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Introduction: All about Ozone

http://eschooltoday.com/ozone-depletion/ozone-information-for-children.html

Like other environmental problems, Ozone Depletion is one that is very troubling, and rightly so, considered as a major environmental issue by all nations on the earth.

Have you ever felt the sun’s intensity ripping through your skin on a hot afternoon? Probably so.

But the sun is no where near the earth. The sun is estimated to be about 150 million kilometers (93 million miles) from our planet earth. Everyday, as the sun rises, we begin to feel the heat. This heat is radiated through millions of space, and yet we still feel it.

The rays from the sun contain Ultra Violet Rays (UV Rays).UV rays is not all bad, because it helps human with Vitamin D. But too much of it is very dangerous. (we shall see why very soon).

Unfortunately, manufacturing activities since the industrial revolution have caused a disturbance in the atmosphere and opened up for more UV rays to come through to the earth. There have been serious consequences, and potentially it can get worse if we do not act responsibly.

To better understand the Ozone Depletion problem, we first need to get a few terms right. Let’s begin with Ozone.

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: Good Ozone and Bad Ozone.

Good Ozone
Good ozone(also called Stratospheric Ozone) occurs naturally in the upper Stratosphere. The stratosphere is the layer of space 6 to 30 miles above the earth’s surface.

Where does good Ozone come from?
The air is full of gases reacting with each other, even though our eyes do not see. When UV light strikes (Oxygen) O2 molecules, they are split into two individual O atoms — O and O. When one of the O atoms combine with O2 molecule, ozone (O3) is created.

Even though Ozone is only a small part of the gases in this layer, it 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.
Note that this kind of smog is different from the deadly London winter type that killed 4000 people. Smog from bad ozone is usually in the summer, caused by the action of sunlight on a mixture of hydrocarbons and oxides of nitrogen. It is known as Photochemical or Summer Smog.
The Ozone Layer

This is simply 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. Many human activities like mountain climbing, gas balloons and smaller aircrafts operate within this region.

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 (12 to 19 mi) 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 simply the wearing out (reduction) of the amount of ozone in the stratosphere. Unlike pollution, which has many types and causes, Ozone depletion has been pinned down to one major human activity.

Industries that manufacture things like insulating foams, solvents, soaps, cooling things like Air Conditioners, Refrigerators and ‘Take-Away’ containers use something called chlorofluorocarbons (CFCs). These substances are heavier than air, but over time, (2-5years) they are carried high into the stratosphere by wind action.

Depletion begins when CFC’s get into the stratosphere. Ultra violet 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 good ozone in that area. One chlorine atom can break apart more than 100,000 ozone molecules.

Ozone layer depletion is best illustrated or explained with the Ozone Bucket Analogy. Click button below to have a look.

There are other Ozone Depleting Substances (ODS) such as 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.

Measurements of CFCs in the stratosphere are made from gas balloons, aircraft and satellites.

Sadly, there isn’t much humans can do to replenish the depleted Ozone, as it tends to recover slowly by itself. All we can do is to be more responsible with our manufacturing needs so that we do not introduce more CFCs into the air.
How do volcanoes affect stratospheric ozone?

When volcanoes erupt, they produce massive clouds of ashes into the troposphere, and then they drift upward into the stratosphere (the upper atmosphere layer where ozone gas protects humans from UV radiation). 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.

Human activities like pollution and emissions already send lots of halogen gases into the stratosphere — but, scientists have noted that halogens from volcanoes contain twice and thrice as much halogens that human activities even produce. This means the potential of depleting the ozone layer is higher with volcanic ‘smoke’

Remember that the stratosphere is high up and that means when volcanic ash gets there, the impact can be over a very large area, even to the size of the entire North American region.

It is believed that the eruption of Mount Pinatubo (Philippines) in 1991 sent thick plumes 34km up into the stratosphere, where it had a significant impact on the ozone levels at the time. Other large eruptions include Tambora, Krakatau and Agung, all of which ad impacts on ozone levels.

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%. (The contribution os volcanoes to the ozone depletion is often disputed… read more here)

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).

This is why it is important to wear UV protection sun-glasses and sun-cream when you stay in the sun to minimise the UV effect on your skin and eyes.

Click below for important notes on UV and its effects on humans.

Plants
The damage that extreme UV levels has on plants is one that our eyes do not see much, but humans can feel the impact. Plant growth, as well as its physiological and developmental processes are all 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 is known to affect the development and growth of phytoplankton, and naturally, the fish that feed on them. UV radiation is also know to have affect 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. (More about the effects of UV here)
What is Ozone Hole?

Top atmospheric researchers confirm that Ozone levels vary by season and latitude. Sometime in 1979, it was observed the there 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.

In the winter, temperatures drop below -78°C (-109°F) in the Poles (Antartic). Thin clouds form of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. This sets the ozone depletion going by spring, a lot of depletion has occurred.

Why does the Ozone hole only occur in the Antarctic?
Researchers say it is not only in the Antarctic, but in many places in other latitudes where populations are dense. It is believed that these places have cloud types that aid in the chemical reactions that cause ozone depletion.

In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.

WHAT CAN BE DONE?

Ozone is a natural gas and is naturally replenished over time. This means if we can do something to balance the natural production with its depletion, there should not be a problem. Unfortunately, it does not quiet work like that.

People ask if we cannot produce our own ozone gas to replenish what is lost in the stratosphere. That’s a good question. The sun naturally produces ozone with immense energy and over time. To do the same, we will be looking at using immense energy too, about twice the energy used in the USA. That is just not practical.

The only way to do that is to remove the excess chlorine and bromine from the stratosphere. And the only way to do that is to stop making CFCs and several other chemicals. This is why in the 1990s a meeting of the worlds big nations met and agreed to reduce the usage of CFCs and also encouraged other nations to do the same. That was decided in the Montreal Protocol.

This is not enough, but at least it was a good starting point. It is always best to talk and discuss problems than to do nothing at all. This is why learning about Ozone depletion, like you are doing, is the most important step towards a safe environment in future.