Introduction

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20 years ago, when I was fifteen, I used to follow science&tech magazines regularly. Actually, a teenager like me would go outside, drink something with his girlfriend or at least play the video games to death. However being interested in science sounded much more impressive to me. In those days, the topic of global warming was one of the ordinary news in the media.

But the hurricane "El Nino" caused a huge destruction and everybody slowly begun to comprehend what global warming could cost humanity. I every time told my parents, relatives, and friends that this natural event will bring much bigger trouble to us in the future. Of course, my warnings fell on stony ground because I was a teenager.

But that was the past! And we're in the future now. Unfortunately, you can not run away your future. As we developed our civilization we also started to dig our own grave. Today, global warming is one of the worrisome factors along with the nuclear war and uncontrolled population growth for us. All the people on earth, particularly the governments must acutely try to find a way to save our future. In this regard, I would like to give a comprehensive review of Greenhouse Gases and global warming with this post.

Which Gases Are The Greenhouse Gases?

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Greenhouse gases are the compounds which absorb and emit radiation in the thermal infrared zone of the spectrum. This process causes an effect called "Greenhouse Effect". The main greenhouse gases in earth's atmosphere are water vapor, carbon dioxide, methane, nitrogen, and ozone. In the solar system, Venus, Mars, Saturn and its biggest satellite Titan has also greenhouse gases. Those gases are affecting earth's temperature in a very dramatic way.

Consuming the fossil fuels since the beginning of industrial revolution contributed to the emission too much by means of raising CO₂ existence from the levels of 280 ppm to 390 ppm.

CO₂ emissions which are originated from human activities are produced by using the carbon included fuels such as wood, oil and natural gas. Let's go on analyzing the Greenhouse Gases by focusing on the gases which are bringing this effect with them.

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First Let's Get Started with the Fundamental Concepts

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The atmospheric density of the Greenhouse Gases is determined by the balance between the sources (gas emissions resulted from human activities and natural mechanisms) and outlets (draining the gases out of the atmosphere by turning them to another chemical compound).

Any emission rate in the atmosphere after a duration is called "Airborne Fraction" ('AF' in short forms). Annual AF is the ratio of the increase of emission in one year to total emission. For CO₂, AF increased as 0.25± %0.21/year in between 1956 to 2006. Now let's take a detailed look at what are Greenhouse Gases that have an impact on the atmosphere and what kind of structures do they have.

1. Water Vapour (H₂O)

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Basic physical and chemical properties of water vapor are shown in Table 1.

Systematic Name	Water Vapor
Liquid Phase	Water
Solid Form	Ice
Molecular Formula	H2O
Molar Mass	18.01528(33) g/mol
Melting Point	0 °C (273 K)
Boiling Point	99.98 °C (373.13 K)
Specific Gas Constant	461.5 J/(kg•K)
Heat Of Vaporization	2.27 MJ/kg

^{Table 1. Water Vapour And It's Physical Properties}

The water in the gas phase is in small quantities but it's a significant component in the atmosphere. Troposphere (The lowermost layer of earth's atmosphere) has about 99.13% part of it. The phase transitions of water vapor to liquid or ice are done by rain and snow. One of the most important energy variety for both local and global aspect is the latent heat of evaporation in consequence of condensing. For instance, the energy release caused by the atmospheric convection is directly responsible for amplifying the destructive storms like tropical cyclones and lethal hurricanes. Water vapor is a very effective Greenhouse gas because it has hydroxyl bonds which strongly absorbs the radiation in the infrared range of electromagnetic spectrum.

Fogs and clouds condense around condensation nuclei. In the absence of nuclei, condensation only occurs at a lower temperature. Under permanent condensation or accumulation, the clouds form drops or snowflakes. When those particles get at a critical mass, they start to fall down as a precipitation.

Meanwhile, let's take a glance at how the water cycle actually occurs from the point of H₂O. The water content of the atmosphere is being constantly drained by precipitation. Also, evaporation extracts the water back from seas, lakes, rivers and humid soil and so replacement becomes done. The other sources of the atmospheric waters are consisting of combustion, respiration, volcanic eruptions, evapotranspiration of the plants and some other biological and geological progress.

