臭氧层 英文
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发布时间：2022-04-30 19:28
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时间：2022-04-12 15:14
import sqlite3import os,sysDATABASE = os.path.dirname(__file__) + /sqlite.dbdef test_db():db = sqlite3.connect(DATABASE)cur = db.cursor()sql = create table post(ID INT PRIMARY KEY NOT NULL,TITLE CHAR(50),CONTENT TEXT,AUTHOR CHAR(30))data =
import sqlite3 import os,sys DATABASE = os.path.dirname(__file__) + '/sqlite.db' def test_db(): db = sqlite3.connect(DATABASE) cur = db.cursor() sql = ''' create table post( ID INT PRIMARY KEY NOT NULL, TITLE CHAR(50), CONTENT TEXT, AUTHOR CHAR(30) ) ''' data = ''' insert into post(id,title,content,author) values(1,'good news','you win the big prize','admin') ''' print 'run the query' query = "select * from post" posts = cur.execute(query) for post in posts: print post[1] db.close() if __name__ == '__main__':test_db()
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时间：2022-04-12 12:22
自然界中的臭氧，大多分布在距地面20Km--50Km的大气中，我们称之为臭氧层。臭氧层中的臭氧主要是紫外线制造出来的。大家知道，太阳光线中的紫外线分为长波和短波两种，当大气中（含有21%）的氧气分子受到短波紫外线照射时，氧分子会分解成原子状态。氧原子的不稳定性极强，极易与其他物质发生反应。如与氢（H2）反应生成水（H2O)，与碳（C）反应生成二氧化碳（C02）。同样的，与氧分子（O2）反应时，就形成了臭氧（O3）。臭氧形成后，由于其比重大于氧气，会逐渐的向臭氧层的底层降落，在降落过程中随着温度的变化（上升），臭氧不稳定性愈趋明显，再受到长波紫外线的照射，再度还原为氧。臭氧层就是保持了这种氧气与臭氧相互转换的动态平衡。
在这么广大的区域内到底有多少臭氧呢？估计小于大气的十万分之一。如果把大气中所有的臭氧集中在一起，仅仅有三公分薄的一层。那么，地球表面是否有臭氧存在呢？回答是肯定的。太阳的紫外线大概有近1%部分可达地面。尤其是在大气污染较轻的森林、山间、海岸周围的紫外线较多，存在比较丰富的臭氧。
此外，雷电作用也产生臭氧，分布于地球的表面。正因为如此，雷雨过后，人们感到空气的清爽，人们也愿意到郊外的森林、山间、海岸去吮吸大自然清新的空气，享受自然美景的同时，让身心来一次爽爽快快的“洗浴”，这就是臭氧的功效，所以有人说，臭氧是一种干净清爽的气体。（臭氧有极强的氧化性，少量的臭氧会使人感到精神振奋；但过强的氧化性也使其具有杀伤作用，详见自由基）。
大气臭氧层主要有三个作用。其一为保护作用，臭氧层能够吸收太阳光中的波长306.3μm以 下的紫外线，主要是一部分UV—B(波长290～300μm)和全部的UV—C(波长＜290μm＝，保护地球上的人类和动植物免遭短波紫外线的伤害。只有长波紫外线UV-A和少量的中波紫外线UV-B能够辐射到地面，长波紫外线对生物细胞的 伤害要比中波紫外线轻微得多。所以臭氧层犹如一件宇宙服保护地球上的生物得以生存繁衍 。其二为加热作用，臭氧吸收太阳光中的紫外线并将其转换为热能加热大气，由于这种作用 大气温度结构在高度50km左右有一个峰，地球上空15～50km存在着升温层。正是由于存在着 臭氧才有平流层的存在。而地球以外的星球因不存在臭氧和氧气，所以也就不存在平流层。 大气的温度结构对于大气的循环具有重要的影响，这一现象的起因也来自臭氧的高度分布。其三为 温室气体的作用，在对流层上部和平流层底部，即在气温很 低的这一高度，臭氧的作用同样非常重要。如果这一高度的臭氧减少，则会产生使地面气温 下降的动力。因此，臭氧的高度分布及变化是极其重要的。
臭氧是无色气体，有特殊臭味，因此而得名“臭氧”。由太阳飞出的带电粒子进入大气层，使氧分子裂变成氧原子，而部分氧原子与氧分子重新结合成臭氧分子。距地面15～50千米高度的大气平流层，集中了地球上约90％的臭氧，这就是“臭氧层”。
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时间：2022-04-12 13:40
From Wikipedia, the free encyclopedia
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The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth.[1] Over 91% of the ozone in Earth's atmosphere is present here.[1] It is mainly located in the lower portion of the stratosphere from approximately 10 km to 50 km above Earth, though the thickness varies seasonally and geographically.[2] The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The "Dobson unit", a convenient measure of the total amount of ozone in a column overhead, is named in his honor.
