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Ozone cycle illustrated over image by NASA astronaut Scott Kelly. Ozone is a ubiquitous yet highly reactive molecule in the atmosphere. Such a highly reactive oxidizer would normally be dangerous to life but ozone's concentration at sea level is usually not high enough to be toxic.
The highest levels of ozone in the atmosphere are in the stratosphere, in a region also known as the ozone layer between about 10 and 50 km above the surface (or between about 6 and 31 miles). However, even in this "layer", the ozone concentrations are only two to eight parts per million, so most of the oxygen there is dioxygen, O 2 , at about ...
About 90% of total ozone in the atmosphere is in the stratosphere, and 10% is in the troposphere. [5] Although ground-level ozone is less concentrated than stratospheric ozone, it is of concern because of its health effects. [6] Ozone in the troposphere is considered a greenhouse gas, and as such contribute to global warming.
The Dobson unit (DU) is a unit of measurement of the amount of a trace gas in a vertical column through the Earth's atmosphere.It originated by, and continues to be primarily used in respect to, the study of atmospheric ozone, whose total column amount, usually termed "total ozone", and sometimes "column abundance", is dominated by the high concentrations of ozone in the stratospheric ozone layer.
The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level. It contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The stratosphere defines a layer in which temperatures rise with increasing altitude.
The atmosphere is 21% oxygen by volume, which equates to a total of roughly 34 × 10 18 mol of oxygen. [2] Other oxygen-containing molecules in the atmosphere include ozone (O 3), carbon dioxide (CO 2), water vapor (H 2 O), and sulphur and nitrogen oxides (SO 2, NO, N 2 O, etc.).
Most of the ozone production occurs in the tropical upper stratosphere and mesosphere. The total mass of ozone produced per day over the globe is about 400 million metric tons. The global mass of ozone is relatively constant at about 3 billion metric tons, meaning the Sun produces about 12% of the ozone layer each day. [1]
Dobson spectrophotometers can be used to measure both total column ozone and profiles of ozone in the atmosphere. [5] [6] Ozone is tri-atomic oxygen, O 3; ozone molecules absorb harmful UV light in the atmosphere before it reaches the surface of the earth. No UVC radiation penetrates to the ground as it is absorbed in the ozone-oxygen cycle.