Lec-9

Ozone layer depletion and Global warming

Ozone layer depletion Ozone and Ozone layer: Ozone gas is found on the upper surface of stratosphere at the height of about 50km in the form of a layer called ozonosphere. Ozone is an unstable gas and for its formation destruction UV ray is essential, which come from the sun. Function: • It regulates the weather and climate of the earth. • It filters away the ultraviolet radiation and protects the earth as protective layer.

Ozone layer depletion Ozone hole: • Ozone hole was at detected at first in 1975. • Some British scientists noticed effects of O3 hole in 1985. Photochemical reaction: O + O2 --------UV-------------- O3 O3 --------------UV-------------- O + O2 In these processes a part of the harmful UV rays is converted in to infra-red (IF- infrared wavelength just below visible light) rays, which is not lethal to man. It has heating effect. When ozone destruction is being greater then the formation known as ozone depletion.

Form: Earth receives UV radiation in 3 forms i.e. – UVA in the wavelength range 315-400 NM – UVB in the wavelength range 289-314 NM – UVC in the wavelength range 100-280 NM Among these UV-B is most dangerous.

Cause of O3 depletion:

CFCs, CCl4, CH4 etc. are main chemicals which check the ozone formation. These carbon compounds produce the chlorine, which breaks the O3 molecules and reduces O3 content in the atmosphere. Reaction: Cl +O3-------------------------- ClO + O2 ClO ---------------------------- Cl + O One atom of Cl is sufficient to destroy a lack of ozone molecules.

Halocarbon:

Cl, Fl, Br, I when make proper combination with carbon (C). • CFCs- Chlorofluorocarbons called Primary halocarbon. • BFCs- Bromofluorocarbons. • CCl4 – Carbon tetrachloride • Methail Chloroform.

CFCs:

CFCs were developed as a replacement for the refrigerants because it is extremely stable, nontoxic and inert, relative to the electrical and mechanical machinery.

Use: • CFCs 11 and 12 developed in 1930s as refrigerants (refrigeration, building and mobile air conditioning). • By 1970s, used as- Aerosol propellant likehair spray, deodorants, insecticide. • Industrial blowing agent for flexible, rigid plastic foams, polyurethane and polystyrene foams and industrial cleaning agents and solvents • CFC-113 used as solvent, especially for microelectronic production.

US Regulatory Action — IMOS Report • June 1975 — Oregon banned CFC aerosols effective 1977 • October 1976 — Regulatory plan announced – Phase 1 — Restrict “non-essential” aerosol uses of CFCs 11 and 12 – Phase 2 — Restrict additional uses of CFCs and other ozone depleters

Alternative sources of CFCs: Two viable substances in the form of HCFC and HFC-34 are considered to be harmless for ozone. Out of these two HFC-34 is the less harmful because, absence of chlorine in it but it has some problem i.e. * It is expensive *Inflammable *Toxic in nature So, we can use instead of these Butane, Propane because it is— - Less expensive - Less harmful - Freely available

Ozone Depletion • Today’s Propellants: – Hydro-fluoro carbons (HFCs) – Chloro-methyl carbons (CMCs) • Disadvantage: Expensive & other effects unknown

– Ammonia • Disadvantage(s): pungent, toxic, and flammable

– Hydrocarbons • Disadvantage(s): flammable

– Carbon Dioxide • Disadvantage: greenhouse gas

Effects of UV rays: The effects of O3 depletion eventually increase the UV rays penetration to the surface of the earth. • 1% drops in stratrospheric O3 increase 2-3 % UV. • In next century UV rays may be increase 3-4% at the tropics and 10-12 % at high altitude. Effects on Agricultural crops: • Agricultural crop losses. • Increase food production costs because of physical damages of growing plant. • Damage is also spread in other plants of the earth’s physical ecosystem.

Effects of UV rays: Effects on health: • Sunburn, Ageing, Wrinkling of skin. • Destruction of protein, Mutation of genes. • EPA ( Environmental Protection Agency) said– By increasing of 1% UVB rays increases basal cell cancer1% and squamous cell cancer 2%. – It may caused melanoma skin cancer – Cataracts disease in eye by about 0.2%.

