Carbon Cycle

1
Carbon Cycle

• Carbon is found as graphite and diamond in
  nature, it also occurs as carbon dioxide (0.03
  V/V) in the atmosphere.
• An atom of carbon can form covalent bonds with H,
  O, N, P and other carbon atoms. It can form four
  such bonds at any one time and because of this
  versatility, the carbon atom is the principal
  building block of many kinds of molecules which
  make up living organisms.
• Hence the carbon cycle is essential for the
  existence and survival of life.
• Carbon is a basic constituent of all organic
  compounds and is involved in the fixation of
  energy by photosynthesis.
• The source of all carbon in both living organisms
  and fossil deposits is CO2 in the atmosphere and
  the waters of Earth.

2

• Carbon may be present as gaseous atmospheric CO2,
  dissolve in surface water and ground water as
  HCO3-, present in minerals (CaCO3, MgCO3),
  petroleum and natural gas.
• The atmosphere is the source of CO2, which is
  utilized by plants in photosynthesis reduced to
  form carbon compounds/living component. Just as
  energy flows through the grazing food chain,
  carbon passes to herbivores and then to
  carnivores. Some of these carbon compounds are
  oxidized during respiration and in the process
  energy and CO2 are released. CO2 also released
  when some carbon compounds are decomposed by
  microorganisms.
• Photosynthesis
• H2O CO2 Solar Energy
  (CH2O)n O2
• Respiration
• (CH2O)n O2 CO2 H2O
  (aerobic respiration)
• 2(CH2O)n CO2 CH4
  (anaerobic respiration)

Chlorophyll of plants
3

• Organic or biological carbon CH2O is contained
  in energy-rich molecules that can react
  biochemically with molecule O2, to regenerate CO2
  and produce energy through aerobic respiration.

• Organic carbon fixed by microorganisms is
  transformed by biogeochemical processes to fossil
  petroleum, coal and etc. Microorganisms degrade
  organic carbon from biomass, petroleum, and
  xenobiotic sources, ultimately returning it to
  the atmosphere as CO2.

• The fossils (coal and petroleum) are the
  important energy source for modern man and
  produce CO2 when burnt. Thus, the C cycle is
  maintained by the processes of photosynthesis,
  respiration, decomposition and fossil fuel
  burning.

• Manufacturing processes are used to convert
  hydrocarbons to xenobiotic compounds with
  functional groups containing halogens, oxygen,
  nitrogen, phosphorus or sulfur. These compounds
  are particularly significant because of their
  toxicological chemical effects.

4

• Oceans regulate the CO2 content in the atmosphere
  and thus play a very important role. Sea water
  contains 50 times more CO2 than air, in the form
  of carbonates and bicarbonates.

• Photosynthesis algae are the predominant
  carbon-fixing agents in water as they consume
  CO2 to produce biomass, the pH of the water is
  raised, enabling precipitation of CaCO3 and
  CaCO3.MgCO3.

• In aquatic ecosystem, CO2 dissolve in water
  before being used by aquatic primary producers.
  The CO2 dissolves in sea water to form carbonic
  acid.
• H2O CO2 H2CO3
• Carbonic acid further dissociates in to a
  hydrogen ion and a bicarbonate ion
• H2CO3 H HCO3-

5

• Bicarbonate may further dissociate into another
  hydrogen ion and a carbonate ion

HCO3- H CO32-

• The carbon dioxide-carbonic acid-bicarbonate
  system is a complex
• chemical system that tends to stay in
  equilibrium. Therefore, if CO2
• is removed from water, the equilibrium is
  disturbed and the equation will shift to the
  left, with carbonic acid and bicarbonate
  producing more CO2 until a new equilibrium is
  produced.

Theoretical percentage of CO2 in each of its
three forms in water in relation to pH
6

• Phytoplankton uses the CO2 that diffuses into the
  upper layers of water or is present as carbonates
  and converts it into plant tissues. The carbon
  then passes through the aquatic food chain. CO2
  produced through respiration process is either
  reutilized or reintroduced to the atmosphere.
• Sea water is alkaline and rich in Ca and
  accelerates carbonate deposition in the bodies of
  mollusks and foraminifers and incorporated into
  their exoskeletons. Some of the carbonates
  dissolved back into solution, while some become
  buried in the bottom mud at very depths when the
  organisms die. In warm climates, greater salinity
  and alkalinity coupled with high temperatures
  favor the formation of coral reefs and thicker
  shells of mollusks.

7
CO2 in the atmosphere
Biodegradation
Photosynthesis
Solubilization and chemical processes
Soluble inorganic carbon, Predominantly HCO3-
Fixed organic carbon, CH2O and xenobiotic carbon
Chemical precipitation And incorporation of
Mineral carbon into Microbial shells
Dissolution with dissolved CO2
Xenobiotics manufacture with petroleum feedstock
Biogeochemical processes
Insoluble inorganic carbon, Predominantly CaCo3
and CaCO3.MgCO3
Fixed organic Hydrocarbon, CxH2x And kerosen
The Carbon Cycle. Mineral carbon is held in a
reservoir of limestone, CaCO3, from which leached
into a mineral solution as dissolved hydrogen
carbonate ion, HCO3-, In the atmosphere carbon is
present as CO2. Atmospheric CO2 is fixed as
organic matter by photosynthesis, and organic
carbon is released as CO2 by microbial decay of
organic matter.
8
The carbon cycle as it occurs in both terrestrial
and aquatic ecosystems
9
Carbon Cycle

