The first regular measurements of ozone began in the 1920s. Sir Gordon Dobson, who devised the ozone spectrophotometer that now bears his name, started making ozone measurements at Oxford University in England. His Dobson spectrophotometer measures the total amount of ozone from the ground to the top of the atmosphere per unit area. The resulting ozone value is referred to as a "column amount." It does this by measuring the amount of solar ultraviolet radiation absorbed by the atmosphere.

One of the first things that Dobson discovered was the variability of the amount of column ozone. He observed that it varies in a reasonably regular manner with the changing of seasons. He also observed that significant day-to-day variability are superimposed on seasonal variations. He noted that this day-to-day variability correlated with the passage of weather systems over his measurement site.

To investigate the variation of the total column ozone amount with weather systems, Dobson had several more instruments built which he distributed throughout Europe. These could then make simultaneous measurements at a number of points on a daily basis. The results showed a regular variation of the total column amount of ozone with weather systems. When a high pressure system was over the south of England, he observed low amounts of ozone. When a low pressure system moved in, he observed that the ozone amount increased. That is, Dobson noted that ozone amount is anticorrelated (i.e., moves in opposite direction) to air pressure, rising when air pressure falls, and falling when air pressure rises.

We now know considerably more about the causes of variations in stratospheric ozone. The concentration of ozone at a location is governed by a balance among ozone production, ozone loss, and ozone transport. These processes interact to determine the amount of ozone in the stratosphere and its distribution with latitude, longitude, and altitude. They contribute to the variability of ozone observed on different time scales.

In this chapter, we will investigate how these processes (production, transport, and loss) interact to change the spatial distribution of ozone over time. In later chapters, this information will be used to help estimate which portions of observed ozone change in a region are due to natural processes and which are due to the influence of manmade pollutants introduced into the atmosphere.

1.1 Lesson Objectives

By the end of this chapter, the students should be able to: