Cigarette is a special kind of consumer goods. Its consumption form is not eating or drinking, but enjoying its smoke by burning and inhaling. The burning of cigarettes is a very complicated physical and chemical change process.
(A) the formation of smoke
Cigarette combustion is a complex chemical system. According to scientific research, when the temperature rises to 300℃ during cigarette ignition, the volatile components in cut tobacco begin to volatilize and form smoke. When the temperature rises to 450℃, the cut tobacco begins to coke; When the temperature rises to 600℃, the cigarette is ignited and begins to burn.
There are two forms of cigarette burning: one is burning when smoking, which is called smoking; The other is the combustion in the suction gap, which is called smoldering (also called static combustion). The smoke sucked from the cigarette filter end during smoking is called mainstream smoke (MS), and the smoke released from the burning end during smoking and directly diffused into the environment through cigarette paper is called sidestream smoke (SS).
(2) Three areas of cigarette burning
When a cigarette burns, the burning end is tapered. When smoking, most of the air enters from the joint between the burning cone and cigarette paper, and a dense carbonized body is formed in the middle of the cone, which makes it difficult for airflow to pass through, and the oxygen content in the center of the cone is low, which limits the combustion, resulting in incomplete combustion. Burning cigarettes can be divided into three different regions according to their temperature changes and chemical reactions, namely, high-temperature combustion region A (as shown in the figure), pyrolysis distillation region B and low-temperature condensation region C.
The combustion zone is located at the front end of the cigarette and is mainly composed of carbonized bodies. When smoking, the highest central temperature is about 825℃ ~ 850℃. The temperature at 0.2 ~ 1.0 mm in front of the burning line of cigarette paper can reach 9 10℃, which is also the place where the air enters the burning zone most. The gas phase temperature in the combustion zone is low, and the temperature changes between 600 ~ 700℃ during the pumping process. After pumping, the solid phase temperature in the combustion zone rapidly cooled from above 900℃ to 600℃ within 65438 0 seconds. Under normal circumstances, there is sufficient oxygen supply on the surface of the combustion cone, and the exothermic reaction of carbon oxidation occurs here, and the generated heat is taken away by the hot air flow and enters the pyrolysis distillation zone C. The products produced in the high-temperature combustion zone are mainly gas-phase substances, such as carbon dioxide, carbon monoxide, water, hydrogen, methane and other lower hydrocarbon compounds and some free radicals, some of which are diffused into the sidestream smoke through the burning carbon.
Behind the combustion cone is pyrolysis distillation zone B, and the pyrolysis distillation zone in the center of the combustion cone lacks oxygen, so the reaction is carried out in an anoxic state. The hot air flow from the high temperature combustion zone provides energy, which leads to complex chemical changes in the pyrolysis distillation zone. Many substances in cut tobacco undergo violent and complicated chemical reactions here, and most compounds in flue gas are formed here. At the same time, under the action of hot air flow, volatile substances in cut tobacco are volatilized into the flue gas flow (semi-volatile nitrogen heterocyclic compounds with 5 yuan and 6 yuan rings contribute significantly to tobacco fragrance). Most of the chemical reactions in the pyrolysis distillation zone are endothermic reactions, where the flue gas flow is rapidly cooled, and the temperature of the hot gas flow in this zone is reduced from 800℃ to 100℃.
Terpenes and phytosterols in tobacco, such as stigmasterol, paraffin, sugar, amino acids, cellulose and other components form volatile and semi-volatile gases, as well as liquid and solid substances (such as tar) through thermal decomposition, thermal synthesis, dry distillation, polymerization, condensation and free radical reaction.
From the pyrolysis distillation zone to the cigarette end, it is called condensation filtration zone C, where the flue gas temperature drops from 100℃ to room temperature. With the sharp drop of temperature, the low volatile components in flue gas reach the saturation point and begin to condense. These low-volatile components condense on the cut tobacco. In the process of air flow, the low-volatile substances in the flue gas condense into larger particles with tiny carbon particles formed during carbon combustion, tiny fragments of organic matter, ions composed of ash and ionized molecules as condensation nuclei. Some of these particles are intercepted by tobacco shreds and filters, and the other part enters people's mouths with mainstream smoke.
