The measurement of atmospheric carbon dioxide (CO2) is a unique indicator of the metabolic rate of the USU campus and surrounding area. The unit of parts per million (ppm) is numerically equivalent to micromoles of CO2 per mole of air. The SI unit for CO2 concentration is µmol per mol.
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 can take until late morning before CO2 removal by photosynthesis becomes apparent. Local CO2 levels also 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 (east = 90 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.
The Utah Department of Environmental Quality provides current air quality measurements in downtown Logan for ozone and PM 2.5 at http://www.airquality.utah.gov. On some days with inversions, the air quality on campus can be better than downtown because of the higher elevation and proximity to the canyon.
These measurements are also being made in the Salt Lake Valley. Their website provides a useful tutorial for interpreting the long-term graphical data: http://co2.utah.edu/co2tutorial.php?site=7&id=1
A review of the long-term, steady increase in the CO2 concentration of our atmosphere is available here: http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_data_mlo.html. Tyler Volk, who spoke at USU two years ago, has written a book called CO2 Rising, which explains the global carbon cycle and discusses the effects of increasing CO2. http://www.youtube.com/watch?v=MRtRdrdQwig