hole became one of the largest ever observed."
The thinnest areas of ozone measured just 120 Dobson Units this year, just slightly better than the 100 Dobson Unit minimum in 2006. Dobson Units are the standard method of measuring ozone, and is based on the height of the column of ozone at a specific location. The latest measurements come courtesy of the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) atmospheric sensor onboard ESA’s Envisat, the Global Ozone Monitoring Experiment (GOME) aboard ESA’s ERS-2 and its follow-on instrument GOME-2 aboard EUMETSAT’s MetOp.
While yearly variations may not bear great significance, it is important to closely monitor ozone levels to detect trends, the ESA's top researchers say. Professor Meyer-Arnek states, "In order to detect these signs of recovery, a continuous monitoring of the global ozone layer and in particular of the Antarctic ozone hole is crucial."
The ESA's measurements this year were special as it used data collected by students from the ESA’s Advanced Atmospheric Training Course at Oxford University.
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