Industrial smog. Smog, types of smog

Smog is a poisonous mixture of smoke, fog and dust.

There are two types of smog:

1. winter smog (London type);
2. summer smog (Los Angeles type).

London smog (a mixture of smoke and fog) in 1952 killed more than 4 thousand people in 3-4 days. The fog itself is not dangerous to the human body. It becomes harmful when extremely contaminated with toxic impurities.

British experts determined that the smog contained several hundred tons of smoke and sulfur dioxide. In London these days it has been found that mortality increases in direct proportion to the concentration of smoke and sulfur dioxide in the air.

Scientists believe that every year thousands of deaths in cities around the world are related to air pollution.

Smog is observed only in autumn-winter time (from October to February). Currently, this meteorological phenomenon is called London-type smog, the main active component of which is sulfur dioxide in combination with an aerosol of sulfuric acid. When this mixture is inhaled, sulfur dioxide reaches the lung alveoli and has a harmful effect on them.

London-type smog produces virtually no new substances, and its toxicity depends entirely on the original pollutants, and it occurs as a result of the combustion of large quantities of fuel.

However, in the 30s. smog began to appear over Los Angeles in the warm season, as a rule, in summer and early autumn, on hot days. Los Angeles smog (photochemical fog) is a dry fog with a humidity of about 70%, which requires sunlight to form, causing complex photochemical transformations in a mixture of hydrocarbons and nitrogen oxides of automobile emissions.

In the photochemical fog of the Los Angeles type, new substances (photooxidants, ozone, nitrites, etc.) are formed in the course of photochemical reactions, which significantly exceed the initial atmospheric pollution in their toxicity. Photochemical fog produces much lower air emissions than London smog, and is more characterized by yellow-green or bluish dry haze rather than solid fog.

The main cause of photochemical fog is vehicle exhaust gases. A passenger car emits about 10 g of nitrogen oxide for every kilometer of travel. And in Los Angeles, where there are more than 4 million cars, about 1000 tons of this gas per day enters the air. In addition, temperature inversions are frequent here - up to 260 days a year.

The inversion layer is located at low altitudes (300-900 m), and the intensity of solar radiation is quite high, so a pronounced photochemical fog is observed in Los Angeles more than 69 days a year. From here came the sad glory of this city as the birthplace of photochemical fog - a phenomenon artificially created by man.

With photochemical fog, as with London smog, an unpleasant odor appears, visibility deteriorates sharply; in humans, the eyes, mucous membranes of the nose and throat become inflamed; symptoms of suffocation, exacerbation of pulmonary and various chronic diseases are noted. Domestic animals, mainly dogs and birds, are also killed. Photochemical fog has a negative effect on the neuropsychic sphere, causing an exacerbation of bronchial asthma. It also damages plants, especially lettuce crops, beans, beets, cereals, grapes, ornamental plantings.

The most important environmental consequences of global air pollution include:

• possible

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- an aerosol consisting of smoke, fog and dust. The English word "smog" is derived from "smoke" - smoke and "fog" - fog. It was the inhabitants of the English capital who were the first to face the problems associated with urban air pollution.

Coal has been burned in London since the 13th century. The townspeople were worried because of the perceptible smell - they believed that it could cause various diseases.

With the complete combustion of fossil fuels (coal or hydrocarbons), rather harmless products are formed - carbon dioxide and water, however, in conditions of lack of oxygen, toxic carbon monoxide is formed. If there is even less oxygen, carbon appears among the combustion products (in the form of soot). At low temperatures and a small amount of oxygen, the destruction of hydrocarbons can be accompanied by their isomerization and polycondensation, leading to the formation of polycyclic aromatic hydrocarbons, including benzopyrene, which has carcinogenic properties.

Air pollution can also be caused by impurities in the fuel, primarily sulfur compounds. Its content in some coals can reach 6%. When such fuels are burned, sulfur dioxide is produced. Dissolving in water droplets that condense around smoke particles, sulfur dioxide significantly reduces its pH. "Acid fog" is dangerous to health; it has a harmful effect on plants and animals, causes the destruction of metals and building materials.

Soot and sulfur dioxide, formed directly from fuel combustion, are primary air pollutants. In the conditions of dampness and fog, characteristic of winter London, they became the causes of prolonged smog, leading to an increase in lung diseases. Over time, smog became commonplace in other major cities and industrial centers as well.

