Discovery of acid rain

The modern industrial revolution, starting with the steam engine, the boiler burns coal, produces steam and drives the machine; As a result, the coal consumption of thermal power plants has increased rapidly. Unfortunately, coal contains impurity sulfur, about 1%, which will release acid gas SO2 when burning. The high temperature produced by combustion can also promote some chemical changes in the combustion-supporting air. Oxygen combines with nitrogen and releases acid gas nitrogen oxides. They were washed and dissolved by rain and snow in the sky, and the rain turned into acid rain; These acidic gases become impurities such as sulfate, nitrate and ammonium ions in rainwater. From 65438 to 0872, the British scientist Smith analyzed the composition of rainwater in Renton and found that it was acidic. The rainwater in rural areas contained ammonium carbonate, not acidic. The rainwater in the suburbs contains ammonium sulfate, which is slightly acidic; Urban rainwater contains sulfuric acid or acidic sulfate, which is acidic. So Smith put forward the proper term "acid rain" for the first time in the book Air and Rainfall: The Beginning of Chemical Climatology.

What is acid rain?

Simply put, acid rain is acid rain. What is acid? Pure water is neutral and tasteless; Lemonade and orange juice are sour, and vinegar is sour. They are all weak acids. Baking soda water's alkalinity is slightly astringent, while caustic soda water has astringent taste and strong alkalinity. They are alkali. Scientists have found that acidity is related to the concentration of hydrogen ions in aqueous solution; The alkaline taste is related to the concentration of hydroxyl ions in aqueous solution; Then an index is established: the negative value of the logarithm of hydrogen ion concentration is called pH value. So the pH value of pure water is 7; The greater the acidity, the lower the pH value. The greater the alkalinity, the higher the pH value. The unpolluted rain and snow are neutral, and the pH value is close to 7. When it is saturated with carbon dioxide in the atmosphere, it is slightly acidic with a pH value of 5.65. Rain with pH less than 5.65, which is polluted by acidic gases in the atmosphere, is called acid rain. Snow with pH less than 5.65 is called sour snow; Fog that spreads at high altitude or high mountains (such as Mount Emei) is called acid fog when its pH value is less than 5.65.

What is the acid rain rate?

It can rain several times a year, some are acid rain, some are not acid rain, so generally speaking, the acid rain rate in a certain area is the number of acid rains divided by the total number of rains in the area. Its lowest value is 0%; The highest value is 100%. If there is snow, it should be regarded as rain.

Sometimes, a rainfall process may last for several days, so the acid rain rate should be based on a complete precipitation process, that is, the acid rain rate is the number of precipitation processes with acid rain in a year divided by the total number of precipitation processes in the whole year.

In addition to the annual precipitation pH value, the acid rain rate is another important indicator to judge whether an area is an acid rain area.

What is an acid rain area?

An acid rain sample collected in a certain place cannot be regarded as an acid rain area, because there may be dozens of rains a year, some of which may be acid rain, and some of which may not be acid rain, so it depends on the annual average. At present, the scientific standard of defining acid rain area in China is still under discussion, but it is generally considered that the annual average precipitation pH value is higher than 5.65 and the acid rain rate is 0-20%, which is a non-acid rain area; The pH value is between 5.30 and 5.60, and the acid rain rate is 10-40%, which is a mild acid rain area; The pH value is between 5.00 and 5.30, and the acid rain rate is 30-60%, which is a moderate acid rain area; The pH value is between 4.70 and 5.00, and the acid rain rate is 50-80%, which is a severe acid rain area; The pH value is less than 4.70, and the acid rain rate is 70- 100%, which is a severe acid rain area. This is the so-called five-level standard. In fact, Beijing, Xining, Lanzhou, Urumqi and other cities have also collected several times of acid rain, but the average annual pH value and acid rain rate are within the standard of non-acid rain area, which belongs to non-acid rain area.

Causes of acid rain

The cause of acid rain is a complex atmospheric chemical and physical phenomenon. Acid rain contains many inorganic and organic acids, most of which are sulfuric acid and nitric acid. Sulfur dioxide emitted by coal combustion in industrial production and civil life, and nitrogen oxides emitted by burning oil and automobile exhaust go through the process of "rain in the clouds", that is, water vapor condenses on condensation nuclei such as sulfate and nitrate, and undergoes liquid-phase oxidation reaction to form sulfuric acid raindrops and nitric acid raindrops; It also goes through the "under-cloud scouring process", that is, the droplets containing acid rain continue to merge, adsorb and scour other droplets containing acid rain and acid gas during the falling process, forming larger raindrops and finally falling to the ground, forming acid rain. The acid rain in China is sulfuric acid rain.

