Causes and harmful effects of acid rain. The process of formation of acid rain: why is it dangerous for people? What substances cause the formation of acid rain
Hydrometeors with a pH below normal and characterized by the presence of harmful substances are acid rain. It could be snow, fog, rain or hail. Any of the species in the atmosphere and on earth can lead to an environmental disaster.
Just a couple of decades ago, only the scientific community was concerned about the negative impact of this phenomenon. Now it is causing great concern not only in the scientific world, but also among the general public, as well as various government agencies.
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History of the problem
The effect of precipitation with a reduced water index on the environment was outlined more than a hundred years ago by the British chemist R. Smith. The scientist became interested in smog and the substances in its composition. Thus was born the concept of acidity, which was immediately rejected by the advanced scientific community of the time. Ten years later, his colleague started talking about the hydrogen index again.
The chemist and engineer S. Arrhenius published a report on chemical substances that can release hydrogen cation. He again drew the attention of scientists to the harmfulness of such precipitation, to the danger the phenomenon poses, and became the person who coined the term: acid/base. Since then, these indicators have been considered the level of acids in the aquatic environment.
Svante Arrhenius
The main elements of hydrometeors are acidic components. This substance is monobasic acids (sulfuric and nitric). Precipitations based on interacting gases (chlorine and methane) are less common. What their composition will be depends on what chemical waste is combined with water.
In short, the mechanism of formation of the phenomenon is the combination of oxides released into the atmosphere with water molecules. During the interaction, the formation of chemical components occurs - sulfuric and nitric acid.
Reasons for appearance
Hydrometeors with low pH levels are caused by increased concentrations of sulfur and nitrogen oxides in the atmosphere. Compounds enter the atmosphere either naturally or man-made. Natural sources are:
The main reason is human activity. What is it? The factor causing precipitation is air pollution. The most famous pollutants are road transport and thermal power plants. A significant role in the occurrence of oxides in the atmosphere is played by emissions from industrial enterprises and nuclear tests. Hydrometeors with acid are formed in large quantities in places where space rockets are launched.
Vostochny Cosmodrome. Launch of the Soyuz-2.1b launch vehicle with 19 satellites
Hydrometeors with acids are not only snow or fog, but also dust clouds. They are formed when toxic gases and vapors rise into the air during dry weather.
The main reasons lie in the huge emissions of harmful substances into the atmosphere. The main ones here include chemical production, oil and gasoline storage facilities, and solvents, which are used by enterprises and in everyday life more and more actively every year. The problem of acid precipitation is very acute in areas where metal processing is concentrated. Production leads to the appearance of sulfur oxides in the atmosphere, which cause irreparable damage to flora and fauna.
Of all the above, the greatest danger is the phenomenon associated with atmospheric pollution by toxic waste from internal combustion engines. Gases rise into the air and cause oxidation. One of the reasons is nitrogen compounds released during the production of materials for construction, building construction, and road construction. They also often result in sediments with low pH.
Interesting facts:
- On Venus, smog is caused by the concentration of sulfuric acid in the atmosphere.
- On Mars, limestone and marble rocks are also corroded by toxic acid fallout in the form of fog.
The facts about such precipitation show that the problem of acid rain has existed for millions of years. Their influence has been known on Earth since prehistoric times. Nearly 300 million years ago, the formation of acid rain led to the extinction of 90 percent of species.
Consequences for nature
Precipitation with low pH levels poses a risk of global disturbances in the biosphere. What harm do they cause? Ecologists talk about the negative consequences of this precipitation:
Consequences for modern humanity
Unfortunately, the substance that makes the greatest contribution to the formation of acid precipitation is only increasing in the atmosphere every year. Acid rain as a global environmental problem has become clear and serious. Their most frequent formation is observed in Denmark, Sweden, Norway and Finland. Why do the Scandinavian countries suffer more than all others? There are several reasons for this. Firstly, wind transport of sulfur formations from Central Europe and Britain. Secondly, lakes poor in limestone contribute to acid rain. Reservoirs do not have much ability to neutralize acids.
In Russia, acid precipitation is increasing every year. Environmentalists are sounding the alarm. The atmosphere over megacities is oversaturated with chemical elements and dangerous substances. Acid rain and smog occur especially often over large cities in calm weather. In the Arkhangelsk region, acid precipitation is caused by the combustion of low-quality fuel. The problem of environmental pollution in the Arkhangelsk region has not changed for the better for the last ten years and is caused by emissions of chemicals into the atmosphere. These are sulfuric and nitric acids, leading to the formation of acid precipitation. The situation in Kazakhstan is not the best. There, acid precipitation is associated with the development of mining deposits and the activities of large test sites.
Negative consequences as a result of acid rain are observed in all countries without exception. As a result of their loss, not only the environment suffers. Chronic diseases such as allergies and asthma are becoming more acute among the population. The problem is becoming more acute because it has a great negative impact on the health of modern people. It has been scientifically proven that they cause an increase in the number of cancer tumors. The main cause of precipitation is harmful emissions, which humans are unable to avoid. This is why doctors advise against getting out in the rain, protecting yourself with raincoats and umbrellas, and washing thoroughly after a walk. The consequences can be intoxication and the gradual accumulation of toxins in the body.
Allergies and asthma affect children, young people and older people
If you ask the question: name the areas where acid rain most often forms? The answer is quite simple: in places with the greatest concentration of various industries and vehicles. However, identifying a top region in this regard is not so easy. Why is acid rain dangerous? Because due to the wind changing its direction, precipitation can fall many kilometers from a metropolis or test site.
