Before undertaking a study of the critical importance of ozone in biological earth sciences, it is necessary to understand the spatial and temporal distribution patterns of ozone in the atmosphere. This chapter attempts to do so. The first two sections detail the various ways in which varying ozone amounts are expressed with height. This includes both as a profile, which gives the ozone amount at any given level, and as a column amount, which gives the summed amount from a specified level all the way to the top of the atmosphere. Next it explains the seasonal and regional characteristics of observed ozone distribution. Finally, it examines long-term trends in ozone.

1.1 Chapter Objectives

When you complete the reading of this discussion you should be able to explain

Ozone is a molecule consisting of three oxygen atoms and is found mainly in the stratosphere where it is created. Figure 3.01 provides a cartoon sketch of how ozone is formed.

First, extreme ultraviolet radiation (EUV) breaks apart oxygen molecules (O2) to free oxygen atoms (O). EUV refers to sunlight with a wavelength less than 240 nanometers. These free O atoms then react with other O2 molecules to form ozone (O3). Because O3 production depends upon sunlight, it is not surprising that the distribution of ozone varies considerably with altitude, latitude, season, year, and time of day. Before we look at the variation of ozone, however, we should first examine the units in which ozone is measured.

Ozone measurements are typically reported in one of four units.

Each of these ways of quantifying ozone provides a different perspective on the ozone distribution.