Given data:
Decrease in the concentration of CO2 in the fall season.
To find:
Reason for the decrease in CO2 concentration.
Step-by-step explanation:
The concentration of CO2 is less in the fall season and is more during the rest of the year.
Plants perform photosynthesis in which they take up CO2 from the atmosphere and release oxygen. The process of photosynthesis is dominant during the fall season. Hence, the concentration of CO2 in the atmosphere is lowest during the fall season in California.