Control measures
The causes of acid precipitation have been studied quite fully. Despite this, the problem of acidic hydrometeors is only growing. There is a lot of talk about how to deal with acid rain, but the size of the environmental disaster is only increasing in scale. Examples of solving the problem are demonstrated in many developed countries.
Acid rain as a global environmental problem, along with such a problem as ozone holes, does not have a radical and quick solution. Many scientists and environmentalists believe that due to the development of modern economics, this is completely impossible to do. To the question: explain, provide evidence, they present graphs and tables of studies that indicate an increase in the degree of danger to nature and humans. Now the solution to the problem is to reduce harmful emissions. The cause of the negative phenomenon must be eliminated. To do this, the following methods of combating acid rain are used:
- reducing the sulfur content in fuel reduces the causes of acid precipitation;
- the operation of high pipes in enterprises represents modern ways to solve the problem;
- improved technology eliminates the causes and consequences of harmful emissions;
- Liming of reservoirs is also an effective way to solve the problem.
It is worth noting that there is still not even a hint that in the foreseeable future methods will be created to minimize the negative impact of acid precipitation on humans and nature.
History of the term
The term “acid rain” was first coined this year by the English researcher Robert Smith. The Victorian smog in Manchester caught his attention. And although scientists of that time rejected the theory of the existence of acid rain, today no one doubts that acid rain is one of the causes of the death of life in water bodies, forests, crops, and vegetation. In addition, acid rain destroys buildings and cultural monuments, pipelines, renders cars unusable, reduces soil fertility and can lead to toxic metals seeping into aquifers. The water of ordinary rain is also a slightly acidic solution. This occurs because natural atmospheric substances such as carbon dioxide (CO2) react with rainwater. This produces weak carbonic acid (CO2 + H2O -> H2CO3). . While the ideal pH of rainwater is 5.6-5.7, in real life the acidity (pH) of rainwater in one area may differ from the acidity of rainwater in another area. This, first of all, depends on the composition of gases contained in the atmosphere of a particular area, such as sulfur oxide and nitrogen oxides. In the same year, the Swedish scientist Svante Arrhenius coined two terms - acid and base. He called acids substances that, when dissolved in water, form free positively charged hydrogen ions (H+). He called bases substances that, when dissolved in water, form free negatively charged hydroxide ions (OH-). The term pH is used as an indicator of the acidity of water. The term pH means, translated from English, an indicator of the degree of concentration of hydrogen ions.
Chemical reactions
It should be noted that even normal rainwater has a slightly acidic (pH about 6) reaction due to the presence of carbon dioxide in the air. Acid rain is formed by a reaction between water and pollutants such as sulfur oxide (SO2) and various nitrogen oxides (NOx). These substances are emitted into the atmosphere by road transport, as a result of the activities of metallurgical enterprises and power plants. Sulfur compounds (sulfides, native sulfur and others) are contained in coals and ores (especially a lot of sulfides in brown coals), when burned or roasted, volatile compounds are formed - sulfur oxide (IV) - SO 2 - sulfur dioxide, sulfur oxide (VI) - SO 3 - sulfuric anhydride, hydrogen sulfide - H 2 S (in small quantities, with insufficient firing or incomplete combustion, at low temperature). Various nitrogen compounds are found in coals, and especially in peat (since nitrogen, like sulfur, is part of the biological structures from which these minerals were formed). When such fossils are burned, nitrogen oxides (acid oxides, anhydrides) are formed - for example, nitrogen oxide (IV) NO 2. Reacting with atmospheric water (often under the influence of solar radiation, so-called “photochemical reactions”), they turn into acid solutions - sulfuric, sulphurous, nitrogenous and nitrogenous. Then, along with snow or rain, they fall to the ground.
Environmental and economic consequences
The consequences of acid rain are observed in the USA, Germany, the Czech Republic, Slovakia, the Netherlands, Switzerland, Australia, the republics of the former Yugoslavia and many other countries around the globe. Acid rain has a negative impact on bodies of water - lakes, rivers, bays, ponds - increasing their acidity to such a level that flora and fauna die in them. There are three stages of the impact of acid rain on water bodies. The first stage is the initial stage. With an increase in water acidity (pH values less than 7), aquatic plants begin to die, depriving other animals of the reservoir of food, the amount of oxygen in the water decreases, and algae (brown-green) begin to rapidly develop. The first stage of eutrophication (swamping) of a reservoir. At pH6 acidity, freshwater shrimp die. The second stage - acidity rises to pH5.5, bottom bacteria die, which decompose organic matter and leaves, and organic debris begins to accumulate at the bottom. Then plankton dies - a tiny animal that forms the basis of the food chain of the reservoir and feeds on substances formed when bacteria decompose organic substances. The third stage - acidity reaches pH 4.5, all fish, most frogs and insects die. The first and second stages are reversible when the impact of acid rain on the reservoir ceases. As organic matter accumulates at the bottom of water bodies, toxic metals begin to leach out. Increased water acidity promotes higher solubility of hazardous metals such as aluminum, cadmium, and lead from sediments and soils. These toxic metals pose a risk to human health. People who drink water with high levels of lead or eat fish with high levels of mercury can become seriously ill. Acid rain harms more than just aquatic life. It also destroys vegetation on land. Scientists believe that although the mechanism has not yet been fully understood, “a complex mixture of pollutants, including acid precipitation, ozone, and heavy metals, collectively lead to forest degradation. Economic losses from acid rain in the US are estimated by one study to be $13 million annually on the East Coast, and by the end of the century losses will reach $1.750 billion from forest loss; $8.300 billion in crop losses (in the Ohio River Basin alone) and $40 million in medical expenses in Minnesota alone. The only way to change the situation for the better, according to many experts, is to reduce the amount of harmful emissions into the atmosphere.
