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4 Environmental Analysis
<br /> 4.8 Greenhouse Gas Emissions
<br /> evaporation from oceans; and volcanic outgassing. Human activities known to emit GHGs include
<br /> fuel combustion, industrial manufacturing, utilities, transportation, residential, and agricultural
<br /> activities. The primary GHGs that enter the atmosphere because of human activities are CO2,
<br /> methane (CH4), nitrous oxide (N2O), and fluorinated carbons (hydrofluorocarbons [HFC],
<br /> perfluorocarbons [PFCs], and sulfur hexafluoride [SF6]).
<br /> CO2 is an odorless, colorless gas with both natural and anthropogenic sources. CO2 is the most
<br /> important and common anthropogenic GHG. Examples of natural sources are respiration of
<br /> bacteria, plants, and animals, evaporation from oceans, and decomposition of organic matter.
<br /> Human activities that emit CO2 include burning coal, oil, natural gas, and wood. Prior to the
<br /> Industrial Revolution, CO2 levels remained at approximately 280 parts per million for close to
<br /> 6,000 years of human civilization. Since then, humans have generated an estimated 1.5 trillion
<br /> tons of CO2 pollution, much of which will continue to warm the atmosphere for thousands of years
<br /> (NOAH 2022).
<br /> CH4 is a flammable gas that is the main component of natural gas. When burned in the presence
<br /> of oxygen, CO2 and water are released. There are no direct health effects from exposure to CH4.
<br /> Sources of CH4 include decay or organic material, natural gas fields, cattle, and landfills.
<br /> N2O is a colorless gas that can cause euphoria, dizziness, and slight hallucinations when exposed
<br /> to higher concentrations. Sources include agricultural sources (e.g., microbial processes in soil
<br /> and water, fertilizer) and industrial processes (e.g., fossil fuel-fired power plants, vehicle
<br /> emissions, nylon production).
<br /> Fluorinated Gases are synthetic and emitted from a variety of industrial processes:
<br /> oo HFCs are human-made chemicals used as a substitute for chlorofluorocarbons (CFC)for
<br /> automobile air conditioners and refrigerants. Because hydrofluorocarbons destroy
<br /> stratospheric ozone, their production was stopped as required by the 1989 Montreal
<br /> Protocol.
<br /> 0o PFCs are very stable and do not break down through the chemical processes in the lower
<br /> atmosphere and have long lifetimes (between 10,000 and 50,000 years). The two main
<br /> sources of PFCs are primarily aluminum production and semiconductor manufacturing.
<br /> oo SF6 is an inorganic, colorless, odorless, nontoxic, nonflammable gas used for insulation
<br /> in electric power transmission and distribution equipment, semiconductor manufacturing,
<br /> the magnesium industry, and as a tracer gas for leak detection.
<br /> 4.8.1.3 Global Warming Potential
<br /> The Intergovernmental Panel on Climate Change (IPCC) developed the global warming potential
<br /> (GWP)concept to compare the ability of each GHG to trap heat in the atmosphere relative to CO2,
<br /> which is used as a reference gas. The GWP of a GHG is defined as the ratio of the time-integrated
<br /> radiative forcing from the instantaneous release of 1 kilogram of a trace substance relative to that
<br /> of 1 kilogram of CO2. Therefore, GWP-weighted emissions are measured in metric tons (MT) of
<br /> carbon dioxide equivalent (CO2e). The GWP for CH4 is approximately 25 times more powerful
<br /> than CO2, and N2O is approximately 298 times more powerful than CO2 in its ability to trap heat
<br /> in the atmosphere (CO2 has a GWP of 1). SF6 has a GWP of 22,800. CO2e is a quantity that
<br /> Griffith Energy Storage Project 4.8-2 Tetra Tech/SCH 2022120675
<br /> Draft Environmental Impact Report August 2023
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