Contents [hide]
1 Origin of ozone
2 Ultraviolet light and ozone
3 Distribution of ozone in the stratosphere
4 Ozone depletion
4.1 Regulation
5 References
6 Further reading
7 External links
[edit] Origin of ozone
Ozone-oxygen cycle in the ozone layer.The photochemical mechanisms that give rise to the ozone layer were discovered by the British physicist Sidney Chapman in 1930. Ozone in the Earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O2), splitting them into indivial oxygen atoms (atomic oxygen); the atomic oxygen then combines with unbroken O2 to create ozone, O3. The ozone molecule is also unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O2 and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle, thus creating an ozone layer in the stratosphere, the region from about 10 to 50 km (32,000 to 164,000 feet) above Earth's surface. About 90% of the ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 km, where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only a few millimeters thick .
[edit] Ultraviolet light and ozone
Levels of ozone at various altitudes and blocking of ultraviolet radiation.Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation emitted from the Sun. UV radiation is divided into three categories, based on its wavelength; these are referred to as UV-A (400-315 nm), UV-B (315-280 nm), and UV-C (280-100 nm). UV-C, which would be very harmful to humans, is entirely screened out by ozone at around 35 km altitude. UV-B radiation can be harmful to the skin and is the main cause of sunburn; excessive exposure can also cause genetic damage, resulting in problems such as skin cancer. The ozone layer is very effective at screening out UV-B; for radiation with a wavelength of 290 nm, the intensity at Earth's surface is 350 billion times weaker than at the top of the atmosphere. Nevertheless, some UV-B reaches the surface. Most UV-A reaches the surface; this radiation is significantly less harmful, although it can potentially cause genetic damage.
UV-B energy levels at several altitudes. Blue line shows DNA sensitivity. Red line shows surface energy level with 10% decrease in ozone
[edit] Distribution of ozone in the stratosphere
The thickness of the ozone layer—that is, the total amount of ozone in a column overhead—varies by a large factor worldwide, being in general smaller near the equator and larger as one moves towards the poles. It also varies with season, being in general thicker ring the spring and thinner ring the autumn in the northern hemisphere. The reasons for this latitude and seasonal dependence are complicated, involving atmospheric circulation patterns as well as solar intensity.
Since stratospheric ozone is proced by solar UV radiation, one might expect to find the highest ozone levels over the tropics and the lowest over polar regions. The same argument would lead one to expect the highest ozone levels in the summer and the lowest in the winter. The observed behavior is very different: most of the ozone is found in the mid-to-high latitudes of the northern and southern hemispheres, and the highest levels are found in the spring, not summer, and the lowest in the autumn, not winter in the northern hemisphere. During winter, the ozone layer actually increases in depth. This puzzle is explained by the prevailing stratospheric wind patterns, known as the Brewer-Dobson circulation. While most of the ozone is indeed created over the tropics, the stratospheric circulation then transports it poleward and downward to the lower stratosphere of the high latitudes. However in the southern hemisphere, owing to the ozone hole phenomenon, the lowest amounts of column ozone found anywhere in the world are over the Antarctic in the southern spring period of September and October.
Brewer-Dobson circulation in the ozone layer.The ozone layer is higher in altitude in the tropics, and lower in altitude in the extratropics, especially in the polar regions. This altitude variation of ozone results from the slow circulation that lifts the ozone-poor air out of the troposphere into the stratosphere. As this air slowly rises in the tropics, ozone is proced by the overhead sun which photolyzes oxygen molecules. As this slow circulation bends towards the mid-latitudes, it carries the ozone-rich air from the tropical middle stratosphere to the mid-and-high latitudes lower stratosphere. The high ozone concentrations at high latitudes are e to the accumulation of ozone at lower altitudes.
