What is the obvious change law of carbon dioxide concentration in the surface layer under clear and windless weather in summer?

In clear and windless weather, the CO2 concentration in the near-surface layer shows an obvious variation law of low day and high night, especially in summer.

Effects of CO2 on crop growth and yield —— Daily and vertical changes of CO2 in farmland

(1) Diurnal variation: At night, due to the continuous release of CO2 by soil and plants after daytime, there is no photosynthesis, and the CO2 concentration in farmland is the highest. During the day, because the crops are in a "hungry" state after a long night, the enhancement of photosynthesis reduces the CO2 concentration, and the photosynthesis rapidly increases to the maximum at 9- 10 before noon, while the CO2 concentration reaches a low point. The external conditions around noon are unfavorable to photosynthesis, so the CO2 concentration changes smoothly. In the afternoon, with the weakening of solar radiation intensity, the temperature drops and the stomata of leaves gradually open. Photosynthetic intensity reached a sub-peak at 15- 16, and CO2 concentration also decreased again. However, in the afternoon, the air turbulence is strong, and CO2 can be supplemented from high altitude, but the decline is not significant.

(2) Vertical variation: In clear and windless weather, the CO2 concentration in the near-surface layer shows an obvious variation law of low day and high night, especially in summer. During the day, the population is the sink of CO2, and the atmosphere is the source of CO2. At this time, carbon dioxide is transferred from the atmosphere to the crowd. This distribution pattern of CO2 concentration increasing with height is called photosynthetic type. At night, the population is the source of CO2, and the atmosphere is the sink of CO2. At this time, carbon dioxide is transported from the crowd to the atmosphere. This distribution pattern of CO2 concentration decreasing with height is called respiratory type. But in the evening and early morning, they will transform into each other.