The Ozone Layer

*Depletion of stratospheric ozone

*What is the stratospheric ozone? The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere.

Ozone is found in two layers of the atmoshpere – the troposphere and the stratosphere. The stratosphere is the layer which blocks the ultraviolet radiation coming from the sun

The layer contains the atoms of oxygen O

Ionization

Data (ODS Ozone depletion substance)Type of ODS Amount in TonnesCFCs 539

HCFCs 150

CFC/HCFC blends 57

Halons 73

ODS solvents 280

TOTAL 1099

The Kinds of Ultraviolet Radiation*Ultraviolet radiation is classified according to wavelength. The shortest wavelength is the most “energetic” and biologically dangerous.*UV-A (longest wavelength): The least damaging form of UV radiation. Most UV-A rays pass right through the ozone layer and reach the Earth.*UV-B: Potentially very harmful. Normally, most of the sun’s UV-B radiation is absorbed by stratospheric ozone. But depletion of the ozone layer will allow more UV-B to get through to the Earth’s surface.*UV-C (shortest wavelength): The most dangerous. Fortunately, all UV-C is absorbed by oxygen and ozone in the stratosphere, and never makes it to the surface of the planet.

Impacts of ozone depletion *Effects on humans UVB (the higher energy UV radiation absorbed by ozone) is

generally accepted to be a contributory factor to skin cancer. In addition, increased surface UV leads to increased tropospheric ozone, which is a health risk to humans.[24]

*Increased UV Ozone, while a minority constituent in the Earth's

atmosphere, is responsible for most of the absorption of UVB radiation. The amount of UVB radiation that penetrates through the ozone layer decreases exponentially with the slant-path thickness/density of the layer. Correspondingly, a decrease in atmospheric ozone is expected to give rise to significantly increased levels of UVB near the surface.

*Continued**

* Biological effects The main public concern regarding the ozone hole has been

the effects of increased surface UV and microwave radiation on human health.

*Effects on crops An increase of UV radiation would be expected to affect

crops. A number of economically important species of plants, such as rice, depend on cyanobacteria residing on their roots for the retention of nitrogen. Cyanobacteria are sensitive to UV light and they would be affected by its increase.

Protecting the Ozone Layer: A Global Effort

*The Vienna Convention for the Protection of the Ozone Layer

*The Montreal Protocol on Substances that Deplete the Ozone Layer

The Montreal Protocol is the first international agreement aimed at co-operative environmental action. Its initial goal was to greatly decrease ODS emissions by reducing the production and importation of the main ozone-depleting substances.