At this point we made a not so smooth transition to carbon monoxide, an important air pollutant.  We'll finish up CO in class on Monday and also cover ozone.

Some basic information about carbon monoxide is shown below (p. 7 in the photocopied Class Notes).   You'll find additional information at the Pima County Department of Environmental Quality website and also at the US Environmental Protection Agency website.

Carbon monoxide molecules bond strongly to the hemoglobin molecules in blood and interfere with the transport of oxygen through your body.  CO is a primary pollutant.  That means it goes directly from a source into the air (nitric oxide, NO, and sulfur dioxide, SO₂, are also primary pollutants).  CO is emitted directly from an automobile tailpipe into the atmosphere for example

CO is produced by incomplete combustion of fossil fuel.  Complete combustion would produce carbon dioxide, CO₂.   Cars and trucks produce much of the CO in the atmosphere.  Vehicles must now be fitted with a catalytic converter which will change CO into CO₂ (and also NO into N₂ and O₂).  In Pima County vehicles must 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.  See if you can figure out why carbon monoxide is often a problem in cities at high altitude (the answer is found at the bottom of today's online notes)

Carbon monoxide is also a serious hazard indoors.  Because it is odorless, concentrations can build to dangerous levels without you being aware of it.  You can purchase a carbon monoxide alarm that 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 outdoors.  Many people are killed indoors by carbon monoxide every year.  You can learn more about carbon monoxide hazards and risk prevention at the Consumer Product Safety Commission web page.

In the atmosphere CO concentrations peak on winter mornings.  Surface temperature inversion layers form on long winter night when the ground becomes colder than the air above.  Air in contact with the cold ground cools and ends up colder than air above.  Air temperature increases with increasing altitude in a temperature inversion and this produces a very stable layer of air at ground level.

When CO is emitted into a thin stable layer (left figure above), the CO remains in the layer and doesn't mix with cleaner air above.  CO concentrations build.

In the afternoon the atmosphere becomes more unstable.  CO emitted into air at the surface mixes with cleaner air above.  The CO concentrations are effectively diluted and don't get as high as they do in the morning.

A portion of a time lapse cloud move was shown at the end of class.  Thunderstorms were developing over the Catalina mountains.  Thunderstorms are a visible indication of unstable atmospheric conditions.

You could see the clouds growing vertically in the movie, evidence of rising air motions.  Falling precipitation also produces a downdraft, sinking air motions.  This downdraft is the source of the strong, often damaging, surface winds that accompany thunderstorms.

We'll finish the section on carbon monoxide today.  Last week we learned that carbon monoxide is a primary pollutant produced by incomplete combustion.  Peak CO concentrations are observed on winter mornings.


Six main pollutants are listed at the top of this page.  Concentrations of some or all of these pollutants are measured daily in many cities.  The atmospheric concentration of lead has decreased significantly since the introduction of unleaded gasoline.  PM stands for particulate matter.  These small particles are invisible, remain suspended in the air, and may be made of harmful materials.. 

CO, O₃ and particulate matter are the pollutants of most concern in Tucson and pollutant concentrations are reported in the newspaper or on television using the Air Quality Index (formerly the pollutant standards index).  This is basically the measured value divided by the allowed value multiplied by 100%.   Current Air Quality Index values for Tucson are available online.


The first graphs shows a typical atmospheric temperature profile near the ground in the winter.  The inversion is the bottom portion of the plot where temperature increases from 47 F to near 60  F with 1000 feet of altitude gain.  The 1000 foot deep layer is a stable layer.

The middle figure shows some of the health effets and symptoms of CO poisoning.  The effect of CO depends on both the concentration and the length of exposure.  The NAAQS values are shown at bottom  of the chart.  Exposure to CO concentrations of these levels shouldn't cause any symptons in a healthy individual.  Concentrations reached 500 ppm in the apartment building near the campus of Virginia Tech.  Several students were unconscious when found by rescue personnel.

The bottom figure shows average monthly AQI values for CO and O₃ in Tucson.  CO concentrations (blue curve) tend to peak on winter mornings. 

This rather busy and confusing picture just illustrates how small changes in how air temperature changes with increasing altitude can determine whether the atmosphere will be stable or unstable.   Just for the purposes of illustration we imagine riding a bicycle from Swan and River Rd up a hill to Swan and Sunrise (fhe figure shows an elevation change of 1000 ft, it is actually quite a bit less than that)

At far left the air temperature drops 6^o F.  This is a fairly rapid rate of decrease with increasing altitude and would make the atmosphere absolutely unstable.  The atmosphere wouldn't remain this way.  Air at the ground would rise, air above would sink, and the temperature profile would change.  In some ways it would be like trying to pour vinegar on top of oil in a glass.  The lower density oil would rise because it would "want" to float on top of the higher density vinegar.

The next picture shows air temperature decreasing a little more slowly with increasing altitude.  This small change makes the atmosphere conditionally unstable (we won't go into the conditions).  The atmosphere is frequently in this state. 

The atmosphere cools only 2^o F in the next picture.  This creates an absolutely stable atmosphere.  Air at the ground will remain at the ground and won't rise and mix with air higher up.  Compare this with the glass containing vinegar and a layer of oil on top.  The two layers won't mix.

Air temperature in the last figure actually increases with increasing altitude, common on winter mornings in Tucson (and worth bicycling up the hill on Swan Rd. just to experience on a cool winter morning).   This is a temperature inversion and produces very stable conditions.   If you do find yourself on a bicycle at Swan and Sunrise, check out the very steep section at the far northern end of Swan.