Session Start: Mon Jul 20 08:59:37 1998

Session Start: Mon Jul 20 08:59:37 1998

comments in blue

corrections mostly in red.

*** Now talking in #brownchem

<alpha137> July 20,1998

<alpha137> Environmental Chem

*** LizK (gloworm4@204-156-198.ipt.aol.com) has joined

#brownchem

<alpha137> hello

<LizK> hello

<alpha137> How are things? Have a nice weekend?

<LizK> I'm sorry, I tried to get onto the Brown Site

several times, but, I couldn't

<LizK> YEs, my weekend was great

<alpha137> Right, my portion of the network is broken.

<alpha137> It should be back sometime today.

<LizK> And I'm still alive, I didn't get into a car crash

<alpha137> I am setting up an alternate web site as well.

<LizK> Ok, but at any rate, I couldn't really look at the

questions on the concept test

<alpha137> So, I take it that you got to drive a car over

the weekend?

<LizK> Yes, my big accomplishment was driving on the

Beltway, the equivialnt to 128 in Boston

<alpha137> Well, if you can drive there you can drive

anywhere!

<LizK> Maybe, but not well

<alpha137> On my sabbatical in Tokyo I bought a car and my

japanese friend told me that driving in Tokyo would be

very difficult.

<alpha137> I told him that if I could drive in Boston I

could drive in Tokyo.

<alpha137> It was true too.

<alpha137> We can discuss the concept test questions-especia

lly since they are conceptual!

<alpha137> For example, Question 2 states that there is a

temperature inversion in the stratosphere.

<LizK> I can imagine (about the driving in Tokyo and bOston)

<alpha137> The temp drops with altitude and then increases.

Why?

<alpha137> Above a city the mechanism is different.

<LizK> I wrote down my first guesses about the various

questions, Maybe something about the way the light hits

it?

<alpha137> What is "it"?

<LizK> The stratosphere and the molecules of gas in it?

<alpha137> Right, the molecules in the stratosphere.

<alpha137> The molecules absorb sunlight-since sunlight has

a whole spectrum of wavelengths.

Click here to see a representation of the solar spectrum at the surface of the earth.

Click here to see a representation of the solar spectrum above the atmosphere.

<LizK> OK

<alpha137> Is that all that can happen? And why will this

heat the stratosphere?

<alpha137> In the test there were three choices.

<LizK> Does it have something to do with the low pressure

and large volume of the area?

<alpha137> Not really.

Well, perhaps. Certainly the low pressure and the mean free path between molecular collisions is important in determining the rate, or speed, of chemical reactions in the atmosphere.

<LizK> ok, nevermind then

<alpha137> Molecules absorb light energy and then what?

<LizK> If the energy is large enough it will break apart

the bonds that make them molecules

<alpha137> Right, and then what might happen?

<LizK> they might bond with something else

<alpha137> React.

<LizK> Thats what I meant

<alpha137> When molecules react what can happen energy/heat

wise?

<LizK> It will be released

<LizK> So the sunlight breaks bonds and causes things to

react which releases heat

<LizK> But why is it only in the stratosphere?

<alpha137> And with collisions, even in the rare

stratosphere, that heat will cause the molecules to move

faster-have more K.E>

<LizK> I see

<LizK> But why does it only happen in the stratosphere?

<alpha137> Why in the stratosphere? Must have something to

do with the pressure (number of collisions) and the

amount of sunlight.

<LizK> ok,

<alpha137> The sunlight is absorbed by the molecules in the

atmosphere and as one gets closer to earth there is less

sunlight of low wavelengths.

<LizK> Ok

<alpha137> Therefore, less dissociation of molecules at

lower altitudes.

<LizK> That makes sense, but then why isn't the temperature

even higher in the mesosphere?

<alpha137> Just exactly where this would occur would depend on all these factors of pressure and radiation and type of molecules.

This has to be a big problem in understanding the physics and chemistry of the atmosphere.

<LizK> ok, I se

<LizK> e

<alpha137> According to the graph in Question 3 (that I

cribbed from some place) the temperature falls then

rises, then falls then rises again.

<LizK> I remember seeing that

<alpha137> So it does go up.

<alpha137> I think that "b" and "c" are OK answers for

Question 2.

<LizK> ok, but then what causes the fall

<LizK> Reallly, then I was right, those were the two I

would guess, I just could't decide between them

<alpha137> I am getting into shaky ground (air?) here, but

the earth is warm due to sunligt and I would expect T to

drop with altitute.