(3) Formation process of sidestream smoke
In the smoldering stage of smoking gap, the natural convection air near the cigarette burning area flows upward to support the cigarette burning, and high-concentration organic vapor is formed in the pyrolysis distillation area inside the cigarette. Due to the lack of suction, most of the organic vapor quickly diffuses into the atmosphere through partially degraded cigarette paper, forming sidestream smoke. After the sidestream smoke diffuses into the atmosphere through cigarette paper, the temperature suddenly drops, and after air dilution, aerosol particles smaller than the mainstream smoke particles are formed. The sidestream smoke and the smoke exhaled by smokers diffuse into the air and are aged and diluted to form environmental tobacco smoke (ETS).
Second, the characteristics of flue gas
Particle characteristics of smoke The newly generated mainstream smoke aerosol contains 109 ~10/0 particles per cubic centimeter, and the initial diameter of the particles is between 0.01~1.2 μ m. As time goes on, the particle diameter increases continuously, and the residence time of the smoke in the smoker's mouth is. The particle distribution of sidestream smoke is different from that of mainstream smoke, the distribution range is 0.08 ~ 1.0μ m, and the average particle size is 0. 15μm ... The cigarette produces 6.3× 109 particles per second during static combustion.
Charged characteristics of smoke Due to high-temperature chemical ionization, cigarette smoke is an aerosol with slight charge, in which about 1/3 particles are positively charged, 1/3 particles are negatively charged, and 1/3 particles are neutral with equal positive and negative charges. So overall, flue gas is electrically neutral.
Due to different combustion methods, the acidity and alkalinity of mainstream smoke and sidestream smoke are also different. Generally speaking, the sidestream smoke produced by smoldering is basically alkaline, and the mainstream smoke produced by smoking is acidic, alkaline and neutral due to different tobacco raw materials, mainly because the amounts of alkaline components and acidic components are different. For various cigarette types, the pH value of mainstream smoke is 5.6 ~ 6.5, while that of cigar mainstream smoke is 7.5 ~ 10.0.
The dynamic nature of cigarette smoke is unstable. Because the concentration of smoke is very high, the particles in it will condense quickly in a short time, and the number of particles in new smoke will drop to a quarter of the initial value in half a second. Due to condensation, the particles in the flue gas increase rapidly. In addition to the physical properties of flue gas, the concentration of compounds in flue gas will also change. For example, methyl nitrite in mainstream smoke actually appears after the new smoke ages 10 seconds.
(1) Composition of flue gas
Cigarette smoke consists of two parts: gas phase and particle phase.
Gaseous substances and particles in flue gas are usually called gaseous substances, which can pass through Cambridge filter (a filter made of glass fiber, which can filter particles with a diameter greater than 0.2μm, with a filtration efficiency of 99%) at room temperature. Gaseous substances account for about 92% of the total flue gas, including air (about 58%), excess nitrogen (about 15%), hydrocarbons, organic vapors, nitrogen oxides and some bioactive substances. The part that can be intercepted by Cambridge filter is called particulate matter. Particulate matter accounts for less than 8% of the total flue gas, mainly water, nicotine and tar. Of course, this is not a clear definition, because some components exist in both gas phase and particle phase, and different separation technologies draw different conclusions, such as water and nitrosamines, both in gas phase and particle phase.
Tar in cigarette smoke The rest of the particulate matter in cigarette smoke except water and nicotine is called tar. Tar is produced by incomplete combustion of organic matter in cigarette cut tobacco under anoxic conditions, and it is a complex compound composed of various hydrocarbons and oxides, sulfides and nitrides of hydrocarbons. At present, it is generally believed that harmful components in cigarette smoke are mainly concentrated in tar. It is reported that 99.4% of the components in cigarette tar are harmless to human body (a considerable part of which is the source of unique flavor of cigarettes), and only 0.6% of the components are harmful to human health. Among these harmful components, 0.2% are carcinogenic and possibly carcinogenic, and 0.4% are auxiliary carcinogenic components, such as polycyclic aromatic hydrocarbons such as 3,4-benzo [a] pyrene.
In addition to particulate and gaseous components, there is also a so-called semi-volatile component that is often mentioned. Semi-volatile components usually refer to substances that can remain on Cambridge filter at room temperature, but can volatilize from the filter at a certain temperature (generally between 100℃ and 200℃) without decomposition. Generally speaking, semi-volatile substances are composed of about 300 substances with boiling points between 70℃ and 300℃, including most of the components that contribute to the taste and aroma of flue gas.
