In general, air pollution has two peaks every day, one before sunrise and the other in the evening. Especially in winter, under the influence of cold and high pressure in the morning and evening, the phenomenon of inverse temperature rise often occurs, that is, the upper air temperature is high, while the ground temperature is low, and the atmospheric convection almost stops. Therefore, the harmful pollutants on the ground cannot spread to the upper atmosphere and stay in the lower respiratory zone. This phenomenon is particularly typical in residential areas with concentrated industries or high-rise buildings and on both sides of roads where cars fly by. At this time, the harmful gas is 2-3 times higher than normal.
A healthy adult breathes 16-20 times per minute and inhales about 10 cubic meter of air every day. During exercise, due to the needs of metabolism, the inhaled air is often 2-3 times that of normal state. Therefore, the choice of environment and time during exercise is particularly important.