<LizK> ok

<alpha137> The real question is why does it increase?

<alpha137> And the answer has to do with chemistry. If

there were no chemistry in the atmosphere (including

absorption of light) the T would continue to drop.

<LizK> BUt isn't that what we just talked about? the

pressure and altitude make it possible for the light to

break up lots of molecules causing many reactions which

relase heat and also there would be more collisions too

<alpha137> Yes, yes. I meant if there were NO chemistry,

but of course there is.

<LizK> Oh, that makes sense

<alpha137> Now there is a question, discussed earlier,

about the meaning of temperature.

<LizK> YEs

<alpha137> Question 3 asks if you stuck you hand out the

space shuttle window and you were in the mesosphere would

it feel hot?

<LizK> I don't know, I guessed answer c

<alpha137> I think that c: No change in T is the practical

ans.

<LizK> So I was right again!

<alpha137> Temperature means kinetic energy. K.E. = k_B*T

<LizK> YEs

<alpha137> When one says the temperature is 950C that is

saying the speed of the molecules is so much.

<alpha137> But up there in the stratosphere, or mesosphere,

or wherever there are not so many molecules per unit

volume.

<LizK> YEs,

<LizK> So it wouldn't feel as hot

<alpha137> They may be moving like mad, but the heat capacity of the volume is low.

The transfer of heat to your hand would be very, very small. Think of it this way. A liter of air in the stratosphere would contain a very small number of molecules even though they are at a high temperature (moving very fast). You could imagine that liter at 1,000 K, but at a very low pressure and containing a very small number of moles of gas. Take that volume of molecules at 1,000K and cool it to 300K and in the process remove a certain amount of heat. It is not going to be much because there are so few moles. Now we can take that many joules of heat (10^-13 perhaps) and apply it to a hand. The hand is practically the same as water so we are heating about 500 g of water to some temperature using that heat. The temperature will rise something like 0.000,000,000,001 degrees, perhaps less.In other words, the hand will feel no temperature rise!

<LizK> ok

<alpha137> Yes, I do not think it would "feel" hot to a

person.

<alpha137> We need a better detector of molecular motion

than a human hand.

<LizK> ok

<alpha137> By the way, the web page should be back up after

lunch time here.

<LizK> ok, great

<alpha137> In the copy of the text that I have (an earlier

version) there is a side bar that says "..you can't get a

tan listening to the radio."

<LizK> YEs, I have that too

<alpha137> Is there anything wrong with this statement?

<LizK> I don't think so, but probably from the way you

<LizK> phrased the question

<alpha137> Well, a radio is a detector not a source of

light for starters.

<alpha137> You could never get a tan from something that absorbs light!

<LizK> OK, and so if you could get a tan from radio waves

you woldn't have to turn on the radio to get it

<alpha137> Right, right!

<LizK> ok

<alpha137> Even if you were in front of a radio transmitter

(source) you would not get a tan. Why?

<LizK> Because they are the wrong frequency, they are not

strong enough, (short enough wavelengths) to tan your

skin?

<LizK> I guess strong was not the right word

<alpha137> Right. The wavelength is wrong for absorbtion by

the molecule in your skin.

<LizK> i see

<alpha137> Strong would refer to the intensity of light

while we are interested in the frequency, or the

wavelength.

<LizK> yes

<alpha137> The wavelengths of light that are absorbed by ozone will be absorbed by the molecules in your skin!

<LizK> Oh, so thats why we need the ozone layer, to prevent

all those harmfull uVA and UVB rays form giving us all

skin cancer

<alpha137> Correct!

<LizK> I thought that it was the UV rays that caused a tan

<LizK> Are they the ones that are used by our skin to form

Vitamin D too?

<alpha137> Yes, UV rays cause a tan, but there is a range of wavelengths considered "UV."

<LizK> ok

<alpha137> Yes, we may find a certain amount of longer

wavelength UV to be useful.

<LizK> ok

<alpha137> Actually, too much sun at the beach (too much UV) is not good. Hence the use of sun blockers.

<LizK> yes

<LizK> unless you want a tan

<alpha137> Causes basal cell carcinoma which crop up in

older ages. Also, messes up the skin.

<LizK> Yes

<alpha137> Tan in moderation.

<LizK> My moms friend has that

<alpha137> There is a lesson in that radio side bar.

<LizK> WHat, that the book isn't always right?