Literature
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See what “Acid rain” is in other dictionaries:
- (acid rain) precipitation (including snow), acidified (pH below 5.6) due to the increased content of industrial emissions in the air, mainly SO2, NO2, HCl, etc. As a result of acid rain entering the surface layer of soil and... Big Encyclopedic Dictionary
- (acid rain), characterized by a high content of acids (mainly sulfuric acid); pH value<4,5. Образуются при взаимодействии атмосферной влаги с транспортно промышленными выбросами (главным образом серы диоксид, а также азота … Modern encyclopedia
Acid rain- rains caused by atmospheric pollution with sulfur dioxide (SO2). They have a biocidal effect, in particular, the death of fish (for example, in the waters of Scandinavia due to the transfer of lawn emissions in the industrial cities of England). Ecological Dictionary. Alma Ata:... ... Ecological dictionary
acid rain- – rains with pH 5.6. General chemistry: textbook / A. V. Zholnin ... Chemical terms
- (acid rain), precipitation (including snow), acidified (pH below 5.6) due to the increased content of industrial emissions in the air, mainly SO2, NO2, HCl, etc. As a result of acid rain entering the surface layer soil... Encyclopedic Dictionary
One of the types of intense environmental pollution, which is the precipitation of drops of sulfuric and nitric acids with rain, resulting from the reaction of sulfur and nitrogen oxides emitted into the air by industrial enterprises and transport... ... Geographical encyclopedia
Acid rain- (acid rain), chemical pollution of water resources, flora and fauna caused by the emission of exhaust gases as a result of the combustion of fossil fuels. The acidity of rain, snow and fog increases due to the absorption of exhaust gases, mainly... ... Peoples and cultures
- (acid rain), atm. precipitation (including snow), acidified (pH below 5.6) due to increased industrial air content emissions, ch. arr. SO2, NO2, HCl, etc. As a result of the entry of acid into the surface layer of soil and water bodies, acidification develops, which... ... Natural science. Encyclopedic Dictionary
Acid rain- are caused by the presence in the atmosphere of sulfur and nitrogen dioxides, which appear due to the oxidation of sulfur and nitrogen during the combustion of fossil fuels. Further oxidation occurs in clouds, reactions in which are catalyzed by ozone,... ... The beginnings of modern natural science
Acid rain is the price for progress
Scientists have long been sounding the alarm: environmental pollution has reached incredible proportions. The dumping of liquid waste into water bodies, exhaust gases and volatile chemicals into the atmosphere, and the burial of nuclear remains underground - all this has brought humanity to the brink of an environmental disaster.
We have already witnessed the beginning of shifts in the planet’s ecosystem: every now and then the news reports about weather phenomena that are atypical for a particular area, Green Peace is sounding the alarm in connection with the mass extinction of entire species of animals, acid rain has become not a rarity, but rather a pattern , regularly passing over industrial cities. A person is faced with an ambiguous situation: an increase in living standards is accompanied by environmental deterioration, which affects health. This problem has long been recognized worldwide. Humanity should think: is technological progress worth the consequences it entails? To better understand this problem, let’s consider one of the “achievements” of modern industry - acid rain, which is even taught about in school these days. Are they really that dangerous?
Acid rain: causes and consequences
Not only rain, but also snow, dew and even fog can be acidic. From the looks of it
normal precipitation, but its acidity levels are much higher than normal, which is why their negative impact on the environment is associated. The mechanism of acid rain formation is as follows: exhaust gases and other industrial wastes containing large doses of sulfur and sodium oxides enter the atmosphere, where they bind with water droplets, forming a weakly concentrated acid solution, which falls to the ground in the form of precipitation, causing irreparable harm to nature. Acid rain poisons the water animals drink; getting into water bodies, they slowly destroy the local flora and fauna, kill agricultural crops, spill over the fields, get into the soil, and poison it. Such precipitation causes significant damage even to engineering structures, corroding the stone walls of buildings and undermining reinforced concrete load-bearing structures. Acid precipitation is the fate of not only large cities and industrial
zones, toxic clouds can be carried by air masses thousands of kilometers and fall over forests and lakes.
How to deal with acid rain?
The consequences of acid rain are disastrous not only for the environment, but also for the economy, and everyone knows this. So why aren't drastic measures being taken to improve the situation? In order to reduce emissions into the atmosphere, multibillion-dollar investments are required: modernization of production technology is necessary, as for automobile exhausts - a transition to more modern types of fuel. The result will be noticeable only when the entire world community is involved in solving this problem. Unfortunately, in the pursuit of prosperity and increasing GDP, the governments of many countries do not pay due attention to the problem of environmental protection.
Acid rain is a serious environmental problem, and its cause can be attributed to global environmental pollution. Frequent occurrence of acid rain causes concern not only among scientists, but also among ordinary people, since such types of precipitation have negative effects on health.
