composition of acid rain. Why is acid rain dangerous? Chemical transformations of sulfur compounds

Acid rain scares people for good reason: while the acidity of ordinary precipitation is 5.6, a drop in this level by only one tenth entails the death of many beneficial bacteria. And if it drops to 4.5, death to amphibians, insects and fish is guaranteed, and burn marks will appear on the leaves of plants.

A walk in such rain will also not bring benefits to the human body. At the same time, even going outside in the first few hours after acid precipitation is extremely harmful: inhaling toxic gases in the atmosphere may well cause asthma, serious lung and heart diseases.

Acid rain refers to all types of meteorological precipitation during which a strongly acidic reaction is observed, caused by a decrease in acidity due to air pollution with hydrogen chloride oxides of sulfur, nitrogen and other acid-forming compounds. According to scientists who study acid rain, this expression does not fully reflect the phenomenon, since in this case the term "acid precipitation" is more suitable, since toxic substances fall out both in the form of rain and hail, snow, fog, and even dust and gas in dry season.

It is worth noting that pH, which is an indicator of the acidity of aqueous solutions, can range from 0 to 14. While the acidity level of neutral liquids is seven, an acidic environment is characterized by indicators below this value, an alkaline environment is higher. In terms of rainfall, normal precipitation has a pH of 5.6 or slightly higher, depending on the region where it rains.

A small level of acidity is found in any rainwater, which is explained by the presence of carbon dioxide in the air, which, after interacting with raindrops, forms a weak carbonic acid. When the pH decreases by one, this means a tenfold increase in the concentration of acid, so rains below 5.3 are considered acidic (in Europe, the maximum recorded acidity of precipitation was pH 2.3, in China 2.25, in the Moscow region 2.15) .

As for the acidity level of ordinary rain, it is 5.6 or slightly higher. This acidity is low, and therefore does not bring any harm to plant and animal organisms. There is no doubt that acid precipitation began to fall on the earth's surface as a result of active human activity.

Precipitation

Speaking about the sources and causes of the formation of acid rain, experts first of all mention the activities of industrial enterprises that emit large amounts of sulfur and nitrogen oxides into the atmosphere (metallurgical production is especially harmful). Exhaust gases of numerous cars, thermal power plants also have their influence.

Unfortunately, at present, purification technologies do not allow filtering out harmful acidic compounds that are formed during the combustion of gas, peat, coal, oil and other types of relevant raw materials.

Therefore, the mechanism for the occurrence of acid rain is as follows: hydrogen chloride, sulfur and nitrogen oxides, once in the air, begin to interact with drops and solar radiation, forming various acidic compounds (nitric, sulphurous, sulfuric and nitrous acids).

After that, harmful compounds do not disappear anywhere and return to the earth in the form of precipitation. If they find themselves in an area where the atmosphere is saturated with moisture, they combine with water drops in the clouds, after which the dissolved acid falls out in the form of rain, hail, snow, fog, causing considerable harm not only to vegetation, but also to fauna: they are extracted from the soil as nutritious substances, as well as toxic metals such as aluminum, lead, etc.

If acid rain enters fresh water sources or reservoirs, the solubility of aluminum in the water increases dramatically, which leads to disease and death of fish, slower development of algae and phytoplankton, and the water becomes completely unsuitable for consumption.

If the air is absolutely dry, acid compounds can fall to the earth's surface in the form of dust or smog. Once on the earth's surface, they lie in wait for some time and, having waited for showers, go into the ground with the flow of water.

The death of the living world

After acid rain falls, the composition of the soil changes significantly, which causes the death of trees, vegetation and crops, and reduces soil fertility. Once in the ground, toxic water penetrates into reservoirs, as a result of which water is polluted and oxidized, which causes the death of almost all living beings (amphibians, fish and bacteria die at pH 4.5, and many representatives of the animal and plant world disappear even at lower acidity ).

The problem is greatly exacerbated in early spring during the snowmelt period: at this time, all pollutants accumulated during the winter are released and penetrate into the ground and water bodies, and fish fry and insect larvae are most vulnerable.

It is worth noting that before falling into the ground, acid rain lowers the purity of the air, negatively affects various structures, monuments, destroys building and facing (limestone, marble) materials, pipelines, dissolves paints, spoils cars, causing corrosion of metal surfaces.

