The Ozone Hole is Definitely Recovering

The ozone layer is a integral part of what makes Earth habitable. This region of the stratosphere is responsible for absorbing the majority of the Sun’s ultraviolet radiation, thus ensuring terrestrial organisms are not irradiated. Since the 1970s, scientists became aware of a steady decline in this layer around the southern polar region, along with and a major seasonal decrease. This latter phenomena, known as the “ozone hole”, has been a major concern for decades.

Attempts to remedy this situation have focused on cutting the use of industrial chemicals, such as chlorofluorocarbons (CFCs). These efforts culminated with the signing of the Montreal Protocol in 1987, which called for the complete phasing out of ozone-depleting substances (ODSs). And according to recent study by a team of NASA scientists, the ozone hole is showing signs of significant recovery as a result.

The study, titled “Decline in Antarctic Ozone Depletion and Lower Stratospheric Chlorine Determined From Aura Microwave Limb Sounder Observations“, recently appeared in the scientific journal Geophysical Research Letters. The study was led by Susan E Strahan and co-authored by Anne R. Douglass, two research scientists with NASA Goddard’s Atmospheric Chemistry and Dynamics Laboratory.

Artist’s impression of the Aura satellite. Credit: NASA

For the sake of their study, the team consulted data from NASA’s Aura satellite, which has been monitoring the southern polar region since 2005. Having launched in 2004, the purpose of the Aura satellite was to conduct measurements of ozone, aerosols and key gases in the Earth’s atmosphere. And according to the readings it has gathered since 2005, the reductions in the use of CFCs has led to a 20% decrease in ozone depletion.

Simply put, CFCs are long-lived chemical compounds that are made up of carbon, chlorine, and fluorine. Since the latter half of the 20th century, they have been used in a number of industrial applications such as refrigeration (as Freon), in chemical aerosols (as propellants), and as solvents. Eventually, these chemicals rise into the stratosphere where they become subject to UV radiation and are broken down into chlorine atoms.

These chlorine atoms play havoc with the ozone layer, where they catalyze to form oxygen gas (O²). This activity begins around July during the Southern Hemisphere’s winter, when the Sun’s rays cause an increase in the catalyzing of CFC-derived chlorine and bromine atoms in the atmosphere. By September (i.e. spring in the southern hemisphere), the activity peaks, resulting on the “ozone hole” that scientists first noted in 1985.

In the past, statistical analysis studies have indicated that ozone depletion has increased since. However, this study – which was the first to use measurements of the chemical composition inside the ozone hole – indicated that ozone depletion is decreasing. What’s more, it indicated that the decrease is caused by the decline in CFC use.

As Susan Strahan explained in a recent NASA press release, “We see very clearly that chlorine from CFCs is going down in the ozone hole, and that less ozone depletion is occurring because of it.” To determine how ozone and other chemicals in the atmosphere have changed from year to year, scientists have relied on data from the Aura satellite’s Microwave Limb Sounder (MLS).

Unlike other instruments that rely on sunlight to obtain spectra from atmospheric gases, this instrument measures these gases respective microwave emissions. As a result, it can measure trace gases over Antarctica during a key time of the year – when the southern hemisphere is experiencing winter and weather in the stratosphere is calm and temperatures are low and stable.

The change in ozone levels from the beginning to the end of Southern Hemisphere’s winter (early July to mid-September) was computed daily using MLS measurements every year from 2005 to 2016. While these measurements indicated a decrease in ozone loss, Strahan and Douglass wanted to be certain reductions in the use of CFCs was what was responsible.

This they did by looking for telltale signs of hydrochloric acid in the MLS data, which chlorine will form by reacting with methane (but only when all available ozone is depleted). As Strahan explained:

“During this period, Antarctic temperatures are always very low, so the rate of ozone destruction depends mostly on how much chlorine there is. This is when we want to measure ozone loss… By around mid-October, all the chlorine compounds are conveniently converted into one gas, so by measuring hydrochloric acid we have a good measurement of the total chlorine.”

Images from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite showing ozone fluctuations between 2010 and 2011. Credit: NASA/Rob Simmon

Another hint came in the form of nitrous oxide levels, another long-lived gas that behaves just like CFCs in much of the stratosphere – but which is not in decline like CFCs. If CFCs in the stratosphere were decreasing, it would mean that less chlorine would be present compared to nitrous oxide. By comparing MLS measurements of hydrochloric acid and nitrous oxide each year, they determined that chlorine levels were declining by about 0.8 percent per year.

As Strahan indicated, this added up to a 20% decrease from 2005 to 2016, which was consistent with what they expected. “This is very close to what our model predicts we should see for this amount of chlorine decline,” she said. “This gives us confidence that the decrease in ozone depletion through mid-September shown by MLS data is due to declining levels of chlorine coming from CFCs. But we’re not yet seeing a clear decrease in the size of the ozone hole because that’s controlled mainly by temperature after mid-September, which varies a lot from year to year.”

This process of recovery is expected to continue as CFCs gradually leave the atmosphere, though scientists anticipate that a complete recovery will take decades. This is very good news considering that the ozone hole was discovered only about three decades ago, and ozone levels began to stabilize about a decade later. Still, as Douglass explained, a full recovery is not likely to take place until the latter half of this century:

“CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time. As far as the ozone hole being gone, we’re looking at 2060 or 2080. And even then there might still be a small hole.”

The Montreal Protocol is often touted as an example of effective international climate action, and for good reason. The Protocol was struck thirteen years after the scientific consensus on ozone depletion was reached, and just two years after the rather alarming discovery of the ozone hole. And in the years that followed, the signatories remained committed to their goals and achieved target reductions.