Acid rain is characterized by a low pH level. Normal precipitation has a level of this indicator of 5.6. It should be noted that even with small deviations from the norm, the consequences for living organisms can be serious.
With significant changes, a reduced level of acidity can cause the death of fish, as well as many insects and even amphibians. In addition, in areas where acid precipitation occurs, acid burns are sometimes noticed on the foliage of trees, and some plants even die. Many people can also feel the negative impact of acid rain. Following such a shower, toxic gases may accumulate in the atmosphere, and breathing such a gas-air mass is extremely undesirable. The consequences will not be long in coming; even with a short walk during such precipitation, cardiovascular and bronchopulmonary diseases, as well as asthma, may appear.
Is acid rain the only threat?
The problem of acid rain has become more global in recent decades, so it would do well for all inhabitants of the Earth to think about their role - positive or negative - in this natural phenomenon. You should know that most of the harmful substances that enter the air are products of human activity and practically do not disappear anywhere. Most of them remain in the atmosphere and will one day return to earth along with precipitation. And the very impact of acid rain is so serious that in some cases it may take hundreds of years to eliminate the consequences.
To become more familiar with the possible consequences of acid rain, it is advisable to understand what the concept itself entails. Most scientists unanimously believe that such a formulation can be considered too narrow in order to capture the full potential of the global problem. You should not study only rains; you need to pay attention to acid hail, fog and snowfall, which are also carriers of harmful substances and compounds, because the process of their formation is mostly identical. We should not forget that persistent dry weather may result in the appearance of toxic gases or dust clouds, or both. But these formations also belong to acid precipitation.
Causes of acid rain
The causes of acid rain are, by and large, directly dependent on the human factor. Continuous pollution of the atmosphere with the use of acid-forming compounds (such as sulfur oxide, hydrogen chloride, nitrogen, etc.) leads to an imbalance. The most important producers of such substances are, of course, large industrial enterprises, for example, metallurgical plants, oil refineries, and thermal power plants that burn coal or fuel oil. Despite filters and cleaning systems, modern technology has still not reached the level that would allow us to completely eliminate not only the negative impacts, but also the industrial waste itself.
In addition, an increase in acid rain has been noticed, associated with the growth of vehicles on the planet. A large amount of exhaust gases, although in small doses, still contributes to the appearance of harmful acidic compounds. And if we count the total number of vehicles, then the degree of pollution can be said to have reached a critical level. In addition to all of the above, many household items also contribute, for example, aerosols, cleaning agents, etc.
Another cause of acid rain, in addition to the human factor, may be some natural processes. In particular, their occurrence can be caused by volcanic activity, during which large amounts of sulfur are released. Moreover, it participates in the formation of gaseous compounds during the decomposition of individual organic substances, which in turn also leads to air pollution.
Mechanism of acid rain formation
All harmful substances that were released into the atmosphere begin to react with elements of solar energy, carbon dioxide or water, resulting in the formation of acidic compounds. Together with moisture evaporation, they rise into the atmosphere, after which clouds form. Thus, the formation of acid rain occurs, the formation of snowflakes or hailstones, which will return to the earth everything that they have absorbed, along with other chemicals.
In some areas of the Earth, some deviations from the norm within 2-3 units were noted. Thus, with an acceptable acidity level of pH 5.6, in the Moscow region and China there were cases of precipitation with a pH level of 2.15. It is impossible to predict the exact location where acid rain will occur because it is possible that the clouds that form may be blown long distances from where the pollution occurs.
Composition of acid rain
The main components of acid rain are sulfuric and sulfurous acids, as well as the presence of ozone formed during thunderstorms. There are also nitrogenous types of sediments, in which nitric and nitrous acids are present as the main ones. Rarely, acid rain can be caused by chlorine and methane. And, of course, other harmful substances may fall with precipitation, based on what was in the household and industrial waste emitted into the atmosphere in specific regions.
Why is acid rain dangerous?
Acid rain, along with its consequences, is the subject of constant observations carried out by scientists from all countries. However, their forecasts are extremely disappointing. Precipitation with a low pH level poses a danger not only to people, but also to flora and fauna.
When acid rain enters the soil, it harms plants by depriving them of the nutrients they need for growth and development. Among other things, toxic metals are drawn to the surface. With a high concentration of acids, trees can die due to precipitation, the soil becomes unusable for further growing crops, and it will take decades to restore it.
The same situation applies to reservoirs. The composition of acid rain leads to an imbalance in the natural environment, after which the problem of river pollution arises. This in turn leads to the death of fish and also slows down the growth of algae. Consequently, entire reservoirs, lakes and rivers may cease to exist for a long time.
Before hitting the ground, acid rain, passing through air masses, leaves particles of toxic substances in the atmosphere. This is considered extremely unfavorable, because it negatively affects the health of people and animals, and also significantly damages buildings. Thus, most paints and cladding materials, metal structures begin to dissolve as soon as drops of the unfortunate rain fall on them.
Global environmental problems of acid precipitation
Global environmental problems caused by acid deposition may include:
- Changes in the ecosystem of water bodies, leading to the death of flora and fauna. It will be impossible to use such sources for drinking, because heavy metals will exceed the norm many times over;
- Damage to roots and leaves will lead to the destruction of protection from cold and disease. This is especially true for coniferous trees in severe frosts;
- Soil contamination with toxins. The flora found in contaminated areas of soil will certainly weaken or die. Harmful elements will arrive along with useful substances, of which less and less will remain.
