GREEN HOUSE EFFECT

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FUTURE REFRIGERANTS.

INTRODUCTION

Arefrigerantis a substance or mixture, usually afluid, used in aheat pump and refrigeration cycle. In most cycles it undergoesphase transitionsfrom aliquidto agasand back again. Manyworking fluidshave been used for such purposes.Fluorocarbons, especiallychlorofluorocarbons, became commonplace in the 20th century, but they are being phased out because of theirozone depletioneffects. Other common refrigerants used in various applications areammonia,sulfur dioxide, and non-halogenated hydrocarbonssuch aspropane.

The ideal refrigerant would have favorablethermodynamicproperties, benoncorrosiveto mechanical components, and be safe, including free fromtoxicityandflammability. It would not causeozone depletionorglobal warming. Since different fluids have the desired traits in different degree, choice is a matter oftrade-off.

The desired thermodynamic properties are aboiling pointsomewhat below the target temperature, a highheat of vaporization, a moderatedensityin liquid form, a relatively high density in gaseous form, and a highcritical temperature. Since boiling point and gas density are affected bypressure, refrigerants may be made more suitable for a particular application by choice of operating pressures.

The inert nature of manyHalons,Chlorofluorocarbons(CFC) andHydrochlorofluorocarbons(HCFC), with the benefits of them being nonflammable and nontoxic, made them good choices as refrigerants, but their stability in the atmosphere and their correspondingglobal warming potentialandozone depletion potentialraised concerns about their usage. In order from the highest to the lowest potential of ozone depletion are Bromochlorofluorocarbon, CFC then HCFC. ThoughHFCandPFCare non-ozone depleting, many have global warming potentials (as measured bycarbon dioxide equivalent) that are thousands of times greater than CO2. Other refrigerants such aspropaneandammoniaare not inert, and are flammable or toxic if released.

New refrigerants were developed in the early 21st century that are safe to humans and to the environment, but their application has been held up by regulatory hurdles due to concerns over toxicity and flammability

What is Greenhouse effect?

Thegreenhouse effectis a process by which thermal radiation from a planetary surface is absorbed by atmosphericgreenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.

Solar radiation at the frequencies ofvisible lightlargely passes through the atmosphere to warm the planetary surface, which then emits this energy at the lower frequencies ofinfraredthermal radiation. Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the surface and lower atmosphere. The mechanism is named after the effect of solar radiation passing through glass and warming agreenhouse, but the way it retains heat is fundamentally different as a greenhouse works by reducing airflow, isolating the warm air inside the structure so that heat is not lost byconvection.

If an ideal thermally conductiveblackbodywere the same distance from the Sun as the Earth is, it would have a temperature of about 5.3 C. However, since the Earth reflects about 30%of the incoming sunlight, this idealized planet'seffective temperature(the temperature of a blackbody that would emit the same amount of radiation) would be about 18 C.The surface temperature of this hypothetical planet is 33 C below Earth's actual surface temperature of approximately 14 C.The mechanism that produces this difference between the actual surface temperature and the effective temperature is due to the atmosphere and is known as the greenhouse effect.

Greenhouse Gases

By their percentage contribution to the greenhouse effect on Earth the four major gases are:

water vapour, 3670%

carbon dioxide, 926%

methane, 49%

ozone, 37%

The major non-gas contributor to the Earth's greenhouse effect,clouds, also absorb and emit infrared radiation and thus have an effect on radiative properties of the atmosphere.

Greenhouse effect from CO2

Carbon dioxide (CO2) is the primary greenhouse gas emitted through human activities. In 2012, CO2accounted for about 82% of all U.S. greenhouse gas emissions from human activities. Carbon dioxide is naturally present in the atmosphere as part of the Earth's carbon cycle (the natural circulation of carbon among the atmosphere, oceans, soil, plants, and animals). Human activities are altering the carbon cycleboth by adding more CO2to the atmosphere and by influencing the ability of natural sinks, like forests, to remove CO2from the atmosphere. While CO2emissions come from a variety of natural sources, human-related emissions are responsible for the increase that has occurred in the atmosphere since the industrial revolution.

