The hazards are as follows:
carbon monoxide
Carbon monoxide is an intermediate product of hydrocarbon fuel combustion, which is mainly produced due to incomplete combustion of hydrocarbons under local hypoxia or low temperature, and is discharged after mixing with exhaust gas of internal combustion engine. When the car is overloaded, running slowly or running in neutral, the fuel can not be fully burned, and the carbon monoxide content in the exhaust gas will increase obviously. Carbon monoxide is a colorless and odorless asphyxiating toxic gas with low chemical reaction ability. Its relative density to air is 0.9670, and its solubility is very small. After carbon monoxide enters human blood from respiratory tract, it will combine with hemoglobin Hb in blood to form carboxyhemoglobin, which will lead to the decline of oxygen carrying capacity and make human body react, such as hypoxia of cochlear nerve cells in ears, which will lead to hearing loss. Inhalation of excessive carbon monoxide can lead to shortness of breath, purple lips, dyspnea and even death. Studies have shown that people's tolerance to carbon monoxide is quite high, and a healthy person can resist the invasion of 20%~40% carbon monoxide in blood in a short time. Although the threshold of no side effects of carbon monoxide has not yet been determined, long-term absorption of carbon monoxide is a potential threat to the health of urban residents.
Compounds of nitrogen and oxygen
Nitrogen oxides are produced in most gases in the cylinder of internal combustion engine, and their emission depends on combustion temperature, time and air-fuel ratio. From the combustion process, more than 95% of the emitted nitrogen oxides may be nitric oxide, and the rest is nitrogen dioxide. At present, no case of people being poisoned by nitric oxide has been found, but nitrogen dioxide is a reddish-brown respiratory irritating gas, and its odor threshold is about 1.5 times the air quality, which has a great impact on human body. Because of its low solubility in water, it is not easy to be absorbed by the upper respiratory tract and penetrate into the lower respiratory tract and lungs, causing bronchitis, pulmonary edema and other diseases. Exposure to 9.4mg/m2 air 10 minute can cause respiratory system disorder. With regard to nitrogen oxides, the Environmental Health Assessment Team of the World Health Organization concluded that the concentration of nitrogen dioxide is 0.94mg/m-3, which is the lowest level of harmful effects caused by short-term contact, and the longest is 0. 19-0.32 mg/m-3/hour, which cannot occur more than twice a month to ensure the health of workers.
hydrocarbon
Hydrocarbons in automobile exhaust have three emission sources. For ordinary gasoline engines, about 60% of hydrocarbons come from the exhaust of internal combustion engines, 20% ~ 25% from the leakage of crankcase, and the rest 15% ~ 20% from the evaporation of fuel system. Methane is a suffocating gas, and its olfactory threshold is 142.8mg, which is harmful to human health only at high concentration. Ethylene, propylene and acetylene are mainly harmful to plants, making street trees unable to grow normally. Benzene is a colorless gas similar to the smell of gasoline, which can cause symptoms such as loss of appetite, weight loss, fatigue, dizziness, headache, vomiting, insomnia and mucosal bleeding. , but also cause blood changes, red blood cells, car exhaust pollution.
Blood can also cause leukemia. Its olfactory threshold is 16.29mg, and its threshold for human health is 34.8mg. The automobile exhaust also contains polycyclic aromatic hydrocarbons (PAHs). Although the content of PAHs is very low, it has attracted people's attention because it contains many carcinogens (such as phenylpropyl pyrene). HC and NOX are exposed to intense sunlight and ultraviolet rays in the atmospheric environment, resulting in complex photochemical reactions, a new pollutant and photochemical smog. In the four days of photochemical smog in London in June 5438+0952+February, the number of deaths was about 4000 more than that in the same period of normal years, the number of deaths over 45 years old was about three times that in normal times, and the number of deaths under/kloc-0 years old was about two times that in normal times. In the week before the incident, the number of people who died of bronchitis, coronary heart disease, tuberculosis and heart failure was 9.3 times, 2.4 times, 5.5 times and 2.8 times that of the week before the incident.
Aldehydes are produced by incomplete combustion of hydrocarbons, which are mainly emitted by exhaust gas from internal combustion engines. The aldehyde composition of automobile exhaust is shown in the table: formaldehyde is the main aldehyde emitted by famous automobile exhaust, accounting for 60%~70%. Formaldehyde is an irritating gas, which will irritate eyes and respiratory tract. Olfactory threshold is 0.06~ 1.2 mg, and high concentration can cause cough, chest pain, nausea and vomiting. Acetaldehyde is a low toxic substance, which has anesthetic effect at high concentration. Acrolein is a kind of irritating and irritating gas, which is strongly irritating to eyes and respiratory tract and can cause damage to bronchial cells. Olfactory threshold is 0.48~4. 1 mg.
Lead compound
Most of the lead-containing particles emitted by automobile exhaust come from the exhaust gas of internal combustion engine. Tetraethyl lead is added to gasoline as an antiknock agent. The lead content of gasoline is between 0.08% and 0.13%, and tetraethyl lead generates lead oxide after combustion. Lead mainly acts on nervous system, hematopoietic system, digestive system, liver and kidney. Lead can inhibit the anabolic process of hemoglobin and directly act on mature red blood cells. Lead particles entering the human body through the respiratory system can be adsorbed on respiratory mucus, mixed with sputum and spit out; Smaller particles are deposited in the deep tissues of the lungs, and they are almost completely absorbed. When lead accumulates in various organs of human body to a certain extent, it will damage people's heart and lungs, make people anemic, stupid, mentally retarded, inattentive, and even lead to infertility and high blood pressure. According to the route of entering the body, up to 60% of the total lead intake can remain in the human body permanently, and more than 0.8mg in adult blood is called lead poisoning. After burning leaded gasoline, about 85% lead is discharged into the atmosphere, causing lead pollution. Lead oxide is not only harmful to human body, but also adsorbed on the catalyst surface of automobile exhaust catalytic purifier, which is "toxic" to the catalyst and obviously shortens the service life of automobile exhaust catalytic purifier, which is one of the difficult problems to be solved by automobile exhaust catalytic purifier. Since the 1940s, millions of tons of lead have been discharged into the atmosphere through automobile combustion, which has become a recognized global pollution.