Mon., Jan. 27, 2014

"Rock Your Soul" from Elisa before the start of class today.  I first saw her together with Andrea Bocelli singing "La Voce del Silenzio" during his Vivere Live in Tuscany concert.  She also sang "Dancing" during that concert.

The first Optional Assignment of the semester was handed out in class today.  The assignment is due on Friday (Jan. 31).  These assignments are the way you can earn extra credit in this class.  To earn extra credit you need to do two things: (i) make a good faith effort to answer all the questions and (ii) have the assignment completed before you come to class on Friday.

We learned a little bit about sulfur dioxide in class last Friday.  It is the first recognized air pollutant (because it has a smell) and is a key ingredient in London type smog.  Sulfur dioxide is also one of the pollutants that can react with water in clouds to form acid rain (some of the oxides of nitrogen can also 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).   You'll find some actual pictures of micrometer sized objects and more information at this interesting site.  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 respiratory 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


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 view of the Catalina mountains taken from the Gould Simpson Building on the south side of campus.  The visibility is good in the first picture.


Some rainy weather had occurred just a day to two earlier and the air was clean and free of particulates and gaseous pollutants.

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




There is still a lot of dust in the air and the visibility is pretty bad.

We looked at some photographs from Beijing (January, 2013) and Harbin (October, 2013) in China in class last week.  These were extreme cases, the particulate concentrations were very high, and the visibility was probably just tens of feet. 

The PM10 annual National Ambient Air Quality Standard (NAAQS) is 50 micrograms/cubic meter (µg/m3)  (see the bottom of p. 13c in the photocopied ClassNotes, the figure wasn't shown in class). 



The World Health Organization recommends that PM2.5 concentrations be kept below 25 µg/m3.  Particulate concentrations during the air pollution event in Beijing in 2013 apparently reached 886 µg/m3 at the US Embassy. (source).

Just this morning I came across an article that indicated that air pollution levels in New Delhi, India, are perhaps even worse than in China.  The article suggests "... a very bad air day in Beijing is about an average one in New Delhi."  For the first three weeks of 2014 the air quality index (AQI) value for PM2.5 pollution averaged 227 in Beijing but 473 in New Delhi.

The following list (p. 13d in the ClassNotes, also not shown in class) shows that there are several cities around the world where PM concentrations are 2 or 3 times higher than the NAAQS value.


In 2008 the Summer Olympics were in Beijing and there was some concern that the polluted air would affect the athletes 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 (you could see the difference clouds and rain make in the two views of the Catalina mountains above).   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.

We'll also see that clouds that from in dirty air containing lots of particles may be more reflective than clouds that form in cleaner air.  Combustion of fossil fuels is adding carbon dioxide to the air and there is concern this might lead to global warming.  Combustion also adds particulates to the air and might change the reflective properties of clouds.  Particulates may also contribute to climate change.  This is another reason to be interested in and to keep track of particulate concentrations.


A couple of small plastic bottles were passed during class.  One contained some water the other an equal volume of mercury (here's the source of the nice photo of liquid mercury below at right).  I wanted you to appreciate how much heavier and denser mercury is than water. 




Thanks for being careful with the mercury.  A spill would have shut down the classroom and perhaps more of the buildinguntil the hazardous materials people could come in and clean it up.  It isn't so much the liquid mercury that is a hazard, but rather the mercury vapor.  Mercury vapor is used in fluorescent bulbs (including the new energy efficient CFL bulbs) which is why they need to be disposed of carefully.  That is something we'll mention again later in the class.

On Wednesday we'll learn that
atmospheric pressure at any level in the atmosphere
depends on (is determined by)
the weight of the air overhead

Today, in preparation,  we will review mass, weight, and density.  Weight is probably the concept to start with because we are most familiar with it.  We can feel weight and we routinely measure weight.


A person's weight also depends on something else.

  A person's weight depends on the person and also on the pull of gravity.

We measure weight all the time.  What units do we use?  Usually pounds, but sometimes ounces or maybe tons. 