The content of average global water vapor in the atmosphere is roughly sufficient to cover our planet's surface with a liquid water layer which is about 25 millimeters of depth. Average annual precipitation of our planet is about 1 meter which means a sudden decrease of air-water. A water molecule stays between 9 to 10 days at troposphere on an average.

^{Fig1. Increasing Water Vapor Over Time!!}

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2. Carbondioxide (CO₂)

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You may see the physical and chemical properties of CO₂ in the table.

Scent	Odourless
Apperance	Colorless Gas
Solid Form	Ice
Molecular Formula	CO2
Molar Mass	44.01 g/mol
Density	1562 kg/m3 (Solid at 1 atm and -78.5 °C) 770 kg/m3(Liquid at 56 atm and 20 °C) 1977 kg/m3 (Gas at 1 atm and 0 °C)
Melting Point	-78 °C (194.7 K), -109 °F (sublimation)
Boiling Point	-57 °C 216.6 K, -70 °F (at 5.185 Bar)
Water Solubility	1.45 g/L at 25 °C and 100 kPa
Acidity (pKa)	6.35, 10.33
Refractive Index (nD)	1.1120
Viscosity	0.07 cP at -78.5 °C
Dipole Moment	zero
Molecular Shape	Linear
Standard Heat of Formation ΔfHo298	-393.5 kJ•mol-1
Standard Molar Entropy	214 J•mol-1K-1

^{Table 2. Carbondioxide Vapour And It's Physical Properties}

^{Figure 2. Structural Formula of CO₂ (left) Ball and stick model (middle) Spatial filling Model of CO₂ (right)}

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The carbon dioxide in the atmosphere is a trace gas which is approximately 390 ppm by volume and 591 ppm by mass. The total mass of atmospheric carbon dioxide is 3.16×10¹⁵kg (appx. 3000 Gigatons). Consentration of the gas varies season after season and it is considerably on a regional basis especially near to low-altitude regions.The concentrations are generally higher around urban areas and indoors. The Carbon dioxiade is a Greenhouse gas.

Below you can see the atmospheric CO₂ concentration increasing trend over time. The measurements are taken at Mauna Loa Observatory.

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^{Figure 3. Atmospheric Carbon dioxide levels are increasing just like the water vapor}

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If we could see how much CO₂ we are pumping in the air, then it would look like below!! What a pity! We are literally polluting our living area. This is untenable...

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CO₂ Drives The Car Little Bit Fast

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Five million years ago, CO₂ was much more drastic than today. It decreased 4-5 times in the Jurassic Period and went on being declined slowly. However today, human activities such as fossil fuel consumption and deforestation increased the atmospheric concentration of CO₂ 35% more since the beginning of the industrial age.

40% of the gas emissions of volcanos comprises CO₂. It is calculated that volcanos release CO₂ to the atmosphere about 130-230 million tons each year. The amount of CO₂ emission which is produced by human 27 billion tons per year. This is 130 times more than the volcanos do!!!

3. Methane (CH₄)

Please see the properties of Methane in Table 3 below.

Scent	Odourless
Apperance	Colorless Gas
Density	655.6 μg mL-1
Molecular Formula	CH4
Molar Mass	16.04 g/mol
Melting Point	-182 °C, 90.7 K, -296 °F
Boiling Point	-164 - -160 °C, 109 - 113 K, -263 - -256 °F
Water Solubility	22.7 mg/L
log P	1.09
kH	14 nm Pa-1 kg-1
Dipole Moment	0 D
Molecular Shape	Tetrahedral
Standard Heat of Formation ΔfHo298	-74.87 kJ•mol-1
Standard Molar Entropy	186.25 J•mol-1K-1
Standard Heat Capacity, C	35.69 JK-1mol-1

^{Table 3. Physical And Chemical Properties of CH₄}

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^{Figure 4. Structural Formula of CH₄ (left) Ball and stick model (middle) Spatial filling Model of CH₄ (right)}

It is the Gas that Cows Gas !!!

