In the busy streets, a light blue smoke gushes from the tail of a motor vehicle, which is commonly referred to as automobile exhaust. This kind of gas emission not only smells strange, but also makes people dizzy and nauseous, affecting people's health. In the case of few vehicles, the self-purification ability of the atmosphere can still dissolve the toxins emitted by the car. [1] However, with the rapid increase in the number of cars, traffic congestion has become a commonplace. The advantages of convenience, comfort and efficiency that cars should have are gradually offset by too many vehicles. "Automobile disaster" has been formed, and the resulting automobile exhaust is harmful.

Scientific analysis shows that there are hundreds of different compounds in automobile exhaust, including solid suspended particles, carbon monoxide, carbon dioxide, hydrocarbons, nitrogen oxides, lead and sulfur oxides. A car emits three times more harmful exhaust gas a year than it does. The British Association for Air Cleaning and Environmental Protection has published a study saying that 10 times more people die of air pollution each year in Britain than in traffic accidents.

Solid suspended particles: The composition of solid suspended particles is very complex, and it has strong adsorption capacity. It can adsorb various metal dust, strong carcinogen benzopyrene and pathogenic microorganisms. Solid suspended particles enter human lungs with breathing, and stay in different parts of the respiratory tract by collision, diffusion and deposition, causing respiratory diseases. [2] When suspended particles accumulate to the critical concentration, they may trigger the formation of malignant tumors. In addition, suspended particulate matter can directly contact the skin and eyes, obstruct the hair follicles and sweat glands of the skin, cause dermatitis and eyelashes, and may even cause corneal damage.

Carbon monoxide: Carbon monoxide binds to hemoglobin in the blood 250 times faster than oxygen. Carbon monoxide enters the blood circulation through the respiratory tract and forms carboxyhemoglobin after it affinity with hemoglobin, thus weakening the function of blood transporting oxygen to various tissues, endangering the central nervous system, causing functional disorders such as sensation, reaction, understanding and memory, and seriously endangering the blood circulation system, leading to life-threatening. Therefore, even a small amount of carbon monoxide inhalation may cause terrible hypoxic damage.

Nitrogen oxides: Nitrogen oxides mainly refer to nitric oxide and nitrogen dioxide, which are harmful to human body, especially to the respiratory system. Exposure to 9.4 mg/cubic metre of nitrogen dioxide for 10 minutes can cause respiratory dysfunction.

Hydrocarbons: It is not clear that they are directly harmful to human health. However, under the action of solar ultraviolet radiation, nitrogen oxides and hydrocarbons will produce a kind of exciting light blue smoke, which contains ozone, aldehydes, nitrates and other complex compounds. The most prominent hazard of this photochemistry smoke to human body is to stimulate the eyes and upper respiratory mucosa, causing eye swelling and laryngitis. In December 1952, photochemistry smog occurred in London. The number of deaths in four days was 4,000 more than that in the same period of the year. The most deaths were over 45 years old, which was about three times as much as usual. The number of deaths under one year old was about two times as much as usual.

Lead: Lead is a toxic heavy metal element. Most automotive oils are mixed with explosion-proof agent tetraethyl lead or methyl lead. Lead and its compounds produced after combustion are toxic substances. More than 60% of the lead in urban atmosphere comes from the combustion of leaded gasoline in automobiles. Excessive lead content in human body can cause cardiovascular diseases, and affect the functions of liver, kidney and other important organs and nervous system. Because of the high lead dust ratio, it usually accumulates in the air at a height of about 1 meter, which poses the greatest threat to children. [2]

Exhaust gas not only directly endangers human health, but also has a far-reaching impact on the environment of human life. Sulphur dioxide in tail gas has a strong stimulating odor. When it reaches a certain concentration, it is easy to cause acid rain, acidification of soil and water sources, and affect the growth of crops and forests. In the past 100 years, the greenhouse effect has become a major human disaster. Glacier melting, sea level rise, El Nio phenomenon, La Nia phenomenon and so on have brought extremely severe challenges to human survival. Carbon dioxide is responsible for the greenhouse effect.

As one of the main sources of air pollution, vehicle exhaust contains a large number of harmful substances, including carbon monoxide, nitrogen oxides, hydrocarbons and solid suspended particles. PM2.5, which has recently become the focus of social attention, belongs to the category of solid suspended particles. Besides being one of the main sources of PM2.5 in large cities, automobile exhaust is also one of the main causes of air pollution in many cities. Photochemical smog is one of its main effects. Photochemical smog refers to the formation of ozone, aldehydes, ketones, PAN and other secondary pollutants by hydrocarbons and nitrogen oxides in the atmosphere under the action of light. Its impact on human body is much greater than that of nitrogen oxides and hydrocarbons. Historically, there have been several serious photochemical smog pollution incidents in the world, all of which are located in large and super-large cities without exception. In 1970, photochemistry smog occurred in Los Angeles, USA, which caused three-quarters of the city's residents to become ill. In 1971, photochemistry smog occurred in Tokyo, Japan, which caused local students to become intoxicated and comatose. It can be seen that automobile exhaust is an insurmountable gap between the city's large-scale and environmental improvement. With the rapid development of China's economy in recent years, a large number of large cities and some super-large cities catching up with the world level have appeared in China.