Harm of acid rain

Sulfur and nitrogen are nutrient elements. Weakly acidic precipitation can dissolve underground minerals for plants to absorb. If the acidity is too high and the pH value drops below 5.6, it will cause serious harm. It can directly kill large areas of forests and make crops wither; It will also inhibit the decomposition of organic matter and the fixation of nitrogen in the soil, leach nutrients such as calcium, magnesium and potassium combined with soil ions, and make the soil barren; It can also acidify lakes and rivers, dissolve heavy metals in soil and water sediments into water, and poison fish; Accelerate the corrosion and weathering process of buildings and cultural relics; May endanger human health.

Governance measures

The fundamental measure to control acid rain is to reduce the emission of sulfur dioxide and nitrogen oxides.

Acid rain, biological control

In the report "Life Characteristics of 1994" published by Worldwatch Research not long ago, it is said: Generally speaking, the situation of the earth is not very good. Of all the indicators to measure the health of the earth, we have only succeeded in reversing the deterioration of one indicator-the reduction of freon that makes the ozone layer empty. Carbon emissions have not decreased, and air pollution has become increasingly serious. According to statistics, humans emit about 654.38 billion tons of SO2 and 50 million tons of NO2 into the atmosphere every year. About half of the world's urban population lives in the atmospheric environment where SO2 exceeds the standard, and 654.38 billion people live in the environment where particulate matter exceeds the standard. Air pollution has become a hidden killer. Sulfur dioxide is the culprit. Recently, 26 European countries and Canada signed a new agreement proposed by the United Nations Economic Commission for Europe, and the United States also promised to reduce SO2 emissions by 87% by 20 10. European countries and Canada praised the new agreement as a milestone in preventing and controlling air pollution. SO2 not only pollutes the air and harms human health, but also is the main substance that forms acid rain. SO2 and NO2 in the atmosphere are dissolved in rainwater under the action of oxidants. When the pH value of rain, freezing rain, snow, hail and other precipitation is less than 5.6, it is acid rain. According to the determination of relevant departments in the United States, sulfuric acid accounts for 60%, nitric acid accounts for 33%, hydrochloric acid accounts for 6%, and the rest is carbonic acid and a small amount of organic acids.

Acid rain has brought serious influence and destruction to the earth's ecological environment and human social economy. Acid rain acidifies soil and reduces soil fertility. Many toxic substances are absorbed by the root system, poisoning the root system, killing root hairs, making plants unable to absorb water and nutrients from the soil and inhibiting the growth and development of plants. Acid rain acidifies rivers and lakes, inhibits the growth and reproduction of aquatic organisms, and even causes the fry to suffocate and die; Acid rain also kills plankton in the water, reduces the food source of fish, and makes the aquatic ecosystem disorder; Acid rain pollutes rivers, lakes and groundwater, directly or indirectly endangering human health. Acid rain directly damages plant surfaces (leaves and stems) or indirectly damages soil, leading to forest decline. Acid rain can also cause pests and diseases, leading to large-scale forest death. Europe emits 22 million tons of sulfur every year, destroying large areas of forests. More than 654.38 million hectares of forests in Sichuan, Guangxi and other provinces are on the verge of death. Acid rain is very corrosive to metals, stones, wood, cement and other building materials. Many ancient buildings and stone carvings in the world have been destroyed by acid rain, such as the Canadian Parliament Building and the Leshan Giant Buddha in China. Acid rain also directly harms electric wires, rails, bridges and houses.

At present, there are three major acid rain areas in the world. One is the Nordic acid rain area centered on Germany, France, Britain and other countries, involving more than half of Europe. Second, acid rain areas in North America, including the United States and Canada, were formed in the late 1950s. The total area of these two acid rain areas is more than 654.38+million square kilometers, and the pH value of precipitation is less than 5.0, and some are even less than 4.0. The acid rain area formed in China in the mid-1970s covering Sichuan, Guizhou, Guangdong, Guangxi, Hunan, Hubei, Jiangxi, Zhejiang, Jiangsu and Qingdao is the third largest acid rain area in the world. Although the area of acid rain area in China is small, its rapid development and expansion and high acidification rate of precipitation are rare in the world. Because air pollution has no national boundaries, acid rain is a global disaster.

