There’s a lot of hullabaloo recently about Natural Gas being too leaky to be a good substitute for coal. The claim is based on the fact that methane has a much larger GHG potential than carbon dioxide. But, the study those claims are based on can be interpreted two ways. I tend to think that the leak issue might be overblown, because if you are a producer, leaks mean money literally going into thin air. There’s a high incentive to fix leaks. Abandoned oil and gas wells, cited in the study, would of course be an exception.
The other reason is the IPCC, which produced this graph in the AR5 draft showing that methane just isn’t cooperating with models, and measurements are out of bounds with projections. Methane just doesn’t seem to be much of a problem:
From The National Renewable Energy Laboratory:
JISEA News: Study on Methane Emissions from Natural Gas Systems Indicates New Priorities
Study findings published in Policy Forum of Journal Science
A new study published in the journal Science says that the total impact of switching to natural gas depends heavily on leakage of methane (CH4) during the natural gas life cycle, and suggests that more can be done to reduce methane emissions and to improve measurement tools which help inform policy choices.
Published in the February 14 issue of Science, the study, “Methane Leaks from North American Natural Gas Systems,” presents a first effort to systematically compare North American emissions estimates at scales ranging from device-level to continental atmospheric studies. Because natural gas emits less carbon dioxide during combustion than other fossil fuels, it has been looked to as a ‘bridge’ fuel to a lower carbon energy system.
“With this study and our larger body of work focusing on natural gas and our transforming energy economy, we offer policymakers and investors a solid analytical foundation for decision making,” said Doug Arent, executive director of the Joint Institute for Strategic Energy Analysis (JISEA) and a co-author to the study. “While we found that official inventories tend to under-estimate total methane leakage, leakage rates are unlikely to be high enough to undermine the climate benefits of gas versus coal.”
The article was organized by Novim with funding from the Cynthia and George Mitchell Foundation and led by Stanford University’s Adam Brandt. It was co-written by researchers from Stanford University, JISEA, Energy Department’s National Renewable Energy Laboratory (NREL), University of Michigan, Massachusetts Institute of Technology, National Oceanic and Atmospheric Administration, University of Calgary, U.S. State Department, Harvard University, Lawrence Berkeley National Laboratory, University of California Santa Barbara, and the Environmental Defense Fund.
“Recent life cycle assessments generally agree that replacing coal with natural gas has climate benefits,” said Garvin Heath, a senior scientist at the NREL and a lead author of the report. “Our findings show that natural gas can be a bridge to a sustainable energy future, but that bridge must be traversed carefully. Current evidence suggests leakages may be larger than official estimates, so diligence will be required to ensure that leakage rates are actually low enough to achieve sustainability goals.”
Among other key findings of the research:
• Official inventories of methane leakage consistently underestimate actual leakage.
• Evidence at multiple scales suggests that the natural gas and oil sectors are important contributors.
• Independent experiments suggest that a small number of “super-emitters” could be responsible for a large fraction of leakage.
• Recent regional atmospheric studies with very high emissions rates are unlikely to be representative of typical natural gas system leakage rates.
• Hydraulic fracturing is not likely to be a substantial emissions source, relative to current national totals.
• Abandoned oil and gas wells appear to be a significant source of current emissions.
• Emissions inventories can be improved in ways that make them a more essential tool for policymaking.
JISEA is operated by the Alliance for Sustainable Energy, LLC on behalf of the National Renewable Energy Laboratory, the University of Colorado – Boulder, the Colorado School of Mines, the Colorado State University, the Massachusetts Institute of Technology, and Stanford University.
Since methane is more potent a GHG than co2, perhaps if we leak methane through our engines converting it to the less potent co2 first? Net gain? Maybe the cash for clunkers money or a fraction of the billions wasted on bankrupt green companies bought up by China at pennies on the dollar would have been better spent on cng conversion R&D?
It doesn’t add up…:
At February 19, 2014 at 5:52 pm you say
Blackbody radiation in the atmosphere is so small relative to greenhouse gas (GHG) radiative effects that it is usually ignored. Simply, blackbody radiation in the atmosphere is so trivial that it can be considered to be zero for all practical considerations.
The blackbody radiative effect occurs within the individual atoms of molecules. When an atom absorbs a photon then it gains the energy of the photon by raising an electron to a higher energy state (i.e. a higher ‘shell’).
The greenhouse effect (GHE) occurs by changing the energy of entire molecules and NOT the energy of electrons within atoms which are parts of molecules.
I explain this as follows.
A photon is a quantum of electromagnetic (EM) radiation which has a wavelength related to the energy it carries. When it is absorbed by a GHG molecule then it increases the vibrational or the rotational or the stretching energy of the molecule.
The effects are quantised by the shape of the molecule and its bonds. Hence, vibrational absorbtion is possible for a CO2 molecule
C – O – C
Because the ‘angle’ between the C atoms attached to the O atom can change to provide the vibration.
But such vibrational excitation cannot occur to an O2 molecule (or an N2 molecule)
O – O
Because the molecule has no ‘angle’ to change.