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Sometimes, some people really love to smell their own gas! I really don't know whether the cows feel the same way but that gas which smells is not CH₄. The bad odor is caused by Sulfur. Yes, I know Sulfur could be toxic but CH₄ is worse.

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^{Do you want this? Huh?... Man, I have the power!!}

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Methane is produced very near to earth's surface. I mainly produced by the microorganisms with a process called methanogenesis. It moves to Stratosphere by the weather which soars in the tropical area. The uncontrolled increase of Methane in the atmosphere is naturally suppressed by a reaction which happens between the hydroxyl radicals created by the singlet Oxygen atoms of CH₄ and water vapor. Luckily this auto-controlling goes on although the humans have an impact on it as well!

CH₄'s net lifetime is ten years. And its expurging is mainly made by the transition into carbon dioxide and water. Methane also makes an effect on the corruption of Ozone layer.
In addition to that, there is a big amount of Methane in the clathrate compounds in the crust of the earth as well as the ocean floor. Dominant creation mechanism is methanogenesis. This is a biological process as I mentioned above.

Ice Age Ends and Methane Rises

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In the Arctic, Methane levels are measured as 1850 nmol/mol. This value is two times more than that of the history for 400,000 years. Considering that from the historical perspective, Methane concentrations are varied from 300 to 400 nmol/mol. However, Its concentration varied from 600 to 700 nmol/mol in between successive ice ages. It means it has a high potential global warming capacity. So that, It appeared as 72 times of CO₂ for the last 20 years and 100 times for the 25 years. This gas in the atmosphere has a big role in global warming. Methane will have an emission effect 25 times more than the effect that same amounted CO₂ will have an effect on the temperature in the upcoming 100 years. Carbon dioxide affects for 100 years which is considered as a relatively large period of time. But Methane's effect is bigger for a relatively shorter period of time (net lifetime is 8.4 years in the atmosphere).

The atmospheric methane concentration of the earth has increased by about 150% since 1750. Methane has 20% of the total radiative forcing of all the long-lasting greenhouse gases.

Actually, excessive Methane collected from dump sites and produced by the natural producers is burnt out. Thus CO₂ is released to the atmosphere instead of CH₄. Because comparing to CO₂, Methane is a more effective greenhouse gas.

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^{Figure 5. Methane Concentration In The Upper Troposphere}

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4. Nitrous Oxide (N₂O)

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Please also see the physical and chemical properties of N₂O below in the table.

Common Name	Laughing Gas
Apperance	Colorless Gas
Molecular Formula	N2O
Molar Mass	44.013 g/mol
Density	1.977 g/L
Melting Point	−90.86 °C (−131.55 °F; 182.29 K)
Boiling Point	−88.48 °C (−127.26 °F; 184.67 K)
Water Solubility	1.5 g/L (15 °C)
Refractive Index (nD)	1.000516 (0 °C, 101,325 kPa)
Dipole Moment	0.166 D
Molecular Shape	linear, C∞v
Standard Molar Entropy	219.96 J•mol-1K-1
Standard Entalpy of Formation	+82.05 kJ•mol-1

^{Table 4. N₂O Structral And Chemical Properties}

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^{Figure 6. Nitrous oxide's canonical forms (top), Ball-and-stick model with bond lengths (middle), Space-filling model of nitrous oxide (down)}

N2O as a Greenhouse gas has the large global warming potential. Compared to carbon dioxide, N2O is 310 times greater in its ability to retain heat in the atmosphere per gas molecule. N2O is produced naturally in solids during microbial processes of nitrification and denitrification.

In 2008, the agricultural activities have contributed 6.1% to the total greenhouse gas emission of the United States and the farms directly contributed as 69%!

Another aspect of N₂O is that it is originated from the vehicles as well. Especially there is a big vehicle density in big cities. The air of the cities is polluted so much because of this vehicle emission. The most dominant polluter is the nitrogen dioxide. It is also called "invisible killer of the cities".

Nitrogen dioxide also causes depletion of the ozone in the air. A relatively new study showed that N₂O emission is the most important factor that is depleting ozone and will be the biggest one during 21. century.

