This Website created and kept up by Nasif Nahle et al.
Copyright© 2007 by Biology Cabinet Organization.
By Adip Said

Carbon Dioxide is an organic compound formed by one atom of Carbon and two atoms of Oxygen (O=C=O).

Carbon Dioxide (CO2) is a natural constituent of the atmosphere with a density of 747 mg per cubic meter of air. Its concentration in the composition of air is roughly 0.032%; however, of all the organic compounds, carbon dioxide is by far the most important one for the sustainability of the biosphere (the whole of life on Earth).

Without CO2 the life of photosynthetic organisms and animals would be impossible, given that CO2 provides the basis for the synthesis of organic compounds that provide nutrients for plants and animals.

Through photosynthesis, organisms with chlorophyll take in atmospheric CO2 or dissolve CO2 in water to form more complex molecules, such as carbohydrates, lipids, proteins and nucleic acids. The general formula of photosynthesis is as follows:

6CO2 + 6H2O + Light = C6H12O6 (Glucose) + 6O2
Created: 13 January 2007.
Update: 08/24/02 (Correction of mystiped "CO2" on the paragraph "CO2 densities have increased to more than 4000 ppmv", and more references added on the same paragraph)

By Nasif Nahle

Pollutants are dangerous compounds for living beings.

Like water, CO2 is vital for life on Earth; thus, CO2 is not a pollutant or contaminant.

The specific heat of CO2 is 850 J/Kg K, which means carbon dioxide is able to absorb, store and emit heat. However, we cannot take this property into account when considering if CO2 is a pollutant because Water has a specific heat of 1,996 J/kg K, which means it is more efficient than CO2 at absorbing, emitting and storing heat. Water, like CO2, is vital for living beings.

CO2 densities have increased to more than 4000 ppmv in some geological eras, for example, during the Ordovician Period (Scotesse; 2002. Avildsen et al; 1998). When CO2 in the terrestrial atmosphere has reached densities this high in the past, life flourished abundantly. Consequently, we cannot consider such a high concentration of atmospheric CO2 as "pollution".

CO2 is the basic nutrient for plants and other photosynthetic organisms. Plants form the base of every food chain. Thus, the greater the density of CO2 in a given environment, the greater will be the production of food for plants and of the animals that feed on them.

In recent times it has become fashionable to relate CO2 to global warming, but water in its liquid or gaseous phase absorbs, stores and emits heat 4 times (400%) more efficiently than CO2. If, therefore, by this property water is not considered a pollutant, CO2 then cannot be considered a pollutant either.

Carbon Dioxide cannot intoxicate because it is a non-poisonous non-toxic substance. The data for CO2 related to human health are next:

  • The density of CO2 in the atmosphere is 0.000747 Kg per cubic meter of air.

Normal CO2 Levels. The effects of an increased level of CO2 on an adult person in good health can be summarized as:

  • Normal outside levels: 350 - 600 ppmv.

  • Acceptable levels: up to 600 ppmv.

  • Stiffness and odors: 600 - 1000 ppmv.

Data provided by the Occupational Safety and Health Administration (OSHA):

  • Standards: 1000 ppmv.

  • Stupor: 1000 - 2500 ppm.

  • Maximum allowed concentration in an 8 hour working period: 5,000 ppmv.

Extreme and Dangerous CO2 Levels:

  • Nausea and increase of the cardiac and respiratory frequencies (from oxygen deficiency): 30,000 ppmv.

  • The above plus headaches and sight impairment: 50,000 ppmv.

  • Unconsciousness and death: 100,000 ppmv (OSHA).

As you can see, Carbon Dioxide does not intoxicate — it suffocates. All of the effects listed above correspond to asphyxia, not to poisoning; however, water and sand also asphyxiate and they are not considered pollutants either. Consequently, CO2 cannot be considered a pollutant merely because it asphyxiates.

Many have tried to tag CO2 as a pollutant simply because it is a product of fossil fuel combustion. However, CO2 is also a product of respiration, fermentation and putrefaction. In any case, the CO2 released by combustion of fossil fuels had previously been taken from the atmosphere by photosynthetic organisms and converted into organic compounds to be used in their metabolic functions as structures for reproduction, etc. When those photosynthetic organisms later died, their remains were subjected to strong geological processes that convert organic matter into oil, coal and methane. (Reccommended reading: The Holocene CO2 Rise: Anthropogenic or Natural?)