(2), the main chemical composition of flue gas
Cigarette smoke is a complex mixture of many compounds. Up to 1988(Roberts reports, 1988 tobacco reporter), 5,068 chemical components have been identified in cigarette smoke, of which 1 172 exist in tobacco itself and 3,896 are unique to cigarette smoke.
Main chemical components of particulate matter in flue gas
Aliphatic hydrocarbons Most of the aliphatic hydrocarbons with low molecular weight exist in flue gas, and the molecular weight of aliphatic hydrocarbons in flue gas particles is high, which mainly comes from C25 ~ C34 wax in tobacco leaves. Someone quantitatively analyzed the saturated hydrocarbons from C 12 to C33 in flue gas, and found that the alkane content in particulate matter of oriental tobacco smoke was as high as 1.56%, Maryland tobacco was 1. 12%, flue-cured tobacco was 0.92%, and burley tobacco was 0.67%. The content of olefins and alkynes in flue gas is less than that of alkanes, which is about 0.05438+0% of particulate matter.
Aromatic hydrocarbons in flue gas are mostly polycyclic aromatic hydrocarbons, and the content in tobacco leaves is less. Most of them are produced by tobacco components such as cellulose and higher alkanes during combustion, which are the main harmful components in flue gas.
Terpenoids There are many terpenoids in tobacco leaves. Cedarane, carotene and Labrador, for example, are derivatives of terpenes. However, due to the large molecular weight of these substances, the amount directly transferred to the flue gas is very small, mainly in the form of their degradation products and their derivatives. The smoke contains monoterpenoids such as geraniol, perillene and α-pinene, which are important flavor components in the smoke.
Carbonyl compounds carbonyl compounds in flue gas, such as ionone, damascenone, solanone, citral, vanillin, etc. It is an important component to form the fragrance and aroma of flue gas.
Phenolic Compounds Phenolic compounds in cigarette smoke particles mainly include scopolamine, chlorogenic acid, catechol and resorcinol. Some are inherent in tobacco leaves, and some are formed during combustion. Among these phenolic compounds, catechol has the highest content. Phenols can enhance the aroma of cigarettes to a certain extent, but people are more concerned about its adverse stimulation to human respiratory tract and other organs. Catechols, etc. It also has a certain promoting effect on cancer and is a harmful substance in smoke. The main source of phenols is carbohydrates in tobacco leaves.
Volatile acids in organic acid flue gas mainly include formic acid, acetic acid, butyric acid, n-valeric acid, isovaleric acid, β-methylvaleric acid, n-caproic acid, isohexanoic acid and so on. Nonvolatile acids mainly include palmitic acid, linolenic acid, linoleic acid, oleic acid and stearic acid. There are also a small amount of free amino acids, such as alanine, proline and glycine.
Nitrogen heterocyclic compounds Nitrogen heterocyclic compounds mainly exist in the alkaline part of flue gas particles, and the most important component in alkaline substances is nicotine. In addition, there are many nitrogen heterocyclic compounds, such as pyridine, pyrrole, pyrazine, indole and carbazole, which are important aromatic substances in cigarette smoke.
There are many kinds of N- nitrosamines in N- nitrosamine flue gas, mainly nitrosodimethylamine, nitrosomethylethylamine, nitrosopyridine and nitrosopyridine. It is generally believed that nitrosamines can induce lung cancer.
Metal elements Most of the metal elements in tobacco remain in ash after combustion, but a very small amount (0.0 1% ~ 4%) enters the flue gas in two forms, one is free metal and metal inorganic salt, and the other is organic metal. In addition, cigarette paper is also the source of metal elements in flue gas.
(3), the main chemical composition phase of flue gas.
Nitrogen, oxygen, carbon dioxide, carbon monoxide and hydrogen are the most important gas phases in mainstream smoke. These five gases account for about 90% of the total gas phase and 85% of the total flue gas emission. In addition, there are some other chemical components.
