Research activities included remote sensing and ocean modeling of El Nino Southern Oscillation , with Anna Matteoda as mentor at the Marine and Remote Sensing Laboratory.
 
 

Ozone
        Ozone (O₃) is a reactive gas that is found in the stratosphere, the second atmospheric layer above the earth, where the temperature rises with altitude.  The reason for the temperature rise is because the ozone absorbs ultaviolet light, increasing the kinetic energy of the molecules, while protecting organisims on the earth from uv cell damage.  Ozone also naturally occurs in the troposhere (the atmsopheric level closest to the earth), as a result of gradient mixing from the stratosphere and from coronal and lightening discharges.  However, ozone is found in urbane areas at levels four to twenty times these natural levels.  In the troposphere ozone is as an irritant and the major contributor to photochemical smog—also called summer smog.
        Ozone is produced through free radical reactions (reactions involving atoms or molecules with an unpaired electron), simplistically written as:
                             O    +     O₂      O₃                                                     [1]
With the first free radical oxygen being produced from the decomposition of the oxygen (O₂) molecule or another type of molecule containing oxygen, by uv light or some other high energy activity, such as lightening or manufacuting.
        Ozone naturally decomposes, reforming oxygen molecules in an oxygen cycle, unless additional pollutants are present in the atmosphere.  A chemcal that can increase the productivity of ozone in the troposphere is NO, nitric oxide.  Combustion produces NO from atmospheric nitrogren and oxygen:
                             N₂     +     O₂      2NO                                                     [2]
        Nitric oxide will react with oxygen to form nitrogen peroxide, NO2, also called nitrogen dioxide.  The ratio of NO and NO2 is referred to as NOx, because there is an equilibrium between the NO and NOx:
                            2NO     +     O₂  2NO₂                                                 [3]
The NO2 will also decompose with uv radiation (<430nm), forming a free radical oxygen, which can then, form ozone according to reaction [1], above.  The decomposition is:
                              NO₂      NO     +     O                                               [4]
        The NO_x levels are typically low enough, however, that ozone is not formed.  Further, the nitrogen oxides will also react with water molecules in the atmosphere, forming relatively short lived acids (HNO₂, nitrous acid, and HNO_3, nitric acid), both of which can precipitate as acid rains, within a few days.  Thus, the NO_x is not particularly problematic in clean air environments, with ozone production increasing in a linear fashion as NO_x increases.
        However, if carbon compound pollutants are added to the atmosphere, the NO_x production of ozone will increase in a nonlinear fashion, even growing exponentially.  Those compounds (called collectively, volital organic compounds or VOCs) include:  carbonyl carbons (carbons double bonded to oxygens, C=O), and hydrocarbons (carbon-hydrogen compounds), such as paraffins (compounds where carbon atoms have only single bonds), olefins (compounds where at least some carbon atoms have double bonds between them, making them more reactive), and aromatics (compounds containing benzene or its derivatives).
        There are a variety of free radical reactions in the atmosphere, but with the NO_x and the VOCs—the ozone precursors—ozone production rates increase significantly according to the following reation:
                         O    +     O₂     +     M      O₃     +     M                         [5]
where M could be any number of atmospherically produced compounds.
        Depletion of the ozone and ozone precursors occur with the production of several water soluble compounds, including several acids (inorganic and organic), hydrogen peroxide (H₂O₂), and organic peroxides.  These compounds dissolve in cloud droplets and precipitate out of the atmosphere.

Atmospheric Ozone Patterns
        Ozone production follows a diurnal pattern, peaking with maximum uv radiation of the atmosphere between the local times of 12:00 N and 15:00, but extending as late as 21:00, depending upon temperatures and weather conditions.  As the sun sets and temperatures drop, forming dew in the early morning hours, ozone levels drop to a minimum near 6:00.  Ozone levels will increase, however, over the summer months, decreasing during the autumn months to a winter low.  Diurnal variations are less prominent on mountain-top measuring sites, primarily because there is less opportunity for inversions, which trap ozone and its precursors in the lower tropsphere.
        Ozone also correlates with concentrations of CO and SO₂, which are not ozone precursors.  The suggested rationale for such correlation is that emissions of CO and SO₂ from industrial sources also emit nonmethane hydrocarbons (NMHC) and NO_x, which are ozone precursors.
        Vegetation in both urban and rural regions is a significant producer of VOC’s and atmospheric nitric oxide (NO) is produced by fertilized, cultivated soils and lightening.  However, all atmospheric ozone precursors increase signficantly from motorized vehicles, from combustion processes, and from industrialization.  Thus, industrialized regions can suffer from a decided increase in torospheric ozone production.

Conclusions
        Besides the irritation to nausal passages or eyes, there are agricultural and economic concerns for reducing ozone production.  Adams, Hamilton, and McCarl have suggested that $1.7 billion could be saved by reducing tropospheric ozone by 25%.  Besides medical savings by such reductions, agriculutural productivity will increase.  It has been found that corn yields have been decidely decreased, if the corn is exposed during the growing season to ozone levels of 80 ppbv for eight hour periods.
        Reduction in NO_x has been found to decrease ozone levels, which can be accomplished by improved combustion techniques.  Even reduction of highway grades has been found to diminish precursor emissions from trucks, for example.

Resources
 
Adams, R.M., Hamilton, S.A., and McCarl, B.A.  1985.  Assessment of the economical effects of
ozone on U.S. agriculture.  Journal of Air Pollution Control Association 35, 9:  938-943.

Fehsenfeld, Fred; Meagher, James, and Cowling, Ellis (Ed.).  1994.  Southern Oxidants Study:  1993
Data Analysis Workshop Report.  Raleigh, North Carolina:  North Carolina State University.

Jeffries, Harvey.  1995.  ENVR 133:  Chemistry within the atmospheric compartment.
ftp://airsite.unc.edu/pdfs/ese_unc/jeffries/class/envr1`33/atmchem.pdf

________.  1995.  Theoretical and analytic advances in understanding aromatic atmospheric oxidation
mechanism.  Chicago:  American Chemical Society 210th National Meeting.  (See Jeffries presentations.)

Pearson, James R.  1994.  A Comparison of photochemistry at rural sites in the southeastern United
States and southeastern China.  Master’s thesis.  Atlanta, GA:  Georgia Institute of
Technology,.

Selected Internet Sites

Levy, Hiram II, publication abstracts and titles on troppsheric ozone
Maryland Department of the Environment, Ozone Information Page
Southern Oxidants Study
Washington University, Saint Louis, Missouri:  Environmental Science Outreach page: Information on Ozone 
 

Email:  gstickel@mindspring.com (or for July 1998, g_stickel@yahoo.com)
 

Woodrow Wilson Leadership Program in Environmental Science lpt@www.woodrow.org
The Woodrow Wilson National Fellowship Foundation webmaster@woodrow.org
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