The distribution of pollutants in the air to a large extent depends on weather and climatic phenomena. Winds increase the rate of dispersion and mixing, and air currents directed from the ground carry pollution into the upper atmosphere. However, conditions can arise in which the atmospheric layers become very stable. Then pollution, instead of moving to the upper layers of the atmosphere, remains near the surface of the earth. An unusual state of the atmosphere in which the air temperature in the troposphere does not decrease with height is called an inversion. This leads to the fact that colder air is located below warmer air, and cannot rise up and dissipate in the atmosphere. Under the “roof” of warm air, pollution accumulates in such large quantities that it becomes dangerous to health.

The very first of the officially registered cases of atmospheric pollution, which had serious consequences, was smog in the city of Donora (USA) in 1948. Within 36 hours, two dozen deaths were recorded, hundreds of residents felt very bad. Four years later, in December 1952, an even more tragic incident occurred in London. More than 4,000 people died in five days due to the pollution accumulated in the air. Although in subsequent years, severe smog in London and other cities was observed repeatedly, fortunately, there were no more such catastrophic consequences.

The transition from coal to hydrocarbon fuels has reduced the danger of air pollution from soot particles. However, new types of pollution have emerged, both primary and secondary, resulting from the reactions of primary pollutants with unburned fuel and atmospheric oxygen. The chemical reactions that produce secondary pollutants are most effective in sunlight, so the resulting air pollution is called photochemical smog. It was first noted in Los Angeles (USA) during the Second World War. The appearance of photochemical smog is associated with the rapid development of road transport.

Under conditions of high temperature, at which fuel is burned in a car engine, the interaction between oxygen and nitrogen, which are part of the atmospheric air, begins. Atomic oxygen formed during the dissociation of oxygen molecules is able to split a molecule of relatively inert nitrogen, initiating a chain reaction:

O + N 2 = NO + N

N + O 2 = NO + O

As a result, nitrogen monoxide appears in the exhaust gases, which, once released into the atmosphere, is oxidized by atmospheric oxygen, turning into nitrogen dioxide. Brown nitrogen dioxide is photochemically active. When it absorbs light, it dissociates:

Thus, a reactive oxygen atom appears in the air, which can react with the formation of ozone:

The presence of ozone is the most characteristic feature of photochemical smog. It is not formed during the combustion of fuel, but is a secondary pollutant. Possessing the strongest oxidizing properties, ozone has a harmful effect on human health and destroys many materials, primarily rubber.

In addition, reactions between nitrogen oxides and unburned organic compounds take place in photochemical smog. Among the products of such reactions are many carcinogens.

The differences between "wet smog" caused by burning coal in London and "dry smog" caused by car exhaust in Los Angeles are summarized in the table.

COMPARISON OF LOS ANGELES AND LONDON SMOG
Characteristic	Los Angeles	London
Air temperature	From 24 to 32°C	From -1 to 4°C
Relative Humidity	<70%	85% (+ fog)
Temperature inversion	At an altitude of 1000 m	At a height of several hundred meters
Wind speed	< 3м/с	Windless
Visibility	<0,8–1,6 км	<30 м
Most frequent months	Aug. Sept	December - January
Main fuels	Petrol	Coal (and gasoline)
Main components	O 3 , NO, NO 2 , CO, organic matter	Fine particles, CO, sulfur compounds
Type of chemical reactions	Oxidation	Recovery
Maximum thickening time	Noon	Early morning
Main health impact	Eye irritation, respiratory disturbance	Respiratory tract irritation
Most damaged materials	Rubber	iron, concrete

In the big cities of our country, three decades ago, cars were not the main source of air pollution. Now the environmental problems of motor transport in large Russian cities have become a serious problem. Thus, automobile exhausts in Moscow and St. Petersburg amount to hundreds of thousands of tons per year. Motor transport confidently came out on top among all other sources of air pollution. Therefore, in Moscow, St. Petersburg and other large cities, smog becomes a frequent visitor, especially in calm weather.

To prevent smog, it is necessary to improve car engines and effectively clean exhaust gases. The amount of carbon monoxide produced in car engines can be reduced by burning it to less dangerous carbon dioxide. An increase in the proportion of air in the combustible mixture helps to reduce the emission of not only CO, but also unburned hydrocarbons. The most effective were catalytic converters, in which carbon monoxide and unburned hydrocarbons are oxidized to carbon dioxide and water, and nitrogen oxides are reduced to molecular nitrogen. Unfortunately, catalytic converters cannot be used when the vehicle is refueled with leaded gasoline. Such gasoline contains lead compounds that irreversibly poison the catalyst. Alas, leaded gasoline is still widely used in our country.

