How ozone is formed and how it affects our atmosphere
Surface-based ozone
Total atmospheric ozone

Observations of total atomospheric ozone were started in Nashville at Berry Field Airport as part of the old Weather Bureau operations. The ozone program was relocated to the upper air site at Langford cove on Old Hickory Lake in the latter part of the 1960's. This allowed better utilization of personnel.

The original ozone dome was used through the mid 1970's when an observer, upon entering the shelter, discovered three snakes lying inside the dome wall. Finding the snakes inside the dome, the observer was startled and immediately rotated the dome crushing the snakes. The snake remains were removed, however the odor left by the dead snakes remained inside the ozone dome for some time. Several attempts to remove the odor were made until it was decided to replace the ozone dome with a new one.

The shelter shown below houses the Dobson ozone spectrophotometer in Nashville. The spectrophotometer, unlike the ozone analyzer used for near-surface ozone observations, actually measures the ozone concentration in a column of atmosphere, extending all the way from the earth's surface up to the top of the atmosphere.

Here's another picture of Nashville's ozone shelter, silhouetted in the afternoon sun.

The retractable door, located on top of the ozone shelter, allows for ozone observations to be taken during periods of dry weather, as well as for protection of the equipment during inclement weather.

Here is a picture of the ozone shelter, with the retractable door open, and ready for ozone measurements to be taken.

This is the spectrophotometer (located inside the ozone shelter). It shows the dials and levers that are set by the observer prior to taking the observations. These settings depend on the type of observation (cloudy or sun) based on a table of values. The values from the table depend on the temperature of the instrument and time of year.

Taking Ozone Measurements with a Spectrophotometer

This picture shows the observer placing the Sun Director into the ozone spectrophotometer, in preparation for a sun type observation. A sun type observation can be taken anytime a distinct shadow exists.

This picture shows the Sun Director in place with the upper part aimed toward the sun. The sun's rays pass down through the Sun Director to inside the ozone spectrophotometer where it passes through a series of lenses so ozone readings can be taken.

This picture shows a National Weather Service technician taking an ozone observation.

The measurements of the relative intensity of certain wavelengths can be used to determine how much ozone is present in the atmosphere. This can be done because certain wavelengths are more effectively scattered and attenuated by ozone than others. For instance, when considering the wavelength pair of 3055 A.U. and 3254 A.U., we find that the 3055 A.U. wavelength intensity decreases when the ozone concetration increases, whereas the intensity of the 3254 A.U. wavelength remains practically unaltered. The computed amount of ozone concentration indicates the total amount of ozone contained in a vertical column of air extending from the ground to the top of the atmosphere in the neighborhood of the instrument. The result is expressed in terms of a thickness of a layer of pure ozone at standard temperature and pressure.

The wavelength pairs used in calculating ozone concentration are referred to as the A, C and D pairs. The mathematical equations used in data reduction take into account light scattering by air molecules and particulate matter. In practice, observations are ordinarily made on double pair wavelengths, e.g., the AD wavelengths. Since both the A and D wavelength pairs are approximately equally scattered by the atmosphere, the scattering effect is nearly cancelled out so that absorption by ozone becomes by far the major factor affecting the relative intensities of the double pair wavelengths on which observations are made.

This is how measurements are made of total atmospheric ozone. However, surface-based ozone is typically of more concern to the general population because of its impact on human health. To learn more about surface-based ozone click here.

After total atmospheric ozone observations are taken, the data is collected and analyzed by The Climate Monitoring and Diagnostics Laboratory in Boulder, Colorado and Aristotle University in Thessalonika, Greece.

Scientific understanding of the stratospheric ozone layer is being advanced through ongoing research at NOAA's Aeronomy Laboratory in Boulder, Colorado.

Additional ozone links:
1. Updated Reports on Ozone Depletion (from the United States Environmental Protection Agency)
2. Northern Hemisphere Total Ozone Maps (provided by Environment Canada)
3. The Dobson Room (General information about ozone and ozone measurements, provided by Oxford University's Department of Atmospheric, Oceanic and Planetary Physics)

Bibliography
1. Environmental Protection Agency. EPA AIRNOW--Smog: Who does it hurt? July, 1999.
2. Environmental Protection Agency. Ozone Monitoring, Mapping and Public Outreach. September, 1999.
3. Grass, R. D. Observers' Manual Dobson Ozone Spectrophotometer (Fourth Edition), U.S. Department of Commerce--NOAA. January 1, 1987.
4. Parson, Robert. Ozone Depletion FAQ. University of Colorado, 1994.

Footnotes
1. Grass, p. iv.
2. Parson, p. 9.
3. Grass, p. v. and Parson, p. 8.
4. Parson, pp. 8, 9
5. Environmental Protection Agency, Smog--Who does it hurt?, pp. 1-2
6. Environmental Protection Agency, Ozone Monitoring, Mapping and Public Outreach, pp. 7-9, 13
7. Grass, p. v.
8. Ibid, p. v-vi.