Ozone (O3), also known as superoxide, is an allotrope of oxygen (O2), which is a light blue gas with a special odor at normal temperature. Why Ozone Layer is Important?

Ozone is mainly distributed in the stratospheric atmosphere at a height of 10 to 50 km, and the maximum value is between 20 and 30 km.

Under normal temperature and pressure, the stability is poor, and it can be decomposed into oxygen by itself. Ozone has the taste of grass, and inhalation is beneficial to the human body.

Excessive inhalation has certain harm to human health. Non-flammable, pure. Oxygen can be changed to ozone by electric shock.

What is Ozone Layer

Ozone is the Earth’s atmosphere of one trace gas which is oxygen molecules in the atmosphere by solar radiation decomposition into oxygen atoms, oxygen atoms and oxygen molecules surrounding and formed containing three oxygen atoms.

Ozone Layer

More than 90% of the ozone in the atmosphere exists in the upper part of the atmosphere or in the stratosphere, 10 to 50 kilometers from the ground. This is the atmospheric ozone layer that needs human protection.

There are also a small number of ozone molecules that are close to the ground and still have a role in blocking UV rays. However, some experts have found that the concentration of ozone in the atmosphere near the ground has a tendency to increase rapidly, which is not good.

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Although ozone plays an important role in protecting humans and the environment in the stratosphere, if it increases in tropospheric concentrations, it will have a detrimental effect on human health.

Ozone has a stimulating effect on the eyes and respiratory tract, and also on lung function. Higher concentrations of ozone are also harmful to plants.

From the nature of ozone, it can help and harm people. It is both a protective umbrella for heaven and human beings, and sometimes it is like a violent poison.

There has been consensus and a lot of work on the positive effects of ozone and what humans should do to protect the ozone layer. However, although the negative effects of the ozone layer have been recognized, there is no real practical way to solve it except for atmospheric monitoring and air pollution forecasting.

Physical and chemical properties

Ozone is an allotrope of oxygen. It is a special smell at room temperature.

Light blue gas. The word “Ozone” comes from the Greek word ozon, which means “sniff”.

Ozone is mainly present in the ozone layer in the lower part of the stratosphere 20 km from the surface of the earth, and the content is about 50 ppm. It absorbs short-wave ultraviolet rays harmful to the human body and prevents it from reaching the earth to shield the earth’s surface organisms from ultraviolet rays.

In the atmosphere, oxygen molecules are decomposed into oxygen atoms (O) by high-energy radiation, and oxygen atoms combine with another oxygen molecule to form ozone. Ozone will react with oxygen atoms, chlorine or other free substances to decompose and disappear.

Due to this repeated generation and disappearance, the ozone content can be maintained in a certain equilibrium state.

Physical properties

The ozone gas is clearly blue, the liquid is dark blue, and the solid is blue-black. Its molecular structure is triangular. At normal temperature, normal state, and normal pressure, the lower concentration of ozone is a colorless gas, and when the concentration reaches 15%, it exhibits a pale blue color.

Ozone is insoluble in liquid oxygen, carbon tetrachloride, etc., soluble in water, and has a higher solubility in water than oxygen. At 0 ° C, a standard volume of water can dissolve 0.494 volumes of ozone.

The solubility of ozone in the water at normal temperature and normal pressure is about 13 times higher than that of oxygen and 25 times higher than that of air. However, the stability of the aqueous ozone solution is greatly affected by the impurities contained in the water.

Ozone Layer

Especially in the presence of metal ions, the ozone can be rapidly decomposed into oxygen and decomposed slowly in pure water. The density of ozone is 2.14 g/L (0°C, 0.1 MP), the boiling point is -111 ° C, and the melting point is -192°C.

The molecular structure of ozone is unstable, and it is more easily decomposed in water than in air. Although ozone is 10 times more soluble in water than oxygen, its solubility is practically small because it obeys Henry’s law and its solubility is proportional to the partial pressure and total pressure in the system.

