Although PM is not a toxic gas, it carries a lot of toxic and harmful substances because of its small diameter, which will affect health when it enters the human body. The smaller the diameter of PM, the greater the harm to human body, and PM2.5 can float far away, so the influence range is larger. In addition, PM2.5 is more harmful to human health, because the smaller the diameter, the deeper the part that enters the respiratory tract. Particles with a diameter of 10μm are usually deposited in the upper respiratory tract, and those below 2μm can penetrate bronchioles and alveoli. After fine particles enter the alveoli, they directly affect the ventilation function of the lungs, making the body vulnerable to hypoxia. Moreover, once this fine particle enters the alveoli, it is difficult to fall off when it is adsorbed on the alveoli, and this adsorption is irreversible.
PM2.5, PM 10, SO2, NO2, O3, CO, etc. As the six pollutants participating in the assessment, they can be converted into air quality index (AQI) through formula calculation, which represents the overall air pollution degree. Because the concentration limits of six pollutants evaluated by AQI are different, each pollutant will be converted into air quality sub-index AQI according to different target concentration limits. The air pollution index is greater than 500. According to the size of the air quality index, the air quality is divided into six grades. Corresponding to the six categories of air quality, the greater the index and the higher the level, the more serious the pollution situation and the greater the harm to human health. Among them, the most serious pollution level is that AQI reaches 30 1 ~ 500, and the corresponding air quality evaluation is dangerous, and 500 is the highest value of AQI. If it exceeds 500, it will be "out of the chart".
AQI is quite different from the original air pollution index (API). The reference standard of API grading calculation is the old ambient air quality standard, and the pollutants evaluated are only SO2, NO2 and PM 10, while AQI adopts stricter grading limit standard. AQI has more pollutant indexes than API, and the evaluation result is more objective. Air pollution index (API) is an air quality evaluation index based on the old air quality standard (ambient air quality standard GB 3095-1996) issued by1996. The evaluation indexes include sulfur dioxide, nitrogen dioxide and inhalable particulate matter (PM 10).
Since the end of 20 1 1, severe smog weather has occurred in many cities, and the actual feelings of citizens are in sharp contrast with the good situation displayed by API, and the voice of improving air evaluation standards is getting stronger and stronger. Since then, the original technical term PM2.5 has gradually become a "hot word". The formation of smog is mainly related to PM2.5 (particles with a diameter less than or equal to 2.5 microns). In addition, ozone indicators reflecting photochemical pollution caused by motor vehicle exhaust are not included in the evaluation system of API. Therefore, a new air quality standard-Ambient Air Quality Standard (GB 3095-20 12+02) was issued at the beginning of 2012, and the corresponding air quality evaluation system became AQI. The "pollution index" became the "quality index". On the basis of API, three pollutant indicators, namely fine particulate matter (PM2.5), ozone (O3) and carbon monoxide (CO), were added, and the release frequency was changed from once a day to once an hour.
Among them, the standard of PM2.5 was put forward by the United States in 1997, mainly to monitor the fine particles that appeared with the increasingly developed industrialization and were ignored in the old standard and were harmful to human health. The PM2.5 index has become an important indicator to measure and control the degree of air pollution. On 201111,Zhang Lijun said that China's atmospheric environmental quality standard for PM2.5 will be issued soon. 2065438+On February 28th, 2003, serious smog weather caused concern. The Chinese name of "PM2.5" was standardized and officially named "Fine Particles".
In a word, the environmental pollution continues and becomes more and more serious, while the air quality assessment system in China is relatively backward, but it is also constantly improving.