Tuesday Aug. 25, 2014
ILC 130 would be a pretty dreary place at 7:40 in the morning were
it not for a little music. Today's selections were
"The Boy in
the Bubble", "Gumboots"
sorry it wasn't louder but I had all the volume controls at
maximum, and "I Know What I
Know". Everything came from Paul Simon's concert in
Zimbabwe in 1987 that followed the release of his Graceland album
in 1986. "Township Jive"
introduces the concert. Time before the 9:30 class for
"Diamonds
on the Soles of Her Shoes" (with Ladysmith
Black Mambazo).
Course Introduction
ATMO 170 is off and running for another semester. We
first briefly discussed the Course
Information handout. Please read through that information
carefully on your own and let me know if you have any
questions.
A textbook is not required for this class. If you want a
different and more complete picture of the subject, you might want
to purchase one of the textbooks that are being used in the other
ATMO 170A1 sections (though the one I saw in the bookstore was
over $200!). Or if you'd like to borrow one of the copies of introductory level textbooks
that I have in my office, just let me know. Otherwise you
should be able to do perfectly well in the class by reading the
online notes. It is important to read through the online
notes even if you are in class.
A set of photocopied ClassNotes (available in the ASUA
Bookstore in the Student Union) is required. You should try
to purchase a copy as soon as you can because we will probably be
using the first page in class on Thursday. If you know
someone with notes from the Fall 2014 or Spring 2015 semesters
they will work fine.
Writing is an important part of
this class and is described in more detail on the Writing Requirements handout. Please have a careful look
at that also and
let me know if you have any questions.
The first half of your writing grade is an experiment
report. You only need to do one of the experiments, so think
about which of the experiments (listed on the handout) you might
like to do. I'll bring a signup sheet to class on
Thursday. I'm planning on bringing Experiment #1 materials
to class next Tuesday for checkout. Checkout is first come
first served.
The so-called One Side of One Page (1S1P) reports make up the
second part of your writing grade. Topics will appear
periodically during the semester on the class webpage. As
you write reports you will earn points (the exact number of points
will depend on the topic and the quality of your report).
Your goal should be to earn 45 1S1P pts, the maximum number
allowed, by the end of the semester.
You'll be allowed to revise and raise your grade on the first
draft of your experiment report. So you should be able to
earn a pretty high score on that. And, unless you
procrastinate, you can just keep on writing 1S1P reports until
you've earned 45 points. There's no reason not to earn a
high writing grade.
Grade example
Your final grade in this class will depend on your quiz scores,
how much extra credit you earn (from optional take home and in
class assignments), your writing grade, and (perhaps) your score
on the final exam. A sample grade report from the Spring
2015 class is shown below (most of the numbers are class
averages).
overall averages (prior to the Final
Exam)
average (no quiz scores dropped): 77.1% + 2.3 =
79.4%
average (lowest quiz score dropped): 79.4% + 2.3 = 81.7%
you DO need to take the final exam
Final exam score: 78.2%
Overall grade:
81.0% (B)
The 4 quiz grades are shown at the top (note how they improved as
the semester went along).
The next entry shows that the average student earned 2.3
points of extra credit points. You will have the opportunity
to earn at least 3 extra credit points.
A score of 34 points on the experiment report and 45 1S1P points
resulted in a writing percentage grade of 98.8%. There's no
good reason not to end up with a writing score close to 100% (or
even greater than 100%)
The overall average without any quiz scores dropped is shown
next. Since the result, 79.4%, is less than 90.0% the
average student last fall did have to take the final exam
The second average (with the lowest score dropped) is a little
higher, 81.7%.
If you do well on the final exam it will count 40% of
your overall grade (trying to maximize the benefit it can
have). If you don't do so well on the final it only counts
20% (minimizing the damage it can cause). In this example
the final exam score (78.2%) was lower than the 81.7% value, so
the final exam only counted 20% and the overall score was
81.0%.
So even though this average student had D+ and C grades on the
quizzes and a C+ on the Final Exam, the student ended up with a B
in the class. That is due largely to the high writing grade
and the fact that the student did have some extra credit points.
Comments about the class
Next a couple of comments about the class from Spring 2014:
comment #1
The important thing is to keep up with material as it's
covered in class. You don't necessarily need to come to
class to do this. You should definitely be reading the
online lecture notes on a regular basis.
comment #2
Don't let concerns like this wait until the end of the
semester. Let me or one of the TAs know of your concerns
so that they can be addressed during the semester. "Chapter 1" - the earth's atmosphere
We did cover a little course material in
class today just so you can get an idea of how that will work.
