Pub #brownchem: alpha137 @craigs
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alpha137: hello
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*** craigs :End of /WHOIS list. craigs: hi, You here for the discussion?
alpha137: Yes.
craigs: Are you Professor Baird?
alpha137: I was late because I had dinner at the Tennis Hall of Fame in New Port RI!
alpha137: Yes, I am that person.
craigs: cool
alpha137: It was fabulous-outside and the weather was perfect.
alpha137: And it was cool which is not what we can expect if the earth warms up!
craigs: It's all right. You gave me a chance to reacqaint myself with IRC
alpha137: Good. IRC has its uses.
craigs: Hehe, nice transition :-)
craigs: So where do we start?
alpha137: I spent dinner thinking about a kind of preamble for this course and will post it in the IRC readings later.
craigs: k
alpha137: Have you read any of the discussions so far?
craigs: I read the first one with LizK, but I forgot exactly what it was about.
craigs: I remember that I was okay with most of the technical stuff.
alpha137: LizK and I were kind of asking what an earth that could sustain life was like and essentially that we need to look to the geological record to find out.
alpha137: We decided that, among other things, water was needed.
alpha137: A reasonable temperature too.
alpha137: On the other hand, there is life of sorts when there are extreme temperatures.
craigs: Yes.
alpha137: But not human life, or animal life.
craigs: So you are saying that chances are that, if intelligent life on other planets were to exist, it would be on a world with conditions quite like our own?
craigs: Do you want to go in a differenct direction with this discussion?
alpha137: I think that is an assumption that people are making.
craigs: oh
alpha137: We can go anywhere you wish. In the evolution of the discussion so far I was thinking of trying to make a model for global warming.
alpha137: A model in words.
craigs: That sounds good.
craigs: Model away
alpha137: First, we were asking the question "does global warming, as an event caused by humans, exist?"
craigs: Based on my limited reading, I'm fairly convinced that it does
alpha137: If you read the discussions of 7/22 and 7/23 and look at some links and some graphs that are posted there you will find that we more or less think that man has had an impact.
craigs: Do you want me to do that now or later?
alpha137: Do that later.
alpha137: Let us discuss models. Like what is a model?
craigs: I like to think of a model as a representation of an actual situation that allows us to understand it more fully
craigs: Thus, we can work with it better
alpha137: Sounds good. What is "understand more fully?"
alpha137: That is, what do we expect from our model?
craigs: "Understand more fully" = Establish a better understanding of what the situation is in reality in order to have the information to take appropriate action
alpha137: OK, but when you read the discussions 7/21, etc. you will find, if you do not know, that this global warming is a very complicated business.
alpha137: Where should we begin with our model?
alpha137: Know any thing about computer programming?
craigs: Let's begin with how the chemical structure of CO2 traps heat
craigs: I know nothing about CP
craigs: I plan on taking a Computer Science course first semester
alpha137: OK, the only point being that one usually starts simply when writing a computer program and then adds to it again and again gaining in complexity.
alpha137: Be carefull of my friend Andy Van Dam.
alpha137: Remember, I warned you first.
craigs: oh, should I be wary?
craigs: Are you using CP as an analogy to our atmosphere, saying that we've royally messed it up...
alpha137: The course Andy teaches is very time consuming and he figures that it is the only one you are taking. If that is the CS course just go into it with your "eyes open."
craigs: so that it's now much more difficult to reverse the effects we've caused than it would have been, say 100 years ago?
alpha137: No, I am not using the analogy to say that we have messed up, but as an analogy to an approach to making a model.
craigs: Hmm, Mr. Van Dam doesn't sound very understanding.
craigs: ok
craigs: let's start out simple.
alpha137: Mr. Van Dam is very demanding.
alpha137: OK, simple. What causes the green house effect?
craigs: Atmospheric gases that trap heat
craigs: And thanks for the warning!
alpha137: OK, what are the most common, most effective, atm gases that trap heat.
craigs: CO2 ?
alpha137: That is one.
alpha137: What is the most common?
craigs: Could you tell me some others?
craigs: Nitrogen?
alpha137: No, I am going to make you guess.
craigs: Just guessing
craigs: Oxygen?
alpha137: Nitrogen does not absorb IR radiation because it has no permanant electric dipole.
alpha137: It is a diatomic molecule.
alpha137: So oxygen is out as well.