Volatile hydrocarbons found in the gas phase of volatile hydrocarbon flue gas include not only aliphatic hydrocarbons but also many volatile aromatic hydrocarbons. Aliphatic hydrocarbons include alkanes, alkenes, alkynes and alicyclic hydrocarbons. Aromatic hydrocarbons include benzene, toluene, ethylbenzene, p-xylene, di-xylene, o-xylene and styrene.
The reported volatile esters in volatile ester flue gas include methyl formate, ethyl formate, methyl acetate, ethyl acetate, vinyl acetate, isopropyl propionate, butyl acetate and ethyl caproate.
Furan compounds in furan smoke are important aroma substances in tobacco and the products of non-enzymatic browning reaction of tobacco leaves. There are furan, 2- methylfuran, tetrahydrofuran and 2,5-dimethylfuran in cigarette smoke, which are all important tobacco flavor substances.
The representative volatile nitrile compounds in the gas phase of volatile nitrile flue gas include acrylonitrile, acetonitrile, propionitrile, isobutyronitrile, valeronitrile, capronitrile and so on. These compounds are formed during cigarette smoking, and their precursors are nitrogen heterocyclic compounds in tobacco, such as pyridine and methylpyrazine, which are generated by pyrolysis of these substances at high temperature.
Other Volatile Components There are many other volatile components in the flue gas, such as ammonia, nitric oxide, nitrogen dioxide, methyl nitrite, hydrogen sulfide, hydrocyanic acid, methyl chloride, methanol, ethanol, propanol and isobutanol.
Three, the main harmful substances in flue gas
Most compounds in smoke are harmless to people, some of which can give tobacco a unique flavor and make it feel pleasant, but a few compounds are harmful to health with different degrees of harm.
At present, it is generally believed that the main harmful substances in flue gas are carbon monoxide, nitrogen oxides, acrolein, volatile aromatic hydrocarbons, hydrocyanic acid, volatile nitrosamines and so on. Polycyclic aromatic hydrocarbons, phenols, nicotine, nitrosamines (especially nitrosamines unique to tobacco), some heterocyclic compounds, trace radioactive elements, etc. And free radicals in gas phase and particle phase.
(A), harmful and beneficial nicotine
Nicotine, also called nicotine, is an alkaloid in tobacco. In tobacco, nicotine mostly exists in the state of combining with organic acids, such as citric acid and malic acid to form salts, and a small amount exists in the free state.
Nicotine enters the human body, 90% is absorbed by the lungs, and reaches the brain 6 seconds after entering the blood.
The most significant effect of nicotine on human body is on sympathetic nerve, which usually shows short-term excitement, followed by inhibition. The function of nicotine is not only to increase the smell of cigarettes and produce a sense of stimulation, but also mainly lies in its physiological intensity, usually called energy, reflecting "addiction" or "non-addiction". Generally speaking, tobacco leaves with high nicotine content have high smoke intensity, and vice versa. Therefore, it is absolutely necessary to contain a certain amount of nicotine in smoke, otherwise tobacco will lose its use value. However, the content of nicotine should not be too high, otherwise it will not only increase the irritation of smoke and affect the taste, but also be a negative factor for smoking safety.
Nicotine is a toxic particulate component in mainstream smoke, and the LD50 of mice is 50 ~ 60 mg/kg. Moderate dose of nicotine can make people breathe faster, vasodilation and vomiting are obviously aggravated, while slightly higher dose of nicotine can cause tremor and spasm. After heavy smokers inhale more nicotine, they will have a short-term respiratory enhancement and high blood pressure. Some experiments and clinical practices show that smoking in large quantities can reduce instinctive desires such as appetite, which is due to the direct effect of smoke on gastric juice secretion and its reflection on oral mucosa and taste buds. Hunger contracture of moderate smokers can also be inhibited by nicotine, but the digestive movement of the stomach is not affected. Nicotine can stimulate gastrointestinal motility.
At present, most studies believe that nicotine has nothing to do with cancer. However, some people think that nicotine is the precursor of N- nitrosamines in tobacco and mainstream smoke, such as N- nitrosodipyridine (NNN).
When smoking cigarettes, part of nicotine in tobacco shreds is completely transferred to mainstream smoke (about 15%), part of nicotine is transferred to sidestream smoke (about 30%), part of nicotine is deposited in cigarette butts (about 18%), and part of nicotine occurs in pyrolysis synthesis reaction (about 30%), and the products are 3- methyl and 4.