The impact of acid rain has an extremely negative impact on both animate and inanimate nature, people and objects created by them. At the same time, toxic precipitation can cause such serious environmental problems as:

• The death of the flora and fauna of water bodies as a result of changes in the ecosystem. For humans, reservoirs as water sources also become completely unsuitable due to the increased amount of salts of heavy metals and various toxic compounds, which are normally absorbed by the microflora of the reservoir.
• The death of trees (especially conifers) due to damage to the leaves, roots, because of which they become defenseless against frost and various diseases.
• As a result of various chemical reactions, the soil partially loses trace elements and becomes less nutritious, which slows down the growth and development of vegetation (at the same time, a lot of toxic substances enter the tree through the roots).
• People living in areas where acid rain is common often have serious problems with their upper respiratory tract.
• Acid rains, eroding cement and negatively affecting facing and building materials, seriously damage architectural monuments, buildings and other structures, making them less durable.

How to prevent harmful precipitation?

Currently, the regions where the most acid precipitation is recorded are Asia (primarily China, whose industrial enterprises burn coal) and the United States of America. Given that rainfall tends to fall at some distance from where clouds form, Canada and Japan are also at risk.

Moreover, with the active growth of industry, the problem of acid rain is becoming more and more intense, and therefore, in the near future, the catastrophic consequences of such precipitation will definitely make themselves felt if scientists do not develop a scheme to prevent toxic precipitation before that.

Speaking about the fight against acid rain, it must be borne in mind that it is first of all necessary to fight the sources that caused the formation of acid rain, since it is impossible to fight the precipitation itself. In order to prevent the negative effects of toxic precipitation, environmentalists and scientists are studying acid rain causes and consequences, working on the development of technologies for the production and purification of atmospheric emissions, the creation of environmentally friendly sources of energy production, environmentally friendly vehicles, etc.

Until the governments of different countries, united, take up the solution of this problem and begin to look for ways out of the approaching ecological catastrophe, the problem will not be solved.

Given that acid rain, like other types of precipitation, can cover a huge area, in the near future, acid rain may well become a common occurrence throughout the planet. At the same time, acidic compounds, having entered into additional chemical reactions, will not stop transforming, as a result of which sulfuric acid may soon begin to pour on the heads of careless passers-by.

Acid rain is a serious environmental problem, and its cause can be called universal environmental pollution. Frequent acid rains cause concern not only for scientists, but also for ordinary people, since such types of precipitation have a negative impact on health.

Acid rain is characterized by a low pH. Ordinary 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 shifts, 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 rain occurs, the presence of acid burns on the foliage of trees is sometimes noticed, and some plants even die off. The negative impact after acid rain has fallen can be felt by many people. Following such a downpour, accumulation of toxic gases in the atmosphere can occur, and it is extremely undesirable to breathe such a gas-air mass. The consequences will not be long in coming, even with a short walk during such precipitation, cardiovascular, bronchopulmonary diseases, and asthma may occur.

Can acid rain alone pose a threat?

The problem of acid rain has become more global in recent decades, so all the inhabitants of the Earth would do well 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 a product of human life 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 more than one hundred years to eliminate the consequences.

In order to become more familiar with the possible consequences of acid rain, it is desirable to understand what the concept itself carries. Most scientists unanimously believe that such a formulation can be considered too narrow in order to capture the full potential of a global problem. One should not study exclusively rains, one should also pay attention to acid hail, fog and snowfall, which also belong to carriers of harmful substances and compounds, because their formation is mostly identical in terms of process. It should not be forgotten that with stable dry weather, toxic gases or dust clouds, or both, may appear. But these formations also belong to acid precipitation.

Causes of acid rain

Causes of acid rain are by and large directly dependent on the human factor. The constant 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, oil refineries, thermal power plants that burn coal or fuel oil. Despite filters and purification systems, modern technology has not yet reached the level that would allow to completely eliminate not only negative impacts, but also industrial waste itself.

In addition, there has been an increase in acid rain 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 you recalculate the total number of vehicles, then the degree of pollution, one might say, has reached a critical level. In addition to all of the above, many household items also contribute, for example, aerosols, cleaners / detergents, etc.

Another cause of acid rain, apart from the human factor, may be some natural processes. In particular, volcanic activity can lead to their occurrence, during which a large amount of sulfur is ejected. Moreover, it is involved in the formation of gaseous compounds in the process of decomposition of individual organic substances, which in turn also leads to air pollution.

