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• ##### The methane threat is overblown considerably here(0+ / 0-)

Methane only lasts 10 years in the atmosphere before it is reduced to CO2. That Science article projects the East Siberia Artic Shoreline release as only ~0.6% of global FF burning, 50 million tons C per year/9000 million tons of fossil fuel burning and cement production. Most methane comes from cows and rice. Long term(centuries) permafrost release is a serious threat but considering the amount of permafrost release is a function on temperatures it seems obvious to focus immediately reducing FF emissions and to ignore permafrost for now.
It's a distraction IMO.

• ##### Not entirely true(0+ / 0-)

It has a half-life of about ten years.

[ Parent ]

• ##### I read methane lasts 10 years at Real Climate.(0+ / 0-)

And the lifetime of methane in the atmosphere is short, about 10 years, so methane doesn’t build up like CO2, SF6, and to a lesser extent N2O do.

http://www.realclimate.org/...

Half-life really refers to radioactivity, not chemical breakdown.

• ##### Checked wikipedia(1+ / 0-)
Recommended by:
enemy of the people

You're right and I was wrong.  The lifetime is 8.4 years.

[ Parent ]

• ##### Half-life is simply a mathematical expression(0+ / 0-)

to capture the net effect of one or multiple processes.

The concept can apply to any time-dependent decay process.

The half-life of chemical reactions depends on the Temperature, Pressure, the concentration of ALL the other reactants, products.  But it also includes the ENERGY put into or released from the system.

Example:  The half-life of a tank of gas in your truck, is the time it takes to go from full to half-empty.  The half-life on any given day, depends on how fast you drive, and how heavy a load you carry.  Another way to say the half-life depends on how efficiently your engine carries out combustion, converts the energy to motion, and whether you are carrying the load uphill or down hill.

Example: Everything you ingest has a half-life.  Drugs you take leave the body by various routes or are metabolized and the net effect is measured.  The half-life is the average amount of time it takes for the amount of the drug in your body to become half of what you ingested.

Make sense?

So the half-life of methane in the atmosphere tells us ONLY what the half-life is right now, based on CURRENT atmospheric conditions and CURRENT inputs, i.e. HALF of what we pump up there this year will still be there 10 years from now - IF and ONLY IF there are no other sources AND the Temperature, Pressure, AND all other atmospheric inputs and outputs remain the same.

I appreciate that you are digesting complex information and stated what seemed to make sense to you, but your  conclusion

Half-life really refers to radioactivity, not chemical breakdown.
is simply not true.
• ##### Radioactive decay is a specific type of (0+ / 0-)

chemical half-life.  It is a chemical decay that occurs coincident with characteristic emissions that depend on the specific element and atomic structure.

It may be useful to understand that radioactive decay is simply one type of chemical decay that is relatively INDEPENDENT of atmospheric Temperature and Atmospheric Pressure, and normal atomic concentrations at the surface of the earth.

• ##### Sorry, radioactivity is nuclear disintegration(0+ / 0-)

it is independent of other factors.

http://scifun.chem.wisc.edu/...

• ##### Not sure if "sorry" in your comment (0+ / 0-)

indicates your agreement or disagreement.

If the former, I'll stop.

You seem to have a decent grasp of radioactivity and how to assess which types of radioactivity raise environmental concerns.  I appreciate your interest in understanding chemistry and being able to decide for yourself when environmental problems are large or small.

If your "sorry" was expressing disagreement, please look at
http://en.wikipedia.org/...

Radioactivity falls within the sub-field of chemistry called  nuclear chemistry, and involves a subset of isotopes that are called "unstable" because they are high energy atomic states that spontaneously decay by emitting ionizing radiation.  (It's a mass to energy conversion that is NOT dependent on factors outside the nucleus - at the normal Temp and Press at the surface of the earth).

There are other sub-sub fields of nuclear chemistry that use the stable isotopes.  The isotopes are called stable because they do not decay by emitting ionizing radiation.   Stable atomic nuclei can be excited and will decay in a variety of processes that decay with characteristic half-lives.

One example is an MRI machine, which relies on nuclear magnetic radiation, NMR.  In an MRI experiment magnetic nuclei (such as Hydrogen or Iron) are excited with radiowaves and then observed as the nuclei decay back to their lower energy state (the ground state).

Unlike radioactive decay, the decay half-life of magnetic nuclei, and other properties of the decay mechanism, ARE dependent on factors outside the nucleus, such as

1. the number and type of atoms nearby,
2. how many bonds separate the two atoms,
3. how large the molecule is,
4. as well as properties of the molecular environment, such as whether the material is liquid or solid.

• ##### Sorry-nice way to say no, you're wrong(0+ / 0-)

Radioactivity has nothing to do with exterior factors, it is
due to instability in the atomic nucleus, an unbalance in numbers of neutrons and protons.
NMR machines work on the 'spin' of
protons and neutrons which of course is influenced by external magnetic fields. There is also something called electron 'spin' reasonance and something else called electron paramagnetic reasonance.

• ##### Sorry, you are applying chemical terms incorrectly(0+ / 0-)

You seem to have some chemistry knowledge or training and I hope this comment will clear up your confusion or motivate you to use correct chemical language when discussing environmental chemistry in a public forum.

