Greenhouse gas overview

Greenhouse gas overview

Greenhouse gases are atmospheric gas that is trapping the heat in the atmosphere and warming the planet. It creates greenhouse effect and climate change. The Kyoto protocol lists 6 categories of GHG emission: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphurhexafluoride (SF6).

        Carbon dioxide CO2

Carbon dioxide is the highest concentration among other GHGs. It is a major contributor to the climate change. In 1990, the concentration is almost 60 percent of the total greenhouse effect. In 2013, it is 82 percent of all GHG emissions from human activities. (USEPA 2015). CO₂ is produced by burning fossil fuels (coal, natural gas and oil) for energy and transportation.

Figure 2 Electricity: Pounds of CO2/kWh

           Electricity: Electricity is a main source to power homes, business and industry. Main source that generates the electricity is combustion of fossil fuels; and depends on the types of fossil fuels, it produces different amount of CO₂. For examples, burning coal produces more CO₂ than natural gas and oil. In 2013, CO₂ emission is about 37 percent of total US CO₂ emission and 31 percent of total GHG emissions in US.

        

The chart in Figure 2 above shows that coal fuel creates 6.39 Pounds of CO₂ when creates one kilowatts per hours while natural gas produce 1.21 and other fuel sources generate 3.47 pounds of CO2 kWh.

Transportation: Gasoline and diesel use in transportation are second largest source of CO₂ emission. It is accounting for 31 percent of total US CO₂ emission and 26 percent of total GHG emission in US.

 

Figure 3 Transportation: Pounds of CO2/gallon

As shown in Figure 3, when use one gallon of gasoline, 19.64 pounds of CO2 are emitted to air while diesel creates 22.38 pounds.

Industry: Combustion of fossil fuels for many industrial processes is about 15 percent of total US CO₂ emission and 12 percent of total GHG emission in US. There are other processes that also produce CO₂ emissions such as production of chemicals, production of metals or cement by chemical reactions.

        Methane CH₄

Nature and human are both sources to provide methane emissions. The main natural sources are from wetlands and ocean. The human sources are from landfills, farming, production, transportation and use of fossil fuels. It creates the majority of CH₄ emission, 64 percent of the total comparing to 36 percent of CH₄ emission from natural sources.

Waste and landfills: Methane is produced by the decomposition of organic waste in landfill sites. The decomposition rate is depended on the waste types. Kitchen garbage such as food, fruit, and vegetable decompose quickly. Newspaper, grass, leaves, and wood take more time to decompose. Plastics do not decompose for long period of time. Garbage and solid waste come to landfill and bury layer by layer. New garbage is pilled over the old garbage. The organic waste gets trapped in no oxygen condition (anaerobic condition) which is good condition for microbes to break down the waste to produce methane. Landfill gas is generated for 20-30 years after the landfill is closed. With the new regulations and policies, waste disposal is recycled, incineration before sending to landfill. Therefore, waste sends to landfill also declining. In addition, landfill gas can be collected and used for other energy purposes. Burning methane can generate electricity and reduce the emission release into the air. In the beginning, the recovery rate of the gas life cycle is minimal and higher in the middle and end stage of the landfill. Maximum efficiency for landfill gas is 55 percent - 60 percent of methane. (Cora, 2009)

Besides, wastewater is also produce methane emissions. During the process of wastewater treatment, the organic material in wastewater decays in anaerobic condition as in landfills and produce methane. (El-Fadel & Massoud, 2001)

Farming: CH₄ from agricultural emission is about one third to two third in the countries. Main source are from manure storage and cattle digestion process. The ratio of ruminants and manure is 8 to 1.5 worldwide. Methane emission in ruminant fermentation is from 3 to 8 percent of the cattle intake. Manure is stored and managed in holding storage produced CH₄ (USEPA, 2015). Another big source of methane emission that releases to atmosphere is rice field. It releases between fifty to one hundred million tones of methane a year. The warm and waterlogged soil of rice field is ideal condition for creating methane. Methane produced by oxidized by methanotrophs in the shallow water and majority released into the atmosphere. Emission from rice field can be various during a year (Van Groenigen, 2013)

        Nitrous Oxide (N₂O)

With the potential of 296 times of carbon dioxide (CO₂) that creates global warming, N₂O is considered as one of the powerful greenhouse gas. Major sources, which contribute to the N₂O creation, are fossil fuel combustion, biomass burning, livestock management, and through the practice of soil cultivation and its usage of profitable and organic fertilizers.

Agriculture: Emission has been decreased due to reduced fertilizers’ applications. In US, there was a decrease of 2.5 percent from 1990 to 2010 in N₂O which total to 304,082 thousand metric tons of CO₂ equivalent. Agriculture accounts for 58.6 percent of the total. In European countries, N-ferteilization rates between 50 kg/ha in Southern European countries to 195 kg in Netherlands. (Gielen & Kram, 1998) (http://wdi.worldbank.org/table/3.9)

                               

Figure 4 N-fertilization and Emissions by Europe Countries

Figure 4 includes two charts: N-fertilization and Emissions.  The charts show that Ireland took lead in N-fertilization by 199 kg per hectare, followed by Belgium, 123, and Germany, 104.  The country that emitted most CO₂  equivalent per hectare, followed by Belgium.  France emitted the least, 0.55.

Transportation: N₂O emisison is created by NOx in exhaust gases conversion in automobiles, trucks and heavy equipments, etc.

        Hydrofluorocarbons (HFCs)

HFCs are commonly used as refrigerants and propellants in aerosols. The HFCs are not considered as significantly contribute to the depletion of the stratospheric ozone layer, but they are powerful greenhouse gases with global warming potentials ranging from 140 (HFC-152a) to 11,700 (HFC-23) (Gielen & Kram, 1998)

        Perfluorocarbons (PFCs)

Although PFCs constitutes less than 0.25 percent of greenhouse gasses emissions, they play an important role global climate change.  With up to 9,500 times of CO₂, PFCs are exceptionally efficient at trapping heat. The aluminum smelters/production is largest factor of PFC emission. Even with economic incentives to reduce PFCs, the aluminum sector accounts for 60 to 70 percent of total emission in 2005.

        Sulfur hexafluoride (SF₆)

Sulfur hexafluoride, SF₆, is an insulating component that is used in electrical convertors.  It can and is often use as an inert blanket. It is an unnaturally produced gas. Waste management and leakages from old equipment cause emissions.  SF₆ leaves a trace of gas that helps determine air movement or ventilations rates in buildings. Waste management and leakages from old equipment cause emissions. Due to the unique nature of SF₆, the property is hard to neither replicate nor using another material to substitute. Emission’s potential of reduction is 20 percent to 40 percent with an estimated cost ranges from 0 to 25 ECU/t CO₂ equivalent.

          The use of SF₆ in magnesium and aluminum casting has been favored in the automotive industry. Comparing to other metals, SF₆ provides a weight advantage. The transportation section accounts for less than 5 percent of SF₆ emission. However, it is forecasted an increase of 2 to 4 times in usage in the next decade. Through enhanced methods for recovery, emission can be reduced.  In 1995, the semiconductor industry used some of SF₆ as solvent, which less than 5 Mt CO₂ equivalent.  There is a anticipatable of rapid growth in this sector as well. Some SF₆ can be use for different applications such as tires for cars, sporting shoes etc. Either declining in SF₆ usage or suggested alternative elements for SF₆ has been mentioned. (Gielen & Kram, 1998)