The content of ozone in the air is extremely low, so the partial pressure is also extremely low, which will force the ozone in the water to escape from the interface between water and air so that the ozone concentration in the water is always in a decreasing state.

Chemical properties

The ozone is very unstable in the room temperature slowly decomposition, rapid decomposition 200 ℃, it is more than oxygen oxidation more, capable of oxidizing metallic silver to silver peroxide, would lead sulfide is oxidized to lead sulfate, it also Oxidizing organic compounds, decolorizing many organic pigments, such as indigo.

It can erode rubber and easily oxidize organic unsaturated compounds. The oxidation potential ( reduction potential ) of ozone, chlorine and hydrogen peroxide is 2.07.1.36.1.28 volts, respectively. It can be seen that ozone is the strongest oxidizing power in treated water.

  1. ozone depletion

Oxidation of ozone results in the breakdown of unsaturated organic molecules. The ozone molecule is bound to the double bond of the organic molecule to form an ozonide.

The spontaneous splitting of the ozonide produces a carboxyl compound and a zwitterion with an acidic and basic group which is unstable and decomposes into an acid and an aldehyde. Its reaction formula is:

2O 3 3O 2 + 285kJ ( 1-2 )

Since a large amount of heat is released during decomposition, when it is more than 25%, it is easy to explode.

However, in general, ozone is in the air, and the ozone content is hard to exceed 10%. In the long process of ozone treatment for drinking water, there is no case of an oxygen explosion.

The ozone has a content of 1% or less has a decomposition half-life of about 20 to 30 minutes in an air of normal temperature and normal pressure. As the temperature increases, the decomposition rate increases.

When the temperature exceeds 100 ° C, the decomposition is very intense. When the temperature reaches 270 ° C, it can be immediately converted into oxygen.

Ozone decomposes faster in water than in air. In an aqueous solution containing impurities, ozone rapidly recovers to the oxygen that forms it. For example, when the concentration of ozone in water is 6.25×10 -5 mol/L (3mg/l), the half-life is 5-30min, but the decomposition rate is slower in pure water.

For example, the half-life in distilled water or tap water is about 20min (20 °C) However, in the double distilled water, the ozone decomposition is only 10% after 85 minutes. If the water temperature is close to 0 °C, the ozone will become more stable. Ozone is extremely stable in ice and has a half-life of 2000 years.

  1. Ozone oxidizing power

Ozone has strong oxidizing power, and its redox potential is second only to fluorine, and this property is mainly used in its application.

Ozone supports combustion, and combustibles can be spontaneously burned when placed in ozone and burn more intensely than oxygen.

  1. Ozone reduction reaction

a. reduction reaction with inorganic substances

Ozone and ferrous, Mn2 +, sulfide, cyanide, cyanide, chlorine, etc. react

Such as:

Ozone

Ozone

Ozone

Ozone

Ozone

Ozone

Ozone

Ozone

Ozone

Ozone

b. the reaction of ozone with organic matter

The reaction of ozone with organic matter in aqueous solution is extremely complicated.

(1) The reaction of Ozone with Olefin Compounds Ozone readily reacts with an olefin compound having a double bond, and the final product of the reaction may be a mixture of monomeric, polymeric, or staggered ozonides. Ozone oxides decompose into aldehydes and acids.

(2) ozone and aromatic compound reaction and ozone slower aromatic compound, in the series benzene <naphthalene <phenanthrene <pyrene <anthracene, its reaction rate constant is gradually increased.

(3) Reacts to nuclear protein (amino acid) and organic ammonia

The oxidation sequence of ozone in the following mixtures is

Alkenes > Amines > Phenols > Polycyclic Aromatic Hydrocarbons > Alcohols > Aldehydes > Paraffins

Toxicity and corrosivity

Ozone is a harmful gas. When the concentration is 6.25×10 -6 mol/L (0.3mg/L), it has a stimulating feeling to the eyes, nose, and throat. Concentration (6.25-62.5)×10 -5 mol/L (3 ~ At 30mg/L), headaches and local paralysis of the respiratory organs occur.

