Here is some information on carbon monoxide, an important air pollutant.  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 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.

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.  This produces a stable layer of air at ground level.  In Pima County special formulations of gasoline (oxygenated) are used during the winter months to try to reduce CO emissions.

Concentrations of several pollutants are measured daily in many cities (particulate matter, ozone, and carbon monoxide are monitored in Tucson) and measured values 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.

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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 drop 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 decreases 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.