Mechanism of acid rain formation

All harmful substances that have been 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 the evaporation of moisture, 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 regions of the Earth, some deviations from the norm within 2-3 units were noted. So, 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 not possible to predict the exact location of acid rain, as it is possible that the clouds that have formed can be blown away by the wind for long distances from where the pollution occurred.

Composition of acid rain

The main components of acid rain are sulfuric and sulphurous acids, as well as the presence of ozone produced during thunderstorms. There are also nitrogen types of precipitation, in which nitric and nitrous acids are present as the main ones. Rarely, chlorine and methane can be the causes of acid rain. And, of course, other harmful substances may fall out with precipitation, based on what was in the composition of household and industrial waste emitted into the atmosphere in specific regions.

Why is acid rain dangerous?

Acid rains, together with their consequences, are the subject of constant observations, which are carried out by scientists from all countries. However, their forecasts are extremely disappointing. Precipitation, in which the pH level is lowered, poses a danger not only to people, but also to flora and fauna.

When it hits the ground, acid rain damages plants by depriving them of the nutrients they need to grow and develop. 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 crop cultivation, and it will take decades to restore it.

The same situation is with 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 bodies of water, lakes and rivers may cease to exist for a long time.

Before hitting the ground, acid rain, passing by 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. So most paint and varnish and facing materials, metal structures begin to dissolve as soon as drops of the ill-fated rain fall on them.

Global Environmental Issues of Acid Rain

Among the global environmental problems caused by acid rainfall can be:

• Changes in the ecosystem of water bodies that led 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 the roots and leaves will lead to the destruction of protection against cold and disease. This is especially true for coniferous trees in severe frosts;
• Soil contamination with toxins. The plant world, located on the contaminated areas of the soil, will certainly weaken or die. Harmful elements will come along with useful substances, which will be less and less.

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 when 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 disease, blockage of nerve channels, and the formation of blood clots. Some of the effects of acid poisoning may take generations to appear.

Ways to deal with acid precipitation

Today, the United States, China, and, of course, Russia are leading the main risk group for acid precipitation. 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 can be replenished with many more candidates, and this will not have to wait long.

Fighting 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 component of acid precipitation is only growing.

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Acid rain is a common problem in many areas around the world. They pose a serious danger to humans and the environment. Therefore, it is necessary to properly deal with this problem, to identify it in a timely manner, which will allow you to protect yourself from such a negative impact.

Acid rain - what is it?

It is believed that any precipitation should have an acidity in the range of 5.6–5.8 pH. In this case, the water that falls in a particular area is a slightly acidic solution. It does not pose a danger to the environment and is harmless to people.

What is acid rain

If the acidity of precipitation increases, they are called acidic. Normally, rain is slightly acidic, which is explained by the chemical reaction that occurs in the air between carbon dioxide and water. As a result of this interaction, carbonic acid is formed. It is she who gives the rain slightly acidic properties. The increase in precipitation acidity is explained by the presence of various pollutants in the composition of the lower layers of the atmosphere.

Most often, this phenomenon is caused by sulfur oxide. It enters into a photochemical reaction, which leads to the formation of sulfuric anhydride. This substance interacts with water, which ends with the formation of sulfurous acid. Gradually, it oxidizes at high humidity. The result is a particularly dangerous sulfuric acid.

Another chemical that causes acid rain is nitric oxide. It reacts chemically with air and water particles in the same way, forming dangerous compounds. The main danger of such precipitation is that they outwardly do not differ from ordinary ones in color or smell.

Causes of acid rain

The causes of precipitation with high acidity are called:

Why does acid rain form?

• vehicle exhaust that run on petrol. When burned, harmful substances enter the atmosphere, polluting it;
• operation of thermal power plants. For energy production, millions of tons of fuel are burned, which negatively affects the environment;
• extraction, processing and use of various minerals(ore, gas, coal);
• consequence of volcanic eruptions when a lot of acid-forming emissions enter the environment;
• active processes of decomposition of biological residues. As a result, chemically active compounds (sulfur, nitrogen) are formed;
• activity of industrial facilities engaged in metalworking, mechanical engineering, production of metal products;
• active use of aerosols and sprays containing hydrogen chloride, which leads to air pollution;
• use of air conditioners and refrigeration equipment. They work at the expense of freon, the leakage of which is especially dangerous for the environment;
• production of building materials. In the process of their manufacture, harmful emissions are formed that provoke acid rain;
• soil fertilization with nitrogen-containing compounds which gradually pollute the atmosphere.