The harm of acid rain has attracted worldwide attention. The United Nations has held many international conferences to discuss the problem of acid rain. Many countries list acid rain control as a major scientific research project. More than 40 countries in the world have restricted automobile emissions through pollution. At the "International Cooperation Conference on the Application of Environment-friendly Biotechnology" held in India from 65438 to 0993, experts put forward measures to prevent, stop and reverse environmental degradation by biotechnology, enhance the sustainable development and application of natural resources, and maintain environmental integrity and ecological balance. Experts believe that there is great potential to harness the environment by biotechnology. Coal is one of the most important energy sources at present, but it contains sulfur and emits harmful gases such as SO2 when burning. There are two kinds of sulfur in coal: inorganic sulfur and organic sulfur. Most inorganic sulfur exists in mineral form, and pyrite (FeS2) is the main one. Biologists use microbial desulfurization to change ferrous iron into trivalent iron, and monomer sulfur into sulfuric acid, which has achieved good results. For example, Japan's Central Electric Power Research Institute isolated a thiobacillus from soil, which is an iron-oxidizing bacterium that can effectively remove inorganic sulfur from coal. A new microbial strain has been screened by the American Natural Gas Research Institute, which can separate organic sulfur from coal without reducing the quality of coal. An acid-hot sulfur bacterium was screened from Czech Republic, which can remove 75% sulfur from pyrite. According to the statistics of 199 1 year, the Czech Republic removed 78.5% of inorganic sulfur and 23.4% of organic sulfur from coal by biotechnology. At present, scientists have found that Thiobacillus ferrooxidans and Thiobacillus thiooxidans can remove sulfur from pyrite. A new technology recently developed by Electric Power Central Research Institute, a Japanese consortium, can remove 70% of inorganic sulfur and reduce 60% of dust. This technology is simple in principle and cheap in equipment, especially suitable for developing countries that can't afford expensive desulfurization equipment. Biotechnology desulfurization conforms to the principles of "source treatment" and "clean production", and it is a promising treatment method, which has been paid more and more attention by countries all over the world.

How to reduce acid rain?

Acid rain is one of the most obvious air quality problems we are facing today. When fossil fuels are burned to generate electricity and provide transportation, acidic substances and compounds that lead to the formation of acidic substances are produced. These substances are mainly acids derived from sulfur oxides and nitrogen oxides. These compounds also have some natural sources, such as lightning, volcanoes, biomass burning and microbial activities, but these natural sources are quite small compared with the exhaust gas of automobiles, power plants and smelters except for rare volcanic eruptions.

The impact of acid rain is most obvious in Europe and the northeastern United States, and it is widely known, but the threatened areas also include Canada, and perhaps the California Mountains, Loki Mountains and China. In some places, it is occasionally observed that the falling rain is as sour as vinegar. The influence of acid rain is a controversial topic. The harm to aquatic organisms in lakes and rivers was initially the focus of attention, but now people have realized that the harm to buildings, bridges and equipment is another costly consequence of acid rain. The impact of polluted air on human health is the most difficult to determine quantitatively.

Lakes with poor buffering capacity suffer the most. When there is a natural alkaline buffer, the acidic compounds (mainly sulfuric acid, nitric acid and a small amount of organic acids) in acid rain will be neutralized. However, lakes on granite (acidic) strata are vulnerable to direct harm, because the acid in rainwater can dissolve metal ions such as aluminum and manganese. This will reduce the growth of plants and algae, and in some lakes, it will also lead to the decrease or disappearance of fish populations. The damage caused by this form of pollution to plants ranges from harmful effects on leaves to damage to fine roots.

In the northeastern United States, the main consideration for reducing pollutants is those coal-fired power plants that burn high sulfur content. One possible remedy is chemical scrubber, which can prevent pollutants from being discharged. Chemical scrubber is a kind of equipment used to treat waste gas, or dissolve, or precipitate, or eliminate pollutants. Catalysts can reduce nitrogen oxide emissions from stationary and mobile sources, which is another example that chemistry can play a role in improving air quality.