Harm of acid rain to people
The death of domestic animals, commercial fish species, crops - all this will, to one degree or another, affect the quality of life and the economy of any state.
Fish or animal meat can be hazardous to health if it is eaten in precisely those places where acid poisoning has occurred. Such meat may contain a critical content of toxic compounds or heavy metal ions. If it enters human bodies, it can lead to severe intoxication, serious liver or kidney diseases, blockage of nerve canals, and the formation of blood clots. Some effects of acid poisoning may take generations to become apparent.
Ways to combat acid precipitation
Nowadays, the main risk groups for acid precipitation are the United States, China, and, of course, Russia. Actually, in these states the coal processing and metallurgical industries are highly developed and, accordingly, there are a large number of such enterprises. However, both Canada and Japan are considered dangerous, in the direction of which acid precipitation can be driven by the wind. According to some studies, if preventive measures are not taken, the list of such states may be replenished with many more candidates, and this will not have to wait long.
Combating acid rain at the local level is almost useless. In order for the situation to change for the better, comprehensive measures must be taken. And they are possible only with the simultaneous and coordinated actions of many countries. Academic science is trying to find new purification systems to minimize emissions of harmful substances into the atmosphere, however, the percentage of acid precipitation is only growing.
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Acid rain
General concept of “acid rain”:
The term “acid rain” was first coined in 1872 by English explorer Angus Smith, whose attention was drawn to smog in Manchester. And although scientists of that time rejected the theory of the existence of acid rain, today it is an obvious fact that acid rain is one of the causes of the death of living organisms, forests, crops, and other types of vegetation. In addition, acid rain destroys buildings and architectural monuments, renders metal structures unusable, reduces soil fertility and can lead to the seepage of toxic metals into aquifers.
The term "acid rain" refers to all types of meteorological precipitation - rain, snow, hail, fog, sleet - whose pH is less than the average pH of rainwater, which is approximately 5.6. “Clean” rain is usually always slightly acidic because carbon dioxide (CO 2) in the air reacts chemically with rainwater to form weak carbonic acid. Theoretically, such “clean”, weakly acidic rain should have a pH = 5.6, which corresponds to the equilibrium between CO 2 in water and CO 2 in the atmosphere. However, due to the constant presence of various substances in the atmosphere, rain is never completely “pure”, and its pH varies from 4.9 to 6.5, with an average value of about 5.0 for the temperate forest zone. In addition to CO 2, various sulfur and nitrogen compounds also naturally enter the Earth's atmosphere, which impart an acidic reaction to rainfall. Thus, “acid rain” can also occur for natural reasons. However, in addition to the natural release of various oxides with an acidic reaction into the Earth’s atmosphere, there are also anthropogenic sources, the emission from which is many times higher than the natural one. Atmospheric pollution with large amounts of sulfur and nitrogen oxides can increase the acidity of precipitation to pH = 4.0, which is beyond the limits tolerated by most living organisms.
Causes of acid rain:
The main cause of acid rain is the presence in the Earth's atmosphere of sulfur dioxide SO 2 and nitrogen dioxide NO 2, which, as a result of chemical reactions occurring in the atmosphere, are converted into sulfuric and nitric acids, respectively, the fall of which on the surface of the earth affects living organisms and the ecotope. in general.
Types of sulfur compounds:
The most important sulfur compounds found in the Earth's atmosphere include:
1. Sulfur dioxide – SO 2
2. Carbon oxysulfide – COS
3. Carbon disulfide – CS 2
4. Hydrogen sulfide – H 2 S
5. Dimethyl sulfide – (CH 3) 2 S
6. Sulfate ion – SO 4 2-
Sources of sulfur compounds:
Natural sources of sulfur emissions into the atmosphere:
I. Biological isolation. Almost without exception, traditional models of the sulfur cycle have shown that about 50% of sulfur appears in the atmosphere due to its biological transformations in soil and water ecosystems. It is assumed that as a result of microbiological processes occurring in these natural ecosystems, sulfur volatilizes in the form of hydrogen sulfide (H 2 S). Numerous scientific data indicate that microorganisms produce hydrogen sulfide mainly in two ways:
1. reduction of sulfates.
2. decomposition of organic matter.
Desulfovibrio as well as related bacteria, sulfate reducers, inhabit swamps, swamps and poorly drained soils in large numbers. These microorganisms use sulfates as the final electron acceptor. Also, an extremely large and diverse group of microorganisms, including aerobes, thermophiles, psychrophiles, bacteria, actinomycetes and fungi, decompose sulfur-containing organic compounds and release hydrogen sulfide. The surface of the sea and its deep layers may also contain significant amounts of hydrogen sulfide. At present, the sources of dimethyl sulfide formation are not entirely known, but it is assumed that seaweed takes part in their occurrence. Biological releases of sulfur do not exceed 30–40 million tons per year, which is approximately 1/3 of the total amount of sulfur released.
II. Volcanic activity. When a volcano erupts, hydrogen sulfide, sulfates and elemental sulfur enter the Earth's atmosphere along with large amounts of sulfur dioxide. These compounds enter mainly the lower layer - the troposphere, and during individual, large eruptions, an increase in the concentration of sulfur compounds is observed in higher layers - in the stratosphere. With volcanic eruptions, an average of about 2 million tons of sulfur-containing compounds enter the atmosphere annually. For the troposphere, this amount of sulfur is insignificant compared to biological release; for the stratosphere, volcanic eruptions are the most important sources of sulfur.