The main human activity that emits CO2is the combustion of fossil fuels (coal, natural gas, and oil) for energy and transportation, although certain industrial processes and land-use changes also emit CO2. The main sources of CO2 emissions in the United States are described below.

Electricity.Electricity is a significant source of energy in the United States and is used to power homes, business, and industry. The combustion of fossil fuels to generate electricity is the largest single source of CO2emissions in the nation, accounting for about 38% of total U.S. CO2emissions and 31% of total U.S.greenhouse gasemissions in 2012. The type of fossil fuel used to generate electricity will emit different amounts of CO2. To produce a given amount of electricity, burning coal will produce more CO2than oil or natural gas.

Transportation.The combustion of fossil fuels such as gasoline and diesel to transport people and goods is the second largest source of CO2emissions, accounting for about 32% of total U.S. CO2emissions and 27% of total U.S.greenhouse gasemissions in 2012. This category includes transportation sources such as highway vehicles, air travel, marine transportation, and rail.

Industry.Many industrial processes emit CO2through fossil fuel combustion. Several processes also produce CO2emissions through chemical reactions that do not involve combustion, for example, the production and consumption of mineral products such as cement, the production of metals such as iron and steel, and the production of chemicals. Fossil fuel combustion from various industrial processes accounted for about 14% of total U.S. CO2emissions and 12% of total U.S.greenhouse gasemissions in 2012. Note that many industrial processes also use electricity and therefore indirectly cause the emissions from the electricity production.

Carbon dioxide is constantly being exchanged among the atmosphere, ocean, and land surface as it is both produced and absorbed by many microorganisms, plants, and animals. However, emissions and removal of CO2by these natural processes tend to balance. Since the Industrial Revolution began around 1750, human activities have contributed substantially to climate change by adding CO2and other heat-trapping gases to the atmosphere.

Chloroflurocarbon(CFC)

Achlorofluorocarbon(CFC) is anorganic compoundthat contains onlycarbon,chlorine, andfluorine, produced as avolatilederivative ofmethane,ethane, andpropane. They are also commonly known by theDuPontbrand nameFreon. The most common representative isdichlorodifluoromethane(R-12 or Freon-12). Many CFCs have been widely used asrefrigerants, propellants (in aerosol applications), and solvents. The manufacture of such compounds has been phased out under theMontreal Protocol, and are being replaced with products such asHFCs(e.g.,R-410A),hydrocarbons, and CO2, because CFCs contribute toozone depletionin the upperatmosphere.

History of CFCs

Carbon tetrachloride(CCl4) was used in fire extinguishers and glass "anti-fire grenades" from the late nineteenth century until around the end ofWorld War II. Experimentation with chloroalkanes for fire suppression on militaryaircraftbegan at least as early as the 1920s.Freonis a trade name for a group of CFCs which are used primarily asrefrigerants, but also have uses in fire-fighting and as propellants inaerosol cans. Bromomethane is widely used as a fumigant. Dichloromethane is a versatile industrial solvent.

The Belgian scientistFrdric Swartspioneered the synthesis of CFCs in the 1890s. He developed an effective exchange agent to replace chloride in carbon tetrachloride with fluoride to synthesize CFC-11 (CCl3F) and CFC-12 (CCl2F2).

In the late 1920s,Thomas Midgley, Jr.improved the process of synthesis and led the effort to use CFC as refrigerant to replaceammonia(NH3),chloromethane(CH3Cl), and sulphur dioxide(SO2), which are toxic but were in common use. In searching for a new refrigerant, requirements for the compound were: lowboiling point, low toxicity, and to be generally non-reactive. In a demonstration for theAmerican Chemical Society, Midgley flamboyantly demonstrated all these properties by inhaling a breath of the gas and using it to blow out a candle in 1930.

Ozone depletion by CFC

Explanation

When ultraviolet light waves (UV) strike CFC* (CFCl3) molecules in the upper atmosphere, a carbon-chlorine bond breaks, producing a chlorine (Cl) atom. The chlorine atom then reacts with an ozone (O3) molecule breaking it apart and so destroying the ozone. This forms an ordinary oxygen molecule(O2) and a chlorine monoxide (ClO) molecule. Then a free oxygen** atom breaks up the chlorine monoxide. The chlorine is free to repeat the process of destroying more ozone molecules. A single CFC molecule can destroy 100,000 ozone molecules.