The Brewer-Dobson circulation moves very slowly. The time needed to lift an air parcel from the tropical tropopause near 16 km (50,000 ft) to 20 km is about 4–5 months (about 30 feet (9.1 m) per day). Even though ozone in the lower tropical stratosphere is proced at a very slow rate, the lifting circulation is so slow that ozone can build up to relatively high levels by the time it reaches 26 km.
Ozone amounts over the continental United States (25°N to 49°N) are highest in the northern spring (April and May). These ozone amounts fall over the course of the summer to their lowest amounts in October, and then rise again over the course of the winter. Again, wind transport of ozone is principally responsible for the seasonal evolution of these higher latitude ozone patterns.
The total column amount of ozone generally increases as we move from the tropics to higher latitudes in both hemispheres. However, the overall column amounts are greater in the northern hemisphere high latitudes than in the southern hemisphere high latitudes. In addition, while the highest amounts of column ozone over the Arctic occur in the northern spring (March-April), the opposite is true over the Antarctic, where the lowest amounts of column ozone occur in the southern spring (September-October). Indeed, the highest amounts of column ozone anywhere in the world are found over the Arctic region ring the northern spring period of March and April. The amounts then decrease over the course of the northern summer. Meanwhile, the lowest amounts of column ozone anywhere in the world are found over the Antarctic in the southern spring period of September and October, owing to the ozone hole phenomenon.
[edit] Ozone depletion
Main article: Ozone depletion
NASA projections of stratospheric ozone concentrations if chlorofluorocarbons had not been banned.The ozone layer can be depleted by free radical catalysts, including nitric oxide (NO), nitrous oxide (N2O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br). While there are natural sources for all of these species, the concentrations of chlorine and bromine have increased markedly in recent years e to the release of large quantities of manmade organohalogen compounds, especially chlorofluorocarbons (CFCs) and bromofluorocarbons.[3] These highly stable compounds are capable of surviving the rise to the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyze a chain reaction capable of breaking down over 100,000 ozone molecules. The breakdown of ozone in the stratosphere results in the ozone molecules being unable to absorb ultraviolet radiation. Consequently, unabsorbed and dangerous ultraviolet-B radiation is able to reach the Earth’s surface.[citation needed] Ozone levels, over the northern hemisphere, have been dropping by 4% per decade. Over approximately 5% of the Earth's surface, around the north and south poles, much larger (but seasonal) declines have been seen; these are the ozone holes.
In 2009, nitrous oxide (N2O) was the largest ozone-depleting substance emitted through human activities. [4]
[edit] Regulation
In 1978, the United States, Canada and Norway, enacted bans on CFC-containing aerosol sprays that are thought to damage the ozone layer. The European Community rejected an analogous proposal to do the same. In the U.S., chlorofluorocarbons continued to be used in other applications, such as refrigeration and instrial cleaning, until after the discovery of the Antarctic ozone hole in 1985. After negotiation of an international treaty (the Montreal Protocol), CFC proction was sharply limited beginning in 1987 and phased out completely by 1996.
On August 2, 2003, scientists announced that the depletion of the ozone layer may be slowing down e to the international ban on CFCs.[5] Three satellites and three ground stations confirmed that the upper atmosphere ozone depletion rate has slowed down significantly ring the past decade. The study was organized by the American Geophysical Union. Some breakdown can be expected to continue e to CFCs used by nations which have not banned them, and e to gases which are already in the stratosphere. CFCs have very long atmospheric lifetimes, ranging from 50 to over 100 years, so the final recovery of the ozone layer is expected to require several lifetimes.
Compounds containing C–H bonds have been designed to replace the function of CFC's (such as HCFC), since these compounds are more reactive and less likely to survive long enough in the atmosphere to reach the stratosphere where they could affect the ozone layer. However, while being less damaging than CFC's, HCFC's also have a significant negative impact on the ozone layer. HCFC's are therefore also being phased out.[6]
到维京百科查ozonosphere就成.
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时间：2022-04-12 15:15
The ozone layer resides in the stratosphere and surrounds the entire Earth. UV-B radiation (280- to 315- nanometer (nm) wavelength) from the Sun is partially absorbed in this layer. As a result, the amount of UV-B reaching Earth’s surface is greatly reced. UV-A (315- to 400-nm wavelength) and other solar radiation are not strongly absorbed by the ozone layer. Human exposure to UV-B increases the risk of skin cancer, cataracts, and a suppressed immune system. UV-B exposure can also damage terrestrial plant life, single cell organisms, and aquatic ecosystems.