III. Surface of the oceans. After the evaporation of water droplets entering the atmosphere from the surface of the oceans, sea salt remains, containing, along with sodium and chlorine ions, sulfur compounds - sulfates.
Together with particles of sea salt, from 50 to 200 million tons of sulfur enter the Earth's atmosphere annually, which is much more than the natural emission of sulfur into the atmosphere. At the same time, salt particles, due to their large size, quickly fall out of the atmosphere and, thus, only an insignificant part of the sulfur gets into the upper layers and is sprayed over the land. However, one should take into account the fact that sulfuric acid cannot be formed from sulfates of marine origin, therefore they are not significant from the point of view of the formation of acid rain. Their influence only affects the regulation of cloud formation and precipitation.
Anthropogenic sources of sulfur emissions into the atmosphere:
Types of nitrogen compounds:
The atmosphere contains a number of nitrogen-containing compounds, of which nitrous oxide (N 2 O) is the most common. This gas in the lower layers of air is neutral and does not participate in the formation of acid rain. Also in the Earth's atmosphere are acidic nitrogen oxides, such as nitrogen oxide NO, and nitrogen dioxide NO2. In addition, the atmosphere contains the only alkaline nitrogen compound - ammonia.
The most important nitrogen compounds found in the Earth's atmosphere include:
1. Nitrous oxide – NO 2
2. Nitric oxide – NO
3. Nitrous anhydride – N 2 O 3
4. Nitrogen dioxide – NO 2
5. Nitric oxide – N 2 O 5
Sources of nitrogen compounds:
Natural sources of emission of nitrogen compounds into the atmosphere:
I. Soil emission of nitrogen oxides. During the activity of denitrifying bacteria living in the soil, nitrogen oxides are released from nitrates. According to data for 1990, about 8 million tons of nitrogen oxides (in terms of nitrogen) are formed annually throughout the world in this way.
II. Lightning discharges. During electrical discharges in the atmosphere, due to the very high temperature and transition to the plasma state, molecular nitrogen and oxygen in the air combine into nitrogen oxides. The amount of nitrogen oxide formed in this way is about 8 million tons.
III. Biomass combustion. This type of source can be of either artificial or natural origin. The largest amount of biomass is burned as a result of the process of forest burning (in order to obtain production areas) and fires in the savannah. When biomass burns, 12 million tons of nitrogen oxides (in terms of nitrogen) enter the air throughout the year.
IV. Other sources. Other sources of natural emissions of nitrogen oxides are less significant and difficult to estimate. These include: the oxidation of ammonia in the atmosphere, the decomposition of nitrous oxide found in the stratosphere, resulting in the release of a mixture of the resulting oxides NO and NO 2 into the troposphere, and, finally, photolytic and biological processes in the oceans. These sources together produce from 2 to 12 million tons of nitrogen oxides (in terms of nitrogen) during the year.
Anthropogenic sources of emissions of nitrogen compounds into the atmosphere:
Among the anthropogenic sources of the formation of nitrogen oxides, the first place is occupied by the combustion of fossil fuels (coal, oil, gas, etc.). During combustion, as a result of the high temperature, nitrogen and oxygen in the air combine. In this case, the amount of nitrogen oxide NO formed is proportional to the combustion temperature. In addition, nitrogen oxides are formed as a result of combustion of nitrogen-containing substances present in the fuel. By burning fossil fuels, humanity annually releases about 12 million tons into the Earth's air basin. nitrogen oxides. Slightly less nitrogen oxides, about 8 million tons. per year comes from the combustion of fuel (gasoline, diesel fuel, etc.) in internal combustion engines. About 1 million tons are emitted by industry worldwide. nitrogen annually. Thus, at least 37% of almost 56 million tons. annual emissions of nitrogen oxide are generated from anthropogenic sources. This percentage, however, will be much higher if biomass combustion products are added to it.
Atmospheric ammonia:
Ammonia, which is alkaline in aqueous solution, plays a significant role in regulating acid rain, since it can neutralize atmospheric acidic compounds:
NH 3 + H 2 SO 4 = NH 4 HSO 4
NH 3 + NH 4 HSO 4 = (NH 4) 2 SO 4
NH 3 + HNO 3 = NH 4 NO 3
Thus, acid precipitation is neutralized and ammonium sulfates and nitrate are formed.
The most important source of atmospheric ammonia is soil. Organic matter in the soil is broken down by certain bacteria, and one of the end products of this process is ammonia. Scientists were able to establish that the activity of the bacterium, which ultimately leads to the formation of ammonia, depends primarily on the temperature and moisture of the soil. In high latitudes (North America and Northern Europe), especially during the winter months, soil ammonia release may be negligible. At the same time, these areas have the highest levels of emission of sulfur dioxide and nitrogen oxides, as a result of which acids in the atmosphere are not neutralized and, thus, the risk of acid rain increases. The breakdown of pet urine releases large amounts of ammonia. This source of ammonia is so significant that in Europe it exceeds the ammonia emission capacity of soils.
