Ozone is a molecule composed of three oxygen atoms (O₃). It is a pale blue gas at room temperature and is characterized by a distinct smell. Ozone occurs naturally in the Earth's atmosphere, primarily in two regions:
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Stratospheric Ozone: Often referred to as the "ozone layer," this is found in the stratosphere, approximately 10 to 30 miles above the Earth's surface. The ozone layer plays a crucial role in protecting life on Earth by absorbing the majority of the Sun's harmful ultraviolet (UV) radiation, thus reducing the risk of skin cancer, cataracts, and other UV-related health issues, as well as protecting ecosystems.
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Tropospheric Ozone: In contrast, ozone is also present at ground level in the troposphere, which is the lowest layer of the atmosphere. Here, it is considered a harmful air pollutant and a major component of smog. Tropospheric ozone is not emitted directly into the air; rather, it forms through chemical reactions between volatile organic compounds (VOCs) and nitrogen oxides (NOₓ) in the presence of sunlight. High concentrations of ground-level ozone can have detrimental health effects on humans, animals, and plants.
In summary, ozone is a molecule that serves both protective and harmful roles depending on its location in the Earth's atmosphere.