Monday Jan. 26, 2009
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The music today was a very catchy tune (or atleast I thought so) called Venice USA from the Red Elvises.  They were playing Saturday night at The Hut.

Coming soon, a Practice Quiz Study Guide.  The Practice Quiz is Wed., Feb. 4.  It won't count but I'd suggest pretending like it does.  There will be late afternoon reviews Monday and Tuesday before the Practice Quiz. 

The Bonus 1S1P Assignment is due next Monday.
Here's a quick review of the three pollutants we have talked about so far:
The last pollutant that we will cover is Particulate Matter (PM), small particles (solid or liquid not gas) that remain suspended in the air.  The designations PM10 and PM25 refer to particles with diameters less than 10 micrometers and 2.5 micrometers, respectively.  A micrometer is one millionth of a meter.  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).


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.

Particles with dimensions of 10 micrometers and less can be inhaled into the lungs (larger particles get caught in the nasal passages).
The figure below identifies some of the parts of the human lung mentioned in the figure 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

Particulates can affect visibility and can make the sky appear hazy.  To understand this better we can look at how sunlight is scattered by clean air and dirty air.


Air molecules scatter sunlight (an individual air molecule doesn't scatter much light, but there are lots of air molecules in the atmosphere).  Because the air molecules are small (relative to the wavelength of visible light) they scatter shorter wavelengths more readily than longer wavelengths.  When you look away from the sun and toward the sky you see this scattered light, it has a deep blue color.  This is basically why the sky is blue.  If the earth didn't have an atmosphere the sky would be black.




Particles also scatter light (remember the chalk dust used in the laser demonstration last week).  But because the particle size is about equal to or somewhat greater than the wavelength of visible light the particles scatter all the colors equally.  The light scattered by particles is white.  This is basically why clouds are white.

As the amount of particulate matter in the air increases the color of the sky changes from deep blue to whitish blue.  The higher the particle concentration, the whiter the sky becomes.
The following figure was not shown in class.
Scattering of sunlight by air molecules turns distant mountains blue and eventually makes them fade from view
(there is eventually much more sunlight being scattered by air than there is sunlight being reflected by the mountains; there is a limit to how far you can see even when the air is very clean).

A nearby mountain might appear dark green or brown.  You are mainly seeing light 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).  As the mountain gets even further the amount of this blue light from the sky increases.  Eventually the mountain gets so far away that you only see blue sky light and none of the light reflected by the mountain itself. 


Note the PM10 annual National Ambient Air Quality Standard (NAAQS) value of 50 micrograms/meter3 at the bottom of p. 13c in the photocopied ClassNotes (shown above).  The following list shows that there are several cities around the world where PM concentrations are 2 or 3 times higher than the NAAQS value.


There was some concern last summer that the polluted air in Beijing would keep athletes from performing at their peaks during the Olympic Games.  Chinese authorities restricted transportation and industrial activities both before and during the games in an attempt to reduce pollutant concentrations.  Rainy weather during the games may have had the greatest effect, however.  The figure below wasn't shown in class.

I included it here just to be sure you wouldn't miss the important fact that clouds are the best way of cleaning pollutants from the air.
Here are the key things to remember about particulate matter.


Next we performed a sort of acid rain demonstration.  The demonstration gives you an idea of how gases can dissolve in water and turn the water acidic.
Today and next Wednesday we will take a brief look at the current concern over increasing concentrations of carbon dioxide in the earth's atmosphere and the worry that this might lead to global warming and climate change.  This is a big, complex, and contentious subject and we will only scratch the surface.

We'll start with the information on the top of p. 3a in the photocopied ClassNotes (the information on p. 3 was broken into three pieces).

1.  Carbon dioxide is one of several greenhouse gases.  Much of what we say about CO2 applies to the other greenhouse gases as well.
2.   Atmospheric CO2 concentrations are increasing.  This is pretty generally accepted as fact.  We'll look at some of the evidence below.

3.   Before we look at enhancement of the greenhouse effect, it is important to understand first that the greenhouse effect has a beneficial side. 
3a.  If the earth's atmosphere didn't contain any greenhouse gases, the global annual average surface temperature would be about 0o F.  That's pretty cold
3b.  The presence of greenhouse gases raises this average temperature to about 60o F.

4.   The concern is that increasing atmospheric greenhouse gas concentrations might cause some additional warming.  This might not sound like a bad thing.  However a small change in average temperature might melt polar ice and cause a rise in sea level and flood coastal areas.  Warming might change weather patterns and bring more precipitation to some areas and less to places like Arizona.

Now some of the data that show atmospheric carbon dioxide concentrations are increasing.


The "Keeling" curve shows measurements of CO2 that were begun in 1958 on top of the Mauna Loa volcano in Hawaii.  Carbon dioxide concentrations have increased from 315 ppm to about 385 ppm between 1958 and the present day.  The small wiggles (one wiggle per year) show that CO2 concentration changes slightly during the course of a year (it also probably changes slightly during the course of a day). 

You'll find an up to date record of atmospheric CO2 concentration from the Mauna Loa observatory at the Scripps Institution of Oceanography site.

Once scientists saw this data they began to wonder about how CO2 concentration might have been changing prior to 1958.  But how could you now,  in 2008, go back and measure the amount of CO2 in the atmosphere in the past?  Scientists have found a very clever way of doing just that.  It involves coring down into ice sheets that have been building up in Antarctica and Greenland for hundreds of thousands of years.


As layers of snow are piled on top of each other year after year, the snow at the bottom is compressed and eventually turns into a thin layer of solid ice.  The ice contains small bubbles of air trapped in the snow, samples of the atmosphere at the time the snow originally fell.  Scientists are able to date the ice layers and then take the air out of these bubbles and measure the carbon dioxide concentration.  This isn't easy, the layers are very thin, the bubbles are small and it is hard to avoid contamination.


Using the ice core measurements scientists have determined that atmospheric CO2 concentration was fairly constant at about 280 ppm between 1000 AD and the mid-1700s when it started to increase.  The start of rising CO2 coincides with the beginning of the "Industrial Revolution."   Combustion of fossil fuels needed to power factories began to add significant amounts of CO2 to the atmosphere.  Concentrations of several of the other greenhouse gases have been increasing in much the same way CO2 has.