If we were using a book we'd
start in Chapter 1 and here's some of what we would first be
looking at in this course.None of this material was mentioned or
covered in class.This is an example
of extra information that I stick in the online notes even
though we didn't cover it in class. Skim
through this, no need to worry about all the details at this
point.
We will come back to the first item - the composition of the
atmosphere. Before we do that however, here
are a few questions to get you thinking about the air around
you. Can
you see air?
Air
is
mostly clear, transparent, and invisible (that would be true
of the air in the classroom). Sometimes the air looks
foggy, hazy, or smoggy. In these cases you are "seeing"
small water droplets or ice crystals (fog) or small particles
of dust or smoke (haze and smog). The particles
themselves may be too small to be seen with the naked eye but
are visible because they scatter (redirect) light.
I didn't really mention or explain what that is but it's a pretty
important concept and we will learn more about it soon.
And to be completely honest air isn't really invisible.
If you shine a bright light through enough air, such as when
sunlight shines through the atmosphere, the air (the sky)
appears blue. This is a little more complicated form of
scattering of sunlight by air molecules. We'll come back
to this later as well.
Can you
smell air?
I don't think you can smell or
taste air (air containing nitrogen, oxygen, water vapor, argon
and carbon dioxide). But there are also lots of other odors
you can sometimes smell (freshly cut grass, hamburgers on a
grill, etc). I don't consider these normal constituents of
the atmosphere.
You can probably also smell certain pollutants. I suspect
our sense of smell is sensitive enough for us to detect certain
air pollutants even when their concentration is very small
(probably a good thing because many of them are
poisonous).
Natural gas (methane) used in
hot water heaters, some stoves, and furnaces is odorless.
A chemical (mercaptan) is added to natural gas so that you can
smell it and know when there is a leak before it builds up to a
concentration that could cause an explosion.
Can you feel air
It is harder to answer this question.
We're always in contact with air. Maybe we've grown so
accustomed to it we aren't aware of how it feels. We can
certainly feel whether the air is hot or cold, but that have
more to do with energy exchange between us and our
surroundings. And we can feel wind.
In a couple of weeks we will see that, here in the classroom,
air pressure is pressing on every square inch of our bodies with
12 or 13 pounds of force. If that were to change suddenly
I'm pretty sure we'd feel it and it would probably really hurt. Now back to material we did cover in
class.
What are the 5 most abundant
gases in air?
Let's start with the most abundant gas in the atmosphere.
I poured some of this same material (in liquid form) into a
Styrofoam cup. Here's a photo I took back in my office.
You can see the liquid, it's
clear, it looks like water. I had the impression
that a lot of students knew this was liquid
nitrogen. It's very cold and begins to boil
(evaporate) at -321o
F.
The most abundant gas in the atmosphere is nitrogen.
We'll use liquid nitrogen in several class demonstration this
semester mostly because it is so cold.
Nitrogen was discovered in 1772 by Daniel Rutherford (a
Scottish botanist). Atmospheric nitrogen is relatively
unreactive and is sometimes used to replace air in packaged
foods to preserve freshness. You don't need to worry
about details like this for a quiz.
Oxygen is the second most abundant gas in the
atmosphere. Oxygen is the most abundant element (by
mass) in the earth's crust, in ocean water, and in the human
body. In liquid form it also becomes visible.
A nice picture of liquid oxygen's pale blue
color from
this source.
A couple of photographs of liquid
oxygen are shown above (it
boils at -297o F).
It has a (very faint) pale blue color (I
was pretty disappointed because I had imagined it might be
a deep vivid blue). When
heated (such as in an automobile engine) the oxygen
and nitrogen in air react to form compounds such as
nitric oxide (NO), nitrogen dioxide (NO2),
and nitrous oxide (N2O). Together as
a group these are called oxides of nitrogen; the first
two are air pollutants, the last is a greenhouse
gas. I'd
love to bring some liquid oxygen to class but
I'm not sure it's available on campus.
I recently learned that liquid ozone (O3)
does have a nice deep blue color.
It's probably very hard to find and is
also very (dangerously) reactive.