The impact of acid rain on humans and the environment

Precipitation contaminated with acidic substances is very dangerous for the entire ecosystem - flora, fauna and humans. Such rains can provoke serious environmental problems that require an integrated approach to their solution.

When acid rain gets into the soil, the nutrients necessary for the normal growth of plants are destroyed. They draw metals (lead, aluminum) dangerous to humans, which were previously in an inactive state, onto the surface of the soil. With prolonged exposure to the soil of this factor, it becomes unsuitable for growing crops. And to restore its properties, it takes more than one year and the painstaking work of specialists.

The same negative impact of precipitation with high acidity is also exerted on the state of water bodies. They become unsuitable for fish and algae growth as the balance of their natural habitat is disturbed.

Also, the high acidity of precipitation leads to air pollution. Air masses are filled with a huge amount of toxic particles that are inhaled by humans and remain on the surface of buildings. They destroy paintwork, facing materials, metal structures. As a result, the appearance of buildings, monuments, cars and everything that is outdoors is disturbed.

Effects of acid precipitation

Acid rain leads to global environmental problems that affect every person:

• the ecosystem of water bodies is changing, which leads to the death of fish and algae;
• water from polluted reservoirs cannot be used due to the increased concentration of toxins in its composition;
• damage to the foliage and roots of trees, which leads to their death;
• soil, where increased acidity of precipitation is constantly noted, becomes unsuitable for the growth of any plants.

Acid rains have a negative impact not only on the state of flora and fauna, but also on human life. The death of livestock, commercial fish species and crops negatively affects the economic situation in the country. And damage to property (cladding of buildings, objects representing architectural or historical memory) leads to additional costs for their restoration.

Such precipitation has an extremely negative impact on the health of the population. People with chronic diseases of the respiratory system, caught in the area affected by acid rain, will feel worse.

Plants, fish, animals located in the territory where such precipitation is constantly observed are very dangerous for people. Regularly eating such food, compounds of mercury, lead, aluminum penetrate into the body. Substances found in acid rain cause serious pathologies in humans. They disrupt the work of the cardiovascular, nervous system, liver, kidneys, cause intoxication, genetic mutations.

How to protect yourself from acid rain

Precipitation with high acidity is a serious problem in China, Russia and the United States, where there are many harmful metalworking and coal mining enterprises. It is impossible to deal with this problem locally. It is necessary to take comprehensive measures to ensure the interaction of several states. Scientists around the world are developing effective treatment systems that will minimize harmful emissions into the atmosphere.

An ordinary person can protect himself from the effects of acid rain with an umbrella and a raincoat. It is recommended not to go out at all in bad weather. During rain it is necessary to close all windows and do not open them for some time after it has ended.

Pollution of the atmosphere with compounds of sulfuric and nitric acids, followed by precipitation is called acidicrains. Acid rains are formed as a result of the emission of sulfur and nitrogen oxides into the atmosphere by enterprises of the fuel and energy complex, motor transport, as well as chemical and metallurgical plants. When analyzing the composition of acid rain, the main attention is paid to the content of hydrogen cations, which determine its acidity (pH). For pure water, pH = 7, which corresponds to a neutral reaction. Solutions with a pH below 7 are acidic, above - alkaline. The entire range of acidity-alkalinity is covered by pH values ​​from 0 to 14.

About two thirds of acid rain is caused by sulfur dioxide. The remaining third is mainly due to nitrogen oxides, which also serve as one of the causes of the greenhouse effect and are part of urban smog.

The industry of different countries annually emits more than 120 million tons of sulfur dioxide into the atmosphere, which, reacting with atmospheric moisture, turns into sulfuric acid. Once in the atmosphere, these pollutants can be carried by the wind thousands of kilometers from their source and return to the ground in rain, snow or fog. They turn lakes, rivers and ponds into "dead" reservoirs, destroying almost all living things in them - from fish to microorganisms and vegetation, destroying forests, destroying buildings and architectural monuments. Many animals and plants cannot survive in conditions of high acidity. Acid rains not only cause acidification of surface waters and upper soil horizons, but also spread with descending water flows to the entire soil profile and cause significant acidification of groundwater.