craigs: yes
craigs: Hydrogen?
craigs: But that isn't common
alpha137: CO_2 is a linear, triatomic molecule which in its lowest state has no electric dipole either.
alpha137: But CO_2 does absorb IR (infrared) radiation.
alpha137: Hydrogen is a diatomic molecule H_2.
craigs: oh
craigs: This is just a side question, but couldn't molecules absorb any type of energy and the convert it into IR radiation?
alpha137: Hydrogen used to be common, but is no more and that was the subject of one of the early discussions that LizK and I had. It lead to a fundamental chemical principle.
alpha137: Yes, molecules could absorb any kind of radiation and on collision with other molecules loose their energy by non-radiative processes converting it to heat.
alpha137: Now we have two questions: 1) what is the most common green house gas and 2) what is heat?
craigs: So you're saying that they must radiate the same type of radiation as they absorb?
alpha137: Molecules in an excited state will radiate to the next lowest allowed state.
craigs: #2 is one of my big questions because of mixed/impartial answers that I have read and heard
alpha137: Unless they collide with something.
craigs: yes, quantum physics
craigs: oh
craigs: then what happens?
alpha137: OK, heat is defined by the First Law of Thermodynamics
alpha137: This law relates internal energy, work done and heat added.
alpha137: It is a conservation principle which we need in our model.
craigs: ok
alpha137: What do you think heat is? Think simply.
craigs: Is heat a type of electromagnetic radiation?
alpha137: You have a flame and you place it under a beaker of water. What happens to the water molecules?
craigs: They move faster. They have more heat/more internal energy
alpha137: Heat is NOT a type of electromagnetic radiation.
alpha137: Correct, they move faster and they have Kinetic Energy.
craigs: Then why is IR radiation given such emphasis in relation to heat?
alpha137: If the beaker of water is the system and if the water (vapor) does no work then the heat added to the beaker = the internal energy (read K.E.) of the water.
craigs: ok
craigs: wait
alpha137: Well, here must be part of the model which I was going to drag out of you. The sun shines on the earth. The solar spectrum is like a black body of about 5700K.
craigs: do you mean the Increase in K.E ?
alpha137: Yes, the increase in K.E.
craigs: ok
craigs: I have no idea what that means, but ok
craigs: I know what a black body is
craigs: but I don't know what 5700K is
alpha137: The solar energy (some is absorbed by molecules in the atmosphere) gets to earth and it is absorbed by the matter of earth. The earth heats up. IT radiates like a black body at whatever the ambient temperature of earth is.
craigs: Ambient temperature = ?
alpha137: 5,700K is the temperature in Kelvin degrees, the absolute temperature.
craigs: That's pretty hot
alpha137: ambient temperature means the outside, ordinary everyday temperature.
alpha137: Right, the sun is hot.
alpha137: By comparison the earth is cool
craigs: ok
alpha137: There is a link in one of the discussions to a black body radiation curve for the sun. The main point is that its maximum (it is a distribution) depends on the temperature.
alpha137: The higher the black body temperature the more displaced is this max towards the ultraviolet. The lower the T the max is more toward lower wavelengths.
craigs: I don't completely understand. Are you saying that the sun radiates more energy at one temperature than all others?
alpha137: I am saying that the sun radiates a lot of energy at a particular wavelength, but that a whole range of wavelengths are there.
craigs: with most falling in a certain wavelength
alpha137: Right. You have to look at a black body curve, or distribution, to get a more accurate pict.
craigs: So is 5700K most disposed for IR radiation?
alpha137: No, 5,700K is hot and favors uv and visible.
alpha137: Whatever the average temperature of earth is, lets say 300K and that would be high, it radiates more wavelengths in the IR. We call IR "heat" radiation for that reason.
craigs: Then why is IR radiation given such close relation with heat?
craigs: is it?
craigs: I see
alpha137: On a microscopic level, IR radiation excites molecular vibrations.
craigs: As does most energy
alpha137: If we have triatomic molecules then we have easily excitable vibrations.
alpha137: The energy of these vibrations is in the micrometer wavelength.
craigs: So are you saying that the sun's UV and visible radiation excites the earth...
craigs: which releases IR radiation...