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5. Ozone (O₃)

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I showed basic physical and chemical properties of Ozone in Table 5. Please see below.

Molecular Formula	O3
Molar Mass	48 g.mol-1
Absolute Mass	47.984743866 g.mol-1
Apperance	pale blue gas
Density	2.144 mg.cm-3 (at 0 °C)
Melting Point	−192 °C (−131.55 °F; 182.29 K)
Boiling Point	−112 °C (−170 °F; 161 K)
Water Solubility	1.05 g/L (at 0 °C)
Refractive Index (nD)	1.2226 (liquid)
Space Group	C2v
Coordination Geometry	Diagonal
Molecular Structure	Dihedral
Hybridization	sp2 for O1
Dipole Moment	0.52 D
Standard Molar Entropy	238.92 J•mol-1K-1
Standard Entalpy of Formation	+142.67 kJ•mol-1

^{Table 5. Ozone's Physical, Structral And Chemical Properties}

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^{Figure 7. Skeleton Formula Of O₃ (top-left), Ball And Stick Model (top-middle), Spatial Filling Model Of Ozone (top-right), Electrostatic Potantial Map of Ozone (bottom)}

Is it Useful Or Harmful?

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In fact, Ozone material itself is considered useful for most of the health and practical applications because of its disinfectant properties. In nature, Ozone is created by lightning and spread very specific and beautiful scent around.
However, as we all know excess gas amount turns this scenario.

Before the Industrial revolution, ozone was at the lowest level. Bu today the concentrations are at the highest level. This increase in Ozone level causes worries. Because Ozone absorbs infrared energy at upper troposphere and acts as a greenhouse gas. It is difficult to determine the greenhouse effect of O₃ quantitively. Because it is hard to find it in uniform concentrations in the air.

The radiative force of tropospheric O₃ is approximately 25%. Since tropospheric ozone has a short-lifetime, this has not powerful global effects. But, it has very powerful radiative forcing in the local scales. On some areas, it is known that tropospheric ozone has radiative forcing up to 150% of carbon dioxide.

• By The Way Radiative Forcing;

In Climatology, the radiative forcing is defined as the net radiation per unit area between the various layers of the atmosphere.

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Incident light from the sun hits on earth. The earth absorps a big portion of this energy and and gets warmer. Heated earth starts to illuminate in the infrared region but the greenhouse gases in the atmosphere holds this energy inside and reflects back to the earth again. This event gives rise to warm of the earth much more. This is exactly the same as a thermos bottle!!!

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6. Other Greenhouse Gases

Fluorinated Compounds:

Some of the most predominant greenhouse gases are produced by the humans. The fluorinated compounds such as CFC (chlorofluorocarbons), HCFC (hydrochlorofluorocarbons), and HFC (hydrofluorocarbons) are used for some production process. Each molecule of these synthetic compounds has the heat retention 1000 times more than that of the carbon dioxide molecule.

CFC compound was synthesized in 1928 for the first time. And it used for a dissolver and a cooler in the production of aerosol sprays. The CFCs are harmless at the lower atmosphere and can be securely used for most applications due to its low toxicity. However, at the upper atmosphere, ultraviolet radiation breaks the CFCs and releases chlorine into the atmosphere.

In the midst of 1970s, the scientists have begun to observe that the higher chlorine levels were demolishing the Ozone level at the upper atmosphere. As we know, the ozone layer protects the World against harmful UV radiation.

As from 1992, an amendment has been made on the Montreal Protocol. Thereby, using and production of the CFCs are forbidden all across the world. Only some specific applications and a few developing countries are allowed for it. The scientists developed HCFCs and HFCs for the substitution of CFCs. But HFCFs are still causing the release of the chlorine which wipes off the ozone layer. And it is decided to stop the production of those chemicals in 2030 as well. On the other hand, HFCs are still the most effective and safest chemicals which can be used instead of the CFCs.

Other Synthetic Chemicals:

Some industrial chemicals which have heat holding capacity are also classified as the derivatives of the greenhouse gases. In 2000, the scientist observed an increasing amount of a compound named trifluoromethyl sulfur pentafluoride which has never been reported before. This gas also becomes a thread on the environment as an effective greenhouse gas even it accumulates a little. Because this gas localizes more heat than all of the other known greenhouse gases. No doubt about that the certain origin of this gas is produced by the industrial processes.

