Over the last seven years, Chinese have become more aware of the devastating effects of air pollution. PM stands for damaging air pollutants called “particulate matter,” and 2.5 refers to their size in microns a unit of measurement that is a millionth of a meter. Exposure to high levels of PM 2.5 can irritate the respiratory tract, worsen asthma and bronchitis, and eventually lead to increased mortality from lung cancer and heart disease.
US embassy twitter feed @beijingair
How the air quality index works, AQI