Sulfur is found in such minerals as coal, oil, copper and iron ores, while some of them are used as fuel, while others are processed in the chemical and metallurgical industries. During processing, sulfur is converted into various chemical compounds, among which sulfur dioxide and sulfates predominate. The formed compounds are partially captured by treatment devices, the rest of them are emitted into the atmosphere.

Sulfates are formed during the combustion of liquid fuels and during industrial processes such as oil refining, the production of cement and gypsum, and sulfuric acid. When burning liquid fuels, about 16% of the total amount of sulfates is formed.

While acid rain does not create global problems such as global warming and ozone depletion, its impact extends far beyond the source country.

Acid rain and reservoirs. As a rule, the pH of most rivers and lakes is 6...8, but with a high content of mineral and organic acids in their waters, the pH is much lower. The process of getting acid rain into water bodies (rivers, ponds, lakes and reservoirs) includes many stages, at each of which their pH can both decrease and increase. For example, a change in the pH of sediments is possible when they move along the forest floor, interact with minerals, products of the activity of microorganisms.

All living things are sensitive to changes in pH, so the increase in the acidity of water bodies causes irreparable harm to fish stocks. In Canada, for example, due to frequent acid rains, more than 4,000 lakes have been declared dead, and another 12,000 are on the verge of death. The biological balance of 18 thousand lakes in Sweden has been disturbed. Fish have disappeared from half of the lakes in southern Norway.

Due to the death of phytoplankton, sunlight penetrates to a greater depth than usual. Therefore, all the lakes that died from acid rains are amazingly transparent and unusually blue.

Acid rain and forests. Acid rain causes great damage to forests, gardens, and parks. Leaves fall, young shoots become brittle, like glass, and die. Trees become more susceptible to diseases and pests, up to 50% of their root system dies off, mainly the small roots that feed the tree. In Germany, almost a third of all spruce trees have already been destroyed by acid rain. In wooded areas such as Bavaria and Baden, up to half of the forest land has been affected. Acid rains cause damage not only to forests located on the plains, a number of damages have been registered in the high-mountain forests of Switzerland, Austria, and Italy.

Acid rain and crop yieldstour. It has been established that the effects of acid rain on agricultural crops are determined not only by their acidity and cationic composition, but also by the duration and air temperature. In the general case, it has been established that the dependence of the growth and maturation of agricultural crops on the acidity of precipitation indicates the relationship between plant physiology, the development of microorganisms, and a number of other factors. Hence, it is obvious that it is necessary to quantitatively take into account all the components of acid rain that affect the yield and quality of products, as well as the complex processes of the functioning of soil biota for each specific region.

Acid rain and materials. The impact of acid rain on a wide range of structural materials is becoming more and more evident every year. Thus, the accelerated corrosion of metals under the influence of acid precipitation, as noted by the American press, leads to the death of aircraft and bridges in the United States. A serious problem, as you know, was the preservation of ancient monuments in Greece and Italy. The main damaging ingredients are hydrogen cation, sulfur dioxide, nitrogen oxides, as well as ozone, formaldehyde and hydrogen peroxide.

The intensity of the destruction of materials depends on: their porosity, since the higher the specific surface, the greater its sorption capacity; from structural features, since in the presence of various recesses they are collectors of acid precipitation; on operating conditions: wind speed, temperature, air humidity, etc.

In practice, the greatest attention is paid to three groups of materials: from metals - stainless steel and galvanized iron; from building materials - materials for external structures of buildings; from protective - paints, varnishes and polymers for surface coatings. When exposed to precipitation and gases, their damaging effect is due to the intensity of catalytic reactions involving metals, as well as synergism (synergism is the ability of one substance to enhance the effect of another), while uniform corrosion is most often observed.

According to the European Parliament, the economic damage from acid rain is 4% of the gross national product. This should be taken into account when choosing a strategy to deal with acid rain in the long term.

Specific measures to reduce sulfur emissions into the atmosphere are implemented in two directions:

use of low-sulphur coals at CHPPs;

emission cleaning.

Low-sulfur coals are considered with a sulfur content of less than 1%, and high-sulfur coals with a sulfur content of more than 3%. To reduce the chance of acid rain formation, sour coals are pre-treated. The composition of coal usually includes pyrite and organic sulfur. Modern multi-stage methods of coal purification make it possible to extract up to 90% of all pyrite sulfur from it, i.e. up to 65% of its total. To remove organic sulfur, methods of chemical and microbiological treatment are currently being developed.

