微小粒子状物質（PM2.5）の健康への影響

The danger of PM2.5 lies in its physical ability to bypass the body’s natural defenses. Larger particles (like PM10) are often trapped in the nose and upper respiratory tract and can be cleared by coughing or sneezing. However, PM2.5 particles are small enough to travel past these defenses, reaching the bronchioles and alveoli—the tiny air sacs in the lungs where gas exchange occurs. Once in the alveoli, they can cause localized inflammation and oxidative stress, impairing lung function and exacerbating conditions like asthma and chronic obstructive pulmonary disease (COPD).

Furthermore, the smallest of these particles can cross the alveolar-capillary barrier and enter the bloodstream. Circulating particles can trigger systemic inflammation and oxidative stress throughout the body. This is a key mechanism linking PM2.5 to cardiovascular disease. The inflammation can promote atherosclerosis (the hardening and narrowing of arteries), increase the risk of blood clots, and lead to hypertension. The chemical composition of PM2.5, which can include heavy metals, sulfates, nitrates, and organic compounds, also contributes to its toxicity. Long-term exposure is considered a leading environmental risk factor for premature death globally, and it has also been linked to neurodevelopmental issues in children and neurodegenerative diseases in adults.