* CFC - chlorofluorocarbon: it contains chlorine, fluorine and carbon atoms.** UV radiation breaks oxygen molecules (O2) into single oxygen atoms.

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.

Global warming caused by CFC

Chlorofluorocarbons (CFCs) are to blame for global warming since the 1970s and not carbon dioxide, according to new research from the University of Waterloo published in theInternational Journal of Modern Physics Bthis week.

CFCs are already known to deplete ozone, but in-depth statistical analysis now shows that CFCs are also the key driver in global climate change, rather thancarbon dioxide(CO2) emissions.

"Conventional thinking says that the emission of human-made non-CFC gases such as carbon dioxide has mainly contributed to global warming. But we have observed data going back to the Industrial Revolution that convincingly shows that conventional understanding is wrong," said Qing-Bin Lu, a professor of physics and astronomy, biology and chemistry in Waterloo's Faculty of Science. "In fact, the data shows that CFCs conspiring with cosmic rays caused both the polarozone holeand global warming."

"Most conventional theories expect thatglobal temperatureswill continue to increase as CO2 levels continue to rise, as they have done since 1850. What's striking is that since 2002, global temperatures have actually declined matching a decline in CFCs in the atmosphere," Professor Lu said. "My calculations of CFCgreenhouse effectshow that there was global warming by about 0.6 C from 1950 to 2002, but the earth has actually cooled since 2002. The cooling trend is set to continue for the next 50-70 years as the amount of CFCs in the atmosphere continues to decline."

The findings are based on in-depthstatistical analysesof observed data from 1850 up to the present time, Professor Lu's cosmic-ray-driven electron-reaction (CRE) theory ofozone depletionand his previous research into Antarctic ozone depletion and global surface temperatures.

"It was generally accepted for more than two decades that the Earth'sozone layerwas depleted by the sun's ultraviolet light-induced destruction of CFCs in the atmosphere," he said. "But in contrast, CRE theory says cosmic rays energy particles originating in space play the dominant role in breaking down ozone-depleting molecules and then ozone."

The Mechanism of Global Warming Caused by Three CFC Alternatives

Global-warming potential

Global-warming potential(GWP) is a relative measure of how much heat agreenhouse gastraps in the atmosphere. It compares the amount of heat trapped by a certain mass of thegasin question to the amount of heat trapped by a similar mass ofcarbon dioxide. A GWP is calculated over a specific time interval, commonly 20, 100 or 500 years. GWP is expressed as a factor of carbon dioxide (whose GWP is standardized to 1). For example, the 20 year GWP ofmethaneis 86, which means that if the same mass of methane and carbon dioxide were introduced into the atmosphere, that methane will trap 86 times more heat than the carbon dioxide over the next 20 years.[1]

The substances subject to restrictions under theKyoto protocoleither are rapidly increasing their concentrations inEarth's atmosphereor have a large GWP.

The GWP depends on the following factors:

the absorption ofinfrared radiationby a given species

the spectral location of its absorbing wavelengths

theatmospheric lifetimeof the species

Thus, a high GWP correlates with a large infrared absorption and a long atmospheric lifetime. The dependence of GWP on the wavelength of absorption is more complicated. Even if a gas absorbs radiation efficiently at a certain wavelength, this may not affect its GWP much if the atmosphere already absorbs most radiation at that wavelength. A gas has the most effect if it absorbs in a "window" of wavelengths where the atmosphere is fairly transparent. The dependence of GWP as a function of wavelength has been found empirically and published as a graph.[2]

Because the GWP of a greenhouse gas depends directly on its infrared spectrum, the use ofinfrared spectroscopyto study greenhouse gases is centrally important in the effort to understand the impact of human activities on globalclimate change.