Nicotine is a very active chemical substance, which is metabolized quickly in human body. The metabolite of nicotine "Ketianning" can be easily detected from urine, and the accumulation of nicotine has not been found in human organs or various tissues. Even if there is, the amount must be too small for the instrument to detect or can be ignored. Judging from the molecular structure of nicotine, it is very unstable and can undergo various changes under neutral or alkaline conditions. In human metabolism, cotinine is the main intermediate, which is almost non-toxic and does not stimulate blood pressure like nicotine.
At present, the amount of nicotine released by each filter-tip cigarette after burning is generally around 1mg, and the amount of nicotine released by each low-nicotine cigarette can be as low as 0.2mg, so such a low dose will not affect human health.
Nicotine was originally considered as a unique chemical component in tobacco. Recent studies have found that some plants, especially Solanaceae plants, can also synthesize nicotine, and many scientific papers report that nicotine exists in food and drink. Researchers in Michigan, USA, found measurable nicotine content in ripe tomatoes, potatoes and broccoli, but not in tea and tap water.
(2) Suspected carcinogens and cancer-promoting substances in smoke.
Polycyclic aromatic hydrocarbons Polycyclic aromatic hydrocarbons (PAHs) are the products of incomplete combustion of tobacco under high temperature and hypoxia conditions. Organic fragments produced by pyrolysis of various organic compounds form various polycyclic aromatic hydrocarbons through complex polymerization processes. There are 100 polycyclic aromatic hydrocarbons in cigarette smoke. About 30 kinds of polycyclic aromatic hydrocarbons with carcinogenicity have been identified in cigarette smoke, among which 3,4-benzo [a] pyrene is the most typical and its carcinogenicity is the highest, followed by polycyclic aromatic hydrocarbons such as dibenzo [a, h] anthracene and benzo [b] fluoranthene.
Polycyclic aromatic hydrocarbons are contact carcinogens, but the content of 3,4-benzo [a] pyrene per 100 cigarette tar is about 2 ~ 3 μ g, which is lower than the carcinogenic threshold (minimum carcinogenicity) of cigarette smoke.
Of course, not all polycyclic aromatic hydrocarbons are carcinogens or auxiliary carcinogens. For example, pyrene and toluene have no carcinogenic activity. The methods to reduce polycyclic aromatic hydrocarbons in cigarette smoke include selecting tobacco varieties and greatly changing the composition of cigarette cut tobacco, such as using tobacco stems, reconstituted tobacco leaves, expanded cut tobacco and cut tobacco. Changing the natural porosity of cigarette paper and filter components can also significantly reduce tar, nicotine and polycyclic aromatic hydrocarbons.
N- nitrosamines At present, more than 300 kinds of N- nitrosamines have been found to be carcinogenic to 40 kinds of animals in the world, and only a few of them exist in tobacco. Because tobacco contains more nitrogen-containing organic compounds and nitrates, there are more N- nitrosamines in the smoke, and one of the amine precursors is tobacco-specific N- nitrosamines (TSNA). Some studies suggest that nicotine and equisetine in tobacco may be precursors of amines. N- nitrosomethylnicotine (NNN) and 4- (methylnitrosamine)-1-(3- pyridyl)-1- butanone (NNK) are produced by nicotine at the moment of tobacco processing, cigarette burning or smoke inhalation. They are all very strong animal carcinogens, inducing mice, rats and Jintian, Syria. Studies have shown that NNK can methylate DNA (deoxyribonucleic acid) in living animals and human tissues during in vitro metabolism, which has been proved by separating 7- methylguanine and O6- methylguanine from various tissues. Molecular biologists believe that carrying O6- methylguanine in cell transmission code is a chemical damage to DNA and may cause cancer.
N- nitrosdiethanolamine (NDELA) is a non-volatile nitrosamine found in tobacco and cigarette smoke, which is derived from diethanolamine and used as a bud inhibitor of tobacco growth in the form of maleic hydrazide. The most abundant amine in tobacco products is tertiary amine nicotine.
There are several nonvolatile N- nitrosamine amino acids in tobacco, including N- nitrosproline and nitroso -2- piperidinic acid, but these nitrosamine acids do not exist in flue gas, and their decarboxylation will lead to the formation of volatile N- nitrosamine in flue gas.
