Where is the best air?

People often think that the air is freshest in the morning, but this is actually a misunderstanding. Whether the air is fresh or not depends on the severity of air pollution. The main sources of air pollution are smoke and dust, exhaust gas from various motor vehicles, smoke and dust from residential stoves and carbon dioxide gas emitted by green plants at night. According to scientists, the air pollution is very light in the morning, noon and afternoon, so the air is relatively fresh and clean, and the air is freshest around 10 in the morning and 3-4 in the afternoon. Air pollution is more serious in the morning, evening and evening, and the peak time of pollution is around 7 pm and 7 am. Of course, the air at this time is the most stale.

The difference of air freshness in a day is caused by meteorological factors. The vertical temperature difference between day and night changes obviously. When the ground temperature is higher than the upper air temperature, the ground air is easy to rise, and pollutants are easy to be carried to the upper air for diffusion. When the ground temperature is lower than the upper air temperature, an "inversion layer" is formed in the sky. This "inversion layer" presses on the ground like a big cover, so that the ground air cannot rise and various pollutants in the air cannot spread. Generally, the inversion layer is easy to appear at night and in the morning and evening, so the air is dirtiest at these times.

When the sun comes out during the day, the ground temperature rises rapidly and the inversion layer will gradually dissipate. So pollutants will spread rapidly. Generally, after 10 in the morning, the ground air is very fresh. Therefore, the morning exercise time should be chosen after sunrise, and it is best to choose 10 am and 3-4pm, because the air is freshest at this time.