Ozone layer showing signs of recovery: UN scientists

On 10^th September 2014, report titled Scientific Assessment of Ozone Depletion 2014 was released.

The report was prepared by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO).

The report revealed that the ozone layer is well on track to recovery in the next few decades.

Actions taken under the Montreal Protocol on Substances that Deplete the Ozone Layer in 1986 are enabling the return of the ozone layer to benchmark 1980 levels.

Highlights of report:

• The Montreal Protocol and associated agreements have led to decreases in the atmospheric abundance of gases, such as CFCs (chlorofluorocarbons) and halons, once used in products such as refrigerators, spray cans, insulation foam and fire suppression.
• Total ozone column has declined over most of the globe during the 1980s and early 1990s. Since 2000, it has remained relatively unchanged, but there are recent indications of its future recovery.
•  The Antarctic ozone hole continues to occur each spring and it is expected to continue occurring for the better part of this century given that ozone depleting substances persist in the atmosphere, even though their emissions have ceased.
• The Arctic stratosphere in winter or spring 2011 was particularly cold that led to large ozone depletion as expected under these conditions.
•  The Montreal Protocol has made large contributions toward reducing global greenhouse gas emissions. 
• In 1987, ozone-depleting substances contributed about 10 gigatonnes of CO₂ equivalent emissions per year. But the guidelines of Montreal Protocol have now reduced these emissions by more than 90 percent.
• The decrease in ozone-depleting substances is about five times larger than the annual emissions reduction target for the first commitment period (2008-2012) of the Kyoto Protocol on climate change.
• Hydro fluorocarbons (HFCs) currently contribute about 0.5 gigatonnes of CO2-equivalent emissions per year. These emissions are growing at a rate of about 7 percent per year. Though HFCS do not harm the ozone layer but many of them are potent greenhouse gases.
• The annual Antarctic ozone hole has caused significant changes in Southern Hemisphere surface climate in the summer due to cooling of the lower stratosphere there is associated impacts on surface temperature, precipitation, and the oceans.
• In the Northern Hemisphere, where the ozone depletion is smaller, there is no strong link between stratospheric ozone depletion and tropospheric climate.
• The concentrations of CO2, methane and nitrous oxide are the three main long-lived greenhouse gases in the atmosphere which will tend to increase global ozone levels.

What is Ozone?

Ozone is a natural gas composed of three atoms of oxygen. It chemical symbol is O₃.

It is blue in color and has a strong odor.

Normal oxygen (O2), which we breathe, has two oxygen atoms and is colorless and odorless.

Environmental scientists have classified O₃ into two:

1.       God Ozone

2.       Bad Ozone.

Good Ozone

Good ozone (also called Stratospheric Ozone) occurs naturally in the upper Stratosphere. The stratosphere is the layer of space, approximately 20 to 30 kilometres above the earth's surface.

Where does good Ozone come from?

When UV light strikes (Oxygen) O₂ molecules, they are split into two individual O atoms — O and O. When one of the O atoms combines with O₂ molecule, ozone (O₃) is created.

This good plays a vital role because it shields us from the sun's harmful UV rays. It is called Good Ozone, for obvious reasons because it protects humans, life and animals on earth.

Bad Ozone

Bad Ozone is also known as Tropospheric Ozone, or ground level ozone.

This gas is found in the troposphere, the layer that forms the immediate atmosphere.

Bad Ozone does not exist naturally. Human actions cause chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC).

Where does bad ozone come from?

Each time there is a reaction of chemicals such as those found in cars, power plants and factory emissions, in the presence of sunlight (UV light), Bad Ozone is created.

Bad ozone contaminates (dirties) the air and contributes to what we typically experience as "smog" or haze.

Ozone Layer

This is a layer in the stratosphere containing a relatively high concentration of ozone.

The earth's atmosphere is divided into several layers, and each layer plays an important role. The first region extending about 10km upwards from the earth's surface is called the troposphere.

The next layer, extending about 15-60 km is called the stratosphere. The ozone layer is mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometres above earth, though the thickness varies seasonally and geographically.

The ozone layer protects the earth from the suns UV Rays.  If the ozone layer is depleted by human action, the effects on the planet could be catastrophic.

What is Ozone Depletion?

Ozone layer depletion, is the process of wearing out (reduction) of the amount of ozone in the stratosphere.

Human activity is major reason for ozone depletion of ozone.

Industries that manufacture things like insulating foams, solvents, soaps, cooling things like Air Conditioners, Refrigerators etc uses chlorofluorocarbons (CFCs).