Global warming: When the solar radiation first fall on the top of the atmosphere the harmful UV radiations are absorbed by the O3 UV rays are essential. In this process a part of the harmful UV rays are converted in to IF rays which is not lethal to man. IF radiations coming to earth from the sun are of short wavelengths but the IF rays reflected from the earth are of long wavelengths. The IF radiation reflected from the earth cannot escape out from the carbon dioxide layer present in the atmosphere. CO2 gas has the ability to absorb IF radiation reflected from the earth surface.

Global warming The heating up of earth’s atmosphere due to trapping in IF rays reflected from the earth surface by the CO2 layer in the atmosphere called Green house effect which cause global warming. • It has been observed that • CO2 can increase temperature by 50% . • CFCs can increase temperature by20%. • Other air pollutants can increase temperature by 10%

Greenhouse gases Greenhouse gases are made out of: •water vapour •carbon dioxide •methane •nitrous oxide •ozone •chlorofluorocarbons (CFCs) They are all natural gases, but extra greenhouses gases can be made by humans from pollution

How are extra greenhouse gases produced? Extra greenhouse gases are produced through activities which release carbon dioxide, methane, nitrous oxide and ozone CFCs (chlorofluorocarbons). These activities include: • Burning coal and petrol, known as 'fossil fuels' • Cutting down of rainforests and other forests • Animal waste which lets off methane

Global Concern: • Montreal Protocol (1987): A conference at a global level Result:

– It was decided to cut level of CFCs to 50% by 1999. – India and China opposed and refused to sign in this protocol – Developing countries were supported their decision.

• Toronto (Canada) (1988): The world conference on the changing atmosphere. Result: -To reduce 20% CO2 emission by 2005. • London protocol (1990): Result: -India China and several other countries demanded more time to reduce CFCs consumption -Developed countries agreed to stop CFCs consumption completely by 2000AD. -Other developing countries by 2010 AD. • Rio de Janerio ( 1992): No result was obtained because of interference of the industrialized country.

Impacts of Global Warming: The world is undoubtedly warming. This warming is largely the result of emissions of carbon dioxide and other greenhouse gases from human activities including industrial processes, fossil fuel combustion, and changes in land use, such as deforestation. Continuation of historical trends of greenhouse gas emissions will result in additional warming over the 21st century, with current projections of a global increase of 2.5ºF to 10.4ºF by 2100, with warming in the U.S. expected to be even higher. This warming will have real consequences for the United States and the world, for with that warming will also come additional sea-level rise that will gradually inundate coastal areas, changes in precipitation patterns, increased risk of droughts and floods, threats to biodiversity, and a number of potential challenges for public health

Impacts of Global Warming If Earth gets hotter, some of the important changes could happen: • Water expands when it's heated and oceans absorb more heat than land, so sea levels would rise. • Sea levels would also rise due to the melting of the glaciers and sea ice. • Cities on coasts would flood. • Places that usually get lots of rain and snowfall might get hotter and drier. • Lakes and rivers could dry up. • There would be more droughts making hard to grow crops. • Less water would be available for drinking, showers and swimming pools. • Some plants and animals might become extinct because of the heat. • Hurricanes, tornadoes and other storms which are caused by changes in heat and water evaporation may get more common.

The following may be the consequences of global warming. • • • • • • • • • • • •

Melting glaciers, snow and mountains ice caps. Flooding of low-lying coastal areas. Increase in sea level. Increase in the flow of rivers and change in rainfall pattern. Chances of submersion of islands. Occurrence of more cyclones and hurricanes. This will cause damage of agricultural crops. Fresh water will be contaminated with the salty water of sea. Human population will be displaced. The forest vegetation will not be able to adapt with the changing temperature and may face destruction. As a result of global warming, the temperature of southern Europe and Central America will rise and affect the rain fall in these areas. The effect of global warming on the Tropics and Southern hemisphere will be uncertain.