The Montreal OZONE: Protocol is celebrating its 25th Anniversary this year

16th September International Day for the Preservation of the Ozone Layer

The Montreal Protocol is celebrating its 25th Anniversary this year

THEME: PROTECTING OUR ATMOSPHERE FOR GENERATIONS TO COME

The ozone layer shields the earth and all its life from harmful ultraviolet radiation from the sun.  What is commonly known is that there is a hole in the ozone layer, and what is less known is the actual substances that create this hole in the ozone layer.

On 16 September 1987, twenty four Parties signed the Montreal Protocol on Substances that Deplete the Ozone Layer.

Health and environmental facts Increased exposure to UV light increases the development of skin cancers and eye cataracts and upsets natural balances in ecosystems.  Upsets to ecosystems can affect food chains including food procurement for human consumption. 

Ozone (O₃, pronounced /ˈoʊzoʊn/), or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope (O₂). Ozone in the lower atmosphere is an air pollutant with harmful effects on the respiratory systems of animals and will burn sensitive plants; however, the ozone layer in the upper atmosphere is beneficial, preventing potentially damaging electromagnetic radiation from reaching the Earth's surface. Ozone is present in low concentrations throughout the Earth's atmosphere. It has many industrial and consumer applications.

The highest levels of ozone in the atmosphere are in the stratosphere, in a region also known as the ozone layer between about 10 km and 50 km above the surface (or between about 6 and 31 miles). Here it filters out photons with shorter wavelengths (less than 320 nm) of ultraviolet light, also called UV rays, (270 to 400 nm) from the Sun that would be harmful to most forms of life in large doses. These same wavelengths are also among those responsible for the production of vitamin D in humans. Ozone in the stratosphere is mostly produced from ultraviolet rays reacting with oxygen:

O₂ + photon (radiation < 240 nm) → 2 O

O + O₂ + M → O₃ + M

It is destroyed by the reaction with atomic oxygen:

O₃ + O → 2 O₂

The latter reaction is catalysed by the presence of certain free radicals, of which the most important are hydroxyl (OH), nitric oxide (NO) and atomic chlorine (Cl) and bromine (Br). In recent decades the amount of ozone in the stratosphere has been declining mostly because of emissions of CFCs and similar chlorinated and brominated organic molecules, which have increased the concentration of ozone-depleting catalysts above the natural background. Ozone only makes up 0.00006% of the atmosphere.

Ground-level ozone is created near the Earth's surface by the action of daylight UV rays on a group of pollutants called ozone precursors. There is a great deal of evidence to show that ground level ozone can harm lung function and irritate the respiratory system. Exposure to ozone and the pollutants that produce it is linked to premature death, asthma, bronchitis, heart attack, and other cardiopulmonary problems.

According to various studies done the thickness of the ozone layer is more at the poles and less dense above the equator. Its variations are also dependant on the season with more in winters than in summer. It was discovered in the year 1970 that a hole is been developed in the ozone layer because of the release of CFC's.Thus the UNEP has come up with a number of ideas and co-operative activities to protect the Ozone layer. The UNEP is also focusing on the elimination of production and use of ozone-depleting substances, including chlorofluorocarbons (CFCs), used as industrial refrigerants and in aerosols, and the pesticide methyl bromide. The ozone layer depletion has also resulted in number of melanoma cases across the world and nearly 66,000 people die from skin cancer every year.

Reports of Ozone layer depletion

Apart from the artificial components like chlorofluorocarbons and bromoflurocarbons which cause damage to Ozone molecules, there are also other sources which produce free radicals like hydroxyl, chlorine, bromine, and nitric oxide responsible for causing damage to the ozone molecules. These radicals are capable of rising even above the stratosphere and catalyze a chain reaction capable of breaking down over 100,000 Ozone molecules. With the growing technology which accounts for both good and bad there are many industries and commercial factories involved in the manufacture of appliances like refrigerator, fire extinguisher, and air conditioners which uses component like chlorofluorocarbons in large quantity which in turn release the free radicals. From the various studies and experiment done by the NASA's Earth-observing Aura satellite the size of the ozone hole is been increasing considerably.

