24-Hour CO2 Concentration

The measurement of atmospheric carbon dioxide (CO₂) is a unique indicator of the metabolic rate of the USU campus and surrounding area.

In the summer months, the CO₂ typically decreases during sunny, warm days as photosynthesis removes CO₂ from the air. At night, the CO₂ increases because the plants are giving off CO₂ in respiration.

It often takes until late morning, before CO₂ removal by photosynthesis becomes apparent. CO₂ levels often change with wind direction. During the day the wind is often from the west (180 to 270 degrees) and the CO₂ reflects photosynthesis from vegetation or anthropogenic activity upwind of the sensor. At night, in the summer months, the prevailing wind is out of the canyon (southwest = 120 degrees), and CO₂ levels reflect respiration upwind of the sensor.

We have graphed the photosynthetic photon flux (the intensity of the portion of sunlight used by plants), since this is the driving force for photosynthesis.

In the winter months, this daily CO₂ cycle does not occur because the plants are dormant. CO₂ increases to more than 450 ppm because of cars and home heating.  During inversions, the CO₂ is trapped in the valley and can increase to over 500 ppm. Although CO₂ is not directly harmful to people at these levels, elevated levels indicate the build-up of other air pollutants, such as PM 2.5 and ozone.