Thursday Jan. 19, 2012
click here to download today's notes in a more printer friendly format

Music before class this morning was Rhapsody in Blue featuring Pearl Kaufman.  I wasn't able to find it on YouTube but here is an alternate selection: Bumble Boogie.

A few more sets of Experiment #1 materials were checked out quickly before class.  Experiment #2 is fully booked at this point also.  So if you haven't yet signed up for an experiment it looks like Experiment #3 is your best choice.

We'll spend today and most of the day next Tuesday periods learning about some of the major air pollutants.  The two photographs below show residents of Linfen, China, which was, in 2007 anyway, one of the most polluted cities on earth.

The Photograph at left comes from an article in The Guardian.  The photograph at right from an article from The Blacksmith Institute.  Pollutants of concern included: Fly-ash, carbon monoxide, nitrogen oxides, PM-2.5, PM-10, sulfur dioxide, volatile organic compounds, arsenic, and lead (PM stands for particulate matter).

I like lists.  Here are lists of the major causes of death in the US and worldwide.  Air Pollution is a serious health hazard in the US and around the globe.  Click here to download a copy of the statistics shown below.



The top list shows the external agent or environmental factor.  The second list is the internal body 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.

Interestingly indoor air pollution is, in many places, a more serious threat than outdoor air pollution.  I'm not sure how the researchers determine that 150,000 people are killed by climate change every year.

The Blacksmith Institute (mentioned above) 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.

We start with a section on 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.

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 last December)

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 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 go directly from a source (automobile tailpipe or factory chimney) into the atmosphere.  Ozone is a secondary pollutant (and here we are referring to tropospheric ozone, not stratospheric ozone).  It doesn't come directly from an automobile tailpipe.  It shows up in the atmosphere only after a primary pollutant has undergone a series of reactions involving other gases in the atmosphere.




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.

Vehicles must now 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 and special formulations of gasoline (oxygenated fuels) are used during the winter months to try to reduce CO emissions. 

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.

In an inversion layer (Point 5) air temperature actually increases with increasing altitude which is 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 decreases with altitude above that).  This 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.  CO emitted into air at the surface mixes with cleaner air above.  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. 

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 a neater version of what is on top of p. 8 in the photocopied 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 4.5 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 4.5 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, stands for "parts per million."  A CO concentration of 4.5 ppm would mean that in 1 million air molecules 4.5 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 readily 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 adequately 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 mentioned earlier in today's notes.  You can learn more about carbon monoxide hazards and risk prevention at the Consumer Product Safety Commission web page.

We had enough time in class today to learn about ozone, a second air pollutant of concern.

The figure above can be found on p. 14a in the photocopied ClassNotes.  Ozone has a Dr. Jekyll (good) and Mr. Hyde (bad) personality.  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 kill us).

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

We'll be making some photochemical smog as 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 ozone in the demonstration rather than 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).  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 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 peak sunlight normally occurs 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 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 takenthe 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.  The product gas condensed, producing a visible smog cloud (the cloud was white, not brown as shown above).  I also shined the laser beam through the smog cloud to reinforce the idea that we are seeing the cloud because the drops or particles scatter light.