Yes, see the black body curves below.
alpha137: If visible light is 500 micrometers, infrared light is 1 to 50 micrometers.
craigs: which easily excites triatomic molecules
craigs: ...
craigs: which give back toward earth a lot of the heat that the earth radiates?
alpha137: Yes, I am saying that the whole spectrum of colors of light from the sun excited the earth which glows like a black body at a certain temperature (pretty low) and this radiation contains a lot in the 1-50 micron range.
Here is a link to black body emissions from a 6,000 K and a 256 K body.
alpha137: We are getting at a part of our model.
craigs: I see
craigs: So what are some of the other gases :) ?
alpha137: Now, you still have not told me which is the most prevalent green house gas.
craigs: methane?
alpha137: Yes, but there is one vastly more prevalent than methane.
craigs: Correct me where I'm wrong...Aren't the most abundant gases in the atmosphere N_2, then O2, then CO2?
alpha137: It is a triatomic molecule. You need triatomic or more than triatomic molecules to have vibrations that can be excited by IR. CO does have an electric dipole moment so it is OK.
Here is a link to the vibrational modes that are excited by absorbing specific radiation in the infrared.
craigs: Is carbon monoxide more abundant than it's cousin?
alpha137: Methane has 5 atoms. The symmetrical form does not have a dipole, but a distortion does.
alpha137: No, CO is not more abundant than its cousin.
alpha137: I am going to blow you out of the water with the answer. So what is it?
craigs: What is "electric dipole moment"?
alpha137: An electric dipole moment is a + seperated by some distance and a - charge.
craigs: Water vapor?
alpha137: C-O the O is a little bit negative and the C a little bit positive.
alpha137: Water vapor is Correct!!
craigs: yes!
alpha137: Our model must contain water vapor.
craigs: Took me awhile, but I finally got it.
craigs: ok
alpha137: Water vapor absorbs IR and there is a lot of water vapor in the atmosphere.
craigs: Does pollution contribute to the amount of water vapor in the atmosphere?
alpha137: What would happen if the earth did not have a green house effect?
craigs: There wouldn't be enough heat for humans to live
alpha137: No, pollution does not contribute the amount of water vapor in the atmosphere providing we do not count carbon dioxide.
alpha137: Right, without the green house effect of water we would not exist.
craigs: What do you mean "providing we do not count carbon dioxide?"
alpha137: Well, carbon dioxide is a green house gas.
craigs: oh, oh
craigs: never mind
alpha137: If you take a look at the discussion of 7/22 and 7/23 we decided that a small temperature change would increase the amount of water vapor in the atm.
alpha137: If water vapor increased then since it is a green house gas more heat would be trapped.
craigs: ok
craigs: so the greenhouse effect multiplies
alpha137: I think that this has to be a part of our simple model.
alpha137: Yes, the greenhouse effect multiplies, feeds on itself.
craigs: That's pretty cool...I bet there's an equation for that somewhere.
alpha137: Feeds on itself means "feedback."
alpha137: Know what feedback is?
craigs: yes
alpha137: OK, I think we need to build in feedback in our simple model.
alpha137: Thermal feedback!
craigs: ok
craigs: Thermal feedback, got it
alpha137: So far our model has these components. CO_2, H_2O, some mechanism for the absorption of IR and a feedback mechanism for T of some sort.
alpha137: Where does the water come from? And the CO_2?
craigs: why do you say "of some sort?"
alpha137: "Some sort" because I do not know just how it works.
craigs: ok
craigs: water from the oceans, CO_2 from respiration
alpha137: In the discn of 7/23 there is a link to feedback and it shows electronic feedback. There are amplifiers in there and we need the analog of all the components.
alpha137: CO_2 from respiration is a very minor component.
alpha137: Where else could CO_2 come from?
craigs: burning of organic substances?
alpha137: Right, burning, the combusion of hydrocarbons.
alpha137: We have a huge source of liquid water in the oceans and this is in a kind of dynamic "equilibrium" with the water vapor in the atmospere.
craigs: But if this combution only began in a big way around 1850, doesn't that imply that there was SIGNIFICANTLY less CO_2 in the atmosphere before then?
craigs: Yes, dynamic equilibrium.
alpha137: To your last statement, it is hard to say.
craigs: Why?
alpha137: We need the geological record to find out what the carbon dioxide levels were in the past.
craigs: Are you saying that this record is for some reason unavailable?
alpha137: It turns out that the geologists have been busy and we do have the record.
craigs: Then this is work that must be done, yes?