<alpha137> It is, read critically. Even though the authors

may be "big shots" they can be wrong, or missleading.

<LizK> Yes

<alpha137> It seems that we have covered the basic elements

of the ozone in the stratosphere problem.

<LizK> ok

<LizK> now what? Global Warming?

<alpha137> Right.

<LizK> ok

<alpha137> I will post a little story about NO in the

stratosphere.

<LizK> Ok

<alpha137> It is not so good either as an attacker of ozone.

<LizK> BUt what about possible solutions of the ozone

problem

<alpha137> Well, what do you think are some?

<LizK> Are there any, other than to cut back on CFC's etc

and just wait for the molecules to decompose/

<alpha137> I think cutting back on CFC's is it. And since NO is also a problem we ought to worry about the number of aircraft in the stratosphere.

<LizK> Isn;t the Concorde the only one though?

<LizK> What about space s huttles?

<alpha137> Yes, and some military aircraft, but if we make

1,000's of Concordes we migt have a problem

<LizK> Yes, I see

<alpha137> Yes, space shuttles, but there are just one at a

time.

<LizK> THen its probably a good thing that the Concorde has been an economic failure

The Concorde has been a matter of French and British pride!

<alpha137> Yes, it is.

<alpha137> Occasonally, someone suggests that we do some

man made chemistry in the stratosphere. Think that is a

good idea?

<LizK> ok

<LizK> Nope

<alpha137> Think we could add some ozone?

<LizK> I don;t think we could add enough or ship enough up

there or put it into the right places, or even make sure

it stayed where we put it

<LizK> And it owuld be expensive

<alpha137> I agree with the "nope" for the simple reason that atmospheric chemistry is so complex that we would not know what we are doing.

<LizK> Thats true

<alpha137> Right, we could not put up enough to make a difference and it would be very costly as well.

<LizK> ok

<LizK> so the only thing to do is stop using bad Chemicals

<LizK> And make sure any new ones won;t pose a danger to

the envoronment

<LizK> But that is eaiseer said than done

<alpha137> Yes, that is the political connection to the

environmental question.

<LizK> ok

<alpha137> Now, what causes global warming?

<LizK> Isn't it exess CO_2 which acts like a temperature blanket (the whole greenhouse effect thing)

What is meant by "excess CO_2?"

<alpha137> Yes, we can blame CO_2, but what does it do?

<LizK> Doesn't it trap the heat inside the earth's

atmosphere and that gradually causes the temperature to

rise

<alpha137> Yes, how does it trap that "heat."

<LizK> It forms a layer that doesn;t let a free exchange of

heat from both the inside out, and the outside in,

<alpha137> What is heat?

<LizK> it doesn;t let the radiation form the earth's

surface out

<alpha137> Right.

<LizK> HEat is like work

<LizK> Temperature measurs it

<alpha137> Well, heat is work and work is heat is an

expression of the first law of thermo.

<LizK> ok

<LizK> So heat is work

<alpha137> But sunlight passes through the atmosphere and

the atmosphere contains CO_2.

<LizK> Is that all?

<LizK> But it all depends upon the concentration

<alpha137> So how is it that CO_2 traps light?

<LizK> Does it trap light?

<alpha137> Sure.

<LizK> I thought it trapped heat

<alpha137> Light, heat what is the difference?

<LizK> Woudln't that mean that the planet is glowing\

<LizK> ok

<alpha137> Well, the planet IS glowing!

<LizK> ok

<alpha137> We think of heat in two ways here.

<LizK> Does it have something to do with the shape of the

molecule and how the light reacts/ affects those

molecules?

<alpha137> Yes.

<alpha137> It has to do with the vibrations of molecules.

<LizK> \ok

<alpha137> The first law says that if no work is done the

heat added to the system IS the internal energy.

<alpha137> Or the heat "becomes" internal energy. This

internal energy we think of

<LizK> SO can it absorb electrons and that causes the

molcule to vibrate which causes more heat?

<alpha137> as the vibrations of the molecles.

<LizK> ok i see

<alpha137> No, we have to have wavelengths the order of hundreds of nanometers to excite electrons.