At present, the most effective way to reduce volatile N- nitrosamines in flue gas is to selectively intercept them with acetate fiber filter, which can intercept more than 80% of the above compounds.
Some studies believe that nitrate content in tobacco is an important factor to form N- nitrosamines and nitrogen oxides in flue gas, so reducing nitrate content is also an effective method to reduce N- nitrosamines and nitrogen oxides in flue gas.
In fact, the newly generated flue gas only contains nitric oxide and trace nitrous oxide, and there is no nitrogen dioxide. With the aging of flue gas, nitrogen dioxide is rapidly formed, and half of nitric oxide in flue gas diluted by air is oxidized into nitrogen dioxide in a few minutes. Nitrogen oxides are one of the main precursors to form N- nitrosamines when cigarettes are smoked, and they can also promote the synthesis of nitrosamines in the body after smoking.
There are auxiliary carcinogens in the acidic components of phenolic flue gas tar, among which catechol and alkyl catechol are the most important, which can promote cancer and increase the carcinogenicity of polycyclic aromatic hydrocarbons when combined with them.
The systematic study of tobacco shows that the main precursors of catechol in smoke are cellulose, glucose, fructose, chlorogenic acid, pectin, starch and hemicellulose. Filters can't selectively reduce catechins like volatile phenols. The use of recombinant tobacco can reduce catechol in cigarette smoke. The research shows that the catechol in cigarette smoke made entirely from recombinant tobacco is about 50% less than that in cigarette smoke made from pure cut tobacco of the same tobacco leaf. Increasing the nitrate content in cut tobacco is a significant means to reduce catechol, but the increase of nitrate will increase the amount of another carcinogen-N-nitrosamine.
Aromatic hydrocarbons in benzene cigarette smoke are formed when cut tobacco is burned, among which benzene is the simplest, which may come from aromatic ring-containing components in tobacco, such as lignin, polyphenols and some amino acids, or from nonvolatile substances. Their fragments tend to form aromatic ring systems with good thermal stability.
According to the International Agency for Research on Cancer, benzene may be a carcinogen, because it increases the chances of leukemia and lymphoma for workers working in high benzene content environment, but smoking does not increase the risk of this tumor.
The use of perforated filters can selectively reduce the benzene content in mainstream smoke.
It seems that a small amount of chlorine (< 1.0%) in chlorinated hydrocarbon tobacco leaves can improve the combustibility of tobacco leaves, while a large amount of chlorine can reduce the combustibility. The content of chlorinated hydrocarbons in flue gas is affected by the chlorine content in tobacco. Chloromethane and vinyl chloride have been identified in the gas phase. Chloromethane is a suspected carcinogen, while the toxicity of vinyl chloride is relatively clear. Workers who work in high concentration vinyl chloride for a long time are prone to induce hepatic hemangioma.
(3) Carbon monoxide can lead to tissue hypoxia.
Carbon monoxide (CO) is one of the harmful substances in flue gas. In the center of the cigarette burning area, if the oxygen supply is insufficient, it is easier to form carbon monoxide. Carbon monoxide is related to cardiovascular diseases and hypoxia poisoning, which can cause organic lesions in severe cases. A cigarette can produce 0.3 ~ 0.4 mg of carbon monoxide. After carbon monoxide is inhaled into the lungs, it quickly enters the blood and combines with hemoglobin to form carboxyhemoglobin. The affinity of carbon monoxide and hemoglobin is much greater than that of oxygen and hemoglobin (200 times higher than that of oxygen), and it is much slower than the dissociation of oxygen and hemoglobin. So once carbon monoxide is inhaled, it competes with oxygen to combine with hemoglobin, and once carbon hemoglobin is formed, it is not easy to separate, which hinders the normal oxygen-carrying function of blood, causes hypoxia in the body, leads to hypoxia, and thus causes hypoxia in tissues and cells. When the concentration of carbon monoxide is high, it can also combine with iron of cytochrome oxidase, inhibit the respiratory process of tissues and cells, and hinder the utilization of oxygen.