Calculating global warming potential

Just asradiative forcingprovides a simplified means of comparing the various factors that are believed to influence the climate system to one another, global-warming potentials (GWPs) are one type of simplified index based upon radiative properties that can be used to estimate the potential future impacts of emissions of different gases upon the climate system in a relative sense. GWP is based on a number of factors, including the radiative efficiency (infrared-absorbing ability) of each gas relative to that of carbon dioxide, as well as the decay rate of each gas (the amount removed from the atmosphere over a given number of years) relative to that of carbon dioxide.[3]

Theradiative forcing capacity(RF) is the amount of energy per unit area, per unit time, absorbed by the greenhouse gas, that would otherwise be lost to space. It can be expressed by the formula:

where the subscriptirepresents an interval of 10inverse centimeters. Absirepresents the integrated infrared absorbance of the sample in that interval, and Firepresents the RF for that interval.[verification needed]

TheIntergovernmental Panel on Climate Change(IPCC) provides the generally accepted values for GWP, which changed slightly between 1996 and 2001. An exact definition of how GWP is calculated is to be found in the IPCC's2001 Third Assessment Report. The GWP is defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1kg of a trace substance relative to that of 1kg of a reference gas:

where TH is the time horizon over which the calculation is considered; axis theradiative efficiencydue to a unit increase in atmospheric abundance of the substance (i.e., Wm2kg1) and [x(t)] is the time-dependent decay in abundance of the substance following an instantaneous release of it at time t=0. The denominator contains the corresponding quantities for the reference gas (i.e. CO2). The radiative efficiencies axand arare not necessarily constant over time. While the absorption of infrared radiation by many greenhouse gases varies linearly with their abundance, a few important ones display non-linear behaviour for current and likely future abundances (e.g., CO2, CH4, and N2O). For those gases, the relative radiative forcing will depend upon abundance and hence upon the future scenario adopted.

Since all GWP calculations are a comparison to CO2which is non-linear, all GWP values are affected. Assuming otherwise as is done above will lead to lower GWPs for other gases than a more detailed approach would. Clarifying this, while increasing CO2 has less and less effect on radiative absorption as ppm concentrations rise, more powerful greenhouse gases like methane and nitrous oxide have different thermal absorption frequencys to co2 that are not filled up (saturated) as much as co2, so rising pmms of these gases are far more significant.

Values of GWP

Carbon dioxidehas a GWP of exactly 1 (since it is the baseline unit to which all other greenhouse gases are compared).

GWP values and lifetimes from 2013 IPCC AR5 p714(with climate-carbon feedbacks)[5]

Lifetime (years)

GWP time horizon

20 years

100 years

Methane

12.4

86

34

HFC-134a(hydrofluorocarbon)

13.4

3790

1550

CFC-11(chlorofluorocarbon)

45.0

7020

5350

Nitrous oxide

121.0

268

298

Carbon tetrafluoride(CF4)

50000

4950

7350

Ozone depletion potential

Theozone depletion potential(ODP) of achemical compoundis the relative amount of degradation to theozone layerit can cause, withtrichlorofluoromethane(R-11 or CFC-11) being fixed at an ODP of 1.0.Chlorodifluoromethane(R-22), for example, has an ODP of 0.055. CFC 11, or R-11 has the maximum potential amongst chlorocarbons because of the presence of three chlorine atoms in the molecule.

The first proposal of ODP came from Wuebbles in 1983. It was defined as a measure of destructive effects of a substance compared to a reference substance

Precisely, ODP of a given substance is defined as the ratio of global loss of ozone due to given substance over the global loss of ozone due to CFC-11 of the same mass.

ODP can be estimated from the structure of a given substance.Chlorofluorocarbonshave ODPs roughly equal to 1. Brominated substances have usually higher ODPs in range 5 - 15, because of more aggressive bromine reaction with ozone.Hydrochlorofluorocarbonshave ODPs mostly in range 0.005 - 0.2 due to the presence of the hydrogen which causes them to react readily in thetroposphere, therefore reducing their chance to reach thestratosphere. Hydrofluorocarbons (HFC) have no chlorine content, so their ODP is essentially zero.

