Since the 2008 Olympic Games, we have often heard the word "PM2.5". Many people only know that the word is related to haze and air quality, but the specific meaning is not clear. So today's editor will sort out the knowledge about PM2.5 for you. Let's call on our friends to learn~
PM2.5 is the toxic waste in the air, referred to as "air drugs". The equivalent aerodynamic diameter of particles is less than or equal to 2.5 microns (solid and liquid particles suspended in the air).
PM2.5 is not a single component air pollutant, but a complex and variable air pollutant composed of a large number of different chemical components from many different human or natural pollution sources. In terms of the generation process, PM2.5 can be directly discharged from the pollution source (called primary particle), or it can be generated by the gaseous pollutants discharged from each pollution source through condensation or complex chemical reactions in the atmosphere (called secondary particle). Most of the components such as sulfuric acid, ammonium bisulfate, ammonium sulfate, ammonium nitrate, elemental carbon (NP) and organic carbon (BP) are present in the air particles.
There are three ways to form PM2.5:
1. Primary particles discharged directly in solid form;
2. It is discharged in the form of gas at high temperature, condensed into solid primary condensable particles in the process of dilution and cooling of plume (exhaust emission);
3. Secondary particles produced by the chemical reaction of gaseous pollutants in the atmosphere.
The primary particles in PM2.5 are mainly produced in the combustion of fossil fuel (mainly oil and coal) and biomass fuel, while the contribution of surface dust from other sources, such as construction, farmland cultivation, wind erosion, etc., to environmental PM2.5 is relatively small. The secondary particles are formed by multi-phase (gas particle) chemical reaction, through which ordinary gaseous pollutants can be transformed into very small particles. In most areas, sulfur and nitrogen are the main components of secondary PM2.5, and secondary organic aerosols may also be an important component in some areas.
The impact of PM2.5 on human health mainly includes
It can improve the mortality of patients with serious and chronic diseases, aggravate the chronic diseases, worsen the diseases of respiratory system and heart system, change the lung function and structure, affect the reproductive ability, change the immune structure of human body, etc. Three kinds of diseases caused by particulate matter deserve attention: infectious diseases, including influenza, tuberculosis and pneumonia; allergies, including asthma and alveolitis caused by natural allergens; and lung cancer. Most of the health effects are thought to be caused by PM2.5 in the small fraction rather than the large fraction. The degree of harm mainly depends on its composition, concentration and particle size.
PM2.5 refers to particles with a diameter of less than or equal to 2.5 microns in the atmosphere, also known as pulmonary particles. Its diameter is less than 1 / 20 of the thickness of human hair, which can only be found by electron microscope. Although PM2.5 is only a small component in the earth's atmosphere, it has an important impact on air quality and visibility. PM2.5 index has become an important index to measure and control the degree of air pollution.
PM2.5 is the residue from combustion in the process of daily power generation, industrial production and automobile exhaust emission, most of which contains toxic substances such as heavy metals. Generally speaking, the fine particles (PM2.5) below 2.5 μ m mainly come from the combustion of fossil fuels (such as vehicle exhaust, coal combustion), volatile organic compounds, etc.
According to the World Health Organization (who), PM2.5 has a huge impact on human health. When the annual average concentration of PM2.5 reaches 35 micrograms per cubic meter, the risk of human death increases about 15% compared with the case of 10 micrograms per cubic meter. Zhong Nanshan, academician of the Chinese Academy of engineering, pointed out: "if it is more than '5, it will go to the trachea and bronchi, but if it is less than 5, especially if it is 1 to 3 microns, it will go into the alveoli. The alveoli are used for gas exchange. Those particles are swallowed by macrophages, and they will stay in the alveoli forever, which will have an impact on the cardiovascular system, the nervous system and others, not just the respiratory system. '
Netizen survey:
'looking at the turbid air in the city and the pedestrians running on the road, I especially envy my parents. They can live leisurely in the countryside, breathe fresh air, and some netizens say they want to approve masks, which are sold by the roadside. Masks have become a hot commodity on taobao.com for a while, with prices ranging from 2 yuan to 30 yuan. Some sellers even suffer from shortage.
Relationship between haze and PM2.5
In fact, fog and haze are two concepts. Fog is a natural phenomenon when the relative humidity is high, and haze is a general phenomenon that a large number of very fine dry dust particles float evenly in the air under certain weather conditions, making the horizontal visibility less than 10km. Although PM2.5 is not related to fog, it is one of various fine particles that cause haze.
From October to march of the following year is the high incidence period of haze in China. During this period, the public should strengthen prevention and reduce going out, and pregnant women, children and the elderly should stay indoors as much as possible to avoid affecting their health.