In the future, it is hoped that similar action can be achieved on climate change, which has been subject to delays and resistance for many years now. But as the case of the ozone hole demonstrates, international action can address a problem before it is too late.

Further Reading: NASA

Planet Earth

In addition to being the birthplace of humanity and the cradle of human civilization, Earth is the only known planet in our Solar System that is capable of sustaining life. As a terrestrial planet, Earth is located within the Inner Solar System between between Venus and Mars (which are also terrestrial planets). This place Earth in a prime location with regards to our Sun’s Habitable Zone.

Earth has a number of nicknames, including the Blue Planet, Gaia, Terra, and “the world” – which reflects its centrality to the creation stories of every single human culture that has ever existed. But the most remarkable thing about our planet is its diversity. Not only are there an endless array of plants, animals, avians, insects and mammals, but they exist in every terrestrial environment. So how exactly did Earth come to be the fertile, life-giving place we all know and love?

Continue reading “Planet Earth”

Venus Express Discovers Venusian Ozone Layer

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Every day brings on new discoveries and now ESA’s Venus Express spacecraft has delivered another… the red-hot planet has an ozone layer. Located high in the Venusian atmosphere, this planetary property will help us further understand how such features compare to Earth and Mars – along with refining our search for extra-terrestrial life.

This wonderful discovery was made while Venus Express was busy watching stars at the periphery. When seen through the planet’s atmosphere, the SPICAV instrument was able to distinguish gas types spectroscopically. By picking apart the wavelengths, ozone was detected through its absorption of ultraviolet light. It forms when sunlight breaks down the carbon dioxide molecules and releases oxygen. From there, they are distributed by planetary winds where the oxygen atoms will either combine into two-atom oxygen molecules, or form three-atom ozone.

“This detection gives us an important constraint on understanding the chemistry of Venus’ atmosphere,” says Franck Montmessin, who led the research.

This is an animation of Venus Express performing stellar occultation at Venus. Venus Express is the first mission ever to apply the technique of stellar occultation at Venus. The technique consists of looking at a star through the atmospheric limb. By analysing the way the starlight is absorbed by the atmosphere, one can deduce the characteristics of the atmosphere itself. Credits: ESA (Animation by AOES Medialab)

To date, ozone has been the sole property of Earth and Mars – but this type of discovery method could aid astronomers in searching for life on other worlds. Why is it important? Because ozone absorbs most of the Sun’s harmful ultra-violet rays… and because it is believed to be a by-product of life itself. When combined with carbon dioxide, this could create a signature as a strong signal for life. But don’t get too excited at the prospects, yet. The amount of ozone detected is also critical to refining models. It will need to be at least 20% of Earth’s value to even be considered.

“We can use these new observations to test and refine the scenarios for the detection of life on other worlds,” says Dr Montmessin.

While we know that chances are almost non-existent that Venus has life, it still brings it one step closer to planets like Mars and Earth.

“This ozone detection tells us a lot about the circulation and the chemistry of Venus’ atmosphere,” says Hakan Svedhem, ESA Project Scientist for the Venus Express mission. “Beyond that, it is yet more evidence of the fundamental similarity between the rocky planets, and shows the importance of studying Venus to understand them all.”

Original Story Source: ESA Space Science News.

Where is the Ozone Layer Located

Ozone layer hole. Image credit: NASA

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The Ozone Layer is the portion of the atmosphere that contains high levels of the oxygen molecule ozone. This molecule plays an important role acting as a natural UV shield for the Earth. You may wonder where is the ozone layer located to play such a vital role so effectively. The Ozone layer is actually located in the stratosphere in a region that is 10 to 50 km above the Earth.

So why is the Ozone layer so important? As mention before the secret lies in oxygen molecules. Normal oxygen in its natural molecular state is made up of only two atoms. However this changes when oxygen in the thermosphere is exposed the Sun’s ultraviolet rays. The rays separate oxygen molecules the free oxygen joins with the remaining two atom oxygen molecules to create ozone. This process might seem simple but it helps to screen out 99.5 percent of the ultraviolet radiation that the Sun sends towards earth. The times that the ozone layer didn’t screen out this type of radiation at such levels life was almost wiped out according to the geologic record.

You might think that this is an exaggeration until you observe the biological damage UV rays can do. We have already seen the harm caused when people don’t take the proper precautions when going to the beach. The least harm comes in the form of sun burn. People overexposed to the UV rays that do make it to earth have their skin damaged by the UV energy that penetrates their skin. However it gets more serious the longer a person is exposed to UV rays. The reason is because the damage gets to the cellular level causing cancers and genetic damage. Essentially it’s like being exposed to a nuclear reactor in melt down. The high energy radiation over time would accumulate harm in living tissue until it killed the organism exposed to it.

Despite its importance industry produced and released chemicals into the air that interfered with the ozone cycle. The main problem chemical CFC’s prevented oxygen molecules from complete the bonding process that is important for the completion of the ozone cycle this caused a major depletion of ozone in key areas of the Earth’s atmosphere. This is huge when the natural concentration of ozone was already quite low. This just goes to show the delicate balance that was upset. Fortunately nations upon hearing the harm caused started bans on CFC’s while industry tried to find alternatives to use in products. The result started to show with ozone depletion actually slowing down and reversing with scientist predicting recovery within the next century.

We have written many articles about the ozone layer for Universe Today. Here’s an article about the depletion of the ozone layer, and here’s an article about the ozone layer.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.