To reduce sulfur dioxide emissions, sulfur compounds are preliminarily removed from the oil, and the flue gases are further purified. The ingress of sulfur compounds into the atmosphere can also be reduced by burning solid fuels in a fluidized bed. Particulate emissions from thermal power plants are reduced by using electrostatic precipitators or vacuum air filters.

In some cities, including Moscow, an important role in preventing smog is the fight against forest and peat fires in the surrounding forests, which also provoke the emergence of sustainable urban air pollution.

Unfortunately, progress in the fight against certain types of air pollution has not yet led to the disappearance of smog. Thus, the decrease in harmful emissions in the exhaust gases of cars per unit of mileage is compensated by the rapid growth in the number of vehicles, so the overall level of pollution does not decrease. Apparently, smog will remain a serious problem for residents of many large cities for a long time to come.

Elena Savinkina

Opalovsky A.A. Planet Earth through the eyes of a chemist. M., Science, 1990
Revel P., Revel Ch. Our environment. In four books (translated from English). M., Mir, 1995
Chemistry and society(translated from English). M., Mir, 1995
Dobrovolsky V.V. Fundamentals of biogeochemistry. Proc. manual for geogr., biol., geol., s.-x. specialist. universities. M., Higher. school, 1998
Andruz J., Brimblecumb P., Jickels T., Liss P. Introduction to Environmental Chemistry(translated from English) M., Mir, 1999

Lecture 10. Chemical transformations in the troposphere. The emergence of smog.

Smog (from the English Smoky fog, literally - “Smoke fog”) is an aerosol consisting of smoke, fog and dust, one of the types of air pollution in large cities and industrial centers. Smog is a combination of gaseous and solid impurities with fog or aerosol haze.

Smog originally referred to the smoke generated by the burning of large amounts of coal (a mixture of smoke and sulfur dioxide SO2). In the 1950s A new type of smog was first described - photochemical, which is the result of mixing in the air of the following pollutants:

Nitrogen oxides, such as nitrogen dioxide (combustion products of fossil fuels);

Tropospheric (surface) ozone;

Volatile organic substances (fumes of gasoline, paints, solvents, pesticides and other chemicals);

Peroxides of nitrates.

All of these chemicals are usually highly reactive and easily oxidized, which is why photochemical smog is considered one of the main problems of modern civilization.

Radiative fog - fog that appears as a result of radiative cooling of the earth's surface and a mass of moist surface air to the dew point. Radiation fog usually occurs at night in anticyclone conditions with cloudless weather and a light breeze. Radiation fog often occurs under conditions of temperature inversion, which prevents the rise of the air mass.

In industrial areas, an extreme form of radiation fog, smog, can occur.

Wet smog of the London type - a combination of fog with an admixture of smoke and gas waste from production. London-type smog is caused by the burning of coal and fuel oil. At high atmospheric humidity, a dense fog is formed with an admixture of soot particles and SO 2. This "smog" got its name after the tragedy in the winter of 1952, when 3,200 people died in London as a result of its formation.

Ice smog of the Alaskan type - smog formed at low temperatures from the steam of heating systems and domestic gas emissions.

Dry smog of the Los Angeles type - smog resulting from photochemical reactions that occur in gaseous emissions under the influence of solar radiation; persistent bluish haze of corrosive gases without fog. Photochemical smog - smog, the main cause of which is considered to be automobile exhaust. Automotive exhaust gases and pollutant emissions from enterprises under conditions of temperature inversion enter into a chemical reaction with solar radiation, forming ozone. In some cases, photochemical smog may contain nitrogen compounds that increase the likelihood of cancer.

Photochemical "smog" was first noted in 1944 in Los Angeles, when a large accumulation of cars paralyzed the life of one of the largest cities in the United States. Photochemical "smog" occurs under the influence of sunlight in the absence of wind at low humidity. There is severe irritation of the mucous membranes of the respiratory tract and eyes. The persistence of the "smog" situation for a long time leads to an increase in morbidity and mortality among the population. It also has a harmful effect on vegetation, causing wilting and death of leaves. In addition, photochemical "smog" enhances the corrosion of metals, the destruction of building structures, rubber and other materials.