Please note that a gas does not get hotter when its GHG molecules absorb photons.
The heat of a gas is expressed by its temperature which is an indication of the average speed (actually RMS speed) of the gas molecules. Increase the average speed of the molecules and the gas gets hotter. Decrease the average speed of the molecules and the gas gets cooler.
A GHG molecule gains energy but does not get hotter when it gets excited by absorbing a photon: it is raised to a higher quantum level (by increasing the vibrational or rotational energy of the molecule). Simply, the energy from the photon is stored in the GHG molecule and the GHG molecule does not change its speed. If that stored energy is supplied by a collision to e.g. a nitrogen molecule then the nitrogen molecule is accelerated: the energy that was stored in the GHG molecule becomes kinetic energy in the nitrogen molecule so the gas gets hotter.
Similarly, if a collision causes kinetic energy of a nitrogen molecule to be transferred to be stored in a GHG molecule then the gas is cooled because the nitrogen molecule is decelerated but the GHG molecule is not accelerated. However, this is an extremely improbable event as the collision would have to occur so as to transfer the energy into e.g. a vibrational mode only, the cross section for this event would be very small. Most of the collisions would transfer mostly translational energy, next likely rotational and least likely vibrational or stretching.
I hope this helps.
Richard
Richard:
A diatomic molecule can absorb energy in a vibration mode that alters its bond length.
O-O O–O O—O O–O O-O
In addition, it has two rotational degrees of freedom corresponding to spinning end over end where the z axis is the molecular axis (think of it as in the plane of the screen, and perpendicular to the screen): such rotations can store energy that is not reflected in temperature, which depends on the (root mean square) speed of the centre of mass of the molecules in the gas. For Oxygen, taking 16 g/mol, the weight per atom is about 2.66E-26 kg. At 273K, the rms velocity is 461 m/s – an average energy of about 5.65 E-21 J per molecule. It has an absorption band at around 6 microns, which is an energy of 3.27E-20 J per photon and a frequency of 50 THz. The molecular dissociation energy is 498kJ/mol O2, or 8.27 E-19 J per molecule – or about 0.23 microns/230nm, which is in the hard UV spectrum. When a molecule is excited in one (or more) of these energy stores and it passes within range of another molecule (“collides”), it can kick out like a punch that sends the other molecule flying away faster, while reducing the energy stored in its own rotation or vibration and so conserving energy.
The following gives a nice introduction to the absorption bands of the main atmospheric gases:
http://irina.eas.gatech.edu/EAS8803_Fall2009/Lec6.pdf
Note that the UV absorption of O3 is by electron energy changes, not molecular vibrational modes.
It doesn’t add up… :
re your post at February 20, 2014 at 8:15 am.
Yes, a diatomic molecule can obtain photonic excitation by bond stretching but this is not pertinent to what happens in the atmosphere. As I said, a photon of EM has a wavelength which related to its energy and it is absorbed when there is an available quantum excitation state of an absorbing atom or molecule.
There is no doubt that GHG molecules are orders of magnitude more important for radiative absorbtion than diatomic molecules in the atmosphere. If you could falsify this then you would surely obtain a Nobel Prize for physics because you would overturn much knowledge and open up vast areas of useful research.
And the ozone issue is not relevant except in polar regions.
Richard
Richard:
Absorption will take place whenever there are photons that match an absorption band. Most atmospheric gases are transparent – i.e. do not absorb – in visible wavelengths that correspond to the more intense levels of solar radiation (but note the UV exception for ozone in particular): their absorption is dominated by IR wavelengths, as my link shows. The sun also radiates in the IR, albeit not as strongly as in the visible spectrum. IR energies are concerned with the motions of atoms in molecules, not electron orbit transfers between different energy levels. For practical purposes, quantisation is not relevant at these energies, because the quantised levels are so close together (and broadened via a variety of mechanisms) they represent a continuum. The Newtonian approximation suffices quite well: you can consider wave/particle duality of photons as the driver of what becomes fundamentally a mechanical system after absorption. Broad resonance peaks behave much as those for a simple driven pendulum or RC electrical circuit fed an AC voltage at varying frequencies – this is quite unlike the energy transitions for electrons in a molecular system, where the peaks are much more sharply defined, and mainly subject to fine structure splitting.
If you actually looked at the reference I cited, you would see that I am not trying to overturn the measured absorption spectra, but merely to illustrate the different physical phenomena involved.
An introduction to molecular vibrations:
http://en.wikipedia.org/wiki/Molecular_vibration
A more advanced treatment does look at the superposition of different quantum states arising from rotations and vibrations.
