OZONE LAYER AND CHEMICALS

WHAT IS OZONE AND OZONE LAYER? Ozone (O3) is a highly-reactive from of oxygen.

Unlike oxygen (O2), ozone has a strong scent and is blue in color.

Ozone exists within both the tropospheric and stratospheric zones of the Earth’s atmosphere

In the troposphere, ground level ozone is a major air pollutant and primary constituent of photochemical smog

In the stratosphere, the ozone layer is an essential protector of life on earth as it absorbs harmful UV radiation before it reaches the earth.

It is a toxic, irritating gas, often encountered in surface air pollution episodes, when it can trigger asthma and irritate mucous membranes.

WHEN WAS IT FIRST MEASURED AND ITS COMPONENTS

Ozone is a compound of oxygen that contains three atoms instead of the two found in the oxygen gas that sustains life. It was discovered in 1839 by a Swiss chemist, Christian Friedrich Schonbein.

Ozone concentrations at the surface were first measured reliably by Robert Strutt (later 4th Lord Rayleigh) in 1918 using spectra of a hydrogen lamp recorded through five kilometers of air. Dry air consists of 78% nitrogen and 21% oxygen and there are normally trace amounts of other gases, principally argon, water and carbon dioxide, present. The concentration of ozone is usually only a few parts per million and even in the ozone layer it is only one part in 100,000.

OZONE LAYER DEPLETION AND OZONE HOLE

OZONE DEPLETION PROCESS

CFC’S AND OZONE DEPLETION

Over the last 50 years we have introduced chemicals into the atmosphere that are capable of destroying ozone through photochemical processes. Chloro-fluoro-carbons (CFCs) are widely known, but there are also other ozone depleting substances such as halons (bromo-fluoro-carbons) and methyl bromide.Chlorofluorocarbons are created and used in refrigerators and air conditioners. These chlorofluorocarbons are not harmful to humans and have been a benefit to us. Once released into the atmosphere, chlorofluorocarbons are bombarded and destroyed by ultraviolet rays. In the process chlorine is released to destroy the ozone molecules.

DESTRUCTION OF OZONE BY CHLORINE

Molecular oxygen is broken down in the stratosphere by solar radiation to yield atomic oxygen, which then combines with molecular oxygen to produce ozone. The ozone is then destroyed by chlorine atoms.

RESPONSIBILITY FOR OZONE DAMAGE EACH YEAR

GLOBAL CFC PRODUCTION

OZONE HOLE

There are many ozone hole depleting substances present in our atmosphere which can react with ozone to turn it back into oxygen. In most parts of the world the reactions are very slow and there is little damage to the ozone layer, however over the Antarctic a dramatic hole opens in the ozone layer every spring and fills in again by mid-summer.

WHY DOES THE OZONE HOLE FORM OVER ANTARCTICA ?

The answer is essentially 'because of the weather in the ozone layer'. In order for rapid ozone destruction to happen, clouds have to form in the ozone layer. In these clouds surface chemistry takes place. This converts chlorine or bromine (from CFCs and other ozone depleting chemicals) into an active form, so that when there is sunlight, ozone is rapidly destroyed. Without the clouds, there is little or no ozone destruction. Only during the Antarctic winter does the atmosphere get cold enough for these clouds to form widely through the centre of the ozone layer. Elsewhere the atmosphere is just too warm and no clouds form. The northern and southern hemispheres have different 'weather' in the ozone layer, and the net result is that the temperature of the Arctic ozone layer during winter is normally some ten degrees warmer than that of the Antarctic. This means that such clouds are rare, but sometimes the 'weather' is colder than normal and they do form. Under these circumstances significant ozone depletion can take place over the Arctic, but it is usually for a much shorter period of time and covers a smaller area than in the Antarctic.

OZONE HOLE MEASUREMENTS OVER THE ANTARCTIC REGION 1980-98

IS THE OZONE HOLE RECOVERING ?