alpha137: There are three graphs as links in the discn of 7/21 to 7/23
alpha137: They show, in effect, a variation of carbon dioxide through the past 750,000 years.
alpha137: They do not show anything about water vapor in the atm.
alpha137: The geo record also shows that from 1850 to present there is a big increase compared to the total geo record.
craigs: how big?
alpha137: But the increase over what was there is only 100 parts per million (v)
alpha137: Do you know what a ppm is?
craigs: ppm = parts per million
alpha137: Right, and we better specify if is by weight or by volume. So ppmv means parts per million by volume.
alpha137: Do you know the ideal gas law?
craigs: Can we compute a possible increase in T that this increase in CO_2 could create
craigs: One mole of ideal gas has 22.4 liters of volume?
alpha137: We could possibly compute an increase in T from that 100 ppmv carbon dioxide.
craigs: I'm reaching back to sophomore chem. for that one.
craigs: Has this computation been done before?
alpha137: OK, but I perfer to remember a simple formula: PV = nRT
craigs: ok
craigs: It's been a long time since I used that equation
alpha137: P is the pressure in atm for us. V the vol in liters, n the number of moles and T the temperature in Kelvin degrees. Thus R = 0.082 liter-atm/mol-K
alpha137: RT for t = 273K is 22.5 liter-atm
alpha137: per mole
craigs: ok
alpha137: The point is, that you should be able to compute for me the ppm of water vapor if I give you the temperature and the vapor pressure for water at that T.
craigs: And what will we do with this information?
alpha137: ppmv is a percentage-has no units.
alpha137: Well, we will use it in our model.
alpha137: I did this earlier and got two answers because I messed up no doubt. In one est I found that at 4 C there were about 4,000 ppm water vapor and in another about 5,000 ppm.
craigs: ok
alpha137: So if water vapor is several thousand ppm why does a few hundred ppm of carbon dioxide make a difference?
alpha137: We are tying to get at a model.
alpha137: What happens when you heat water?
alpha137: You know, in that beaker.
craigs: I don't know why it makes a difference.
craigs: It moves faster, and more turns into vapor
alpha137: More turns into vapor. (it does have more KE)
alpha137: If you heat water its vapor pressure increases.
craigs: ok
alpha137: We can look it up in a table of vapor pressure as a function of temperature.
craigs: And how does vapor pressure fit into our model?
alpha137: It is going to be a part of a feedback.
craigs: Why?
alpha137: The more water vapor the more IR is absorbed and the more greenhouse heating that occurs.
alpha137: The more greenhouse heating the more water vapor, etc.
craigs: And is pressure going to be the limiting factor to the amount of water vapor in the atmosphere?
alpha137: Well, the pressure is pretty close to 1 atm.
at the earth's surface.
craigs: ok
alpha137: At a given T the atm will only hold so much water vapor and it will condense out as rain.
craigs: ok
alpha137: In any event, this water vapor-temperature thing has been going on for a long, long time. More than 750,000 years!
craigs: ok
alpha137: If you look at the 750,000 year graph you will see that we have ups and downs in T-ice ages and inter glacial periods.
alpha137: Water must be a huge part of this.
craigs: I've always wondered why there were such large variations over time.
alpha137: It is complex and no one really understands the details.
alpha137: We can just take the record as a given.
alpha137: We are now in an interglacial period (non-ice age).
craigs: Yes, but aren't we slowly heading for one now?
alpha137: Perhaps, but it is a ways off (10,000 years perhaps).
craigs: Yes.
craigs: Maybe there won't ever be one because of the increase in greenhouse gases
alpha137: So, we are in a relatively stable T region.
craigs: ok
alpha137: Now, assuming that water vapor and T are just chunking along over the millennia how is it that an additional 100 ppmv of carbon dioxide can make a difference if it does?
alpha137: (don't worry about my spelling, I will take care of it later).
craigs: Maybe a small increase is all that's needed
alpha137: Long term (the 750,000 year range) there are fluctuations in T from ice age to ice age, but right now we can consider the water vapor - T thing in some kind of quasi equilibrium
craigs: Even with the change in CO_2 ?
alpha137: A small increase would be the idea. Why?
alpha137: Lets suppose the CO_2 does it. How?
craigs: Thermal feedback?
craigs: Or do you mean something else?
alpha137: That is going to be the model.