ODP is often used in conjunction with a compound'sglobal warming potential(GWP) as a measure of how environmentally detrimental it can be. GWP represents the potential of a substance to contribute toglobal warming.

In a broad sense, haloalkanes that contain no hydrogen are stable in the troposphere and decompose only in the stratosphere. Those compounds that contain hydrogen also react with OH radicals and can therefore be decomposed in the troposphere, as well. The ozone depletion potential increases with the heavier halogens since the C-Xbond strength is lower.

Present status of CFCs in world

Montreal Protocol

TheMontreal Protocol on Substances that Deplete the Ozone Layer(a protocol to theVienna Convention for the Protection of the Ozone Layer) is an internationaltreatydesigned to protect theozone layerby phasing out the production of numerous substances that are responsible forozone depletion. The treaty was opened for signature on September 16th, 1987, and entered into force on January 1st, 1989, followed by a first meeting inHelsinki, May 1989. Since then, it has undergone seven revisions, in 1990 (London), 1991 (Nairobi), 1992 (Copenhagen), 1993 (Bangkok), 1995 (Vienna), 1997 (Montreal), and 1999 (Beijing). If the international agreement is adhered to, the ozone layer is expected to recover by 2050.Due to its widespread adoption and implementation it has been hailed as an example of exceptional international co-operation, withKofi Annanquoted as saying that "perhaps the single most successful international agreement to date has been the Montreal Protocol".The two ozone treaties have been ratified by 197 parties, which includes 196 states and the European Union,making them thefirst universally ratified treatiesin United Nations history

Since the Montreal Protocol came into effect, the atmospheric concentrations of the most important chlorofluorocarbons and related chlorinated hydrocarbons have either leveled off or decreased.Halon concentrations have continued to increase, as the halons presently stored in fire extinguishers are released, but their rate of increase has slowed and their abundances are expected to begin to decline by about 2020. Also, the concentration of the HCFCs increased drastically at least partly because for many uses (e.g. used as solvents or refrigerating agents) CFCs were substituted with HCFCs. While there have been reports of attempts by individuals to circumvent the ban, e.g. by smuggling CFCs from undeveloped to developed nations, the overall level of compliance has been high. Statistical analysis from 2010 show a clear positive signal from the Montreal Protocol to the stratospheric ozone.In consequence, the Montreal Protocol has often been called the most successful international environmental agreement to date. In a 2001 report, NASA found the ozone thinning over Antarctica had remained the same thickness for the previous three years]however in 2003 the ozone hole grew to its second largest size.The most recent (2006) scientific evaluation of the effects of the Montreal Protocol states, "The Montreal Protocol is working: There is clear evidence of a decrease in the atmospheric burden of ozone-depleting substances and some early signs of stratospheric ozone recovery.

The Kyoto Protocol

The Kyoto Protocol to theUnited Nations Framework Convention on Climate Change(UNFCCC) is an international treaty that sets binding obligations on industrialized countries to reduce emissions ofgreenhouse gases. The UNFCCC is an environmental treaty with the goal of preventing dangerous anthropogenic (i.e., human-induced) interference of the climate system.According to the UNFCC website, the Protocol "recognises that developed countries are principally responsible for the current high levels of GHG emissions in the atmosphere as a result of more than 150 years of industrial activity, and places a heavier burden on developed nations under the principle of 'common but differentiated responsibilities'."There are192 parties to the convention: 191 states (including all the UN members except Andorra, Canada, South Sudan and the United States) and theEuropean Union.The United States signed but did not ratify the Protocol and Canada withdrew from it in 2011.The Protocol was adopted by Parties to the UNFCCC in 1997, and entered into force in 2005.

The main goal of the Kyoto Protocol is to contain emissions of the main anthropogenic (i.e., human-emitted) greenhouse gases (GHGs) in ways that reflect underlying national differences in GHG emissions, wealth, and capacity to make the reductions.The treaty follows the main principles agreed in the original 1992 UN Framework Convention.According to the treaty, in 2012, Annex I Parties who have ratified the treaty must have fulfilled their obligations of greenhouse gas emissions limitations established for the Kyoto Protocol's first commitment period (20082012)

Some of the principal concepts of the Kyoto Protocol are:

Binding commitments for the Annex I Parties. The main feature of the Protocolis that it established legally binding commitments to reduce emissions of greenhouse gases for Annex I Parties. The commitments were based on the Berlin Mandate, which was a part of UNFCCC negotiations leading up to the Protocol.

