Tuesday Sept. 3, 2013
click here to download today's notes in a more printer friendly format

Before class music this morning from Brandi Carlile.  You heard most (if not all) of Late Morning Lullaby, Turpentine, My Song, and The Story.

1S1P Assignment #1 now has a due date, two weeks from today, i.e. Tue., Sep. 17.  You can do 0, 1, or 2 reports as part of this assignment.  Something I forgot to mention - please print out your report(s) and turn in a hard copy on or before the due date. 

Now why would you even bother to do a report if 0 reports is an option?  Your goal should be to earn 45 1S1P points by the last day of classes.  You can write two reports as part of this assignment and try to get the work done early in the semester, you might spread out the effort over the full semester in which case you could write just a single report, and you could procrastinate by not writing any reports now and turning in a flood of reports late in the semester.  It's up to you but I would encourage you to write at least one report this time around, if only to get some feedback on how the grading will be done.

An additional topic will added later today or tomorrow to give you a total of 3 topics to choose from.  There will be at least two more assignments like this one and probably several bonus assignments later in the semester.  You'll have lots of opportunities to earn 1S1P points.

Names of all the students that checked out Experiment #1 materials as well as people that signed up for one of the later experiments should all now be online.  You can check the Report Signup Lists to see if everything was transcribed correctly.

Today and Thursday we will be looking at four air pollutants.  They are carbon monoxide, tropospheric ozone, sulfur dioxide, and particulate matter.  They're listed below together with an idea of the number of main points you should remember and understand about each. 


Today's class will also feature a light scattering demonstration.  It's a fairly simple concept and helps to make photochemical smog and particulate matter visible.  Light scattering also shows up in lots of additional and unexpected places.  We will also produce some photochemical smog in a second separate demonstration (safely confined in a glass bottle).
 
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 later in the week.

Air pollution is a serious hazard worldwide.  Interestingly 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 have 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.

You may have heard of the record setting levels of air pollution that sometimes affect Beijing, China.  Here's a link to a pretty good collection of photographs.  Much of this is particulate pollution which is something we'll cover later this week.  In addition to being a health hazard, particulates can have a dramatic effect on visibility.

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 earlier this year.

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 come back to carbon monoxide briefly on Thursday.  Here's where we stand:




We'll spend the next 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 later today.  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.




The instructor would have been able to see the beam if he had stood at the end of the beam of laser light and looked back along the beam of light toward the laser.  That wouldn't have been a smart thing to do, though, because the beam was strong enough to possibly damage his eyes (there's a warning on the side of the laser). 

Everybody was able to see a bright red spot where the laser beam struck 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.

Next we turned our attention to ozone,  another outdoor pollutant of concern.

Ozone has a kind of Dr. Jekyll and Mr Hyde personality.


The figure above can be found on p. 14a in the photocopied ClassNotes.  The ozone layer (ozone in the stratosphere) is beneficial, it absorbs dangerous high energy ultraviolet light (which would otherwise reach the ground and cause skin cancer, cataracts, etc.  There are some types of UV light that would quite simply kill us).

Ozone in the troposphere is bad, it is toxic and a pollutant.  Tropospheric ozone is also a key component of photochemical smog (also known as Los Angeles-type smog)

We'll be making some photochemical smog in a class demonstration.  To do this we'll first need some ozone; we'll make use of the simple stratospheric recipe (shown above) for making what we need instead of the more complex tropospheric process (the 4-step process in the figure below).  You'll find more details a little further down in the notes.



At the top of this figure (p. 15 in the packet of ClassNotes) you see that a more complex series of reactions is responsible for the production of tropospheric ozone.  The production of tropospheric ozone begins with nitric oxide (NO).  NO is produced when nitrogen and oxygen in air are heated (in an automobile engine for example) and react. 

The NO can then react with oxygen in the air to make nitrogen dioxide, the poisonous brown-colored gas that I used to make in class.

Sunlight can dissociate (split) the nitrogen dioxide molecule producing atomic oxygen (O) and NO.  O and O2 react in a 4th step to make ozone (O3) just like happens in the stratosphere.  Because ozone does not come directly from an automobile tailpipe or factory chimney, but only shows up after a series of reactions in the air, it is a secondary pollutant.   Nitric oxide (NO) would be the primary pollutant in this example.

NO is produced early in the day (during the morning rush hour).  The concentration of NO2 peaks somewhat later.  Because sunlight is needed in step #3 and because sunlight is usually most intense at noon, the highest ozone concentrations are usually found in the afternoon.  Ozone concentrations are also usually higher in the summer when the sunlight is more intense than at other times of year.


Once ozone is formed, the ozone can react with a hydrocarbon of some kind to make a product gas.  The ozone, hydrocarbon, and product gas are all invisible, but the product gas sometimes condenses to make a visible smog cloud or haze.  The cloud is composed of very small droplets or solid particles.  They're too small to be seen but they are able to scatter light - that's why you can see the cloud.

Here's a pictorial summary of the photochemical smog demonstration.

We started by putting a small "mercury vapor" lamp inside a flash.  The bulb produces a lot of ultraviolet light (the bulb produced a dim bluish light that we could see, but the UV light is invisible so we had no way of really telling how bright it was).  The UV light and oxygen in the air produced a lot of ozone (you could easily have smelled it if you had taken the cover off the flask).

After a few minutes we turned off the lamp and put a few pieces of lemon peel into the flash.  Part of the smell that comes from lemon peel is limonene, a hydrocarbon.  The limonene gas reacted with the ozone to produce a product gas of some kind.  The product gas condensed, producing a visible smog cloud (the cloud was white, not brown as shown above).  I meant (but forgot)  to shine the laser beam through the smog cloud to reinforce the idea that we are seeing the cloud because the drops or particles scatter light.

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