Mass is a better way of expressing the amount of matter in an object.





Grams (g) and kilograms (kg) are commonly used units of mass (1 kg is 1000 g). 



Weight is mass times gravity.  We tend to use weight and mass interchangeably: one kilogram (units of mass) equals 2.2 pounds (units of weight) because we spend all our lives on earth where gravity never changes. 

On the earth's surface you determine the weight of an object by multiplying the object's mass by g.  As long as you're on the surface of the earth g has a constant value; it's called the gravitational acceleration. 




The masses are all the same.  On the earth's surface the masses would all be multiplied by the same value of g.  The weights would all be equal.  The masses of the three objects would be multiplied by the same value of g and the weights would be the same. 

The moon is smaller than the earth and gravity on the moon is weaker than on the earth.  If you were to carry a brick to the moon the mass, volume, and density of the brick would stay the same but the brick would weigh less.

Here's a situation where two objects with the same mass would have different weights


On the earth a brick has a mass of about 2.3 kg and weighs 5 pounds.  If you were to travel to the moon the mass of the brick wouldn't change (it's the same brick, the same amount of stuff).  Gravity on the moon is weaker (about 6 times weaker) than on the earth because the moon is smaller.  The brick would only weigh 0.8 pounds on the moon.  The brick would weigh almost 12 pounds on the surface on Jupiter where gravity is stronger than on the earth.

Here's a little more information (not covered in class) about what determines the value of the gravitational acceleration (Newton's Law of Universal Gravitation).  You'll need to read this to answer the last question on the Optional Assignment.

The three objects below were not passed around class (one of them is pretty heavy).  The three objects all had about the same volumes.  One is a piece of wood, another a brick, and the third something else. 




A student volunteer was able to determine relatively easily which was which by lifting each of the objects and judging its weight.



The brick in the back weighed about 5 pounds, the piece of wood about 1 pound.  The third object was made out of lead and weighed 15 pounds.

Here we had three objects of about the same size with different weights.  That means they each had different masses since weight depends on mass.  Thee different amounts of material, three different masses, were squeezed into roughly the same volume. 


The three objects have very different densities.

The bottle of mercury passed around class weighed more than the bottle of water even though the volumes were equal.  The mercury had more mass and a higher density than the water.  Densities of some common materials are shown below.

 
material
 density g/cc
air
 0.001
redwood
 0.45
water
 1.0
iron
 7.9
lead
 11.3
mercury
 13.6
gold
 19.3
platinum
 21.4
iridium
 22.4
osmium
 22.6


I wish I could bring in brick size pieces of gold, platinum, iridium, or osmium to pass around class.  They're even denser and would be even heavier than the lead and mercury. 

Don't worry about the units of density, but g/cc stands for grams per cubic centimeter.  A cubic centimeter is a volume about the size of a sugar cube.

Here's a question that we didn't have time to answer in class.  What if the 3 wrapped blocks (wood, brick, and lead) we were in outer space, where they would be weightless.  Could we tell them apart then?  They would still have very different densities and masses but we wouldn't be able to feel how much they weighed.  You'll find a little more information further down in today's notes that might help you answer this question.  We'll come back to it on Wednesday.

We'll be more concerned about air in this class than wood, brick, or lead.

In the first example below we have two equal volumes of air but the amount in each is different (the dots represent air molecules).  No one as far as I could tell had any trouble determining that the right box had the higher density. 

The amounts of air (the masses) in the second example are the same but the volumes are different.  The left example with air squeezed into a smaller volume has the higher density. 

One more point, something we didn't have time for in class.  Here's another definition of mass.



I think the following illustration will help to understand inertia.




Two stopped cars.  They are the same size except one is made of wood and the other of lead.  Which would be hardest to get moving (a stopped car resists being put into motion).  It would take considerable force to get the lead car going.  Once the cars are moving they resist a change in that motion.  The lead car would be much harder to slow down and stop.

This is the way you could try to distinguish between blocks of lead, wood, and brick in outer space.