Tuesday Aug. 22, 2017

Music while waiting for class to start featured a local group, Orkesta Mendoza, playing at the Yuca Cafe in Cologne Germany in Dec. 2015.  You heard "La Cucharita" (6:43) and "Las Calles de Tucson" (6:52).

Today's lecture notes are shown below.


Information about this class and course requirements
Class began with a quick look at the Course Information handout.  Please read through that information carefully on your own and let me know if you have any questions or concerns.

A textbook is not required for this class.  It seems unreasonable for me to expect you to purchase a text knowing that we will only cover a small portion of the material in it.  You are certainly free to purchase one of the textbooks that are being used in the other ATMO 170A1 sections.  I have 20 - 25 instructor copies of introductory level textbooks in my office.  If you'd like to borrow one of those just let me know.  Otherwise you should be able to do perfectly well in the class by reading the online lecture notes.  You should read 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 may well be using them in class on Thursday. 

Important note: I revised the ClassNotes this summer.  Unfortunately some of the copies that were initially available in the Bookstore were of an earlier version.  I think they have now all been removed and replaced with the newer revised version.  If you ended up with the earlier version of the ClassNotes you can get a set of "replacement pages" at the Fast Copy office in the Student Union (not at the Bookstore).  By inserting these replacement pages into your set of ClassNotes you'll end up with a perfectly good version of the revised notes.  I will have sets of the replacement pages in class as well. 

-------

Writing is an important part of this class.  The details are described 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 also hoping to bring about 40 sets of Experiment #1 materials to class on Thursday for checkout.  Because I'm teaching two sections back to back I need to bring materials for both classes.  That's a lot of boxes and there's a limit to what I can fit on my cart.  Checkout is first come first served.  Materials for the other two experiments will be handed out at roughly 3-week intervals.


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.  The writing grade gets averaged in with your quiz scores and, as the example below shows, can have a significant and beneficial effect on your overall 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 Fall 2016 8 am section of this class is shown below (most of the numbers are class averages).


Doe_J
quiz1 -47 (175 pts possible) 73.1%   quiz scores
quiz2 -48 (180 pts possible) 73.3%
quiz3 -45 (155 pts possible) 71.0%
quiz4 -41 (180 pts possible) 77.2%

2.0 EC points (3.3 pts possible)      extra credit earned on optional assignments

writing scores
writing scores: 32.0 (expt/book report) + 45.0 (1S1P pts)
writing grade: 96.3%

overall averages (prior to the Final Exam)
average (no quiz scores dropped): 78.2% + 2.0 = 80.2%    
average (lowest quiz score dropped): 80.0% + 2.0 = 82.0%

Final exam score: 76.2%    


Overall grade: 80.8% (B)

The 4 quiz grades are shown at the top.

S
tudents that did turn in the Optional Assignments earned on average 2.0 pts of extra credit during the semester.  You will have the opportunity to earn at least 3 extra credit points this semester. 

A score of 32 points (out of 40) on the experiment report and 45 1S1P points resulted in a writing percentage grade of 96.3%.  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, 80.2%, 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, 82.0%.

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 (76.2%) was lower than the 82.0% value, so the final exam only counted 20% and the overall score was 80.8%. 

Be sure to note that even with C grades on each of the quizzes and a C on the Final Exam you could well end up with a B in the class.  That is possible when you have a high writing grade and also have some extra credit points.



"Chapter 1" - the earth's atmosphere
I do try to cover a little course material on this first day of class so that you can get an idea of how that will work.  Also I won't feel so bad about not covering new material on the last day of class in December.

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. 

We will come back to the first item, the composition of the atmosphere, today.  Understanding the causes of air pressure and how/why it changes with altitude is important.  Pressure is a force and can cause the wind to blow and create storms.  It is also probably the most difficult concept in this list to understand.


Short detour (not covered in class)
Here are a few questions to get you thinking about the air around you.

Can we see air?



Air is mostly clear, transparent, and invisible.  Most gases are invisible.  Sometimes the air looks foggy, hazy, or smoggy.  In those cases you are probably "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 t
here are also lots of other odors you can sometimes smell (freshly cut grass, cooked food, etc).  I don't consider these normal constituents of the atmosphere. 

Air often has a distinctive smell after a rain shower.  This comes sometimes from materials in the soil that somehow or another become airborne.  Here in southern Arizona the smell is usually attributed to the Creosote Bush

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.


2 objectives for today:

1. You should be able to list the 5 most abundant gases in air and say something (maybe more than one thing) about each of them

2. You should be able to define or explain dew point temperature and you should know the meaning of the term monsoon.

Let's start with the most abundant gas in the atmosphere.  I poured some of that 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.  Probably a lot of you knew this was nitrogen.  Liquid nitrogen is very cold and begins to boil (evaporate) at a temperature of -321o F.

The most abundant gas in the earth's 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, the main point is that it is the most abundant gas in air.

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.









from: http://www.webelements.com/oxygen/
The web elements site credits Prof. James Marshall's Walking Tour of the Elements.
from: http://en.wikipedia.org/wiki/Oxygen
Wikipedia credits Dr. Warwick Hillier of Australia National University
A nice picture of liquid oxygen's pale blue color from this source.


