Background

Work at the Woodrow Wilson Environmental Science Institute includes two components:
• El Nino and the Southern Oscillation (ENSO)
• Presentation on photochemical smog

I chose to work with the El Nino group because of former work with remote sensing in the GLOBE Global Positioning System (GPS) work which produced the 1996 teacher resources for GLOBE GPS, and because of an interest in earth's energy systems. The research project was completed using data from Internet sources.

El Nino and the Southern Oscillation (ENSO)

Procedure:  Internet data were collected (see Links to Data page) and compared with area climate data.

Climate Data:

• Southeast Regional Climate Center

South Carolina Department of Natural Resources
Water Resources Division
1201 Main Street Suite 1100
Columbia, South Carolina 29201
(803) 737-0800M
• El Nino/Southern Oscillation

for S.E. U.S.
• Information on El Niño for S.E. U.S.
• How Does El Niño Affect the Weather in the Southeast (Georgia link)?
• Rainfall Patterns during La Niña Years
1. Georgia:  Spring – Summer
2. Georgia: Winter - Early Spring
• Rainfall Patterns during El Niño Years for Georgia
• El Nino Impacts : Georgia

The Southern Oscillation Index graphs 1947 to 1998, measures the El Nino & La Nina ocean pressures, and provides an index of intensities of each event. Those events, however, do not match precisely the NOAA El Nino events on their distribution maps. From those U.S. distribution maps, for El Nino events (1914, 1918, 1940, 1941, 1957, 1963, 1965, 1972, 1982, 1986, 1987, 1991, and 1994), Georgia has been impacted in the following ways:

Table 1: Precipitation and Temperature Changes During El Nino Months for Georgia

Table 2: Georgia Statewide Average Monthly Temperature and Precipitation for El Nino Years

 Year     Temperature Averages                        Precipitation Averages

Generally, the hypothesis is affirmed, but there are more data sets that need to be analyzed. The Pacific Sea Surface Temperatures need to be correlated with the Southern Oscillation Index, then compared with all the precipitation and temperature data for Georgia, before final conclusions can effectively drawn. 

Photochemical Smog

Each teacher made a presentation to colleagues at the Institute, often sharing teaching materials, resources, or leading colleagues in activities. The following was made based upon research done at the Air Quality Laboratory at Georgia Institute of Technology.

Key words: ozone, photochemical smog, VOCs, NO_x

Ozone

Ozone is produced through free radical reactions (reactions involving atoms or molecules with an unpaired electron), simplistically written as: O + O₂  O₃

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 manufacturing.

Ozone naturally decomposes, reforming oxygen molecules in an oxygen cycle, unless additional pollutants are present in the atmosphere. A chemical that can increase the productivity of ozone in the troposphere is NO, nitric oxide. Combustion produces NO from atmospheric nitrogen and oxygen:

1. N₂ + O₂  2NO

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 NO_x, because there is an equilibrium between the NO and NO_x:

2. 2NO + O₂ 2NO₂

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:

3. NO₂ + NO + O

The NOx 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 NOx is not particularly problematic in clean air environments, with ozone production increasing in a linear fashion as NOx increases.

However, if carbon compound pollutants are added to the atmosphere, the NOx production of ozone will increase in a nonlinear fashion, even growing exponentially. Those compounds (called collectively, volatile organic compounds or VOCs) include:

• carbonyl carbons (carbons double bonded to oxygens, C=O)
• 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)
• aromatics(compounds containing benzene or its derivatives)
There are a variety of free radical reactions in the atmosphere, but with the NOx and the VOCs—the ozone precursors—ozone production rates increase significantly according to the following relation:
4. O + O₂ + M O₃ + M

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 troposphere.

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 non methane hydrocarbons (NMHC) and NOx, 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 significantly from motorized vehicles, from combustion processes, and from industrialization. Thus, industrialized regions can suffer from a decided increase in tropospheric ozone production.

Conclusions

Besides the irritation to nasal 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, agricultural productivity will increase. It has been found that corn yields have been decidedly decreased, if the corn is exposed during the growing season to ozone levels of 80 ppbv for eight hour periods.

Reduction in NOx 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 13 3: Chemistry within the atmospheric compartment. 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 tropospheric ozone
• Maryland Department of the Environment, Ozone Information Page
• Southern Oxidants Study
• Washington University, Saint Louis, Missouri: Environmental Science Outreach page: Information on Ozone
(Return to the top of the page.)

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