Wednesday Jan. 10, 2007

The first day of class.  We first briefly discussed the Course Information handout.  Note the various options you have for purchasing a copy of the course textbook.  You should try to purchase a copy of the photocopied Classnotes (in the bookstore) right away as we will probably be using some of them in class on Friday.

Next we looked at the Writing Requirements handout.  You should be thinking about which of the experiments (or book or scientific paper reports) you would like to do so that you can sign up in class on Friday.  Distribution of the materials for the first experiment could begin as early as Wednesday next week (Jan. 17).

Your grade in this class will depend on your quiz scores, how much extra credit you earn, your writing grade, and (perhaps) your score on the final exam.  A sample grade report from the Fall 2006 NATS 101 class was shown.

Don't worry about what all of this means at this point, it will become clearer as the semester progresses.  Do note, however that, even with C grades on all the quizzes and the final exam, this student ended up with a B in the course.  This is because the student earned quite a bit of extra credit and had a high writing grade.
We will start this course in Chapter 1 of the textbook.  Before reading the first few pages in Chapter 1 (see the Reading Assignments link on the class home page) you should try to guess what you might find covered there.  The following question might suggest some things.


Here are responses from students in class.


The first three characteristics are discussed in Chapter 1.

What is the most abundant gas in the atmosphere?  Some of that material, in liquid form, was poured from a thermos into a styrofoam cup.

The liquid (and the most abundant gas in the atmosphere) was nitrogen (you can fill in the blank above with the word nitrogen).  You can see liquid nitrogen.  Once it has evaporated and turned into a gas it is invisible. 

Oxygen is the second most abundant gas in the atmosphere.  Liquid oxygen is supposed to be blue, not clear like liquid nitrogen.  Click here to see a photograph of some liquid oxygen.

Here is a list of the 5 most abundant gases in the earth's atmosphere:


Water vapor and argon occupy 3rd and 4th place, but they sometimes switch places.  The variable concentration of water vapor means it is sometimes more abundant & sometimes less abundant than argon.

Water plays an important role in the formation of clouds, storms, and weather.  Meteorologists are very interested in knowing how much water vapor is in the air at a particular place and time.  The dew point temperature provides a measure of the amount of water vapor in the air.

The figure below gives a rough equivalence between dew point temperature and percentage concentration.


  Think of the dew point as being just a number.  When the value is low the air doesn't contain much moisture.  The higher the dew point value, the more water vapor in the air.

The air has been pretty dry in Tucson for the last several days with dew point temperatures in the teens.  You might expect to see an increase in the dew point in the next few days as wetter unsettled weather moves in.

Click here to see current dew point temperatures across the U.S.

You can see liquid water, just as was true with the liquid nitrogen.  Once water evaporates and forms water vapor it is invisible.  When you see steam, fog, or a cloud you are seeing small drops of liquid water or small ice crystals not water vapor.
The dew point temperature tells you how much you must cool moist air in order for a cloud to form.
Here are some other gases found in the earth's atmosphere that we will cover (this list was not covered in class).  Most are found in very low concentrations but that doesn't mean they are not important.


Water vapor, carbon dioxide, methane, nitrous oxide (N2O = laughing gas), chlorofluorocarbons, and ozone are greenhouse gases.  We will cover the greenhouse effect in more detail when we get to Chapter 2.  The "natural" greenhouse effect has a beneficial role on the earth.  Without the greenhouse effect average surface temperatures on the earth would be much colder than they are now (0o F rather than about 60o F ).  Atmospheric concentrations of many greenhouse gases are increasing however.  This could enhance or strengthen the greenhouse effect and cause global warming which could have many detrimental effects.

Carbon monoxide, nitric oxide, nitrogen dioxide, ozone, and sulfur dioxide are some of the main air pollutants.

Ozone in the stratosphere absorbs dangerous high energy ultraviolet (UV) light coming from the sun.  Without the protection of the ozone layer life as we know it would not exist on the surface of the earth.  Chlorofluorocarbons are of concern in the atmosphere because they destroy stratospheric ozone.
The following material wasn't covered in class either. 
Our present atmosphere is very different from the earth's original atmosphere. 

The earth's first atmosphere was composed mainly of hydrogen and helium.  These light-weight gases escaped into space and were lost.  The next atmosphere was built up of gases emitted during volcanic eruptions, mostly water vapor, carbon dioxide, and nitrogen.  As the earth began to cool the water vapor condensed and began to create oceans.  Carbon dioxide dissolved in the oceans and was slowly turned into rock.  Much of the nitrogen remained in the atmosphere.

Note the volcanoes didn't add oxygen to the atmosphere.


The oxygen is thought to have first come from photodissociation of water vapor and carbon dioxide by ultraviolet light (the high energy radiation splits the H20 and CO2 into pieces).  The O and OH react to form O2 and H.

Once O2 begins to accumulate in the air it can react with O to form ozone, O3. The ozone then begins to absorb ultraviolet light, life forms can move from the oceans (which would absorb UV light in the absence of ozone) onto land.  Eventually plants and photosynthesis would become the main source of atmospheric oxygen.