Here is a complete
list of the 5 most abundant gases in air. And a note about the figures you'll find in these
online notes. They may differ somewhat from
what was done in class. I often redraw them after class, or
use neater versions from a previous semester for improved clarity
(and so I can get the notes online more quickly).
With a little practice you should be able to start with a blank
sheet of paper and reproduce the list below.
Water vapor and argon are the 3rd and 4th most abundant gases
in the atmosphere. A 2% water vapor concentration is listed
above but it can vary from near 0% to as high as 3% or 4%.
Water vapor is, in many locations, the 3rd most abundant gas in
air. In Tucson most of the year, the air is dry enough that
argon is in 3rd position and water vapor is 4th.
Water vapor and carbon dioxide are circled because they are two of
the most important greenhouse gases.
Water vapor, a gas, is invisible. Water is the only
compound that exists naturally in solid, liquid, and gaseous
phases in the atmosphere.
Argon is an unreactive noble gas (helium, neon, krypton, xenon, and radon are also inert gases).
Here's a
picture of solid argon ("argon ice"). It melts
at melts
at -309o F and
boils at -302o F;
it's doing both in this picture. (image source).
Here's a little more
explanation (from Wikipedia)
of why noble gases are so unreactive. Don't worry about
all these additional details, none
of this was covered in class. The noble
gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are
normally the only electrons that participate in chemical bonding. Atoms
with full valence electron shells are extremely stable and
therefore do not tend to form chemical bonds and have little
tendency to gain or lose electrons (take electrons from or
give electrons to atoms of different materials).
Noble gases are often used used in neon signs; argon produces
a blue color. The colors produced by Argon (Ar), Helium
(He), Kryton (Kr), Neon (Ne) and Xenon (Xe), which are also
noble gases, are shown above (source of the
images). The inert gases don't react with
the metal electrodes in the bulbs. Neon bulbs and
fluorescent bulbs (including energy saving CFLs) often also
contain mercury vapor (which means you should dispose of them
carefully when they burn out). The mercury vapor emits
ultraviolet light that strikes phosphors of different kinds on
the inside of the bulb. Different colors are emitted
depending on the particular type of phosphor used in the bulb.
This is solid carbon dioxide, better known as
dry ice. It doesn't melt, it sublimates, i.e. it changes
directly from solid to gas. (source).
The concentration of carbon dioxide is much smaller than the
other gases (you don't need to remember the actual value).
That doesn't mean it isn't important. We'll spend a lot of
time this semester talking about water vapor and also carbon
dioxide. Water vapor and carbon dioxide are the two best
known and most important greenhouse gases. The greenhouse
effect warms the earth. Concentrations of greenhouse gases
such as carbon dioxide are increasing and there is concern this
will strengthen the greenhouse effect and cause global
warming. That's a topic we'll look at during the semester.
If we were using a textbook we'd probably find something like
the following table near the beginning of the book ( I found this
table a few years ago in a Wikipedia
article about the earth's atmosphere ).
~0.40% over full atmosphere, typically 1%-4% at surface
I like our list of the 5 most abundant gases better. It's
much more manageable. There is almost too much information
in a chart like this, you might be overwhelmed and not remember
much. Also unless you are familiar with the units on the
numbers they might be confusing. And notice you don't find
water vapor in 3rd or 4th position near the top of the
chart. That's because this is a list of the gases in dry
air. Unless you're very attentive, you might miss that fact
and might not see water vapor way down at the bottom of the chart.
If you click on the link above to the Wikipedia article on the
earth's atmosphere you'll find that the list above has been
replaced with a shorter simpler list (much more like the one we
created in class).
Dew point temperature and the
summer monsoon
Water plays an important role in the formation of
clouds, storms, and weather. Meteorologists are very
interested in knowing and keeping track of how much water vapor is
in the air at a particular place and time. One of the
variables they use is the dew point temperature. The value
of the dew point gives you an idea of how much water vapor is
actually in the air. A high dew point value means more water
vapor in the air and higher the water vapor concentration.
The chart below gives a rough equivalence between dew point
temperature and percentage concentration of water vapor in the
air.
For every 20 F increase in dew point
temperature, the amount of water vapor in the air
doubles.
Air temperature will always be equal to or warmer than the
dew point temperature. Experiencing 80o F dew points would be
very unpleasant and possibly life threatening because your
body might not be able to cool itself ( the air
temperature would probably be in the 90s or maybe even
warmer). You could get
heatstroke and die.