Various strategic measures to reduce acid rain may require billions of dollars of investment every year. Because the cost is so huge, it is very important to understand the atmospheric processes involving pollutant migration, chemical transformation and destination.

Acid deposition consists of two parts, namely "wet" precipitation (such as rain and snow) and dry deposition (aerosol or gaseous acid compounds deposited on the surfaces of soil particles and plant leaves). The substances that eventually settle down usually enter the atmosphere in a very different chemical form. For example, sulfur in coal is oxidized to sulfur dioxide, which is a gaseous form discharged from a chimney. As it moves in the atmosphere, it will slowly oxidize and react with water to produce sulfuric acid-a form that may be deposited hundreds of miles downwind.

The formation, reaction and final removal of nitrogen oxides from the atmosphere are also very complicated. When nitrogen and oxygen are heated at high temperature in power plants, civil stoves and automobile engines, they will produce nitric oxide (NO), which will react with oxidants to produce nitrogen dioxide (NO2) and finally nitric acid (HNO3). The global statistics of nitrogen oxides-the quantitative estimation of where they come from and where they go is still quite uncertain.

It is easy to see that it is difficult to choose air pollution control strategies with confidence until we thoroughly understand the biogeochemical cycles of different chemical forms of nitrogen, sulfur and carbon and the global sources and destinations of these chemical species. Atmospheric chemistry and environmental chemistry are the core to realize a cleaner and healthier environment. Developing reliable methods for determining trace chemical species in the air, important atmospheric reaction kinetics, and finding new and more effective chemical processes that can be used to reduce pollutant emissions are the goals that the country must promise in the next 10 year.

Black humor of acid rain

pickled vegetables

After acid rain acidified the soil, it further acidified the groundwater. A housewife in the Black Triangle area where Germany, Poland and the former Czech Republic meet (the local area was first famous for its forests, and then the forests were destroyed by acid rain) said, "There are only a few wells in our area to drink. We often joke that as long as we soak the vegetables in the well, we can make good kimchi (ester axillary vegetables). "

Dye the hair

Acidified groundwater can also corrode water pipes. In the village of Sirina in Markshire, southern Sweden, the hair of three children in a family changed from golden yellow to green. This is the "green hair" incident that made Mark County famous. The reason is that they changed the zinc tube in the well into copper tube, and the water with pH less than 5.6 is very corrosive to copper and will produce copper rust. So the bathroom and washstand of this family were dyed bronze green. This kind of water dissolved with copper or zinc ions can also cause unexplained diarrhea in infants. This is also the reason for the collective "food poisoning" in kindergartens in Mark County (about half of Swedes use groundwater as their drinking water source). In Lancashire, England, the faucet releases turbid water containing a lot of rust due to corrosion of water pipes. Acid rain even caused water pipes to rupture due to corrosion. Four days before Christmas (1985), the water pipeline with a diameter of 1 m in Yorkshire, England, was broken, and the spare one could not be used, leaving 200,000 people in a state of water shortage.

slow train

In Tokaviz, Poland, the speed of the train is less than 40 kilometers per hour because the tracks are corroded by acid rain, which is quite dangerous.

Discoloration of Taj Mahal

Marble contains much calcium and is most afraid of acid rain erosion. For example, there are two famous Cologne cathedrals in Germany, the spires are 157 meters high, and the surface of the stone walls has been corroded and uneven, and there are many "acid tendons". The stone statues of angels and Maria leading to the population area have been eroded and it is difficult to recover. Among them, sandstone (more corrosive) stone carvings even eroded 10 cm in the past 15 years. The famous Taj Mahal in India, which entered the World Heritage List, lost its luster due to air pollution and acid rain corrosion, and its milky white gradually turned yellow and some of it became rusty.

Imperial academy suffers.

The "Jinshi Stele Forest" (plot * * 198) in the Confucius Temple in Guozijian Street, Beijing, China has a history of 700 years. It is engraved with the names, places of origin and rankings of 5 1624 students in Yuan, Ming and Qing dynasties, which is valuable information for studying the imperial examination system in ancient China. In recent years, due to air pollution and acid rain, the surfaces of many stone tablets have been seriously corroded and peeled off, and stone tablets with precious historical value have changed beyond recognition. According to the managers, these stone tablets were seriously damaged in the last three years, so 198 Jinshi tablet is only less than a hundred years ago, but its damage is no less than other stone tablets. In fact, other stone cultural relics in Beijing, such as the clock sculpture of Dazhong Temple, the white marble railings and stone carvings of the Forbidden City, and the stone lions of Lugou Bridge, have also been corroded or peeled off to varying degrees.