alpha137: Here is the idea to be tested. 100 ppmv carbon dioxide is added by humans
craigs: ok
alpha137: This 100 ppmv CO_2 causes a small temperature increase, maybe tenths of a degree C.
craigs: ok
alpha137: We look up in a table to see how much the vapor pressure of water increases when the T is increased by a tenth of a degree.
craigs: ok
alpha137: If it is significant (say hundreds of ppm water vapor) then that will be an effective green house effect multiplying the effect of the carbon dioxide.
alpha137: This looks like a temperature amplifier to me.
alpha137: And a feedback mechanism.
craigs: but how much does it amplify?
alpha137: A feedback amplifier with two feedback loops.
craigs: Wouldn't the feedback loops keep going until their limits go toward 0 ?
alpha137: To know how much it amplifies we need to know how carbon dioxide and water each absorb IR radiation as you suggested a while ago.
alpha137: No, if the type of feedback is right they go till their effect if infinity, or oscillation.
alpha137: That is, in the electrical analog, you get an oscillation. That happens with mics and HiFi.
craigs: Why is there oscillation?
alpha137: Here we would just have thermal runnaway.
craigs: Why don't they keep building off each other until the effects of their building become unimportant, say in the tenth feedback loop...
craigs: or whenever?
alpha137: There is oscillation in the HiFi because the signal becomes so large that it shuts down the circuit for a moment.
alpha137: There are two kinds of feedback. In one kind, the amplified signal is reduced. This is so because the voltage fed back is out of phase with the incomming signal.
alpha137: This is used in an audio system to reduce distortion.
craigs: I'll take your word for it.
alpha137: The other kind of feedback adds to the incomming signal, this is amplified and becomes larger and larger as time progresses.
alpha137: It is this latter analog to the electrical amplifier that the greenhouse gas behaves like.
alpha137: So I think.
craigs: isn't there a series equation that can be used for this?
alpha137: In other words, humans produce carbon dioxide which warms the atmosphere making more water vapor. The water vapor itself warms the atm making even more water vapor and the atm gets hotter and hotter.
alpha137: There must be general equations one can use for this.
alpha137: The electrical analogies are good not because they have to do with electronics, but because they are general ideas that apply in many places.
craigs: Yes, but I would think that with each successive feedback loop, the feedback would be less
alpha137: We are after a model in words. Equations come later and after that computer models.
craigs: ok
alpha137: Yes, and no. As I said a bit ago, one kind of feedback would lead to less and less, but the other kind leads to more and more.
alpha137: I think we have the more and more kind.
craigs: Are you sure?
alpha137: The more water vapor the more heating and the more heating the more water vapor. That is more and more.
alpha137: What is the mechanism where the temperature goes up and the amount of water vapor goes down?
craigs: Then our descendents had better like it hot
craigs: I don't know
alpha137: I think it is more and more. I cannot think of a way for the T to go up and the greenhouse gases to be reduced.
alpha137: On the other hand, this is a complicated business and perhaps we can come up with ways to reduce greenhouse gases, some of them, as T goes up.
craigs: No, but let me bring in a mathematical analogy.
alpha137: OK
craigs: 1 + .5 + .25 + .125 + ... does not equal infinity
alpha137: It depends what the +... means.
craigs: It equals 2
alpha137: Oh, I missed the decimal point.
alpha137: But this is a series that is analogous to the less is less feedback.
alpha137: More and more would be 1 + 5 + 25 + 125 + ...
alpha137: Each stage represents greater signal.
craigs: Professor, I have to go.
alpha137: A way I can think of that would do what you
suggest 1 + 0.5 + ... is that as T increases the algea in the oceans increase
and as the algea grow they consume carbon
dioxide from the atmosphere. Thus reducing T from CO_2. But the model we are developing
uses the CO_2 as the trigger for a greenhouse effect caused by the increase in water
vapor due to this higher T.
alpha137: OK, I should go as well.
craigs: My mom has to use the computer.
alpha137: See you some time?
craigs: Sure, what time?
alpha137: I will be on tomarrow evening 6:30 pm EDT on.
alpha137: By the way, where are you time zone wise?
craigs: Illinois - Central
craigs: Near Chicago
alpha137: OK. Mothers that use computers are pretty modern!
Perhaps it is just that you have been using the phone for quite a while!
alpha137: See you. bye
craigs: Believe me, I use the term "use" very loosely
craigs: bye
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