On October 17, 2013 (September 13, 2013 in the lunar calendar), the World Health Organization first identified PM2.5 as carcinogenic. On October 17, 2013, the International Agency for Research on Cancer (IARC), a subsidiary of the World Health Organization (WHO), released a report identifying air pollution as carcinogenic to humans for the first time, and regarded it as a common and major environmental carcinogen. However, although air pollution has been proposed as a global carcinogen, its harm to the human body may be the result of the simultaneous action of several major pollutants it contains. Long-term exposure to particles can cause cardiovascular and respiratory diseases, as well as lung cancer. When the concentration of PM2.5 in the air is higher than 10ug/m ^ 3 for a long time, it will bring an increase in the risk of death. For every 10ug/m ^ 3 increase in concentration, the total risk of death increases by 4%, the risk of death from heart and lung diseases increases by 6%, and the risk of death from lung cancer increases by 8%. In addition, PM2.5 easily adsorbs organic pollutants such as polycyclic aromatic hydrocarbons and heavy metals, which significantly increases the probability of carcinogenesis, teratogenicity and mutation. Smoggy days are more likely to cause cancer than smoking. "Hazy weather is more likely to cause cancer than cigarettes." Zhong Nanshan, an academician of the Chinese Academy of Engineering and director of the Guangzhou Institute of Respiratory Diseases, once pointed out when participating in relevant forums that in the past 30 years, the smoking rate of the public in our country has been declining, but the prevalence of lung cancer has increased by more than 4 times. This may be related to the increase in smoggy days. Zhong Nanshan emphasized that weather with thick fog and very low visibility will have an impact on human health The composition of smog is very complex, including hundreds of kinds of atmospheric particulate matter. Among them, aerosol particles with a diameter of less than 10 microns are the main ones that endanger human health. They can directly enter and adhere to the upper and lower respiratory tract and lung lobes of the human body, causing rhinitis, bronchitis and other diseases. Long-term exposure to this environment can also induce lung cancer. What is PM2.5? Fine particulate matter is also known as fine particles, fine particles, and PM2.5. Fine particulate matter refers to particulate matter with an aerodynamic equivalent diameter of less than or equal to 2.5 microns in ambient air. It can be suspended in the air for a long time. The higher the concentration in the air, the more serious the air pollution. On April 19, 2013, the National Committee for the Examination of Scientific and Technological Terms named the Chinese name of PM2.5Fine particulate matter. The chemical composition of fine particulate matter mainly includes organic carbon (OC), elemental carbon (EC), nitrates, sulfates, ammonium salts, sodium salts (Na), etc. Is it fog or haze? Fog is a natural weather phenomenon and is not necessarily related to human pollution; haze is caused by particulate pollution. The main difference between the two is the air humidity, which is usually called fog when the humidity is greater than 90%, haze when the humidity is less than 80%, and haze when the humidity is between 80% and 0%. Later, some people used the word smog to refer to the mixture of particulate matter and fog formed by industrial emissions. In history, many countries have experienced air pollution incidents caused by particulate matter.