Similar methods should be applied to sour crudes. World reserves of oil with a low sulfur content (up to 1%) are small and do not exceed 15%.

When burning fuel oil with a high sulfur content, special chemical additives are used to reduce the content of sulfur dioxide in emissions.

One of the simplest ways to reduce the amount of nitrogen oxides during fuel combustion is to carry out the process under conditions of oxygen deficiency, which is ensured by the rate of air supply to the combustion zone. In Japan, the technology of "afterburning" of primary combustion products has been developed. In this case, first, the fuel (oil, gas) is burned in the optimal mode for the formation of nitrogen oxides, and then the unreacted fuel is destroyed in the afterburning zone. At the same time, reactions leading to the reduction of oxides and their release are reduced by 80%.

The next direction in solving this problem is to abandon the practice of dispersing gaseous emissions. They should not be scattered, relying on the vast scale of the atmosphere, but, on the contrary, should be captured and concentrated.

The most effective way to clean emissions from sulfur dioxide is based on its reaction with crushed lime. As a result of the reaction, 90% of sulfur dioxide binds to lime, forming gypsum, which can be used in construction. Thus, a thermal power plant with a capacity of 500 MW, equipped with an installation for cleaning emissions, produces 600 thousand m 3 of gypsum per year.

A promising measure to reduce harmful impacts is the establishment of emission limits. Thus, the US Environmental Protection Agency has set a limit on the total emission of sulfur dioxide in the country, providing for its annual reduction. This event had a certain positive effect.

Causes of acid rain

Main cause of acid rain— the presence in the atmosphere due to industrial emissions of sulfur and nitrogen oxides, hydrogen chloride and other acid-forming compounds. As a result, rain and snow are acidified. The formation of acid rain and its impact on the environment is shown in fig. 1 and 2.

The presence in the air of noticeable amounts, for example, ammonia or calcium ions, leads to the precipitation of not acidic, but alkaline precipitation. However, they are also called acidic, since they change their acidity when they enter the soil or into a reservoir.

The maximum recorded acidity of precipitation in Western Europe is with pH = 2.3, in China with pH = 2.25. In 1990, the author of the textbook registered rain with pH = 2.15 at the experimental base of the Ecological Center of the Russian Academy of Sciences in the Moscow region.

Acidification of the natural environment has a negative impact on the state. In this case, not only nutrients are leached from the soil, but also toxic metals, such as lead, aluminum, etc.

In acidified water, the solubility of aluminum increases. In lakes, this leads to disease and death of fish, to a slowdown in the development of phytoplankton and algae. Acid rain destroys facing materials (marble, limestone, etc.), significantly reduces the service life of reinforced concrete structures.

In this way, environmental oxidation is one of the most important environmental problems that needs to be addressed in the near future.

Rice. 1. Formation of acid rain and its impact on the environment

Rice. 2. Approximate acidity of rainwater and some substances in pH units

The acid rain problem

The development of industry, transport, the development of new energy sources lead to the fact that the amount of industrial emissions is constantly increasing. This is mainly due to the use of fossil fuels in thermal power plants, industrial plants, car engines and residential heating systems.

As a result of the combustion of fossil fuels, compounds of nitrogen, sulfur, chlorine, and other elements enter the Earth's atmosphere. Among them, oxides of sulfur - S0 2 and nitrogen - NO x (N 2 0, N0 2) predominate. Combining with water particles, sulfur and nitrogen oxides form sulfuric (H 2 SO 4) and nitric (HNO 3) acids of various concentrations.

In 1883, the Swedish scientist S. Arrhenius coined two terms - "acid" and "base". He called acids substances that, when dissolved in water, form free positively charged hydrogen ions (H +), and bases - substances that, when dissolved in water, form free negatively charged hydroxide ions (OH -).

Aqueous solutions can have a pH (an indicator of the acidity of water, or an indicator of the degree of concentration of hydrogen ions) from 0 to 14. Neutral solutions have a pH of 7.0, an acidic environment is characterized by pH values ​​​​less than 7.0, alkaline - more than 7.0 (Fig. 3 ).