^{Figure 8. Ozone Consuming Gas Trend}

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Image Source

Greenhouse Effect happens as a result of the interaction between the greenhouse gas layer and the sunlight which occurs above 100 kilometers of the earth's surface. Sunlight is consisting of a series of radiating energies which are known as the solar spectrum. Visible light, infrared light, gamma rays, X-rays and the ultraviolet rays are in those radiating energies. When the sun's radiation reaches the earth's atmosphere, the 25% of the incident energy becomes reflected back to space by the clouds and other atmospheric particles.

The gas molecules of the greenhouse gases absorb the gamma rays and the X-rays of the sun at the upper layers of the atmosphere. And the ultraviolet radiation of the sun is absorbed by the ozone layer above 19-43 kilometers from the earth's surface. 50% of the Solar energy largely passes through the atmosphere as the visible light and reaches to the earth's surface.

Soil, plants, and oceans absorb about 85% of this incident energy. The rest is reflected back to the atmosphere by the reflective surfaces like snow, ice, desert sand. Additionally, some part of the sun's radiation which is absorbed by the surface turns into the heat energy in the form of long-wave infrared radiation and this energy is released back to the atmosphere again.

The greenhouse gases absorb this infrared heat and temporarily prevents going into the deep space. When this atmospheric gas warms up, this time, they start to spread their own infrared rays omnidirectionally. Whilst a part of this heat returns back to the earth for warming a little more (this is the "greenhouse effect"), another part of this heat is released into space forever.

This heat transfer makes a stabilization between the total heat amount which reaches to the earth from the sun and the heat which the earth releases to space. This balance of the energy is very important for forming a climate that provides a diversity of the life.

The greenhouse gases which keeps the heat inside the atmosphere acts like a window of a greenhouse. These let most of the sun's ray in but going on retaining them inside. If there were not any of the greenhouse gases, the average surface temperature would be -19 Celcius instead of 15.

In order to comprehend the importance of this mechanism which lets most of the life forms become on the earth, we should compare the earth to Mars and Venus. Mars has a thin atmosphere including a trace amount of heat-holding gases. As a result of this, Mars doesn't any sign of life and it is largely a frozen planet. On the contrary, Venus has a high-level accumulation of the carbon dioxide in its atmosphere. This heat-holding gas prevents the heat which reflects back from the surface to escape to space. Due to this, the average of Venus' surface heat is 462-celsius centigrades, meaning it is very hot for a life form to be on it.

Conclusion

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I tried to share with you the details of the greenhouse gases which are directly responsible for the Global Warming. This issue is in the issues which humanity must be worried for. As much as anyone learns more knowledge on the greenhouse effect, greenhouse gases, and global warming. He or she will understand the importance of this topic on his/her daily life most importantly the effect on his/her child's life in the future.

I believe humans don't have the luxury for global warming and its bad effects on our and other living beings on this world. If we initiate this then we must be the one who will stop this. I thank you for reading my post and kindly looking forward to hearing from you in the comments about this issue.

If you are a science enthusiast, don't forget to follow me. And also follow #steemstem for more high-quality science-related posts on Steemit.

Note: All the Images are directly linked to the sources!

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References and Further Reading

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[1]. Greenhouse Gases
[2]. Benefits of Renewable Energy Use
[3]. What is the greenhouse effect?
[4]. Greenhouse Effect
[5]. Radiative forcing by long-lived greenhouse gases: Calculations with the AER radiative transfer models
[6]. Greenhouse Gases in Intensive Agriculture: Contributions of Individual Gases to the Radiative Forcing of the Atmosphere
[7]. What Is the Greenhouse Effect?
[8]. Air Pollution Causes, Effects, and Solutions
[9]. What Effects do Chlorofluorocarbons Have on Humans?
[10]. Greenhouse gas: why nitrous oxide is no laughing matter for the environment
[11]. What are the main man-made greenhouse gases?

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