Stratospheric Ozone: Environmental Issues

Stratospheric Ozone: Environmental Issues

Abstract

In the stratosphere, the region of the Earth's atmosphere from 10 to 50 kilometers above the surface, the chemical compound ozone plays a vital role in absorbing harmful ultraviolet radiation from the sun. During the past 20 years, concentrations of this important compound have been threatened by human-made gases released into the atmosphere, including those known as CFCs. These chemical compounds as well as meteorological conditions in the stratosphere affect the concentration of stratospheric ozone. Stratospheric ozone is produced after photolysis of molecular oxygen. Far-UV wavelengths (0.175μm < λ < 0.245μm) break down molecular oxygen to produce excited state and ground state atomic oxygen. Excited state atomic oxygen rapidly converts to the ground state. Then ground state oxygen combines to molecular oxygen to give ozone molecule. Ozone is destroyed naturally in stratosphere to give molecular oxygen and excited state atomic oxygen by absorbing λ<310nm or molecular oxygen and ground state atomic oxygen by absorbing λ>310nm. Oxides of nitrogen, hydroxyl radical, hydroperoxy radical etc. are responsible for ozone depletion. CFCs along with other chlorine-and bromine-containing compounds, have been implicated in the accelerated depletion of ozone in the Earth’s stratosphere. Catalytic destruction of ozone removes the odd oxygen species [atomic oxygen (O) and ozone (O3)] while leaving chlorine unaffected. Global monitoring of ozone levels from space by the Total Ozone Mapping Spectrometer instrument has shown statistically significant downward trends in ozone at all latitudes outside the tropics. The troposphere is the layer where most weather activities takes place. The top of the thundercloud has flattened out at the tropopause, the boundary between the two layers. Interaction between the troposphere and stratosphere provide a number of important connections between ozone depletion and climate change, which is the subject matter of this paper.

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