ETOP, I'm not trying to give you a hard time but I can't let stand the confusion your incorrect authoritative statements have added to the comments of this diary.

For readers who are trying to understand the material as it relates to environmental science and policy, and who haven't taken any advanced chemistry, I'll address a few related terms that have well-established IUPAC definitions that chemists and those in overlapping fields rely upon.

For the non-chemists: IUPAC is the International Union of Pure and Applied Chemistry. http://www.iupac.org/  Since this is a political forum, I'll state outright that IUPAC is NOT a political organization for the chemical industry.

IUPAC IS an international standard setting body that arose in the late 19th century, from a need to reduce ambiguity when recording, reporting, and discussing chemicals and chemical phenomena.  The first international conference was convened early in the 20th century and continues to meet regularly to hammer out in detail, all the rules and syntax of chemical nomenclature.  They have many projects and resources available for specific subfields within in chemistry.

IUPAC also maintains a dictionary/textbook, the IUPAC Compendium of Chemical Terminology - the Gold Book, so that classes of molecules, chemical reactions and chemical phenomena can be published worldwide in a common language, with limited ambiguity.

The IUPAC Gold Book is free, available for download as a pdf, and also organized online as a very useful hyperlinked dictionary/textbook http://goldbook.iupac.org/...

EOTP, this statement in your earlier comment is incorrect:
"Half-life really refers to radioactivity, not chemical breakdown."
Half-life has a well-defined meaning and has much broader uses in chemistry, physics and biology.

According to IUPAC, the term "half-life" is used in chemical reactions to describe the time it takes to deplete starting materials half-way:

http://goldbook.iupac.org/...
Half-life or t(1/2): For a given reaction the half life t 1 2 of a reactant is the time required for its concentration to reach a value that is the arithmetic mean of its initial and final (equilibrium) values. For a reactant that is entirely consumed it is the time taken for the reactant concentration to fall to one half its initial value... [italics mine]
EOTP, this statement in your earlier comment is also incorrect:
"radioactivity is nuclear disintegration"
EOTP, this statement in your earlier comment applies only to a subset of radioactive decay processes:

"Sorry, radioactivity is nuclear disintegration (0+ / 0-)
it is independent of other factors."
http://scifun.chem.wisc.edu/....

According to IUPAC,
radioactive is
"The property of a nuclide undergoing spontaneous nuclear transformations with the emission of radiation." http://goldbook.iupac.org/...

nuclide is
"A species of atom, characterized by its mass number, atomic number and nuclear energy state, provided that the mean life in that state is long enough to be observable." http://goldbook.iupac.org/...

radioactivity is
"The property of certain nuclides showing radioactive decay." http://goldbook.iupac.org/...

natural radioactivity is
"Radioactivity of naturally occurring nuclides in materials where the isotopic abundance of that nuclide is natural."

induced radioactivity is
"Radioactivity induced by irradiation." http://goldbook.iupac.org/...

radioactive decay is
"Nuclear decay in which particles or electromagnetic radiation are emitted or the nucleus undergoes spontaneous fission or electron capture." http://goldbook.iupac.org/...

While nuclear decay is
"A spontaneous nuclear transformation." http://goldbook.iupac.org/...

radiation is
"A term embracing electromagnetic waves as well as fast moving particles. In radioanalytical chemistry the term usually refers to radiation emitted during a nuclear process (radioactive decay, nuclear reaction, nuclear fission, accelerators)."  http://goldbook.iupac.org/...

nuclear fission is
"The division of a nucleus into two or more parts with masses of equal order of magnitude, usually accompanied by the emission of neutrons, gamma radiation and, rarely, small charged nuclear fragments." http://goldbook.iupac.org/...

radioisotope is a
"A radioactive isotope of a specified element." http://goldbook.iupac.org/...

EOTP, nuclear decay is much broader than nuclear disintegration.

Your statement about radioactive half-life being independent of external factors is limited to reactions in which the starting material is completely consumed and there is NO reverse reaction pathway.  That subset includes, all radioactive decay processes that involve nuclear fission, or that involve alpha particle emissions, but only SOME of the radioactive decay processes that involve beta particle emissions, and NONE of the radioactive decay processes that involve gamma ray emissions.

Your example, a radioactive clock, based on Uranium, is one example of radioactive decay, in which spontaneous nuclear transformation, with particle emission does indeed have a fixed half-life, independent of external factors.

• ##### Part of my run-on comment to ETOP was not (0+ / 0-)

what I meant to write and should instead read:

Your statement about radioactive half-life being independent of external factors is limited to reactions in which the starting material is completely consumed and there is NO reverse reaction pathway.  That subset includes, all radioactive decay processes that involve nuclear fission, or that involve alpha particle emissions, but only SOME of the radioactive decay processes that involve beta particle emissions.  and NONE of the Radioactive decay processes that involve gamma ray emissions occur after particle emissions or from irradiation, and merely involve relaxation of a high energy nucleus back to a lower energy state.
Bottom line:

Nuclear decay processes are a subset of chemical transformations.

All of nuclear decay processes can be described in terms of a half-life, but only some of them have half-lives that are independent of external factors.

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