Friday Jan. 18, 2013
click here to download today's notes in a more printer friendly format

"Up to the Mountain" a song written by Patty Griffin in honor of Martin Luther King before class this afternoon.  I had a shorter version ready just in case we were short on time.  It has some nice documentary photography.  And if there had been more time I would have played "Heavenly Day".

You probably weren't aware of it (I wasn't either) but January is National Radon Action Month.  With that in mind I've made radon the 1st 1S1P report topic of the semester.  Your goal should be to earn 45 1S1P points by the end of the semester.  How you go about that is up to you.  You might write a bunch of reports early in the semester and get this requirement out of the way. You can spread the work out throughout the semester or you might procrastinate and try to do everything at the end of the semester (that's a little risky). 

I am planning to add a couple more report topics to 1S1P Assignment #1.  Then you will be allowed to write up to two reports as part of this assignment.  There will be at least two more assignments during the semester (also most likely with a 2 report per assignment limit).   I would recommend that you do at least one report as part of Assignment #1.

The radon reports are due on Mon., Jan. 28.

The first Optional Assignment of the semester was handed out in class today.  The assignment is due at the beginning of class next Friday, Jan. 25.  Making an honest attempt at answering all the questions on these assignments is how you can earn extra credit in this class.  You will have the opportunity to earn up to 3 points of extra credit during the semester.  You don't have to answer all the questions correctly, you just have to try to answer all the questions.  And you should have the assignment done before you come to class.  Trying to complete the assignment in class on the day it is due or copying the answers from a friend won't earn you any extra credit.

Note: A student sent me an email after class to point out an error:
Answer a. on Question #7 should be ozone (O3) not nitrogen (N2).

We finished up the section on air pollutants today.  Here's a table summarizing what we have done so far (shaded grey) and what we covered today (shaded yellow):

CO (carbon monoxide)
 O3 (ozone)
 SO2 (sulfur dioxide)
 PM (particulate matter)
1. colorless, odorless,
    toxic
 1. secondary
    pollutant
 1. 1st recognized
    pollutant
 1. Health hazard
2. primary pollutant
 2. summer
    afternoon
 2. London type smog
 2. Affects visibility
3. incomplete combustion
 3. photochemical
    (Los Angeles)
    smog
 3. Reacts with water in clouds
    to make acid rain
4. winter morning
5. temperature inversions

Sulfur dioxide is one of the pollutants that can react with water in clouds to form acid rain (some of the oxides of nitrogen can react with water to form nitric acid).  The formation and effects of acid rain are discussed on p. 12 in the photocopied Class Notes.


Acid rain is often a problem in regions that are 100s even 1000s of miles from the source of the sulfur dioxide that forms the acid rain.  Acid rain in Canada could come from sources in the US, acid rain in Scandinavia came from industrialized areas in other parts of Europe. 

Note at the bottom of the figure above that natural "pristine" rain has a pH less than 7 and is slightly acidic.  This is because the rain contains dissolved carbon dioxide gas.  The acid rain demonstration described below and done in class should make this point clearer.


Some of the problems associated with acid rain.

Click on this acid rain demonstration link for a detailed description of the demonstration done in class.

The last pollutant that we will cover is Particulate Matter (PM) - small solid particles or drops of liquid (but not gas) that remain suspended in the air (particulates are sometimes referred to as aerosols). 

The designations PM10 and PM2.5 refer to particles with diameters less than 10 micrometers and 2.5 micrometers, respectively.  A micrometer (µm) is one millionth of a meter (10-6 m).  The drawing below might give you some idea of what a 1 micrometer particle would look like (actually it would probably be too small to be seen without magnification).  You'll find some actual pictures and more information at this source.  Red blood cells are 6-10 µm in diameter.  A nanometer (nm) is 1000 times smaller than a micrometer (10-9 m).  An atom is apparently 0.1 to 0.3 nm across, depending on the particular element.



Particulate matter can be produced naturally (wind blown dust, clouds above volcanic eruptions, smoke from lightning-caused forest and brush fires).  Human activities also produce particulates.  Gases sometimes react in the atmosphere to make small drops or particles (this is what happened in the photochemical smog demonstration).  Just the smallest, weakest gust of wind is enough to keep particles this small suspended in the atmosphere.
One of the main concerns with particulate pollution is that the small particles might be a health hazard ( a health advisory is sometimes issued during windy and dusty conditions in Tucson)

Particles with dimensions of 10 µm and less can be inhaled into the lungs (larger particles get caught in the nasal passages).  These inhaled particles may be poisonous, might cause cancer, damage lung tissue, or aggravate existing repiratory diseases.  The smallest particles can pass through the lungs and get into the blood stream (just as oxygen does) and damage other organs in the body.

