Nowadays, people are more and more concerned about air quality, PM2.5, a technical term consisting of English and numbers, is gradually entering our lives, so what is PM2.5 and what is the impact on human health? PM2.5 refers to particulate matter with a diameter less than or equal to 2.5 microns in the atmosphere, also known as lung-accessible particulate matter. The amount of PM2.5 per cubic meter of air represents the degree of air pollution. Above PM5 can reach the tracheobronchial tubes, but below PM5, especially particles of 1 to 3 microns, will enter the alveoli, where these particles are engulfed by alveolar macrophages and can stay in the alveoli and also affect the cardiovascular system and the nervous system, not just the respiratory system alone. In fact, the greatest harm to the human body is not the particles themselves, but the particles adsorbed chemical substances, such as adsorption of carcinogens have a carcinogenic effect, adsorption of diffing has reproductive harm, if adsorbed heavy metals have heavy metal hazards.