This rate of decline is about three times faster than that recorded in the 1970's. In addition to Antarctica, ozone depletion now affects almost all of North America, Europe, Russia, Australia, New Zealand, and a sizeable part of South America. Short term losses of ozone can be much greater than the long term average. In Canada, ozone depletion is usually greatest in the late winter and early spring. Emissions of chlorine and bromine containing synthetic compounds known as industrial halocarbons are the cause of stratospheric ozone depletion.
Industrial halocarbons are effective ozone-depleters for two reasons.
The first is that they are not reactive, which means they survive long enough in the atmosphere to drift up into the stratosphere. The second is that they help the natural reactions that destroy ozone. They simply do not break down in the lower atmosphere and they can remain in the atmosphere from 20 to 120 years or more. Both chlorine and bromine activate and speed up the ozone destruction reactions without being altered or destroyed themselves. Thus, a single chlorine atom can destroy up to 100,000 ozone molecules before it finally forms a stable compound and diffuses out of the stratosphere.