Wednesday Jan. 22, 2014

A very unusual fusion of different musical styles before class today with Laura Marling, Mumford & Sons and Dharohar Project.  You heard Devil's Spoke but should also checkout Meheni Rachi and  Laura Marling's solo version of Blackberry Stone.

The first selection of 1S1P topics is now online for your consideration.  By consideration I mean you do not need to write reports on any of these topics.  But if you don't write any reports you won't earn any points.  And if you don't have any 1S1P pts by the end of the semester your grade will suffer.  You can try to get all the work done early in the semester, spread the work out throughout the semester, or try to squeeze it all in at the end.  The choice is yours.  I would suggest doing a report on at least one of the topics if only to get some feeling for how the reports will be graded.

The names of all the students that checked out Experiment #1 materials as well as people that signed up for Experiment #2 are online.  You can check to see if everything was transcribed correctly.  The remaining experiments should appear soon.

Class started with quick mention of some of the important trace gases in our atmosphere.  We didn't have time for this last Friday but I stuck the list below at the end of the online notes anyway.



We'll be covering carbon monoxide, ozone and sulfur dioxide, three of the main air pollutants, this week and early next week.  We'll also look at particulate matter next week.




The numbers are placeholders that we will be filling in as we go.  There are anywhere from 2 to 5 main points that you should remember about each of these pollutants.

You might have heard news of record setting levels of air pollution in China recently.   Here's a link to dramatic photographs of polluted air in Beijing in early 2013.  More recently (Oct. 2013) Harbin in NE China was affected.  Here's a link to some photographs of that event that appeared in the Huffington Post.   You could "see" the air pollution in these examples because the pollution (probably mostly particulates) scatters light.  Today's class will feature a light scattering demonstration that I hope will help you to understand this fairly simple concept.  It's a phenomenon that shows up in lots of additional and unexpected places. 

Air Pollution is a serious health hazard in the US and around the globe  (click here to download a copy of the information below).  The lists below give some idea of how serious a threat it is.



The top list shows the external or environmental agent that causes death.  The second list is the physiological or internal bodily function that ultimately leads to your demise.  Keep in mind that many of these numbers are difficult to measure and some may contain a great deal of uncertainty.  The row that is highlighted, toxic agents, contains estimates of deaths caused by indoor and outdoor air pollution, water pollution, and exposure to materials such as asbestos and lead both in the home and at the work place.  It is estimated that 60% of the deaths are due to exposure to particulate matter, something that we will examine in a little more detail next week.

Pollution in all its forms is a serious hazard worldwide.  Indoor air pollution is, in many places, a more serious threat than outdoor air pollution.  In that regard, here's a link to the article "Open-Fire Stoves Kill Millions.  How Do We Fix It?" that I might mentioned in class (it appeared in the Dec. 2012 issue of Smithsonian Magazine). 
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I'm not sure how the researchers determine that 150,000 people are killed by climate change every year.

The Blacksmith Institute  listed the Top 10 polluted places in the world in a 2007 report.  The report has received a lot of worldwide attention.  If you go to this address (click on 2007 at the top left edge of the page) you can view the report online or download and print a copy of the report.  This is just in case you are interested (click on some of the other years also if you do go to the site).  And note they are concerned with all types of pollution, not just air pollution.


We'll start our section on air pollutants with carbon monoxide.  You'll find additional information on carbon monoxide and other air pollutants at the Pima County Department of Environmental Quality website and also at the US Environmental Protection Agency website.

The material above is from page 7 in the photocopied ClassNotes.  We will mostly be talking about carbon monoxide found outdoors, where it would rarely reach fatal concentrations.  CO is a serious hazard indoors also where it can (and does) build up to deadly concentrations (several people were almost killed in Tucson in December 2010 for example).    Here's a report of two people that were killed in their car in Connecticut in early 2013.

Carbon monoxide is insidious, you can't smell it or see it and it can kill you (Point 1).  Once inhaled, carbon monoxide molecules bond strongly to the hemoglobin molecules in blood and interfere with the transport of oxygen throughout your body.  The first article above mentions that the CO poisoning victims were put inside a hyperbaric (high pressure) chamber filled with pure oxygen.  This must force oxygen into the blood and displace the carbon monoxide.

CO is a primary pollutant (Point 2 above).  That means it goes directly from a source into the air,  CO is emitted directly from an automobile tailpipe into the atmosphere for example. The difference between primary and secondary pollutants is probably explained best in a series of pictures.



In addition to carbon monoxide, nitric oxide (NO) and sulfur dioxide (SO2), are also primary pollutants.  They all travel directly from a source (automobile tailpipe or factory chimney) into the atmosphere.  Ozone is a secondary pollutant (and here we mean tropospheric ozone, not stratospheric ozone).  It wouldn't be present in the exhaust coming out of a car's tailpipe.  It shows up in the atmosphere only after a primary pollutant has undergone a series of reactions without other chemical compounds in the air.


