- Branża: Education
- Number of terms: 13055
- Number of blossaries: 0
- Company Profile:
Founded in 1879 and named after Texas' greatest hero General Sam Houston, Sam Houston State University is public shcool within the Texas state university system and located in Huntsville, Texas.
It's a multicultural institution that offers 79 bachelorette degree programs, 54 masters and five ...
In the atmosphere or biosphere a sequence of events in repetitive motion in which the final output feeds back into the initial input. Examples of this include biogeochemical cycles, including the nitrogen, carbon, and sulfur cycles in which these species are chemically processed in gas, solid, and solution phase by physical and biological processes which change their form, oxidation state, and physical state.
Industry:Chemistry; Weather
In the atmosphere sulfur oxides (see sulfur dioxide) are converted to sulfuric acid. Oxides of sulfur and nitrogen combine with atmospheric moisture to produce acid rain. Although some sulfur oxides are introduced into the atmosphere by natural means, such as volcanic eruptions, the majority of the sulfur oxides responsible for the damaging effects of acid rain come from anthropogenic sources, mainly the burning of fossil fuels. Areas in the northeastern United States , eastern Canada , and northern Europe have suffered damage due to the effects of acid rain. In many areas damage to forests, crops, lakes, and streams are so severe that they are completely devoid of any life forms. Steps are now being taken in many parts of the world to reduce the amount of sulfur dioxide introduced into the atmosphere. In 1990, amendments where made to the Clean Air Act that places restrictions on the release of sulfur dioxides by power plants. The amendment calls for the reduction of sulfur emissions from a 1990 level of nearly 20 million tons per year to approximately 10 million tons per year by January 1, 2000.
Industry:Chemistry; Weather
In the atmosphere, the region immediately above the stratosphere and immediately below the thermosphere. The mesosphere begins about 50 kilometers high at the stratopause and ends about 80 kilometers high at the mesopause. The temperature in the mesosphere decreases sharply with increased altitude.
Industry:Chemistry; Weather
In the event of a significant nuclear war, researchers (Paul Crutzen and John Birks initially) predicted that a barrier of smoke (from incinerated urban centers and forests) would fill tropospheric skies--and punch oxides of nitrogen and bomb debris into the stratosphere. Tropospheric smoke would---depending on the extent of the exchange---eventually surround the earth, reducing the tropospheric temperature and causing damage to ecosystems and atmospheric components such as stratospheric ozone. Others have calculated the size of nuclear explosions that are required to get bomb debris into the stratosphere: at mid to high latitudes where the tropopause is lower only 30 kiloton weapons are required; the U. S. atomic bombs used during the Second World War averaged less than 18 kilotons. At low latitudes, where the tropopause is highest, >1 megaton weapons are required to loft bomb debris into the stratosphere. ~Ambios, v11, pages 115-125, 1982. `
Industry:Chemistry; Weather
In the gas phase this process happens when compounds like nitrogen oxides and sulphur oxides are converted in a chemical reaction in the gas phase or in clouds into acidic substances. These acids are rained-out or dry deposited. Significant amounts of the compounds containing nitrogen and sulfur are a direct result of anthropogenic activity. An example reaction that takes place in soil occurs from the oxidation of reduced sulfur (for instance, pyrite) exposed during, for instance, strip mining of lignite. This can be represented as:
2FeS<sub>2</sub> + 6H<sub>2</sub>O + 7O<sub>2</sub> = 4SO<sub>4</sub><sup>2-</sup> + 8H<sup>+</sup> + 2Fe(OH)<sub>2</sub>
Industry:Chemistry; Weather
In the Northern Hemisphere occurs on about June 21 of each year. The summer solstice is the longest day of the year and marks the beginning of the summer season. If the earth's axis were not tilted in relation to the plane of earth's orbit around the sun (the ecliptic) there would be no seasonal changes on earth. But because the earth's axis is tilted in relationship to its plane of orbit around the sun (
Industry:Chemistry; Weather
In the Northern hemisphere, March 21 or 22; on these dates, the rays of the sun are striking vertically at noon at the equator (0 degrees latitude), for the earth is in such a position in its orbit that the axis is tilted neither toward nor away from the sun. For latitudes above the equator, the dates are earlier then these dates.
Industry:Chemistry; Weather
In the ocean (or in lakes) this is the area near the surface with enough light to support photosynthesis. In this zone, both the chemical and biological activity can be enhanced by penetrating solar radiation. This zone is about 20 meters in depth in the ocean. In the upper surface of this zone, the marine photochemistry is most vigorous. Changes in the ultraviolet light content penetrating this region because of changes in the UV-blocking ability of the ozone layer may create unexpected biological results there.
Industry:Chemistry; Weather
In the oceans, a well-defined steep vertical gradient of salinity, a change in aquatic salinity with depth. Though this varies with latitude, the halocline is from about 70 to 200-300 meters below the surface. The Arctic halocline could be influenced by fresh water influx from Arctic rivers. A sudden change in the North Atlantic's halocline could, for instance, effect the long-range oceanic currents such as the Gulf Stream; this could, for instance, effect the climate of Northern Europe.
Industry:Chemistry; Weather
In the stratosphere, anthropogenic chlorine, mostly from chlorofluorocarbons is released as atomic chlorine (a radical) and becomes involved in a chemical cycle that destroys stratospheric ozone:
CF<sub>2</sub>Cl<sub>2</sub> + hv ---> Cl + CF<sub>2</sub>Cl (this reaction produces chlorine radicals and the other chlorine atom is ultimately also freed for O<sub>3</sub> destruction)
catalytic cycle:
Cl + O<sub>3</sub> ---> ClO + O<sub>2</sub> (chlorine reacts with ozone to form chlorine monoxide)
O<sub>3</sub> + hv ---> O + O<sub>2</sub> (ozone is also photolyzed to produce atomic oxygen)
ClO + O ---> Cl + O<sub>2</sub> (chlorine radicals are reformed)
---------------------
NET: 2O<sub>3</sub> -> 3O<sub>2</sub> (the result is conversion of ozone to molecular oxygen)
Atmospheric data have recently shown that the systematic banning of anthropogenic chlorine-containing compounds, CFCs such as Freon-11 and Freon-12, beginning with the Montreal Protocol in 1986, have stopped the degradation of stratospheric ozone, and a healing of this important atmospheric component is underway. And although recent estimates put the return to pre-damage stratospheric levels (< 1979) as being achieved by about 2050, the use of cheap air conditioning systems (using banned CFCs or replacement HCFCs that have otherwise been phased out) in developing countries like India and China may push that "cured" date back by decades.
Industry:Chemistry; Weather