In an environment with a pH of 6.0, fish species such as salmon, trout, roach and freshwater shrimp die. At pH 5.5, pubic bacteria that decompose organic matter and leaves die, and organic debris begins to accumulate at the bottom. Then plankton dies - tiny unicellular algae and protozoan invertebrates that form the basis of the food chain of the reservoir. When the acidity reaches pH 4.5, all fish die, most frogs and insects, only a few species of freshwater invertebrates survive.

Rice. 3. Acidity scale (pH)

It has been established that the share of technogenic emissions associated with the combustion of fossil coal accounts for about 60-70% of their total amount, the share of petroleum products - 20-30%, and other production processes - 10%. 40% of NO x emissions are vehicle exhaust gases.

The effects of acid rain

Characterized by a strongly acidic reaction (usually pH<5,6), получили название кислотных (кислых) дождей. Впервые этот термин был введен британским химиком Р.Э. Смитом в 1872 г. Занимаясь вопросами загрязнения г. Манчестера, Смит доказал, что дым и пары содержат вещества, вызывающие серьезные изменения в химическом составе дождя, и что эти изменения можно заметить не только вблизи источника их выделения, но и на большом расстоянии от него. Он также обнаружил некоторые вредные effects of acid rain: discoloration of fabrics, corrosion of metal surfaces, destruction of building materials and death of vegetation.

Experts argue that the term "acid rain" is not accurate enough. For this type of pollutant, the term "acid precipitation" is better suited. Indeed, pollutants can fall not only in the form of rain, but also in the form of snow, clouds, fog (“wet precipitation”), gas and dust (“dry precipitation”) during the dry period.

Although the alarm sounded more than a century ago, industrialized nations have long ignored the dangers of acid rain. But in the 60s. 20th century Ecologists have reported a decrease in fish stocks and even its complete disappearance in some lakes in Scandinavia. In 1972, the problem of acid rain was first raised by environmental scientists in Sweden at the UN Conference on the Environment. Since that time, the danger of global acidification of the environment has become one of the most acute problems that have befallen humanity.

As of 1985 in Sweden, fisheries in 2,500 lakes have been severely affected by acid rain. In 1750, out of 5,000 lakes in southern Norway, fish completely disappeared. A study of the reservoirs of Bavaria (Germany) showed that in recent years there has been a sharp decrease in the number, and in some cases, the complete disappearance of fish. When studying 17 lakes in the autumn, it was found that the pH of the water ranged from 4.4 to 7.0. In lakes where the pH was 4.4; 5.1 and 5.8, not a single fish was caught, and in the remaining lakes only individual specimens of lake and rainbow trout and char were found.

Along with the death of lakes, degradation of forests occurs. Although forest soils are less susceptible to acidification than water bodies, the vegetation growing on them reacts extremely negatively to an increase in acidity. Acid precipitation in the form of aerosols envelop the needles and foliage of trees, penetrate into the crown, flow down the trunk, and accumulate in the soil. Direct damage is expressed in a chemical burn of plants, a decrease in growth, a change in the composition of the undergrowth vegetation.

Acid precipitation destroys buildings, pipelines, renders cars unusable, degrades soil fertility, and can allow toxic metals to seep into aquifers.

Many monuments of world culture are exposed to the destructive effect of acid precipitation. So, for 25 centuries, the marble statues of the world-famous monument of architecture of Ancient Greece, the Acropolis, were constantly exposed to wind erosion and rain. Recently, the action of acid rain has accelerated this process. In addition, this is accompanied by the deposition of soot crusts on the monuments in the form of sulfur dioxide emitted by industrial enterprises. To connect individual architectural elements, the ancient Greeks used small rods and staples made of iron coated with a thin layer of lead. Thus, they were protected from rust. During the restoration work (1896-1933) steel parts were used without any precautions, and due to the oxidation of iron under the action of an acid solution, extensive cracks form in the marble structures. Rust causes an increase in volume, and the marble cracks.

The results of studies initiated by one of the UN commissions show that acid precipitation also has a detrimental effect on ancient stained glass windows in some Western European cities, which can completely destroy them. More than 100,000 stained glass samples are at risk. Ancient stained glass windows were in good condition until the beginning of the 20th century. However, over the past 30 years, the process of destruction has accelerated, and if the necessary restoration work is not carried out, the stained-glass windows may die in a few decades. Colored glass made in the 8th-17th centuries is at particular risk. This is due to the peculiarities of the production technology.