Wednesday Aug. 30, 2006

The Practice Quiz is one week from today.  In anticipation of that event, a preliminary version of the Practice Quiz Study Guide is available online.  There may be some small changes made between now and the beginning of next week.  Locations of the reviews will be added to the study guide once they are known.  Note there won't be a review next Monday afternoon; Monday is a holiday.

The packet containing old quizzes and an old final exam is now available for purchase ($2.50).

Tropical storm Ernesto is moving through Florida and into the SE United States.  Meanwhile in the Pacific, off the west coast of Mexico, Hurricane John has strengthened into a category 4 hurricane.  Hurricane John may influence our weather by the end of the week.

A short new reading assignment was made.
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 6o 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 2o 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   This is a temperature inversion and produces very stable conditions.
Sulfur dioxide is the next of the air pollutants that we will discuss.



Sulfur dioxide is produced by the combustion of sulfur containing fuels such as coal.  Combustion of fuel also produces carbon dioxide and carbon monoxide.  People probably first became aware of sulfur dioxide because it has an unpleasant smell.  Carbon dioxide and carbon monoxide are odorless.



The Great London smog is still the deadliest air pollution event in history.  Because the atmosphere was stable, SO2 emitted into air at ground level couldn't mix with cleaner air above.  The SO2 concentration was able to build to dangerous levels.




Acid rain often falls hundreds or thousands of miles away from the source of the SO2.  Coal fired factories and electric power plants in the Ohio River Valley could produce acid rain in New England and Canada.  Acid rain in Scandinavia could be the result of SO2 emissions in England and Belgium.  Oxides of nitrogen (NO, NO2, and N2O) also react in clouds to form acid rain (nitric acid).


An acid rain demonstration was performed in class to give you a general idea of how acid rain is produced.  Carbon dioxide rather than SO2 was bubbled through Tucson tap water.  The tap water is initially slightly basic (pH > 7).  Dissolved CO2 however turned the tap water acidic.

We will discuss tropospheric ozone, a pollutant, in class on Friday.  It is important to understand that ozone is found in the stratosphere where it is beneficial.  It is the ozone that is found in the troposphere that is considered a pollutant and is one of the key ingredients in photochemical smog.

It is relatively easy to make ozone in the statosphere.  We will make use of this simple two step reaction in class on Friday.  We will see that ozone production in the troposphere is a little more complicated.