Monday Aug. 27, 2012
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I mentioned to a friend that I was having trouble finding new music to play in class and he suggested I checkout the Raveonettes.  You heard a couple of songs ("Ignite" and "No Joy") from them before class today.

The 1st of the 1S1P Assignments was announced in class today (I meant to make the announcement last Friday).  You can do 0,1, or 2 reports.  What you are trying to do is earn 45 1S1P pts by the end of the semester.  There will be future assignments, so you don't have to do any reports this time.  But I would suggest you write at least one report just so you can get a feel for how the reports are graded.

All of the names on the various experiment signup sheets should now be online.  You can check by clicking on the Report Signup Lists link.

We spent a few minutes going over some material about temperature inversions that I stuck onto the end of the Friday Aug. 24 online notes.  Temperature increases with increasing altitude (the opposite of what we are used to) in an inversion layer and creates stable atmospheric conditions.

Here's a little supplementary (and optional) reading with additional information about atmospheric stability, temperature inversions, and bicycle riding.

A large city like Tucson is required to continuously monitor concentrations of several air pollutants.  The main ones are shown below (this is an improved version of information at the  top of p. 8 in the ClassNotes).

The concentration of lead in air has decreased significantly since lead was removed from gasoline (the following quote is from a Wikipedia article on gasoline: "In the US,standards to phase out leaded gasoline were first implemented in 1973 ..... In 1995, leaded fuel accounted for only 0.6% of total gasoline sales ...... From 1 January 1996, the Clean Air Act banned the sale of leaded fuel for use in on-road vehicles. Possession and use of leaded gasoline in a regular on-road vehicle now carries a maximum $10,000 fine in the US.")

In Tucson, carbon monoxide, ozone, and particulate matter are of primary concern and daily measurements are reported in the city newspaper.  Let suppose a CO concentration of 3 ppm (8 hour average) was measured yesterday in Tucson.  Would this be an acceptable or hazardous value?  Most people wouldn't be able to answer that question.  So rather than report the actual measured values, an Air Quality Index value is reported instead.    The AQI is the ratio of the measured to accepted concentrations multiplied by 100%.

If we plug in the 3 ppm value mentioned above for carbon monoxide, the AQI value would be

The air quality in this case would be good.  Air becomes unhealthy when the AQI value exceeds 100%.  The units "ppm", by the way, stand for "parts per million."  A CO concentration of 3 ppm would mean that in 1 million air molecules 3 of them would be carbon monoxide.

This information is found on the bottom of p. 8 in the photocopied ClassNotes.
  Current Air Quality Index values for Tucson are available online.

Carbon monoxide is a serious hazard indoors where is can build to much higher levels than would ever be found outdoors.  This next link is to a newspaper article describing an incident at Virginia Tech (that occurred near the beginning of the school year in 2007).   Carbon monoxide from a malfunctioning hot water heater sickened 23 Virginia Tech students in an apartment complex.  The CO concentration is thought to have reached 500 ppm.  You can get an idea of what kinds of health effects concentrations this high could cause from the figure. on p. 9 in the photocopied ClassNotes.

You would begin to show symptoms of carbon monoxide exposure (headache, dizziness, nausea) after breathing a 400 ppm CO concentrations after about 1 hour.  After several hours exposure you would approach the level where CO would cause coma and death.  At Virginia Tech several students were found unconscious and one or two had stopped breathing but they were revived.

Carbon monoxide alarms are relatively inexpensive (~$50) and are available at most hardware stores.  They will monitor CO concentrations indoors and warn you when concentrations reach hazardous levels. Indoors CO is produced by gas furnaces and water heaters that are either operating improperly or aren't being properly vented to the outdoors.  A few hundred people are killed indoors by carbon monoxide every year in the United States.  An operating carbon monoxide alarm probably saved the lives of the 6 Tucson residents in December 2010.  You can learn more about carbon monoxide hazards and risk prevention at the Consumer Product Safety Commission web page.

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've been thinking about making 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 most intense.

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.

Here are the main points that we covered so far, for carbon monoxide (CO) and ozone.  We'll cover sulfur dioxide and particulate matter later in the week and finish the table.