Point 3 explains that CO is produced by incomplete combustion of fossil fuel (insufficient oxygen).  Complete combustion would produce carbon dioxide, CO2.   Cars and trucks produce much of the CO in the atmosphere in Tucson.

Special formulations of gasoline (oxygenated fuels) are used during the winter months to try to reduce CO emissions.  The added ethanol has the effect of adding more oxygen to the combustion process.
 
Vehicles must also be fitted with a catalytic converter that will change CO into CO2 (and also NO into N2 and O2 and hydrocarbons into H2O and CO2).  In Pima County, vehicles must also pass an emissions test every year to insure that the car is burning fuel as cleanly as possible.

In the atmosphere CO concentrations peak on winter mornings (Point 4).  The reason for this is surface radiation inversion layers.  They are most likely to form on cold winter mornings.

When we say inversion layer (Point 5), we mean a temperature inversion, a situation where air temperature increases with increasing altitude,   just the opposite of what we are used to.  This produces stable atmospheric conditions which means there is little up or down air motion.

 There is very little vertical mixing in a stable air layer.




In the left figure above, notice how temperature increases from 40 F to 50 F in the thin air layer next to the ground (it then begins to decrease as you move further up).  This bottom layer is the stable inversion layer.  When CO is emitted into the thin stable layer, the CO remains in the layer and doesn't mix with cleaner air above.  CO concentrations build.

In the afternoon, the ground warms, and the atmosphere becomes more unstable.  Temperatures decrease with increasing altitude in the right figure above.  The atmosphere turns unstable and up and down air motions mean that CO emitted into air at the surface mixes with cleaner air above.  The same amount of CO is added to the air but it is mixed in a larger volume.  The CO concentrations are effectively diluted.





Thunderstorms contain strong up (updraft) and down (downdraft) air motions.  Thunderstorms are a sure indication of unstable atmospheric conditions. 

We'll probably come back to carbon monoxide briefly on Friday.  Here's where we stand:




We spent the last portion of today's class learning about the scattering of light.  You are able to see a lot of things in the atmosphere (clouds, fog, haze, even the blue sky) because of scattering of light.  I'm going to try to make a cloud of smog in class on Friday.  The individual droplets making up the smog cloud are too small to be seen by the naked eye.  But you will be able to see that they're there because the droplets scatter light.  So we took some time for a demonstration that tried to show you exactly what light scattering is.

In the first part of the demonstration a narrow beam of intense red laser light was directed from one side of the classroom to the other.

 




Looking down on the situation in the figure above.  Neither the students or the instructor could see the beam of light.  Nobody could see the beam because there weren't any rays of light pointing from the laser beam toward the students or toward the instructor.



If I were to move to near where the beam hits the wall and look back toward the laser I'd see the light.  That wouldn't be a smart thing to do, the laser light is too intense and could damage my eyes (there's a warning on the laser).

Everyone was able to see the red spot where the laser beam hits the wall.
 



This is because when the intense beam of laser light hits the wall it is scattered (splattered is a more descriptive term).  The original beam is broken up into a multitude of weaker rays of light that are sent out in all directions.  There is a ray of light sent in the direction of every student in the class.  They see the light because they are looking back in the direction the ray came from.  It is safe to  look at this light because the original intense beam is split up into many much weaker beams.

Next we clapped some erasers together so that some small particles of chalk dust fell into the laser beam.



Now instead of a single spot on the wall, students saws lots of points of light coming from different positions along a straight segment of the laser beam.  Each of these points of light was a particle of chalk, and each piece of chalk dust was intercepting laser light and sending light out in all directions.  Each student saw a ray of light coming from each of the chalk particles.

We use chalk because it is white, it will scatter rather than absorb visible light.  What would you have seen if black particles of soot had been dropped into the laser beam?

In the last part of the demonstration we made a cloud by pouring some liquid nitrogen into a cup of water.  The cloud droplets are much smaller than the chalk particles but are much more numerous.  They make very good scatterers.



 

The beam of laser light was very bright as it passed through the small patches of cloud.  The cloud droplets did a very good job of scattering laser light.  So much light was scattered that the spot on the wall fluctuated in intensity (the spot dimmed when lots of light was being scattered, and brightened when not as much light was scattered).  Here's a photo I took back in my office.


The laser beam is visible in the left 2/3 rds of the picture because it is passing through cloud and light is being scattered toward the camera.  There wasn't any cloud on the right 1/3rd of the picture so you can't see the laser beam over near Point 1.