Ozone and peroxyacetyl nitrates give the oxidizing character to photochemical “smog”. Measurements made in the 1950s in Los Angeles show that an increase in ozone concentration is associated with a characteristic change in the relative content of NO 2 and NO.

The deterioration of visibility during "smog" (the appearance of a bluish haze) is associated with the formation of aerosol particles. The emergence of aerosols and their subsequent removal in the processes of sticking, dry and wet (with atmospheric precipitation) deposition is one of the main ways of self-purification of the atmosphere.

Atmospheric organic aerosols can be formed by a homogeneous or heterogeneous mechanism. The first of them includes gaseous oxidation of organic compounds with the formation of solid or liquid particles, the second involves sorption, catalytic oxidation, polymerization on the surface of already existing solid and liquid aerosols.

Aerosol particles either enter the atmosphere ready-made (as a result of volcanic activity, fires, sea salt, dust, etc.) or are formed from gaseous emissions directly into the atmosphere as a result of chemical processes.

Of the numerous organic compounds that enter the atmosphere, terpene hydrocarbons show the greatest tendency to form aerosols. Thus, the bluish haze observed over coniferous forests in summer is an aerosol resulting from the photochemical oxidation of terpenes.

The formation of aerosol particles in the air of cities is often associated with SO2, which, when oxidized, gives H2SO4, which turns into ammonium sulfate in the presence of ammonia in the atmosphere.

The amount of particulate matter in the air varies greatly by location. In the lower troposphere, at heights less than 2 km, in rural areas the concentration of particles is about 104 cm-3, and over cities it exceeds 105 cm-3. In the background areas, in the absence of anthropogenic activity, the air contains only 200 - 600 cm-3 of aerosol particles.

Probably, in general terms, every modern student can answer what he could. And if we ask him a similar question, then, most likely, we will hear something like this: "Smog is a haze over a city that occurs as a result of excessive exhaust gases."

Is it really? Let's try to find out the nature and causes of this from a scientific point of view.

What is smog? What is the nature of its occurrence?

The name of this phenomenon, which first appeared in London several decades ago, has purely English roots. It happened when adding two nouns "smoke", which translated into Russian means "smoke" and "fog" - "fog".

This type of precipitation is typical for regions with very polluted air. A feature is the presence in the atmosphere of a large percentage of foreign particles on which steam condenses. It is believed that the main culprits in the occurrence of smog are the abundance of vehicles on the roads and certain weather conditions.

What is smog? Why is he dangerous?

Probably, it is unlikely that anyone will argue with the fact that living in cities for which smog has become an almost everyday phenomenon is risky and quite dangerous for human life. By the way, it is the bad ecology that doctors consider guilty of the pallor of the skin of local residents. It's not all about the lack of vitamins, as many believe. In megacities, getting a tan is simply unrealistic, because. smog, mixing with smoke and dust, does everything possible to prevent the energy of the sun's rays from reaching the earth.

But that's not all. Probably, residents of megacities have noticed that recently our cities in winter are increasingly threatened by heavy snowfalls, and showers have become almost a common occurrence. And this is no coincidence. Due to the fact that the air contains a huge amount of various kinds of small solid particles, it forms many times more droplets or snowflakes than, say, in rural areas, which means more clouds and precipitation as a result.

Of course, it is hardly possible to protect yourself from all the costs of urbanization. Remember the recent smog in Moscow? It was during that period in the capital's hospitals that the number of patients complaining of profuse lacrimation, annoying and frequent, increased. But that's not all. If harmful particles still enter our body, then their neutralization occurs in the liver, which means that the body is poisoned deep from the inside.

What is smog? His examples in the world

Unfortunately, in the modern world, when the prevailing situation in many parts of the world leaves much to be desired, smog is not such a rare occurrence.

For example, wet precipitation of this type was characteristic of the capital of Great Britain and some other parts of this country about 100 years ago. And at that time, cars were not responsible for his education, as you understand. Around the 12th-13th century, in this state, residents heated their homes exclusively with coal, polluting the environment more and more. As you know, fogs for this area are not at all uncommon. Particles of combustible fuel mixed with heavy rainfall, forming a haze that was impenetrable and detrimental to the health of residents - London smog. This kind of heating was eventually banned by King Edward on pain of death.

First seen in Los Angeles. He, according to the point of view of modern scientists, is formed in the upper only in the summer and under the influence of ultraviolet radiation. Industrial emissions, falling under the influence of sunlight, form more and more new, and often more toxic products.