When the ozone concentration is 3.125×10 -4 to 1.25×10 -3 mol/L (15 to 60 mg/L), it is harmful to the human body. The toxicity is also related to the contact time.

For example, long-term exposure to ozone below 1.748 × 10 -7 mol / L (4ppm) can cause permanent heart disease, but exposure to ozone below 20ppm does not exceed 2h, no permanent harm to the human body. Therefore, the allowable value of the ozone concentration is set to 4.46 × 10 -9 mol / L (0.1 ppm) 8 h.

Since the odor of ozone is very concentrated, the concentration is 4.46 × 10 -9 mol / L (0.1 ppm), people feel So, the world has been using ozone for more than a hundred years, and there has been no report of death from ozone poisoning.

Ozone is highly oxidizing, and in addition to gold and platinum, ozonized air has a corrosive effect on almost all metals. Aluminum, zinc, lead, and ozone are strongly oxidized, but chrome-containing alloys are substantially free of ozone corrosion.

Ozone Layer

Based on this, ferrochrome alloy (stainless steel) containing 25% Cr is often used in production to manufacture parts of ozone generating equipment and filling equipment that are in direct contact with ozone.

Ozone also has a strong corrosive effect on non-metallic materials. Even if it is used in a fairly stable polyvinyl chloride plastic filter plate, etc., loose, cracked and perforated are soon used in ozone filling equipment.

In the ozone generating equipment and the metering equipment, ordinary rubber cannot be used as the sealing material, and it is necessary to use a silicone rubber or an acid-resistant rubber which is highly resistant to corrosion.

High concentrations of ozone near the ground can stimulate and damage mucosal tissues such as the eyes and respiratory system, which have a negative effect on human health.

Experts said that from the long-term observation, although the ozone exceeded the standard from April to September with sufficient sunshine, combined with the experience of foreign governance, with the increase of PM2.5 treatment in the country, the visibility of air increased, the probability of ozone exceeding the standard It will continue to increase, and ozone pollution control will be more difficult than PM2.5 governance.

Pan Xiaochuan, a professor at Peking University School of Public Health, said, “The toxicity of ozone is mainly reflected in its strong oxidative properties, which can damage the cell wall.

The hazards are acute. The harm to the human body is mainly affecting the respiratory system, and it is easy for the lungs. Acute hazards such as emphysema, as well as increasing asthma in recent years, some may be related to ozone pollution.”

Nature-effect

Ozone (O 3 ) is an allotrope of oxygen (O 2 ), a light blue gas with a distinctive odor. The molecular structure is triangular, the bond angle is 116°, its density is 1.5 times that of oxygen, and its solubility in water is 10 times that of oxygen.

Ozone is a strong oxidant. Its redox potential in water is 2.07 eV, second only to fluorine (2.5eV). Its oxidation capacity is higher than chlorine (1.36eV) and chlorine dioxide (1.5eV ), which can destroy decomposing bacteria.

cell wall, quickly penetrate into the intracellular diffusion, oxidation and decomposition of bacteria necessary for the internal oxidation of glucose, glucose oxidase and the like, may affect the bacteria, viruses occurs directly, damage cells, ribonucleic acid (an RNA), decomposition of deoxyribonucleic acid ( Macromolecular polymers such as DNA), RNA, proteins, lipids, and polysaccharides destroy the metabolism and reproduction of bacteria.

The killing of bacteria by ozone is caused by the breakage of the cell membrane. This process is called cell dissipation. It is caused by the cytoplasm being pulverized in water. It is impossible for cells to regenerate under dissipated conditions.

It should be noted, and hypochlorite-based disinfectant is different from the ozone disinfection PH value changes and the influence of ammonia, which is larger than the chlorine disinfection 600-3000 times, its sterilization, disinfection occurs almost instantaneously, When the ozone concentration in water is 0.3 – 2 mg / L, the bacteria can be killed within 0.5 – 1min.