Those products are the fossil fuels that we use today to power our industries and vehicles; therefore, we are only returning CO2 to the place it once occupied during the Carboniferous Period. CO2 cannot then be considered a pollutant just because it is released back into the atmosphere by combustion of organic fuels and from many other natural processes unrelated with life.



Lodish, H., Berk, Arnold, et al. Molecular Cell Biology. 1999. W. H. Freeman and Company; New York, New York.

Boyer, Rodney. Concepts in Biochemistry. 1999. Brooks/Cole Publishing Company: Thomson Corporation; Stamford, CT.

Krupp, Marcus A. and Chatton, Milton J. Current Medical Diagnosis and Treatment. 1984; Lange Medical Publications. New York, NY.

Callen, Jean-Claude. Biologie Cellulaire. Des Molécules aux Organisms. Cours et questions de révision. 1999. Dunod. Paris, France.

EOS. Vol. 87, No. 3, 17 January 2006. Last revision on 01/1/2007:

Scotesse. Paleoclimatology. http://www.scotese.com/climate.htm

Avildsen et al. Life of the Ordovician. http://www.ucmp.berkeley.edu/ordovician/ordolife.html


A grosso modo, photosynthesis consists of two reactions, light reaction and light-independent reaction.

During light reaction, molecules of chlorophyll and other pigments absorb energy from photons. As photons strike on those molecules, the energy of those photons is absorbed by photosynthetic pigments and transformed into potential energy of electrons which is raised from a fundamental state (also called ground state) to an excited state. The excited state is metastable, i.e. the molecule is hot, so that, the excited electrons return to their fundamental state in about 1 nanosecond, emitting the excess of absorbed energy as heat, or thermal radiation, if you prefer.

In this process, light is converted into dynamic energy and stationary energy as it is transferred to molecules of Adenosine Triphosphate (ATP), after which the light-independent process continues until the production of food (carbohydrates); consequently, visible light is thermal radiation because it can be exerted as work and transformed into heat. Any expenditure of work produces heat, i.e. dynamic energy that cannot be transformed into static energy. From this fact, the first law of thermodynamics was established.

Thermal radiation covers the range of wavelengths from 0.1 to 100 <i>μm</i> of the electromagnetic spectrum. Visible light covers from 0.39 to 0.75 <i>μm</i>; consequently, visible light is identified as thermal radiation; in this case –i.e. photosynthesis, a portion of visible light is exerted as work (process function) that makes the electrons to raise from fundamental microstates to higher microstates, and an equal portion is transformed into heat (process function). Actually, when visible light is in transit, before it is absorbed, reflected, and/or transmitted, it does not relies on any state function; it would go over and over, and over, until it stumbles upon obstructive particles.

Carbon Dioxide is fixed in the chloroplast stroma. Thus fixed, carbon dioxide is then used by cytoplasm to synthesize sucrose. (See a Graphic Outline of Photosynthesis Here).

An organism with chlorophyll absorbs light, CO2 and water from its surrounding environment. The water molecule is broken and the Hydrogen molecule bonds with carbon dioxide molecules to form glucose. Oxygen from the water molecule is released to the atmosphere, whereas the energy provided by photons is stored in the bonds of the glucose molecule.

Any nutritional chain begins with producer organisms; that is, with those organisms that produce their own food. These organisms are called autotrophs. Plants are autotrophs because they produce their own food; the raw materials for photosynthesis are water, carbon dioxide and light.

It has been determined experimentally that the density of carbon dioxide needed for the optimal development of all kinds of plants is 895 mg per cubic meter of air (about 500 ppmv).

Certain plants grow much better in atmospheres with very high densities of carbon dioxide; for example, the pteridophyte and certain species of conifers develop more successfully in humid atmospheres with 5000 ppmv of carbon dioxide.

Carbon Dioxide is not an environmental polluting agent because it is not detrimental or poisonous to life. Carbon dioxide cannot kill living cells by altering their structure or physiology in the same way, for example, as a snake venom will. It can only suffocate an organism when Oxygen is not present at a sufficient concentration to sustain life.

The difference between carbon dioxide and carbon monoxide is one less oxygen atom in the molecule of carbon monoxide. This small difference renders carbon monoxide toxic and carbon dioxide vital.

If you was to lock yourself in an air tight room and light a stove (NEVER DO IT!), it would not be the carbon dioxide that kills you, but poisoning by carbon monoxide and asphyxia from the depletion of oxygen consumed by the burning stove. If carbon dioxide was to accumulate in the same room to a density of 5 grams per cubic meter of air (3078 ppmv) you would not be asphyxiated, providing the density of oxygen in the room remained stable.