Implementation. In order to meet the objectives of the Protocol, Annex I Parties are required to prepare policies and measures for the reduction of greenhouse gases in their respective countries. In addition, they are required to increase the absorption of these gases and utilize all mechanisms available, such as joint implementation, the clean development mechanism and emissions trading, in order to be rewarded with credits that would allow more greenhouse gas emissions at home.

Minimizing Impacts on Developing Countries by establishing an adaptation fund for climate change.

Accounting, Reporting and Review in order to ensure the integrity of the Protocol.

Compliance. Establishing a Compliance Committee to enforce compliance with the commitments under the Protocol.

Kyoto Protocol to the United Nations Framework Convention on Climate Change

Kyoto Protocol participation map(commitment period: 201320)

Parties; Annex I & II countries with binding targets

Parties; Developing countries without binding targets*

States not Party to the Protocol

Signatory country with no intention toratifythe treaty, with no binding targets

Countries that have renounced the Protocol, with no binding targets

Parties with no binding targets in the second period, which previously had targets

Difficulty in phasing-out of CFCs

Use of certain chloroalkanes as solvents for large scale application, such as dry cleaning, have been phased out, for example, by theIPPCdirective ongreenhouse gasesin 1994 and by thevolatile organic compounds(VOC) directive of theEUin 1997. Permitted chlorofluoroalkane uses are medicinal only.

Bromofluoroalkanes have been largely phased out and the possession of equipment for their use is prohibited in some countries like the Netherlands and Belgium, from 1 January 2004, based on theMontreal Protocoland guidelines of the European Union.

Production of new stocks ceased in most (probably all) countries as of 1994.However many countries still require aircraft to be fitted with halon fire suppression systems because no safe and completely satisfactory alternative has been discovered for this application. There are also a few other, highly specialized uses. These programs recycle halon through "halon banks" coordinated by the Halon Recycling Corporation to ensure that discharge to the atmosphere occurs only in a genuine emergency and to conserve remaining stocks.

The interim replacements for CFCs are hydrochlorofluorocarbons (HCFCs), which deplete stratospheric ozone, but to a much lesser extent than CFCs.Ultimately,hydrofluorocarbons (HFCs)will replace HCFCs. Unlike CFCs and HCFCs, HFCs have an ozone depletion potential (ODP) of 0. DuPont began producing hydrofluorocarbons as alternatives to Freon in the 1980s. These included Suva refrigerants and Dymel propellants.Natural refrigerants are climate friendly solutions that are enjoying increasing support from large companies and governments interested in reducing global warming emissions from refrigeration and air conditioning. Hydrofluorocarbons are included in theKyoto Protocolbecause of their very highGlobal Warming Potentialand are facing calls to be regulated under theMontreal Protocoldue to the recognition of halocarbon contributions to climate change.

On September 21, 2007, approximately 200 countries agreed to accelerate the elimination of hydrochlorofluorocarbons entirely by 2020 in aUnited Nations-sponsoredMontrealsummit. Developing nations were given until 2030. Many nations, such as theUnited StatesandChina, who had previouslyresisted such efforts, agreed with the accelerated phase out schedule.

Alternative refrigerants - Applications and characteristics

R422D (MO29)

Applications:

Versatile R22 replacement in equipment with direct evaporation

(air-conditioning systems, chilled water and refrigeration systems

for normal and low-temperature operation)

Characteristics:

- In most systems, performance and efficiency similar to that of R22

- Lower pressurised gas temperatures compared to R22 may

extend the service life of the compressor in some systems.

R417A (MO59)

Applications:

Air-conditioning systems < 15 kW

Caution, for water chillers, R422D is recommended

Characteristics:

- Lower pressurised gas temperatures and compression pressures

compared to R22 may extend the compressor's service life.

- Energy savings possible in some systems.