Ozone Depletion Potential of Different Refrigerants

1. Ozone
Depletion
Potential of
different
Refrigerants
Group Members
Gc Haroon ur Rashid
GC Hassan Rabbani
GC Jibran Naveed Cheema
GC Rao Mehboob

2. 1
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

3. 2
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.

4. 3
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, R115
HCFCs (Hydrochlorofluorocarbons): R22, R123
HFCs (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% R115
R-503 : 40.1% R23 and 59.9% R13

5. 4
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

6. 5
How Ozone is destroyedby CFCs
Chemical Equation
CFCl3 + UV Light ==> CFCl2 + Cl
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
The free chlorine atom is then free to attack another ozone
molecule
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
And again...
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
And again... for thousands of times.

7. 6
Ozone and CFCs Chain Reaction

8. 7
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

9. 8

10. 9
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.

11. 10
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

12. 11
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.

13. 12
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.

14. 13
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.