The figure below identifies some of the parts of the human lung mentioned above. 




 
Crossectional view of the human lungs
from: http://en.wikipedia.org/wiki/Lung

1 - trachea
2 - mainstem bronchus
3 - lobar bronchus
4 - segmental bronchi
5 - bronchiole
6 - alveolar duct
7 - alveolus
from http://en.wikipedia.org/wiki/Image:Illu_quiz_lung05.jpg


Note the PM10 annual National Ambient Air Quality Standard (NAAQS) value of 50 micrograms/cubic meter (µg/m3) at the bottom of p. 13c in the photocopied ClassNotes. 

The following list (p. 13d in the ClassNotes) shows that there are several cities around the world where PM concentrations are 2 or 3 times higher than the NAAQS value.



The World Health Organization recommends that PM2.5 concentrations be kept below 25 µg/m3.  Particulate concentrations during the recent air pollution event in Beijing apparently reached 886 µg/m3 at the US Embassy in Beijing (source).

In 2008 the Summer Olympics were in Beijing and there was some concern that the polluted air would affect the atletes performance.  Chinese authorities restricted transportation and industrial activities before and during the games in an attempt to reduce pollutant concentrations.  Rainy weather during the games may have done the greatest amount of good.



Clouds and precipitation are the best way of cleaning pollutants from the air.   We'll see later in the semester that cloud droplets form on small particles in the air called condensation nuclei.  The cloud droplets then form raindrops and fall to the ground carrying the particles with them.

The second main concern with particulates is the effect they may have on visibility (esthetics below should actually be spelled aesthetics - i.e. qualities that might make something appear beautiful or not).


Here's a photograph of the Catalina mountains taken last year about this time from the Gould Simpson Building on campus.


Some rainy weather had occurred just a day to two earlier and the visibility was very good.

Windy weather a few days later stirred up a lot of dust that was carried into town. 




This photo was taken the day after the windy weather.  There is still a lot of dust in the air and the visibility is pretty bad.

Here are some pretty good pictures of the pollution in Beijing earlier this week and the effect it had on visibility.

Because you have learned a little bit about the scattering of light you can understand why particulates affect visibility




In this first picture we start out with clean air.  When we look at a mountain we see the light that is reflected off the soil and trees on the mountain (shown at left above).  I've colored this reflected light green and brown.  When you look at the mountain it's green and brown (right figure above).



Now we'll add some particles.  When you look at the mountain you see brown and green light plus some white light that is coming from sunlight being scattered by the particles (the white light is colored yellow in the figure at left).  Some white specks of light have been superimposed on the view of the mountain at right.

A student asked a question about why, if particles scatter white light, did the haze in the photograph of the Catalina mountains appear brown.  I checked with our resident atmospheric chemist after class and got an interesting answer.  Part of the brown color is due to nitrogen dioxide, the bown-colored, poisonous gas that I've been thinking about making in class.  We'll come back to this briefly next Wednesday and I think I probably will try to make some NO2 in class after all.

Just a single picture now, what you would see when you look at the mountain.  More particles, more scattered light, and more white light being mixed in with the brown and green reflected light from the mountain.




Even more particles.  Now the white light from scattering from particles begins to dominate.  Eventually it becomes difficult to even make out the mountain because of all the scattered light.  Light from the mountain also runs into particles on its way toward your eyes and gets redirected so that you don't see it.  Of course there was considerable artistic license used in this illustration.

One last thing and I know I'm really trying your patience on a Friday afternoon before a 3-day weekend.

You might think that when the air is clean that visibility might be unlimited.  That isn't the case.  Scattering of sunlight by air molecules alone puts a limit on visibility.  The following figure tries to explain why this is so.


The nearby mountain appears green and brown.  You are mostly seeing sunlight reflected off the mountain.

As the mountain gets further away you start seeing increasing amounts of blue light (sunlight scattered by air molecules in between you and the mountain) being added to the brown and green reflected light.  This is because there is more air between you and the mountain.  The mountain at medium range now appears brown, green, and blue.    As the mountain gets even further away the amount of this blue light from the sky increases.  The most distant mountain in the picture above is now blue.  Eventually the mountain gets so far away that you only see blue light from the sky and none of the light reflected by the mountain itself.  The mountain has faded from view.

Here's a photograph of the Blue Mountains in Australia (source of this image)




If you look closely I think you can see 5 mountain ranges in this picture (1 is closest, 5 is the most distant).  Notice how they became fainter and fainter and lighter and lighter blue.  It is becoming hard to distinguish mountain range 5 from the blue color of the sky.