In the context of my original post on this topic I was responding to Policycritic, who appeared to consider that blackbody/graybody radiation only occurs at the wavelength given by Wien’s Law for the peak or characteristic wavelength. I don’t understand why you even chose to respond in the manner you did, introducing several errors along the way. The reason why GHGs heat up is because they absorb radiation in the first place: that radiation is a combination of the earth’s “blackbody” radiation and “blackbody” radiation from the sun and radiation scattered/emitted in the atmosphere. There is no magic transition between photons that excite electrons into different orbits and photons that cause changes in the vibration of molecules. The same energy of photon may have different effects. Photons generated by blackbody radiation are no different from photons generated when an atom, particle or molecule emits via other mechanisms. All photons have the same flavour, only distinguished by their energy/wavelength/frequency as described by E=hv=hc/λ. You implied that there were no absorption modes for O2, when there are, and that the only absorption mode for CO2 is scissoring of the bond angle, ignoring synchronous and asymmetric bond stretching.
Richard
i agree with most of what you write, but you appear to have overlooked the Equipartition Theorem.
In my opinion, rotational and vibrational energy is also a form of kinetic energy that can be passed on in molecular collisions and which does affect temperature measurements. I know there are divided opinions on this, so you are sure to find someone saying otherwise. But, either way, an increase in these degrees of freedom must then be shared with the translational DoF’s as well.
It doesn’t add up… :
Among other errors in your post at February 20, 2014 at 5:48 pm you assert to me
THE “ERRORS” ARE YOURS! Indeed, the reason I wrote was to correct some of your errors.
For example, in the brief quotation I here provide you write
I had explained that GHG’s DON’T “HEAT UP” when I wrote
Richard
Alex Hamilton:
Your post at February 20, 2014 at 7:58 pm begins says to me
NO! I did not ignore the Equipartition Theorem.
It is a matter of reality – n.b. NOT a matter of opinion – that internal energy of a molecule is NOT kinetic energy of a molecule. I explained that such internal energy can be transferred to other molecules and, thus, become kinetic energy (i.e. heat) of the gas.
Simply,
(a) radiative absorbtion increases the energy in a gas but does NOT heat the gas.
However,
(b) collisions between molecules can transfer the absorbed energy such as to convert that energy to kinetic energy with resulting heating of the gas.
I stated this when I wrote
Hence, I am surprised that you think I “overlooked the Equipartition Theorem”.
The important point I tried to explain is that the warming of non-GHG molecules results from the photonic absorbtion by GHG molecules and would not occur in the absence of GHG molecules.
My purpose was not to attempt the impossible task of explaining this entire field of quantum behaviour and there is much, much more than the Equipartition Theorem which I have not explained.
Richard
Richard
Nitrogen and oxygen molecules (and GHG ones too) are warmed by conduction at the surface / atmosphere boundary. GHG molecules absorb and emit radiation, but also receive and impart kinetic energy in collisions with any other molecules. So they act like holes in the blanket getting rid of surplus thermal energy that is being absorbed by the atmosphere or energy that has been transferred into the atmosphere as sensible (non-radiative) energy. That is why you don’t use moist air between the panes of double glazed windows – it reduces the insulating effect.
When radiation strikes a target what happens depends on the relative temperatures of the source of spontaneous radiation and the target. I trust we don’t disagee that the electro-magnetic energy in direct solar radiation from the Sun does warm Earth’s surface. So its energy is converted to thermal (kinetic) energy in surface molecules. The Equipartition Theorem tells us this new kinetic energy will end up being shared equally between the degrees of freedom (DoF) which comprise three translational DoF’s and more DoF’s which are vibrational and rotational kinetic energy. You seem to think the latter can have different values to those of each translational DoF, but you will need to get through an edit for Wikipedia to convince others, though not myself.
Now, the reason molecules only emit and absorb photons of particular wavelengths is that there must be changes in electron energy which exactly match the energy in the photon. If the radiation comes from a cooler source it merely resonates with a warmer target that is already emitting equivalent radiation as a part of its Planck spectrum. We can think of the energy momentarily changing an electron state and then that state immediately reverting back to its initial state as it emits an equivalent photon back out again. Physicists call the process “pseudo scattering” because it looks as if the incident radiation was just randomly scattered – rather like diffuse reflection. The energy did not go through the complicated internal process of being converted to thermal (kinetic) energy shared equally among those other degrees of freedom.
But if the source of radiation had been hotter than the target, then some of its radiation (corresponding to the area between the Planck curves) does not resonate and its energy is converted to thermal (kinetic) energy, and so the Sun can warm the surface, but back radiation can only slow down that portion of surface cooling which is itself by radiation.
Kinetic energy is shared in molecular collisions (heat diffusion) and when some molecules become significantly “hotter” than others around, the kinetic energy may firstly raise the energy state of an electron and that then leads to emission of a photon. So sensible energy transfers from the surface to the atmosphere, as well as absorption of radiation by the atmosphere (including nearly a fifth of all incident solar radiation) does firstly warm the atmosphere, and then radiating molecules also get warmed by sensible heat transfer (diffusion) and energy is radiated in all directions. That radiation which strikes a warmer target is pseudo scattered, and eventually all the radiated energy gets to cooler regions and then to space. However, there is a limit to the cooling (which continues into the night) because the Sun starts more warming the next day and radiative balance is automatically maintained because the whole Earth+atmosphere system acts like a black body.
.