To achieve the same sterilization effect (such as killing E. coli 99%), the amount of ozone water required is only 0.0048% of chlorine.

Ozone is also active against yeasts, parasites, etc., for example, it can be used to remove the following types of microorganisms and viruses.

1 The virus has been shown to be very virulent to the virus. For example, the Poloi virus loses activity at 2 min when the ozone concentration is 0.05 – 0.45 mg/L.

2 The cysts were completely removed after the action of 2.3 min at an ozone concentration of 0.3 mg/L.

3 spores are 10-15 times more resistant to ozone than the growth of bacteria due to the protection of spores.

4 fungi Candida albicans and Penicillium can be killed.

5 Parasites (such as aphids) were killed after 3 minutes.

6 can quickly kill E. coli, Staphylococcus aureus, Candida albicans and other pathogens in the air.

7 can decompose the smell of the air, the smell of smoke, the smell of perfume.

In addition, ozone can also oxidize and decompose pollutants in water and has significant effects on odor removal, decolorization, sterilization, removal of phenol, cyanide, iron, manganese, and reduction of COD and BOD in water treatment.

It should be noted that although ozone is a strong oxidant, its oxidizing power is selective, and substances such as ethanol, which are easily oxidized, do not easily interact with ozone.

Ozone pollution

Where did the ozone come from? [2]  with lead contamination and sulfide, as it is derived from human activities, vehicles, fuel, petrochemical and other important sources of ozone. Walking on the bustling streets, it is often seen that the air is slightly light brown and has a spicy and pungent odor, which is commonly referred to as photochemical smog.

Ozone is the main component of photochemical smog. It is not directly emitted but is converted, such as nitrogen oxides emitted by automobiles, which can generate ozone under solar radiation and suitable meteorological conditions.

With the increase in emissions from automobiles and industry, ground-level ozone pollution has become commonplace in many cities in Europe, North America, Japan, and China.

According to the information available to experts, by 2005, the near-surface atmospheric ozone layer will become the main pollutant affecting the air quality in North China.

Ozone Layer

Studies have shown that the concentration of ozone in the air causes a certain reaction of people to a concentration of 0.5-1ppm. If the time is long, it will feel discomfort such as dry mouth, and the concentration of 1-4ppm will cause coughing.

The reason is that as a strong oxidant, ozone can react with almost any biological tissue. When ozone is inhaled into the respiratory tract, it quickly reacts with cells, fluids, and tissues in the respiratory tract, causing impaired lung function and tissue damage.

Ozone damage is more pronounced in people with asthma, emphysema and chronic bronchitis.

Benefits and hazards

Harm to humans

Low concentrations of ozone can be sterilized. Generally, the ozone concentration in forest areas can reach 0.1ppm, but ozone exceeding the standard is an invisible killer!

In the summer, due to the influence of industrial and automobile exhaust gases, ozone is formed and aggregated on the surface of the earth, especially in large cities and agricultural and forestry areas. Surface ozone has erosive and damaging effects on the human body, especially on the eyes and respiratory tract. Surface ozone is also harmful to crops or forests.

▲Ozone can stimulate the mucous membrane, which is toxic to the human body. It is unsafe to breathe in air containing 0.1ppm ozone for a long time.

▲ It strongly stimulates the respiratory tract, causing sore throat, chest tightness, and cough, bronchitis, and emphysema;

▲ Ozone can cause human neurotoxicity, dizziness, headache, decreased vision, memory loss, shortness of breath, fatigue, nose bleeding;

▲ Ozone can damage vitamin E in human skin, causing wrinkles and dark spots on human skin ;

▲ Ozone can also destroy the body’s immune function, induce lymphocyte chromosomal lesions, accelerate aging, and cause pregnant women to have deformed children;

Therefore, the harm caused by ozone and organic waste gas must be highly valued.

