Ozone Depletion Potential of different

Refrigerants

Group Members

Gc Haroon ur Rashid GC Hassan Rabbani GC Jibran Naveed Cheema GC Rao Mehboob

Table of Contents

Page No# Topic

2 Introduction to Ozone Depletion

Potential

3-4 Types of Refrigerants

5-6 Ozone and CFCs

7-8 Ozone and HCFCs

9-11 Steps in Depletion of Ozone

11-12 Ways to prevent Ozone Depletion

13 Recent International Developments in Saving

the Ozone Layer

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Ozone Depletion Potential

When CFCs and HCFCs reach the stratosphere, the ultraviolet radiation from the sun causes them to break apart and release chlorine atoms which react with ozone, starting chemical cycles of ozone destruction that deplete the ozone layer. One chlorine atom can break apart more than 100,000 ozone molecules.

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Types of Refrigerants

The most common types of refrigerants in use nowadays are presented below:

- Halocarbons or freons.- Azeotropic refrigerants.- Aeotropic refrigerants

Halocarbons are generally synthetically produced. Depending on whether they include chemical elements hydrogen (H), carbon (C), chlorine (Cl) and florine (F) they are named after as follows:

CFCs (Chlorofluorocarbons): R11, R12, R113, R114, R115HCFCs (Hydrochlorofluorocarbons): R22, R123HFCs (Hydrofluorocarbons): R134a, R404a, R407C, R410a

Azeotropic mixtures are mixtures of two or more refrigerants whose vapour and liquid phases retain identical compositions over a wide range of temperatures. Typical examples of azeotropic mixtures can be seen below:

R-502 : 8.8% R22 and 51.2% R115R-503 : 40.1% R23 and 59.9% R13

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Zeotropic mixture is one whose composition in liquid phase differs to that in vapour phase. The word zeotropic is a combination of Greek words zeo (meaning boiling) and tropi (meaning change)

Typical examples of zeotropic mixtures can be seen below:

R404a : R125/143a/134a (44%,52%,4%)R407c : R32/125/134a (23%, 25%,R410a : R32/125 (50%, 50%)

Chart with typical refrigerants ODP values

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How Ozone is destroyed by CFCs

Chemical Equation

CFCl3 + UV Light ==> CFCl2 + ClCl + O3 ==> ClO + O2ClO + O ==> Cl + O2

The free chlorine atom is then free to attack another ozone molecule

Cl + O3 ==> ClO + O2ClO + O ==> Cl + O2

And again...

Cl + O3 ==> ClO + O2ClO + O ==> Cl + O2

And again... for thousands of times.

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Ozone and CFCs Chain Reaction

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Hydro chlorofluorocarbons (HCFCs)

These are refrigerants that contain Hydrogen, Chlorine, Fluorine, and Carbon. They have only about 10% of the ozone depleting potential as CFCs. They are energy-efficient, low-in-toxicity, cost effective and can be used safely. They have allowed the CFCs consumption of the world to fall by about 75%. Unfortunately HCFCs are Greenhouse gases, despite their very low atmospheric concentrations

Ozone Depletion in the Antarctic Springtime

1) HCl + ClONO2 → HNO3 + Cl2

2) Cl2 + sunlight → Cl + Cl

3) 2Cl + O3 → 2ClO + 2O2

4) 2ClO + 2O → 2Cl + 2O2

______________________

NET = 203 to 302

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Principal Steps in Depletion of Stratospheric Ozone

Emission

The process begins with the emission, at Earth’s surface, of source gases containing the halogens chlorine and bromine. The halogen source gases, often referred to as ozone-depleting substances (ODSs), include manufactured chemicals released to the atmosphere in a variety of applications, such as refrigeration, air conditioning, and foam blowing. Chlorofluorocarbons (CFCs) are an important example of chlorine-containing gases. Emitted source gases accumulate in the lower atmosphere (troposphere) and are transported to the stratosphere by natural air motions.

Accumulation

The accumulation occurs because most source gases are highly unreactive in the lower atmosphere. Small amounts of these gases dissolve in ocean waters. The low reactivity of these manufactured halogenated gases is one property that makes them well suited for specialized applications such as refrigeration. Some halogen gases are emitted in substantial quantities from natural sources.

Transport

These emissions also accumulate in the troposphere, are transported to the stratosphere, and participate in ozone destruction reactions. These naturally emitted gases are part of the natural balance of ozone production and destruction that predates the large release of manufactured halogenated gases.