Click here
to see current dew point temperatures across the U.S. Here's
a
link concerning unusually high, even record setting dew
point temperatures.
At one time the dew point temperature was used to
identify the official start of the summer monsoon season in Tucson
(the summer thunderstorm season).
monsoon = a seasonal change in the
direction of the prevailing winds.
For most of the winds come from the west
and are relatively dry. For 2 or 3 months every summer
the winds start to come from the east and southeast and are
moister. Thunderstorms are able to form in this moister
air.
Dates on the x-axis, average daily dew
point values on the y-axis blue = this
summer's data, red =
average values, green = 54o
F
Dates (running from June 1 through to the
end of September) are plotted along the x-axis and dew point
temperature is shown on the y-axis. Average observed
daily dew point values for this year are in blue. The red line shows average daily
dew point values for this time of the year.
Traditionally the summer monsoon would start when the
daily average dew point remained at or above 54 F (the green line above) for 3 days in
a row. That occurred on June 25 this year. That's
a little earlier than normal. Note how the red line
crosses and stays above 54 F around July 11. The red
line stays above 54 F for all of August then around Sept. 10
it drops below 54 F. The summer monsoon season normally
extends from July 10 through about Sept. 10.
Beginning in 2008 a monsoon of fixed June 15 through Sept.
30 duration began being used regardless of what the dew point
values were doing.
Dew point temperature continued
Now let's go back to the cup of liquid
nitrogen
Two things are going on here.
First, the liquid nitrogen (visible) is evaporating -
turning into invisible nitrogen gas.
Second invisible water vapor (gas)
comes into contact with the cold cup of liquid
nitrogen. The moist air cools enough that water
vapor begins to condense and form a forming a cloud
consisting of very small drops of liquid water and small
crystals of ice. The cloud is visible.
We're seeing a demonstration of the dew
point's second "job."
If you cool air next to the ground to its dew point, water
vapor will condense and coat the ground (or your car) with
water. The ground will be covered with dew. If a
little thicker layer of air is cooled fog will form. A soda
bottle in the refrigerator cools to about 40 F. In the
summer in Tucson the dew point will be in the 50s or 60s.
The soda bottle is cold enough that when removed from the
refrigerator it can cool the air to and below its dew point and
water vapor will condense onto the side of the bottle as shown
below.
Except for the summer, the air is usually too dry in Tucson
for this to happen. Dew points might only be in the 20s. The
40 F soda bottle isn't able to get the air cold enough and dew
doesn't form on the bottle. (source of
the photo above)
Pluto's Gate to Hell
We were nearing the top of the hour at this point which is
probably enough for the first day of class. The material below was only mentioned briefly
in class.
Pluto's Gate to Hell was discovered in
early 2013 at the ancient city of
Hierapolis in southwestern Turkey
(Pluto was the Roman god of the
underworld, he was called Hades by the
Greeks)
The
picture above at left shows the site
as it appears now (source
of this photograph).
The gate is the opening in the
wall near the center of the
picture. The site as it
might have appear in ancient
times is shown above at
right. This photograph,
credited to Francesco D'Andria,
the lead Italian archaeologist
that announced the discovery in
March 2013, is found in a news
report from the National
Geographic Society.
The
"gate" was built on top of a
cavern and, in ancient times, a
mist of deadly vapors could be
seen coming from the cave (the
mist is shown in the right
picture above). Here's a
quote from the Slate
article where I first read
about the discovery:
"Two
millennia ago, visitors to Pluto's
Gate could buy small birds or
other animals (the sale of which
supported the temple) and test out
the toxic air that blew out of the
mysterious cavern. Only the
priests, high and hallucinating on
the fumes, could stand on the
steps by the opening to
hell. They would sometimes
lead sacrificial bulls inside,
later pulling out their dead
bodies in front of an awed crowd.
As
the Greek geographer, philosopher,
and prolific traveler Strabo, who
lived from 64/63 B.C. to 24 A.D.,
so enticingly described it: 'This
space is full of a vapor so misty
and dense that one can scarcely
see the ground. Any animal
that passes inside meets instant
death. I threw in sparrows
and they immediately breathed
their last and fell.' "
The Italian archaeologists working at the
site would occasionally notice birds dying if they flew into the
vapors coming from the came. The deadly gas was carbon
dioxide. Carbon dioxide is not ordinarily thought of as a
poisonous gas but in high enough concentrations it can
asphyxiate you (cause you to suffocate).