Chemical transformations of sulfur compounds:
As a rule, sulfur is included in emissions not in a completely oxidized form (the oxidation state of sulfur in its dioxide is 4, i.e. one sulfur atom is added to two oxygen atoms). If sulfur compounds are in the air for a sufficiently long time, then under the influence of oxidizing agents contained in the air they are converted into sulfuric acid or sulfates. In the process of oxidation of sulfur dioxide (SO 2) by oxygen (O 2), sulfur increases its oxidation state and turns into sulfur trioxide (SO 3), which in turn, being a very hygroscopic substance and interacting with atmospheric water, very quickly turns into H 2 SO4. It is for this reason that, under normal atmospheric conditions, sulfur trioxide is not found in the air in large quantities. As a result of the reaction, sulfuric acid molecules are formed, which quickly condense in the air or on the surface of aerosol particles.
In addition to sulfur dioxide, there are also significant amounts of other naturally occurring sulfur compounds in the atmosphere, which are ultimately oxidized to sulfuric acid (or sulfates).
Chemical transformations of nitrogen compounds:
The most common nitrogen compound included in emissions is nitrogen oxide NO, which, when interacting with atmospheric oxygen, forms nitrogen dioxide. The latter, as a result of reaction with the hydroxyl radical, is converted into nitric acid NO 2 + OH = HNO 3. The nitric acid obtained in this way, unlike sulfuric acid, can remain in a gaseous state for a long time, since it does not condense well. This is due to the fact that nitric acid is more volatile than sulfuric acid. Nitric acid vapor can be absorbed by cloud or precipitation droplets or aerosol particles.
Acid sedimentation (acid rain)
The final stage in the cycle of pollutants is sedimentation, which can occur in two ways:
1. leaching of sediments, or wet sedimentation
2. precipitation, or dry sedimentation
The combination of these two processes is called acid sedimentation.
Impact of acid rain on the environment
The result of acid sedimentation is that acidic atmospheric microelements, sulfur and nitrogen compounds fall onto the Earth's surface, which leads to strong changes in the acidity of water bodies and soils. First of all, increased acidity affects the condition of freshwater bodies and forests. Acid rain has different effects. Initially, precipitation with a high nitrogen content initially promotes the growth of trees in the forest, as the trees are supplied with nutrients. However, as a result of their constant consumption, the forest is oversaturated with them, which leads to acidification of the soil. As a result of changes in soil acidity, the solubility of heavy and toxic metals in them changes, which can enter the body of animals and humans and be transmitted along the trophic chain in which their accumulation will occur. Under the influence of acidity, the biochemical structure of the soil changes, which leads to the death of soil biota and some plants.
Under the influence of acid rain, inorganic compounds are washed out of plants, which include all the main micro- and macroelements. For example, potassium, calcium, magnesium and manganese are usually washed out in the largest quantities. Various organic compounds are also leached from plants, such as sugars, amino acids, organic acids, hormones, vitamins, pectin and phenolic substances, etc. As a result of these processes, the loss of nutrients necessary for plants increases, which ultimately leads to their damage.
Hydrogen ions entering the soil with acid rain can be replaced by cations found in the soil, resulting in either leaching of calcium, magnesium and potassium, or their sedimentation in a dehydrated form. The mobility of toxic heavy metals such as manganese, copper, and cadmium is increasing. The solubility of heavy metals is highly dependent on pH. Dissolved and therefore easily absorbed by plants, heavy metals are poisons for plants and can lead to their death. One of the most dangerous elements for living organisms living in the soil is aluminum dissolved in a strongly acidic environment. Many soils, such as those in northern temperate and boreal forest zones, uptake higher concentrations of aluminum than concentrations of alkali cations. Although many plant species are able to withstand this ratio, when significant amounts of acid precipitation occur, the aluminum-calcium ratio in soil water changes so much that root growth is weakened and the existence of trees is endangered.
Changes in soil composition can transform the composition of microorganisms in the soil, affect their activity and thereby influence the processes of decomposition and mineralization, as well as nitrogen fixation and internal acidification.
Despite the acidic precipitation, the soil has the ability to equalize the acidity of the environment, i.e. to a certain extent, it can resist increased acidity. Soil resistance is usually determined by the presence of limestone and sandstone rocks (which include calcium carbonate CaCO 3), which have an alkaline reaction as a result of hydrolysis.
Acidification of fresh waters.
Acidification of fresh water is the loss of its ability to neutralize. Acidification is usually caused by strong acids such as sulfuric and nitric acid. Over long periods, sulfates play a more important role, but during episodic events (melting snow), sulfates and nitrates act together.
The process of acidification of water bodies can be divided into 3 phases:
1. Loss of bicarbonate ions, i.e. decrease in the ability to neutralize at a constant pH value.
2. Decrease in pH when the amount of bicarbonate ions decreases. The pH value then drops below 5.5. The most sensitive species of living organisms begin to die already at pH = 6.5.
The death of living beings, in addition to the action of the highly toxic aluminum ion, can also be caused by the fact that under the influence of the hydrogen ion, cadmium, zinc, lead, manganese, as well as other toxic heavy metals are released. The amount of plant nutrients begins to decrease. The aluminum ion forms with the orthophosphate ion insoluble aluminum phosphate, which is deposited in the form of a bottom sediment: Al 3+ + PO 4 3- ª AlPO 4 . As a rule, a decrease in water pH goes in parallel with a decrease in populations and death of fish, amphibians, phyto- and zooplankton, as well as many different other organisms.
Acidification of lakes and rivers has reached its greatest scale in Sweden, Norway, the USA, Canada, Denmark, Belgium, Holland, Germany, Scotland, Yugoslavia and a number of other European countries. A study of 5,000 lakes in southern Norway found that fish populations had disappeared in 1,750 of them, and that 900 other lakes were in serious danger. In southern and central Sweden, fish loss has been observed in 2,500 lakes, and the same is expected in another 6,500 lakes where signs of acidification have already been detected. Almost 18,000 lakes have a water pH of less than 5.5, which has a very adverse effect on fish populations.
