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CT: Stratospheric ozone protects the earth’s surface from damaging short-wave ultraviolet (UV) radiation. Ozone is produced in the upper stratosphere by short-wave sunlight, which together with chemical reactions dissociates the ozone again to create a dynamic balance between production and loss. Anthropogenic emissions of inert compounds containing chlorine and bromine affect this balance. A single chlorine or bromine atom can destroy thousands of ozone molecules before being removed from the atmosphere.
S: EEA – https://www.eea.europa.eu/publications/92-9167-205-X/page010.html#:~:text=Stratospheric%20ozone%20protects%20the%20earth’s,balance%20between%20production%20and%20loss. (last access: 10 December 2020)
N: 1. – stratospheric (adj): 1908, from French stratosphère, “sphere of layers”, coined by French meteorologist Léon-Philippe Teisserenc de Bort (1855-1913) from Latin stratus “a spreading out” (from past participle stem of sternere “to spread out”, from PIE root *stere- “to spread”) + French -sphère, as in atmosphère.
– ozone (n): modified form of oxygen, 1840, from German Ozon, coined in 1840 by German chemist Christian Friedrich Schönbein (1799-1868) from Greek ὄζον ozon, neuter present participle of ozein “to smell”. A reference for its pungent odor.
2. The stratospheric ozone absorbs a portion of the radiation from the Sun, preventing it from reaching the planet’s surface. Most importantly, it absorbs the portion of UV light called UVB. UVB has been linked to many harmful effects, including skin cancers, cataracts, and harm to some crops and marine life.
3. The troposphere, the lowest layer of Earth’s atmosphere, the stratosphere is the second layer as you go upward. The next layer above the stratosphere is the mesosphere.
4. The bottom of the stratosphere is around 10 kilometers (6.2 miles) above the ground at middle latitudes. The top of the stratosphere occurs at an altitude of 50 kilometers (31 miles). The height of the bottom of the stratosphere varies with latitude and with the seasons. The lower boundary of the stratosphere can be as high as 20 kilometers (12 miles) near the equator and as low as 7 kilometers (4 miles) at the poles in winter. The lower boundary of the stratosphere is called the tropopause; the upper boundary is called the stratopause.
5. Ozone, an unusual type of oxygen molecule that is relatively abundant in the stratosphere, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun. Temperatures rise as one moves upward through the stratosphere. This is exactly the opposite of the behavior in the troposphere in which we live, where temperatures drop with increasing altitude. Because of this temperature stratification, there is little convection and mixing in the stratosphere, so the layers of air there are quite stable. This is why commercial jet aircrafts fly in the lower stratosphere as turbulence is avoided as turbulence is quite common in the troposphere below. Air is roughly a thousand times thinner at the top of the stratosphere than it is at sea level. This is another reason that jet aircraft and weather balloons reach their maximum operational altitudes within the stratosphere.
6. The stratosphere is very dry; air there contains little water vapor. Because of this, few clouds are found in this layer; almost all clouds occur in the lower, more humid troposphere. Polar stratospheric clouds (PSCs) are the exception. PSCs appear in the lower stratosphere near the poles in winter. They are found at altitudes of 15 to 25 kilometers (9.3 to 15.5 miles) and form only when temperatures at those heights dip below -78° C. They appear to help cause the formation of the infamous holes in the ozone layer by “encouraging” certain chemical reactions that destroy ozone. PSCs are also called nacreous clouds.
7. Due to the lack of vertical convection in the stratosphere, materials that get into the stratosphere can stay there for long times. Such is the case for the ozone-destroying chemicals called CFCs (chlorofluorocarbons). Large volcanic eruptions and major meteorite impacts can fling aerosol particles up into the stratosphere where they may linger for months or years, sometimes altering Earth’s global climate. Rocket launches inject exhaust gases into the stratosphere, producing uncertain consequences.
8. Various types of waves and tides in the atmosphere influence the stratosphere. Some of these waves and tides carry energy from the troposphere upward into the stratosphere; others convey energy from the stratosphere up into the mesosphere. The waves and tides influence the flows of air in the stratosphere and can also cause regional heating of this layer of the atmosphere.
9. Human activities are projected to deplete substantially stratospheric ozone through anthropogenic increases in the global concentrations of key atmospheric chemicals. Human-induced perturbations may be occurring already.
10. When chlorine and bromine atoms come into contact with ozone in the stratosphere, they destroy ozone molecules. One chlorine atom can destroy over 100,000 ozone molecules before it is removed from the stratosphere. Ozone can be destroyed more quickly than it is naturally created. Some compounds release chlorine or bromine when they are exposed to intense UV light in the stratosphere. These compounds contribute to ozone depletion, and are called ozone-depleting substances (ODS). ODS that release chlorine include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs). carbon tetrachloride, and methyl chloroform. ODS that release bromine include halons and methyl bromide. Although ODS are emitted at the Earth’s surface, they are eventually carried into the stratosphere in a process that can take as long as two to five years. This contributes to ozone depletion.
11. Some natural processes, such as large volcanic eruptions, can have an indirect effect on ozone levels. For example, Mt. Pinatubo’s 1991 eruption did not increase stratospheric chlorine concentrations, but it did produce large amounts of tiny particles called aerosols (different from consumer products also known as aerosols). These aerosols increase chlorine’s effectiveness at destroying ozone. The aerosols in the stratosphere create a surface on which CFC-based chlorine can destroy ozone. However, the effect from volcanoes is short-lived.
S: 1. OED – https://www.etymonline.com/search?q=stratospheric, https://www.etymonline.com/search?q=ozone (last access: 8 December 2020). 2. EPA – https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science (last access: 9 December 2020). 3 to 8. UCAR – https://scied.ucar.edu/shortcontent/stratosphere-overview (last access: 9 December 2020). 9. SCIENCE – https://science.sciencemag.org/content/237/4810/35.abstract (last access: 8 December 2020). 10&11. EPA – https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science (last access: 9 December 2020).
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CR: air pollution, biosphere, carbon dioxide, carbon monoxide, chlorofluorocarbon, climate change, contaminant, ecology, environment, global warming, greenhouse effect, greenhouse gas, hydrocarbon, ionosphere, mesopause, mesosphere, methane, nitrogen dioxide, nitrogen oxide, nitrous oxide, ozone layer, pollution, stratosphere, tropospheric ozone.