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Conversion

Halogen source gases do not react directly with ozone. Once in the stratosphere, halogen source gases are chemically converted to reactive halogen gases by ultraviolet radiation from the Sun . The rate of conversion is related to the atmospheric lifetime of a gas ). Gases with longer lifetimes have slower conversion rates and survive longer in the atmosphere after emission. Lifetimes of the principal ODSs vary from 1 to 100 years . Emitted gas molecules with atmospheric lifetimes greater than a few years circulate between the troposphere and stratosphere multiple times, on average, before conversion occurs.

Reaction

The reactive gases formed from halogen source gases react chemically to destroy ozone in the stratosphere. The average depletion of total ozone attributed to reactive gases is smallest in the tropics and largest at high latitudes. In Polar Regions, surface reactions that occur at low temperatures on polar stratospheric clouds (PSCs) greatly increase the abundance of the most reactive chlorine gas, chlorine monoxide (ClO). This results in substantial ozone destruction in Polar Regions in late winter and early spring. After a few years, air in the stratosphere returns to the troposphere, bringing along reactive halogen gases.

Removal.

These gases are then removed from the atmosphere by rain and other precipitation or deposited on Earth’s land or ocean surfaces. This

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removal brings to an end the destruction of ozone by chlorine and bromine atoms that were first released to the atmosphere as components of halogen source gas molecules. Tropospheric conversion. Halogen source gases with short lifetimes (less than 1 year) undergo significant chemical conversion in the troposphere, producing reactive halogen gases and other compounds. Source gas molecules that are not converted are transported to the stratosphere. Only small portions of reactive halogen gases produced in the troposphere are transported to the stratosphere because most are removed by precipitation. Important examples of halogen gases that undergo some tropospheric removal are the hydrochlorofluorocarbons (HCFCs), methyl bromide (CH3Br), and gases containing iodine.

Ways to prevent ozone depletion

1. Limit private vehicle driving

A very easy way to control ozone depletion would be to limit or reduce the amount of driving as vehicular emissions eventually result in smog which is a culprit in the deterioration of the ozone layer. Carpooling, taking public transport, walking, using a bicycle would limit the usage of individual transportation

2. Use eco-friendly household cleaning products

Usage of eco-friendly and natural cleaning products for household chores is a great way to prevent ozone depletion. This is because many of these cleaning agents contain toxic chemicals that interfere with the ozone layer. A lot of supermarkets and health stores sell cleaning products that are toxic-free and made out of natural ingredients.

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3. Avoid using pesticides

Pesticides may be an easy solution for getting rid of weed, but are harmful for the ozone layer. The best solution for this would be to try using natural remedies, rather than heading out for pesticides. You can perhaps try to weed manually or mow your garden consistently so as to avoid weed-growth.

4. Developing stringent regulations for rocket launches

The world is progressing in scientific discoveries by leaps and bounds. A lot of rocket launches are happening the world over without consideration of the fact that it can damage the ozone layer if it is not regulated soon. A study shows that the harm caused by rocket launches would outpace the harm caused due to CFCs. At present, the global rocket launches do not contribute hugely to ozone layer depletion, but over the course of time, due to the advancement of the space industry, it will become a major contributor to ozone depletion. All types of rocket engines result in combustion by products that are ozone-destroying compounds that are expelled directly in the middle and upper stratosphere layer – near the ozone layer.

5. Banning the use of dangerous nitrous oxide

Due to the worldwide alarm caused by a study in the late 70s about the alarming rate at which the ozone was being depleted, nations around the globe got together and formed the Montreal Protocol in the year 1989 with a strong aim to stop the usage of CFCs. However, the protocol did not include nitrous oxide which is the most fatal chemical that can destroy the ozone layer and is still in use. Governments across the world should take a strong stand for banning the use of this harmful compound to save the ozone layer.

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Recent International Developments in Saving the Ozone Layer

191 Countries Agree to Strengthen Protection of the Earth's Ozone Layer

At the 19th Meeting of the Parties in Montreal on September 17-21, 2007, the Parties agreed to more aggressively phase out ozone-depleting hydrochlorofluorocarbons (HCFCs). The final agreement resulted from discussion of six proposals submitted by governments from both developed and developing countries - Argentina and Brazil; Norway, Iceland and Switzerland; the United States; Mauritania; Mauritius; and the Federated States of Micronesia.

HCFCs originally emerged as replacement chemicals for use in air conditioning, some forms of refrigeration equipment and foams.

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