Q. What is ozone and where is it in the atmosphere?
Ozone is a gas that is naturally present in our atmosphere. Each ozone molecule contains three atoms of oxygen and is denoted chemically as O3. Ozone is found primarily in two regions of the atmosphere. About 10% of atmospheric ozone is in the troposphere, the region closest to Earth (from the surface to about 10–16 kilometers (6–10 miles)). The remaining ozone (about 90%) resides in the stratosphere between the top of the troposphere and about 50 kilometers (31 miles) altitude. The large amount of ozone in the stratosphere is often referred to as the “ozone layer.

Q. How is ozone formed in the atmosphere?
Ozone is formed throughout the atmosphere in multistep chemical processes that require sunlight. In the stratosphere, the process begins with an oxygen molecule (O2) being broken apart by ultraviolet radiation from the Sun. In the lower atmosphere (troposphere), ozone is formed by a different set of chemical reactions that involve naturally occurring gases and those from pollution sources.

Q. Why do we care about atmospheric ozone?
Ozone in the stratosphere absorbs a large part of the Sun’s biologically harmful ultraviolet radiation. Stratospheric ozone is considered “good” ozone because of this beneficial role. In contrast, ozone formed at Earth’s surface in excess of natural amounts is considered “bad” ozone because it is harmful to humans, plants, and animals. Natural ozone near the surface and in the lower atmosphere plays an important beneficial role in chemically removing pollutants from the atmosphere.

Q. How is total ozone distributed over the globe?
The distribution of total ozone over the Earth varies with location on timescales that range from daily to seasonal. The variations are caused by large-scale movements of stratospheric air and the chemical production and destruction of ozone. Total ozone is generally lowest at the equator and highest in polar regions.

Q. How is ozone measured in the atmosphere?
The amount of ozone in the atmosphere is measured by instruments on the ground and carried aloft on balloons, aircraft, and satellites. Some instruments measure ozone locally by continuously drawing air samples into a small detection chamber. Other instruments measure ozone remotely over long distances by using ozone’s unique optical absorption or emission properties.

Q. What are the principal steps in stratospheric ozone depletion caused by human activities?
The initial step in the depletion of stratospheric ozone by human activities is the emission, at Earth’s surface, of gases containing chlorine and bromine. Most of these gases accumulate in the lower atmosphere because they are unreactive and do not dissolve readily in rain or snow. Natural air motions transport these accumulated gases to the stratosphere, where they are converted to more reactive gases. Some of these gases then participate in reactions that destroy ozone. Finally, when air returns to the lower atmosphere, these reactive chlorine and bromine gases are removed from Earth’s atmosphere by rain and snow.

 Q. What emissions from human activities lead to ozone depletion?
Certain industrial processes and consumer products result in the emission of ozone-depleting substances (ODSs) to the atmosphere. ODSs are manufactured halogen source gases that are controlled worldwide by the Montreal Protocol. These gases bring chlorine and bromine atoms to the stratosphere, where they destroy ozone in chemical reactions. Important examples are the chlorofluorocarbons (CFCs), once used in almost all refrigeration and air conditioning systems, and the halons, which were used in fire extinguishers. Current ODS abundances in the atmosphere are known directly from air sample measurements.

NAAQS –INDIA

The National Ambient Air Quality Standards (NAAQS) are standards established by apply for outdoor air throughout the country. Standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory diseases TO protect public welfare from any known or anticipated adverse effects of a pollutant

Clean air is a basic necessity for sustenance of life. In spite of introduction of cleaner technologies in industry, energy production and transport sectors, air pollution remains a major health risk. Recent epidemiological studies have provided evidence that even low pollution levels increase mortality and morbidity. Air quality standards provide a legal framework for air pollution control.  An air quality standard is a description of a level of air quality that is adopted by a regulatory authority as enforceable. The basis of development of standard should be to provide a rational for protecting public health from adverse effects of air pollutants, to eliminate or reduce exposure to hazardous air pollutants, and to guide national and local authorities in their air quality management decisions.