Some reports in the media suggest that the ozone layer over Antarctica is now recovering. This message is a little confused. Recent measurements at surface monitoring stations show that the loading of ozone destroying chemicals at the surface has been dropping since about 1994 and is now about 6% down on that peak. The stratosphere lags behind the surface by several years and the loading of ozone depleting chemicals in the ozone layer is at or near the peak. Satellite measurements show that the rate of decline in ozone amount in the upper stratosphere is slowing, however the total ozone amount is still declining. The small size of the 2002 ozone hole was nothing to do with any reduction in ozone depleting chemicals and it will be a decade or more before we can unambiguously say that the ozone hole is recovering. This assumes that the decline in ozone depleting chemicals continues and that there are no other perturbations to the ozone layer, such as might be caused by a massive volcanic eruption or Tunguska like event. It will be the middle of this century or beyond before the ozone hole ceases to appear over Antarctica. What we saw in 2002 is just one extreme in the natural range of variation in the polar stratosphere and is the equivalent of an extreme in 'stratospheric weather'. By contrast the 'weather' in 2003 moved to the opposite extreme and we saw one of the largest ozone holes on record.

GLOBAL WARMING AND THE OZONE HOLE

The ozone hole is a completely different phenomenon to global warming, however there are links between them. The ozone hole is caused by ozone depleting chemicals in the atmosphere, which have been produced by industry, for example CFCs. One link is that CFCs are also 'greenhouse gasses'. Enhanced global warming is a probable consequence of increasing amounts of 'greenhouse gasses', such as carbon dioxide and methane, in the atmosphere. Although the surface of the earth warms, higher up the atmosphere cools, thus increasing the area where stratospheric clouds can form. This makes a larger area susceptible to ozone depletion and provides another link between the two issues.

OZONE DESTRUCTION BY UV RAYS

UV radiation from the sun releases the radicals Cl and ClO.

Ozone is a highly unstable molecule so it readily donates its extra oxygen molecule to free radical species such as hydrogen, bromine, and chlorine.

These compound species act as catalysts in the breakdown of ozone molecules.

EFFECTS OF UV RAYS ON AQUATIC ECOSYSTEMS

Ozone depletion causes increases in UV rays’s effects on aquatic ecosystems by:

1. decreasing the abundance of phytoplankton – affects the food stock for fishes and the absorption of CO2.

2. decreasing the diversity of aquatic organisms – reduces food stock and also destroys several fish and amphibians.

HARMFUL EFFECTS OF UV RAYS ON PEOPLE

Skin cancer: UV radiation is the primary cause of skin cancer .When UV light damages DNA , it impairs its ability to control skin growth.

Other skin problems: Overexposure to UV light can lead to skin effects that resemble premature aging.

Immune suppression: Evidence suggests that the body's immune system will begin to weaken as a result of too much UV light.

Eye problems: Cataracts can develop from UV exposure, and can lead to blindness.

CORRELATION BETWEEN OZONE DEPLETION AND SKIN DISEASES

FACTORS AFFECTING UV EXPOSURE

Clouds cover - partly cloudy days do little to reduce UV exposure but rainy or substantially overcast days reduce UV exposures.

The time of day – peak exposure time is 12:00 noon - 1:00 p.m. UV intensity is reduced by about half at three hours before and three hours after the peak exposure time.

WAYS TO LIMIT OZONE DETERIORATION

Encourage growth of plants that produces oxygen, and discourage deforestation

Eliminate production and release of known ozone depleting chemicals (such as CFCs and HCFCs) where remotely possible.

An easy way to help combat ozone deterioration is to limit the amount of driving. Motor vehicles produce quantities of emissions which help to create smog. Smog is a leading factor with regard to ozone deterioration.

Another easy way to help prevent ozone deterioration is to use environmentally friendly cleaning products. There are many non-toxic, non-ozone depleting cleaning supplies.

POLICY RESPONSES TO OZONE DEPLETION

On an international scale, banning

the use of CFC will slow down the destruction of ozone. This is being achieved by through the Montreal Protocol, an international agreement to reduce the use of CFCs and eventually ban them completely. CFCs have now been banned in more economically developed countries. However, in some less economically developed countries CFCs are still being used due to the high cost of replacing it with a more ozone friendly substance.

The efforts seem to be working. Reports show that by 2049, the ozone will recover to 1979 thickness, which is when scientists believe the hole began to form. Many scientists believe the Montreal Protocol is responsible for this joyous recovery.

 

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