On Fri, 31 Oct 2008 16:32:48 -0400, AR- wrote:



Bill Ward wrote:

On Fri, 31 Oct 2008 14:20:37 -0400, AR- wrote:



Bill Ward wrote:


On Fri, 31 Oct 2008 08:36:36 -0700, Bolaleman wrote:



On Oct 31, 6:07 am, chemist wrote:


On Oct 31, 1:45 am, Roger Coppock wrote:







The TV science series "Mythbusters" did a "Young Scientists
Special." It aired on 4/26/08 (Season 6, Episode 8). One of the
items they put to the test was greenhouse gas theory. They made 4
large rectangular chambers added CO2 to one, CH4 to another, and
used the remaining two for controls.

They simulated the Earth by shining a light through the clear mylar
on one side onto a black painted surface at the other side. the
greenhouse gas chambers were warmer and melted more ice than the
control groups. They confirmed that CO2 and CH4 can cause greenhouse
warming.

Tom Bolger should look at this demonstration to see how to do this
correctly. He's failed too many times and he needs help.

I found my copy on the LImewire™ network. This episode is
probably also available on DVD. Please see:

http://www.imdb.com/title/tt1225053/

Give us more detail such as
were the containers open.
METHANE DOES NOT WARM FASTER THAN AIR.- Hide quoted text -

- Show quoted text -

Chemist, here is the reason:
When heat is lost to the air, some is absorbed by nitrogen, some is
absorbed by oxygen, and a tiny amount is absorbed by argon, carbon
dioxide, water vapor, and trace gases. You can write:

Heat absorbed by one mole of air = heat absorbed by O2 + heat absorbed
by N2 + ...
= xO2Cp(O2) T + xN2Cp(N2) T + ...

where xO2 and xN2 are moles of oxygen and moles of nitrogen per mole
of air, and Cp(O2) and Cp(N2) are the constant pressure molar heat
capacites for pure oxygen and nitrogen gases.

Assuming that air is 21% oxygen, and 79% nitrogen by volume. If you
can assume that the air behaves ideally, Avogadro's law says that the
volume fraction for each gas is also its mole fraction. However, gases
like CO2, H2O and methane (CH4) do not behave like an ideal gas.

As O2 and N2 are di-atomic gases, but CO2, H2O and methane are three-
and four- atomic gases, they have more degrees of freedom, i.e.
infrared energy can be converted more easily into intra-molecular
atomic vibrations which is equal kinetic energy or heat energy. As a
result, these gases (including water as vapor) are heated up more
easily than oxygen and nitrogen by Infrared (IR) radiation. This
conversion of radiation energy to kinetic energy by the way is the
principal of IR spectroscopy. The higher energetic ultraviolet
radiation (UV) is causing excitations of outer electrons (used for
instance in the UV spectroscopy). This “absorbed” energy can be
converted partially in kinetic swinging energy (resulting in heat
production) and partially is emitted again as radiation energy.


Fine, but IR has nothing to do with it. The experiment heated the
gases by conduction and convection from the black background.

Unfortunately there is no link to the video so I have only a sketchy
idea of how this experiment was conducted. But if there was a black
background behind the chambers it would generate IR radiation. The
original light source that passed through the chambers would also
(unless it was of a type or specifically designed not to). Thus, IR
should have been involved in this experiment. Though what you maybe
saying, is that the main heating effect (i.e.,much greater than the
contribution from IR) given this experimental set up, was conduction and
convection.


That is correct. Conduction and convection (mass transport) are far
more effective than radiation at ambient temperatures. That's why most
computers have fans, for example.

Even back in the

1850's, Tyndall pointed out the need to keep the radiation source and
detectors completely thermally isolated from the sample gas. It's
still true.

Those demonstrations do not show anything but the density and thermal
properties of the gases. They are being shown to gullible children as
propaganda.

You may be right, but that seems rather unnecessary. It surely cannot be
that difficult to set up a simple laboratory experiment, even one that's
portable, which shows the differential ability of some gasses to absorb
radiation.


It is difficult (and expensive), because of the need to thermally
isolate the sample gas with IR transparent optics, and the expensive,
cooled IR sensors necessary to detect IR in the 15u band in question.

There's not much serious dispute about the absorption spectrum of CO2,
it's the relevance to global warming, in view of the larger effect of
water and its phase changes, at issue. The only effect CO2 could have
is above the troposphere, and negative feedbacks from water make even
that unlikely.

Do you have some addition sources you could point me to so that I could
better understand and evaluate these assertions?

This may get you started:

http://en.wikipedia.org/wiki/Infrared_spectroscopy

I haven't got the link handy, but Tyndall's 1865(?) book is available on
Google books. He did some of the original work on gas IR absorption.

Then you might see what a new mid-IR instrument would cost. Perkin Elmer
will give you a quote he

http://las.perkinelmer.com/Catalog/P...uctID=L125402A


Are there any assertions in particular that require clarification?

Don't believe anything until you are satisfied you clearly understand
it. The burden of explaining a theory in a clear, accurate and
understandable manner lies with the proponents, not the skeptics. Be
very suspicious of those who try to convince you that you are so stupid
you can't understand their explanation.

I have rarely found that to be the case for people trying to explain a
theory.

That's just their way of discouraging you from asking
questions they can't answer without exposing their ignorance.