The content of carbon monoxide in mainstream smoke is very small, which is not enough to cause obvious harm to human body. The release of carbon oxides in mainstream smoke is greatly influenced by the physical state of tobacco, the porosity of filter, cigarette paper and cigarette paper additives. The carbon monoxide content in mainstream cigarette smoke has been selectively reduced by diluting the smoke using perforated filters or filters with longitudinal air slots.
(4) Toxic substances of cilia in smoke.
Hydrogen cyanide Hydrogen cyanide is the most toxic substance in flue gas, and it is also a very active inhibitor of several respiratory enzymes. In the liver, hydrogen cyanide is rapidly metabolized into thiocyanate, and the concentration of thiocyanate in saliva, blood and urine of smokers is often used as an indicator of smoke inhalation and different inhalation depths. Hydrogen cyanide in flue gas mainly comes from protein and amino acids in tobacco, especially glycine, proline and aminodicarboxylic acid. In addition, nitrate in tobacco can also promote the formation of hydrogen cyanide.
Filters containing activated carbon, perforated filters or filters with longitudinal air slots can selectively reduce the concentration of hydrogen cyanide in cigarette smoke.
Some aldehydes and ketones in the gas phase of volatile aldehydes and ketones are the result of direct transfer of tobacco components, and these compounds are formed by non-enzymatic browning reaction in tobacco. In the process of cigarette smoking, the non-enzymatic browning reaction between carbonyl compounds and nitrogen-containing compounds in tobacco is more intense, and volatile aldehydes and ketones account for a large proportion of the products. At present, at least 20 aldehydes and 6 ketones have been found in the gas phase, among which formaldehyde, acetaldehyde, propionaldehyde, acrolein, crotonaldehyde, furfural and acetone have the highest contents. Some volatile carbonyl compounds, especially formaldehyde, acrolein and crotonaldehyde, are toxins in respiratory cilia. When inhaled with hydrogen cyanide, they will inhibit the clearance of lung excreta, which may lead to lung diseases. It is reported that formaldehyde can also induce nasal cancer. Filters containing activated carbon can selectively remove some volatile aldehydes and ketones from cigarette smoke, thus greatly reducing the toxicity of the whole smoke to respiratory cilia. Perforated filters can also remove volatile aldehydes and ketones from cigarette smoke.
(4) Radioactive substances in flue gas
Radioactive substances in flue gas come from phosphate fertilizer applied in tobacco growth. Phosphorus fertilizer contains uranium, which becomes lead -2 10 and polonium -2 10 after a series of decay, and its radioactive substances are absorbed by the fluff on tobacco. When tobacco containing radioactive isotopes burns, fluff becomes insoluble and is inhaled into lung tissue. Alpha rays were also found in cigarettes. However, the content of these substances in flue gas is extremely small, which can not pose harm to human body.
Free radicals that can cause cell damage
A burning cigarette is like a small chemical plant, which can produce thousands of compounds, including tar and nicotine, and also contains a lot of free radicals. Recent studies have found that a large number of free radicals distributed in cigarette smoke can directly or indirectly attack the genetic material of cells and play a certain role in inducing and promoting cancer. Free radicals, also known as free radicals, generally refer to the valence bonds in the molecules of compounds that are evenly split into atoms, atomic groups, molecules or ions containing valence electrons under the action of light, heat, high-energy radiation or metabolism in vivo, which are customarily called solitary electron systems, such as Cl, R and RO. It also includes some neutral molecules, such as NO radical and NO2 radical. Because these substances have unpaired electrons, they are chemically active and easily react with other substances, thus gaining or losing an electron and becoming a stable structure. Generally speaking, the larger the volume of free radicals, the higher the degree of charge dispersion and the more stable their properties; On the contrary, those smaller and lighter radicals are more chemically active.
Smoke contains free radicals. The free radical content reaches 106 every time the smoke is inhaled. Free radicals are mostly produced by the homogeneous cracking of related stable compounds. Some free radicals produced during smoking can be enriched in tar after being filtered by Cambridge filter paper, which is called smoke particle free radicals. The gas phase of flue gas also contains a large number of free radicals, which are different from the particle free radicals in flue gas. They are small in size, light in weight and poor in stability. It is found that the main components of gas-phase free radicals in flue gas are alkane free radicals (R) and alkoxy free radicals (RO), among which alkoxy free radicals account for about 60% ~ 70%. These free radicals are formed by the airflow formed by smoking and burning during the flowing process.