Some photographs of liquid oxygen (O2) are shown above (it boils at -297o F).  It has a (very faint) pale blue color (I was pretty disappointed when I first saw it because I had heard it was blue and imagined it was a deeper more vivid blue).    I'd love to bring some liquid oxygen to class but I'm not sure it's available on campus and you probably need to be careful with it because it is reactive.

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 recently learned that liquid ozone (
O3) does have a nice deep blue color. 


Liquid ozone (source of this photograph).

It's probably even harder to find and probably more reactive and dangerous than liquid oxygen.  Ozone gas is also poisonous.

Note that, even though they are both made up of oxygen atoms (O), there is a world of difference between the chemical properties of
O2 and O3.

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 those drawn 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 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.  You can gloss over all these additional details if you want to, 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).   An electric current is traveling through and heating the gas in the tube causing it to emit light.  You're seeing the light emitted by the gas itself.  The inert gases don't react with the metal electrodes in the bulbs. 





This is solid carbon dioxide, better known as dry ice.  It doesn't melt, it sublimes.  Sublimation is a solid to gas phase change, evaporation is a liquid to gas change.  (source of the image above).

The concentration of carbon dioxide in air is much smaller than the other gases (it's about 0.04% but 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 ).

Composition of dry atmosphere, by volume
ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume (thermodynamics))
Gas Volume
Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 394.45 ppmv (0.039445%)
Neon (Ne) 18.18 ppmv (0.001818%)
Helium (He) 5.24 ppmv (0.000524%)
Methane (CH4) 1.79 ppmv (0.000179%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)
Xenon (Xe) 0.09 ppmv (9×10−6%) (0.000009%)
Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)
Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)
Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)
Ammonia (NH3) trace
Not included in list above (dry atmosphere):
Water vapor (H2O) ~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 which is included 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 many important roles in the atmosphere.  One of them is the formation of clouds, storms, and precipitation.  Meteorologists are very interested in knowing and keeping track of how much water vapor is in the air.  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 a high water vapor concentration.





The chart below gives a rough equivalence between dew point temperature and percentage concentration of water vapor in the air.



Note that for every 20 F increase in dew point temperature, the amount of water vapor in the air roughly 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. 



Tucson's summer monsoon

Tucson usually gets between 11 and 12 inches of rain per year.  About half of that comes during the summer monsoon, i.e. the summer thunderstorm season.  Many people mistakenly think the term monsoon is just another word for thunderstorm. 


For most of the year in SE Arizona winds come from the west and are relatively dry.  For 2 or 3 months every summer the winds switch direction and start to blow from the east, southeast, and south.  This air is generally much moister.  The combination of moist air and summertime heating make it much easier for thunderstorms to form. 



Tucson residents generally look forward to the start of the summer thunderstorm season because the rain brings some relief from the hot dry weather of May and June.  Recall that the dew point temperature gives you an idea of how much water vapor is in the air. 
The switch in wind direction and the arrival of moister air is often indicated by a fairly abrupt increase in the daily average dew point temperature.

The figures below are from the Tucson National Weather Service Office and show a plot of average daily dew point temperatures (red curve) for June - September.




 

"Traditional" start of the summer monsoon season.
This figure above shows average dew point values (probably a 30 year average).
 
Traditionally the summer monsoon would start when the daily average dew point remained at or above 54 F green line for 3 days in a row.  Using the chart above we can see that occurs on July 9 on average.  The average dew point temperature drops below 54 F around Sept. 11. 
Using this traditional definition, the summer monsoon season normally extends from July 9 through September 11.

In any given year the measured daily dew point values can depart appreciably from average.  The figures below show monthly variations of the measured daily dew point values from this summer, 2017.  Measured values are in blue.  The red line again shows average daily dew point values and the green line is 54 F.
 



Measured and average dew points in Tucson for June and July 2017

The average dew point value reached and stayed above 54 F on July 9 in 2017.  Measured dew points for August and September (to be filled in later in the semester).




Measured and average dew points in Tucson for August and September 2017.





This last figure shows all of summer 2017.  As you can see there are brief periods once the summer monsoon is underway when Td dips below 54 F.  I am not sure what defines the end of the monsoon.  It's usually pretty obvious; something will cause a sharp and dramatic drop in Td.

Newer and now official definition of the start and end of the summer monsoon season.  To avoid the uncertainties in the beginning and end of the summer monsoon period, the National Weather Service has, since 2008, just assumed a summer monsoon season of fixed duration, June 15 through Sept. 30, regardless of what the actual dew point values were
.
 


If you're in Tucson during the summer, you might travel downtown on June 24 for the El Dia De San Juan celebration.  "El Día de San Juan Fiesta saw its origins in 1540. Francisco Vásquez de Coronado, a Spanish conquistador, traversed through Southern Arizona when he, and his colony, encountered a destructive drought. Their fields dried up and their animals began to die. Legend says that, during this time of desperation, he turned to his Catholic beliefs, and prayed to St. John the Baptist near the Santa Cruz River. Shortly after, it began to rain." (source of the quote)