Direct effects of acid precipitation on the environment
1. Death of plants. Direct death of plants is most observed close to the direct source of emissions, as well as within a radius of several tens of kilometers from this source. The main reason is the high concentration of sulfur dioxide. This compound is adsorbed on the surface of the plant, mainly on its leaves, and penetrating into the plant body takes part in various redox reactions. Under their influence, the oxidation of unsaturated fatty acids of membranes occurs, thereby changing their permeability, which subsequently affects such vital processes as respiration and photosynthesis. First of all, the death of lichens occurs, which can only exist in a very clean environment. Lichens are sensitive indicators of various types of air pollution. Recent research from the University of Nottingham has shown that cushion-forming species of the genus Cladonia can serve as sensitive indicators of acid rain.
2. Direct impact on humans. Aerosol particles of an acidic nature pose a particular danger to human health. The degree of their danger depends primarily on their size. Large aerosol particles are retained in the upper respiratory tract, while small (less than 1 micron) droplets consisting of a mixture of sulfuric and nitric acids can penetrate into the most remote areas of the lungs and cause significant damage there. In addition, metals such as aluminum (and other heavy metals) can enter the food chain at the top of which a person stands, which can lead to his poisoning.
3. Corrosion of metals, buildings and monuments. The cause of corrosion is an increase in the concentration of hydrogen ions on the surface of metals, on which their oxidation largely depends. In suburban areas, the degree of corrosion of metal structures is several micrometers per year, while in polluted urban areas it can reach 100 microns. per year. Acid rain can cause damage not only to metals, but also to buildings, monuments and other structures. Monuments built of limestone and sandstone are destroyed very quickly when exposed to acid rain. CaCO 3 contained in sandstones and limestones turns into calcium sulfate and is easily washed away by rainwater.
Currently, the main fuel in Estonia is fossil oil shale, which has a fairly high sulfur content. However, due to its thermal use, basic oxides that neutralize acidic components are also released into the atmosphere. Therefore, burning oil shale does not cause acid rain. On the contrary, in North-Eastern Estonia there is alkaline precipitation, the pH of which can reach 9 or more units.
Ways to solve the problem
To solve the problem of acid rain, it is necessary to reduce emissions of sulfur dioxide and nitrogen oxide into the atmosphere. This can be achieved by several methods, including by reducing the energy received by humans from burning fossil fuels and increasing the number of power plants using alternative energy sources(energy of sunlight, wind, energy of tides). Other opportunities to reduce emissions of pollutants into the atmosphere are:
1. Reducing sulfur content in various types of fuel. The most acceptable solution would be to use only those fuels that contain minimal amounts of sulfur compounds. However, there are very few such types of fuel. Only 20% of the world's oil reserves have a sulfur content of less than 0.5%. And in the future, unfortunately, the sulfur content in the fuel used will increase, as oil with low sulfur content is produced at an accelerated pace. The same is true with fossil coals. Removing sulfur from the fuel turned out to be a very expensive process in financial terms; moreover, it is possible to remove no more than 50% of sulfur compounds from the fuel, which is an insufficient amount.
2. Use of tall pipes. This method does not reduce the impact on the environment, but increases the efficiency of mixing pollutants in higher layers of the atmosphere, which leads to acid precipitation in more distant areas from the source of pollution. This method reduces the impact of pollution on local ecosystems, but increases the risk of acid rain in more remote regions. In addition, this method is very immoral, since the country in which these emissions occur transfers part of the consequences to other countries.
3. Technological changes. The amount of nitrogen oxides NO that is formed during combustion depends on the combustion temperature. In the course of the experiments, it was possible to establish that the lower the combustion temperature, the less nitrogen oxide is produced, moreover, the amount of NO depends on the time the fuel is in the combustion zone with excess air. Thus, appropriate changes in technology can reduce emissions. Reductions in sulfur dioxide emissions can be obtained by cleaning the end gases from sulfur. The most common method is the wet process, where the resulting gases are bubbled through a limestone solution, resulting in the formation of sulfite and calcium sulfate. In this way, the greatest amount of sulfur can be removed from the final gases.
4. Liming. To reduce acidification of lakes and soils, alkaline substances (CaCO 3) are added to them. This operation is very often used in Scandinavian countries, where lime is sprayed from helicopters onto the soil or onto the catchment area. The Scandinavian countries suffer the most in terms of acid rain, since most Scandinavian lakes have granite or limestone-poor beds. Such lakes have a much lower ability to neutralize acids than lakes located in areas rich in limestone. But along with the advantages, liming also has its own number of disadvantages:
· In flowing and rapidly mixing lake water, neutralization does not occur effectively enough;
· There is a gross violation of the chemical and biological balance of water and soil;
· It is not possible to eliminate all the harmful effects of acidification;
· Heavy metals cannot be removed by liming. During a decrease in acidity, these metals turn into poorly soluble compounds and precipitate, but when a new portion of acid is added, they dissolve again, thus representing a constant potential danger to lakes.
It should be noted that a method has not yet been developed that, when burning fossil fuels, will reduce emissions of sulfur dioxide and nitrogen to a minimum, and in some cases completely prevent it.