I mean that the major heating has to do with vibrations of the molecules, and collisions between these molecules. But I am being too restrictive. If we excite electrons to a higher configuration by visible, or uv light, then these molecules may do a couple of things. First, they may emit that radiation and go to the ground state, and second they may make a collision transfering the energy of excitation to the kinetic and other forms of energy. That is, producing heat.The non-radiative transfer of energy may go into "other forms" by which I mean: vibrational and rotational energy. These rotations and vibrations may become excited as well. Chemists speak of vibrational temperatures and rotational temperatures. The meaning of this is that at thermal equilibrium the rotational and vibrational energy states will have a certain number distribution among them. The lower states having the most and the higher states fewer molecules. This equilibrium distribution is called a Boltzmann distribution and it represents thermal equilibrium.Deviations from this distribution are said to be either "hot" or "cold." To speak of temperature in the precise thermodynamic sense we must have equilibrium and this equilibrium is brought about by collisions.What if we have a solid?

<LizK> ok, so maybe not, but then why do they vibrate>

<LizK> ?

<alpha137> The wavelengths we are considering here excite

the vibrations of the molecules.

<LizK> ok i see now

<alpha137> These wavelength are are greater than 1,000

nanometers.

<LizK> SO the wavelenghs can't exite electrons, but they cause the molecules to vibrate and that causes heat. ANd since there are lots of light rays coming at all times, lots of molcules will be vibrating

<alpha137> They are very weak compared to bond breaking

photons.

<alpha137> Right to your last statement.

<LizK> ok

<alpha137> It must be that sunlight comes to the surface of

the earth (after doing all that chemistry we discussed

earlier) and it absorbed.

<alpha137> It contains all wavelengths that can get through

the atmosphere.

<LizK> ok

<alpha137> These light waves heat the earth. Are absorbed by everything, or are reflected back.

<LizK> ok, that makes sense

<alpha137> The earth glows with heat radiation-greater than

1,000 nm.

<LizK> oh, i see

<alpha137> It heads back into outer space. What stops it if

anything?

<LizK> Isn't it the CO_2 absorbtion/vibration which stops

these molecules and traps them in the earth's atmosphere

<LizK> I meant the CO_2 stpos the radiation

<alpha137> Yes, but why do you just pick on poor ole

CO_2-what to give it a complex or something?

<LizK> ok, but I thought that CO_2 was the major cause of

this trapping of radiatipm

<LizK> radiation

<alpha137> Is it?

<LizK> Perhaps not, but thats what I've always heard

<alpha137> What else might there be?

<alpha137> For tomarrow make a list of so called

"greenhouse" gases.

<LizK> Other cemicals like Methane?

<alpha137> Methane sounds good. What else?

<alpha137> See if you can get an estimate of the

concentration of the "greenhouse" gases in your list.

<LizK> oh, I found a whole list, ther is N2O and H_2O and

ozone, and the CFC's too

<alpha137> In the atmosphere that is.

<LizK> CO_2 is the most concentrated, and so thats why it

gets all the bad press

<alpha137> I want to have a list of the concentrations and

discuss why CO_2 seems to be a focus.

<LizK> Especaially since some of the chemiscals are doing

other bad stuff

<alpha137> Also, there is a section in that chapter about

the vibrations of molecules.

<LizK> ok, there is a list in this chare

<LizK> chart,

<LizK> yes, I didn't quite finish reading this chapter

<LizK> BUt I'll finish it for tommorow

<alpha137> There is also a section on the Carbon Cycle. We

need to know something about that as well.

<LizK> I'll read that too

<alpha137> And if we are to really understand this

greenhouse thing we need to know how fast things occur.

<LizK> Yers

<LizK> Yes

<alpha137> That is, at what rate does carbon dioxide

dissolve in the ocean and become limestone?

<LizK> ok

<alpha137> Questions like that.

<LizK> I see how those would all be important considerations

<alpha137> Some of these are questions for geologists and

some for chemists and some for physicists and some for

biologists.

<alpha137> Cross disciplinary right?

<LizK> of course, nothing is really disconnected from

anything else

<alpha137> Make that list. Read that material. Lets discuss

why we pick on carbon dioxide and IF we really think

global warming is true. OK?

<LizK> Ok I will

<alpha137> See you 9:30 am Tues. Now, I am going to work on

my computer.

<alpha137> bye

<LizK> Wait!

<alpha137> OK

<LizK> I have to tell you that I am going to leave on

thursday night to go on vacation for two weeeks

<LizK> But I'll be here until them

<LizK> n

<alpha137> OK, Tue and Wed are in?

<LizK> See you tommorow at 9:30

<LizK> And thursday too

<alpha137> bye

<LizK> Bye, and thank you

*** LizK has quit IRC (Leaving)

Session Close: Mon Jul 20 10:50:52 1998