• The carbon cycle is the biogeochemical cycle by
  which carbon is exchanged between the biosphere,
  geosphere, hydrosphere, and atmosphere of the
  Earth (other astronomical objects may have
  similar carbon cycles, but nothing is yet known
  about them).
• The cycle is usually thought of as four major
  reservoirs of carbon interconnected by pathways
  of exchange. The reservoirs are the atmosphere,
  the terrestrial biosphere (which usually includes
  freshwater systems and non-living organic
  material, such as soil carbon), the oceans (which
  includes dissolved inorganic carbon and living
  and non-living marine biota), and the sediments
  (which includes fossil fuels). The annual
  movements of carbon, the carbon exchanges between
  reservoirs, occur because of various chemical,
  physical, geological, and biological processes.
  The ocean contains the largest active pool of
  carbon near the surface of the Earth, but the
  deep ocean part of this pool does not rapidly
  exchange with the atmosphere.

10
Global Carbon Budget

• The global carbon budget is the balance of the
  exchanges (incomes and losses) of carbon between
  the carbon reservoirs or between one specific
  loop (e.g., atmosphere - biosphere) of the carbon
  cycle. An examination of the carbon budget of a
  pool or reservoir can provide information about
  whether the pool or reservoir is functioning as a
  source or sink for carbon dioxide.

11
Carbon cycle modeling

• Models of the carbon cycle can be incorporated
  into global climate models, so that the
  interactive response of the oceans and biosphere
  on future CO2 levels can be modelled. There are
  considerable uncertainties in this, both in the
  physical and biogeochemical submodels (especially
  the latter). Such models typically show that
  there is a positive feedback between temperature
  and CO2. For example, Zeng et al. (GRL, 2004 2)
  find that in their model, including a coupled
  carbon cycle increases atmospheric CO2 by about
  90 ppmv at 2100 (over that predicted in models
  with non-interactive carbon cycles), leading to
  an extra 0.6C of warming (which, in turn, may
  lead to even greater atmospheric CO2).

12
Carbon footprint

• Carbon footprint is a measure of the amount of
  carbon dioxide or CO2 emitted through the
  combustion of fossil fuels in the case of an
  organization, business or enterprise, as part of
  their everyday operations in the case of an
  individual or household, as part of their daily
  lives or a product or commodity in reaching
  market. In materials, is essentially a measure of
  embodied energy, the result of life cycle
  analysis.

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A carbon footprint is often expressed as tons of
carbon dioxide or tons of carbon emitted, usually
on a yearly basis. There are many versions of
calculators available for carbon footprinting.

• This is directly related to the amount of natural
  resources consumed, increasingly used or referred
  to as a measure of environmental impact. Carbon
  dioxide is recognized as a greenhouse gas, of
  which increasing levels in the atmosphere are
  linked to global warming and climate change.
• The Clean Development Mechanism (CDM) under the
  Kyoto Protocol sets forth a methodology by which
  voluntary emission reduction can be monetized in
  the form of a carbon project. These standards
  involve the use of an environmental proof called
  additionality.
• A carbon label - which shows the carbon footprint
  embodied in a product in bringing it to the shelf
  was introduced in the UK in March 2007 by the
  Carbon Trust. Examples of products featuring
  their carbon footprint are Walkers Crisps,
  Innocent Smoothies and Boots shampoos.
• CarbonCounted, which launched in early 2007, is a
  Canadian based GHG carbon label system that
  allows companies to link with and leverage their
  supply chain. By displaying the CarbonCounted
  footprint on a product, a supplier is publishing
  their footprint and committing to emissions
  reduction.

14
Kyoto Protocol

• The Kyoto Protocol to the United Nations
  Framework Convention on Climate Change is an
  amendment to the international treaty on climate
  change, assigning mandatory emission limitations
  for the reduction of greenhouse gas emissions to
  the signatory nations.
• The objective of the protocol is the
  "stabilization of greenhouse gas concentrations
  in the atmosphere at a level that would prevent
  dangerous anthropogenic interference with the
  climate system."1
• As of December 2006, a total of 169 countries and
  other governmental entities have ratified the
  agreement (representing over 61.6 of emissions
  from Annex I countries).23 Notable exceptions
  include the United States and Australia. Other
  countries, like India and China, which have
  ratified the protocol, are not required to reduce
  carbon emissions under the present agreement.
• There is some debate about the usefulness of the
  protocol, and there have been some cost-benefit
  studies performed.

15
Capture of CO2 from Industrial
SourcesAbsorption/Stripping Technology

• The main industrial sources of CO2 NG reformer
  gases, refinery gases,
• power plant/incinerator flue gases
• The majority of CO2 emissions come from thermal
  power plants fired
• with fossil fuels.
• In 2003, 32.4 of total CO2 produced in the US
  came from coal-fired
• power plants.
• The predicted increase in CO2 emissions is 1.8
  per year and by 2030
• it will be 70 above 2000 levels IEA World
  Energy Outlook (2002).
• There is an urgent need for research into the
  development of cost effective
• and viable technologies for CO2 capture and
  sequestration.
• This presentation focuses on current
  technology options, technology
• development and future opportunities.