The "2.5" of PM2.5 is 2.5 microns, 1000 microns =1 millimeter, 2.5 microns is equal to 1/20 of the diameter of a human hair.So fine particles 2.5 microns in diameter are invisible to the naked eye.Excessive inhalation of PM2.5 has obvious harm to human body:

1. Cause airway obstruction or inflammation

Studies show that 75 percent of particulate matter 2.5 micrometers or less is deposited in alveoli.

2. Disease-causing microorganisms, polycyclic aromatic hydrocarbons, lampblack and so on take the "tailwind" into the body to cause cancer

In addition to their own "do bad things", fine particles also like a vehicle can freely enter the respiratory system of the car, other pathogenic substances such as bacteria, viruses, riding the "tailwind", to the depths of the respiratory system, causing infection.

Epidemiological investigation has found that pahs in urban particulate matter are associated with the incidence and mortality of lung cancer in residents.When pahs enter the human body, fine particles play a role of "tailwind". Most of the pahs in the atmosphere are adsorbed on the surface of particles, especially those with particle size less than 5 mm, and few of them are found on large particles.So the more fine particles we have in the air, the more we're exposed to the carcinogen pahs.

3.The impact of fetal development caused by defects

Other findings are more worrying.Some reports in recent years show that human's reproductive ability is decreasing obviously, and environmental pollution is considered as the main culprit.A study of pregnant women exposed to high levels of PM2.5 in northern Bohemia found that high levels of fine particulate pollution may affect the development of embryos.

More studies have found that atmospheric particulate matter concentration is associated with increased perinatal and neonatal mortality, low birth weight, intrauterine developmental delay (IURG), and congenital functional defects.

4. PM2.5 particles can enter the blood vessels through air and blood exchange.