In the past 60 years or so human activity has contributed to the deterioration of the ozone layer.
Only 10 or less of every million molecules of air are ozone. The majority of these ozone molecules resides in a layer between 10 and 40 kilometers (6 and 25 miles) above the Earth's surface in the stratosphere.
Each spring in the stratosphere over Antarctica (Spring in the southern hemisphere is from September through November.), atmospheric ozone is rapidly destroyed by chemical processes.
As winter arrives, a vortex of winds develops around the pole and isolates the polar stratosphere. When temperatures drop below -78°C (-109°F), thin clouds form of ice, nitric acid, and sulphuric acid mixtures. Chemical reactions on the surfaces of ice crystals in the clouds release active forms of CFCs. Ozone depletion begins, and the ozone “hole” appears.
Over the course of two to three months, approximately 50% of the total column amount of ozone in the atmosphere disappears. At some levels, the losses approach 90%. This has come to be called the Antarctic ozone hole.
In spring, temperatures begin to rise, the ice evaporates, and the ozone layer starts to recover.
The Antarctic ozone hole was discovered in 1985 by British scientists Joesph Farman, Brian Gardiner, and Jonathan Shanklin of the British Antarctic Survey.
The ozone "hole" is really a rection in concentrations of ozone high above the earth in the stratosphere. The ozone hole is defined geographically as the area wherein the total ozone amount is less than 220 Dobson Units. The ozone hole has steadily grown in size (up to 27 million sq. km.) and length of existence (from August through early December) over the past two decades.
After a series of rigorous meetings and negotiations, the Montreal Protocol on Substances that Deplete the Ozone Layer was finally agreed upon on 16 september 1987 at the Headquarters of the International Civil Aviation Organization in Montreal.
The Montreal Protocol stipulates that the proction and consumption of compounds that deplete ozone in the stratosphere--chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform--are to be phased out by 2000 (2005 for methyl chloroform). Scientific theory and evidence suggest that, once emitted to the atmosphere, these compounds could significantly deplete the stratospheric ozone layer that shields the planet from damaging UV-B radiation.
Man-made chlorines, primarily chloroflourobcarbons (CFCs), contribute to the thinning of the ozone layer and allow larger quantities of harmful ultraviolet rays to reach the earth.
Satellite observations show a decrease in global total ozone values over more than two decades. The graph above compares global ozone values (annual averages) with the average from the period 1964 to 1980. Seasonal and solar effects have been removed from the data. On average, global ozone decreased each year between 1980 and the early 1990s. The decrease worsened ring the few years when volcanic aerosol from the Mt. Pinatubo eruption in 1991 remained in the stratosphere. Now global ozone is about 4% below the 1964- to-1980 average.
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时间：2022-04-12 17:06
Because of the strong absorption of solar ultraviolet radiation by molecular oxygen and ozone, solar radiation capable of procing ozone cannot reach the lower levels of the atmosphere, and the photochemical proction of ozone is not significant below about 20 km (12 miles). This absorption of solar energy is very important in procing a temperature maximum at about 50 km, called the stratopause, or the mesopeak. Also, the presence of the ozone layer in the upper atmosphere, with its accompanying absorption, effectively blocks almost all solar radiation of wavelengths less than 290 nanometres from reaching the Earth’s surface, where it would injure or kill most living things.
Certain air pollutants, particularly chlorofluorocarbons and halons (chlorofluorobromine compounds), can diffuse into the ozonosphere and destroy ozone. In the mid-1980s scientists discovered that a “hole” developed periodically in the ozonosphere above Antarctica; it was found that the ozone layer there was thinned by as much as 40–50 percent from its normal concentrations. This severe regional ozone depletion was explained as a natural phenomenon, but one that was probably exacerbated by the effects of chlorofluorocarbons and halons. Concern over increasing global ozone depletion led to international restrictions on the use of chlorofluorocarbons and halons and to scheled rections in their manufacture.
Even though the ozone layer is about 40 km (25 miles) thick, the total amount of ozone, compared with more abundant atmospheric gases, is quite small. If all of the ozone in a vertical column reaching up through the atmosphere were compressed to sea-level pressure, it would form a layer only a few millimetres thick.
参考资料：http://www.britannica.com/EBchecked/topic/437240/ozonosphere
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时间：2022-04-12 19:14