Free goddess makeup

Acid rain can also corrode metal cultural relics. For example, the famous Statue of Liberty in new york Harbor, USA, the thin copper sheet wrapped in reinforced concrete became loose due to acid rain, and fell off at the first touch (1932 was still intact when it was inspected), so it had to be overhauled (1986 Statue of Liberty 100 was repaired during its anniversary). Four bronze horses on the balcony above the facade of Saint Mary's Church in Venice, Italy, were once taken to Paris by Napoleon and returned to Zhao. Recently, due to the serious damage of acid rain, it could not be repaired well, so we had to move it indoors and change a replica in situ. There are many similar situations in the world. In the temple of Utrecht in central Netherlands, there is a set of combined sound clocks, which were cast in17th century. For 300 years, people have been very fond of listening to its voice. However, after 30 years, the interval between the clocks has gone wrong, and the timbre has gradually become less loud. Because the clock is made of 80% copper, the corrosion of acid rain has entered the interior of the clock because of the repeated vibration and gradual peeling of copper rust when ringing the clock.

Acid rain hits Antarctica.

Shockingly, acid rain has also been observed in Antarctica, and it is a relatively strong acid rain. For example, eight acid rains were observed at the Great Wall Station in Antarctica in April 1998, and the lowest pH value was only 4.45. The iron buildings and iron towers at the Great Wall Station have rusted and peeled off, and some of them have to be updated. In order to slow down corrosion, paint should be brushed 2-3 times a year.

Pierce precious stained glass

In Europe, there are more than 654.38 million churches with medieval stained glass. These colored glasses are very precious. They were removed and evacuated in World War II, and most of them were safe and sound. But like other ancient buildings, it cannot escape the attack of acid rain. These stained glasses gradually lose their mysterious luster and turn brown, and some even fade completely. Look at the glass surface carefully, there are countless holes. Acid rain continues to react with potassium, sodium and calcium in the pores (calcium only exists in glass produced in the Middle Ages). For example, gypsum is produced by chemical reaction with calcium. Acid rain destroyed the glass from the inside.

Calligraphy and painting were robbed.

Fine dust (dry deposition) with acidity enters the room, and when the relative humidity of the air is high, it begins to erode the ancient books in the library. The paper is oxidized to brown, and the paper quality becomes worse or even damaged. The leather covers of the books of the British Library in the 1920s and 1930s were also damaged by sulfuric acid, and they are changing color, as if floating with red rust. The same is true of murals. Fortunately, since the mid-to-late 1980s, air pollution control in Europe has been accelerated, and the speed of all kinds of corrosion damage has obviously slowed down. Fear of oil painting corrosion has also expanded among collectors. White or transparent crystal particles are sprayed out like powder not only on the surface of the painting, but also on the back of the canvas. After a period of time, these particles will go deep into the paint surface and completely destroy the paint containing chemical pigments. The part that is not exposed to the air does not have this phenomenon. It can be seen that the harm of air pollution and dry deposition is great.

Acid rain is slippery.

The appearance of "acid rain skating" in buildings is another "new thing" harmed by acid rain. Concrete is dissolved by acid rain, and then water evaporates in the process of dripping, while solid components such as calcium sulfate remain, forming "stalactites" similar to limestone caves. The calcium sulfate dripping on the ground remains to form "stalagmites". It is called "ice walk" because this kind of "stalactite" is very similar to the cold water flowing from the eaves in winter, and gradually freezes in the flow, forming a drooping "ice walk". This kind of acid rain lingers under overpasses and buildings in many cities in Japan. Make the building loose and unstable, and even become a dangerous building. Regarding the losses caused by acid rain to buildings, the Federal Environmental Protection Agency of the United States estimated in 1985 that the losses caused by acid rain in 17 states were as high as $5 billion. The main reasons are accelerated damage of buildings, rapid peeling of paint decoration and corrosion of window frames. In addition, the loss caused by the decrease in tourism income is also $2 billion.

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