What are the current ozone levels in the stratosphere? The National Aeronautics and Space Administration (NASA), can provide you with the values. In fact, if a satellite is sending data as you read this, you may be able to get today's ozone level in the stratosphere right above where you live.

a. Determine your latitude and longitude from a map, from a nearby airport, or from a web site such as this one that provides maps by zip code or by city. Note that in the continental U.S., latitude has a positive value (north) and longitude has a negative value (west).

b. Access satellite data from the NASA page for TOMS, the Total Ozone Mapping Spectrophotometer . Enter your latitude and longitude from part a. to find the total column ozone amount at your location. If today's value is not available, request an earlier date. As you will see later in the chapter, 320 Dobson units^* is the average ozone level over the northern US. How does your value compare with the average?
^*During recent months, the link at EPA that explains the Dobson unit has been broken. Use this link to the Dobson unit instead.

c. Again using the link to NASA, obtain ozone values for some other parts of the world. How do these compare with where you live?

The UV Index indicates the amount of UV radiation reaching the Earth's surface at solar noon (which may be closer to 1 pm, if you are on daylight time). It is generated daily for more than 50 cities in the United States.

a. The UV Index depends on latitude, the day of the year, the time of day, the amount of ozone above the city, the elevation, and the predicted cloud cover. How is the UV Index affected by each of these?

b. The UV Index Forecast is available on the web, compliments of a satellite launched by NOAA, the National Oceanographic and Atmospheric Administration. Account for the range of values that you see on today's map of the United States.

c. Surfaces such as snow, sand and water all can intensify your exposure to UV radiation, because they can reflect it back at you. Which outdoor activities might increase your risk from exposure?

In Consider This 2.1, you used the web to get stratospheric ozone data at a location of your choice (presumably above your head). Now go to NASA's archive of satellite data on stratospheric ozone levels to find out how the values have varied between 1979 and 1992 over the lower northern hemisphere latitudes. You may wish to coordinate your efforts with others, so that together you cover a range of years.

a. Obtain values of stratospheric ozone levels at latitudes from +45 degrees north to +0 (the equator) for a year of your choice. Enter -90 degrees west (the middle of the U.S.) as the longitude, use the Nimbus-7 satellite, and the date of June 15th. Obtain readings 5 degrees apart. Make a table of the stratospheric ozone values and compute the average.

b. Compare with others in your class data over these 13 years. Note that you may not always be able to use the average as a meaningful comparison, because satellite data may be missing at some latitudes.

NASA satellites provide stratospheric ozone data over time that can be tabulated in a number of ways including global images, Antarctica ozone minima, and size of the ozone hole.

a. Look first at the global images that are centered on Antarctica. Describe what is happening with the passage of time.

b. Now look at the graphs that show the minimum ozone levels and the size of the region affected. What information does each plot give you?

c. Use the information from all three views to write a description of what is meant by the term "ozone hole". In your statement, include references to the region of the globe, area affected, amount of ozone and time.

Figure 2.17 in the text gives the ozone map of the Northern Hemisphere as of February 13, 1999. Visit the World Meteorological Organization to obtain the latest map. Compare this map with the one in the text and offer some possible explanations for the differences observed.