These CFCs substances are heavier than air, but over time (2-5years) they are carried high into the stratosphere by wind action.

Depletion of ozone begins when CFC’s get into the stratosphere. Ultra violet (UV) radiation from the sun breaks up these CFCs.

The breaking up action releases Chlorine atoms. Chlorine atoms react with Ozone, starting a chemical cycle that destroys the ozone in that area.

One chlorine atom can break apart more than 100,000 ozone molecules.

There are other Ozone Depleting Substances (ODS)  are methyl bromide used in pesticides, halons used in fire extinguishers, and methyl chloroform used in making industrial solvents.

Other chemicals that naturally destroy Ozone are Noy, Hox, Clx, which belong to the Nitrogen, Hydrogen and Chlorine families.

What is Ozone Hole?

Top atmospheric researchers confirm that Ozone levels vary by season and latitude.

In 1979, it was observed that there is considerable Ozone depletion in the upper latitudes, Arctic and 

Antarctic. This massive stretch of ozone depletion (hole) is estimated to be about the size of America.

Particularly in the antarctic, satellite images were released showing a disturbing thinning of the ozone layer. The phenomenon is what we usually call the Ozone hole, and it was most observed over the Antarctic every year during the spring.

Why does the Ozone hole only occur in the Antarctic?

The hole is Antarctica occurs in the spring (September to December).

It begins with this overall ozone thinning, but it is assisted by the presence of polar stratospheric clouds (PS clouds).

During the extreme cold of winter, with no sun for six months, polar winds create a vortex which traps and chills the air; the temperature is below -80 Celsius. The ice in these PS clouds provides surfaces for the chemical reactions that destroy the ozone. This needs light to kick-start the reactions.

In spring the sun rises above the horizon and provides energy which starts the photochemical reactions. The clouds melt and the trapped compounds (chlorine and chlorine monoxide from the CFCs) are released. Ozone in the lower stratosphere is destroyed and the ozone hole appears.

By the end of spring warmer December temperatures break up the vortex and destroy the PS clouds. Sunlight starts creating ozone again and the hole begins to repair.

Impact of volcanic eruptions on stratospheric ozone

When volcanoes erupt, they produce massive clouds of ashes into the troposphere, and then they drift upward into the stratosphere.

These ashes contain high concentration of bromine and chlorine.

Ashes can stay in the stratosphere for about two to five years, and within this period, there are chemical reactions that destroy the stratospheric ozone molecules.

In these volcanic ashes are some chemicals including bromine and chlorine belong to a group of highly reactive elements called halogens, that need electrons to become stable. They get these electrons from the Ozone gas.

Ozone destroying gases like hydrogen chloride, can also be found in volcanic ashes, but they dissolve readily in water. In many cases rain can wash down these chemicals before they get high up into the stratosphere, but some do escape into it.

All in all it is known that volcanoes contribute about 18%-20% of Chlorine entering the atmosphere, and human activities also contribute about 80%-82%.

How Ozone Depletion Affects UV Levels?

Depletion of the ozone layer has consequences on humans, animals and plants. This typically results from higher UV levels reaching us on earth.

Humans

Research confirms that high levels of UV Rays cause non-melanoma skin cancer.

Additionally, it plays a major role in malignant melanoma development. UV is also linked to cataracts (a disease of the eye which clouds the eye’s lens).

Plants

Plant growth, as well as its physiological and developmental processes is affected negatively.

These include the way plants form, timing of development and growth, distribution of plant nutrients and metabolism, etc.

These changes can have important implications for plant competitive balance, animals that feed on these plants, plant diseases, and biogeochemical cycles.

Marine (or water) Ecosystems:

Phytoplankton form the foundation of aquatic food webs. These usually grow closer to the surface of water, where there is enough sunlight.

Changes in UV levels affect the development and growth of phytoplankton, and naturally, the fish that feed on them.

UV radiation is also known to have affected the development stages of of fish, shrimp, crab, amphibians and other animals.

When this happens, animals in the upper food chain that feed on these tiny fishes are all affected.

Effects on Biogeochemical Cycles

The power of higher UL levels affect the natural balance of gasses (and greenhouse gases) in the biosphere: e.g., carbon dioxide (CO2), carbon monoxide (CO), carbonyl sulfide (COS) and ozone.

Changes in UV levels can cause biosphere-atmosphere feedback resulting from the atmospheric buildup of these gases.