Human benefit

Ultraviolet rays affect human health in many ways. The human body can cause sunburn, eye disease, immune system changes, photoreactive reactions, and skin diseases (including skin cancer ).

Skin cancer is a stubborn disease, and the growth of ultraviolet light increases the risk of developing this disease. Ultraviolet photons have enough energy to break double bonds.

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The short- and medium-wave ultraviolet rays will penetrate deep into the skin, causing inflammation of the human skin, and the genetic material (deoxyribonucleic acid) of the human body is damaged, causing the normally growing cells to become cancer cells and continue to grow into a whole piece of skin cancer.

There is also a surface layer in which sunlight penetrates into the skin. Ultraviolet radiation bombards the basic unit of DNA in the nucleus of the skin, causing many units to dissolve into inactive fragments.

The repair process of these problems may occur abnormally, leading to cancer. Epidemiology has confirmed that the incidence of non-melanoma skin cancer is closely related to sun exposure.

People with various types of skin have the potential to develop non-melanoma skin cancer, but the incidence is higher in people with light skin. Animal experiments have found that ultraviolet light, the ultraviolet B wavelength region is the most intense wavelength region of carcinogenesis.

It is estimated that the total ozone volume is reduced by 1% (ie, UV B is increased by 2%), and the basal cell cancer rate will increase by about 4%. The study found that UVB can change the function of the immune system.

Some experimental results indicate that infectious skin diseases may also be associated with enhanced UVB caused by reduced ozone.

It is estimated that total ozone loss is reduced by 1%, the incidence of skin cancer will increase by 5%-7%, and cataract patients will increase by 0.2%-0.6%. Since 1983, the incidence of skin cancer in Canada has increased by 235%. In 1991, there were as many as 47,000 patients with skin diseases.

The US Environmental Protection Agency said that the United States will die of skin cancer in the next 50 years, an increase of 200,000 people than expected in the past. Australians like to sunbathe and tan their skin.

Although scientists have repeatedly warned that more sun exposure can lead to skin cancer, they are still tired of black skin.

As a result, it was not until the incidence of skin cancer in Australians was twice as high as in other parts of the world. The world suffering from skin cancer in people accounted for 1/3 of the total number of cancer patients.

The United Nations Environment Program has warned that if the Earth’s ozone layer continues to decrease and thin at this rate, then by 2000 the proportion of skin cancer worldwide will increase by 26% to 300,000. If the ozone layer is reduced by another 10% at the beginning of the next century, the number of people suffering from cataracts worldwide may reach 1.6 million to 1.75 million.

It can also cause measles, chickenpox, malaria, pityriasis, fungal disease, tuberculosis, leprosy, and lymphoma.

The increase in ultraviolet light can also cause a large number of deaths of marine plankton and shrimp, crab larvae, and shellfish, causing some organisms to become extinct. Ultraviolet radiation also causes myopia in rabbits, and thousands of sheep are blind.

Earth umbrella

It plays a role in protecting humans and other organisms. Ozone is formed by the combination of oxygen molecules and oxygen molecules under the action of ultraviolet radiation and lightning from the sun.

In 1913, the French physicist Fabri found that in the lower layer (below 20 km), the atmosphere has less chance of generating ozone due to the lack of oxygen atoms; at 20 to 27 km, the oxygen molecules are enhanced due to solar radiation.

Decomposition under the action of ultraviolet radiation increases the oxygen atom, resulting in an increase in the chance of oxygen atoms and oxygen molecules combining to form ozone, which makes this layer form the maximum ozone content, namely the ozone layer.

The ozone layer can absorb most of the short-wavelength rays (such as ultraviolet rays with a wavelength shorter than 0.29μm), raise the temperature of the atmosphere, and protect the earth’s organisms from excessive ultraviolet rays.

However, chlorine and fluoride promote the decomposition of ozone into oxygen, which destroys the ozone protective layer and becomes one of the important environmental issues of human concern.

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