Ozone depletion

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Atmospheric ozone
Ozone cycle
Ozone altitude UV graph
TOMS Global Ozone 65N-65S
Min ozone
Uars ozone waves

Ozone depletion refers to the thinning and reduction of the ozone layer in the Earth's stratosphere. The ozone layer is crucial for life on Earth as it absorbs the majority of the Sun's harmful ultraviolet (UV) radiation, which can cause skin cancer, cataracts, and other health issues in humans, and also affect other living organisms. Ozone depletion has significant environmental impacts, including effects on climate, ecosystems, and biogeochemical cycles.

Causes[edit | edit source]

The primary cause of ozone depletion is the release of chlorofluorocarbons (CFCs), halons, and other ozone-depleting substances (ODS) into the atmosphere. These compounds are stable in the lower atmosphere, allowing them to reach the stratosphere, where they are broken down by UV radiation, releasing chlorine and bromine atoms. These atoms then catalytically destroy ozone molecules, leading to thinning of the ozone layer. Sources of CFCs and other ODS include refrigeration, air conditioning systems, foam blowing agents, and aerosol propellants.

Effects[edit | edit source]

The most well-known consequence of ozone depletion is the increase in UV radiation reaching the Earth's surface. This can lead to higher rates of skin cancer, cataracts, and other health issues in humans. It can also affect wildlife, particularly marine ecosystems where UV radiation penetrates the upper layers of the ocean, affecting phytoplankton, which form the basis of aquatic food webs. Additionally, changes in UV radiation can affect plant growth and crop yields.

Measurement and Monitoring[edit | edit source]

Ozone concentration in the atmosphere is measured in Dobson Units (DU), which represent the thickness of the ozone layer in a column directly above the measurement point. Satellite instruments, ground-based observations, and balloon sondes are used to monitor ozone levels globally. The most significant decrease in ozone has been observed over the Antarctic, leading to the formation of the so-called "ozone hole" in the late 20th century.

International Response[edit | edit source]

The discovery of the ozone hole over Antarctica in the 1980s led to international efforts to address ozone depletion. The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted in 1987 and has been ratified by all countries of the world. The protocol controls the production and consumption of CFCs, halons, and other ODS. Its success has led to a decrease in the emissions of these substances and is expected to lead to the recovery of the ozone layer by the middle of the 21st century.

Recovery and Future Challenges[edit | edit source]

Recent studies suggest that the ozone layer is slowly recovering, thanks to the measures taken under the Montreal Protocol. However, challenges remain, including the potential increase in emissions of some unregulated substances that can also affect the ozone layer. Climate change may also impact the recovery of the ozone layer through changes in atmospheric circulation and temperature.


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Contributors: Prab R. Tumpati, MD