Why greenhouses add carbon dioxide

Plants build sugar from carbon dioxide and light, and a sealed greenhouse full of crop can pull CO2 below outdoor levels by midmorning. Growers burn clean fuel or release bottled CO2 to raise the level to roughly 800 to 1,300 ppm, which speeds photosynthesis until the leaves approach saturation.

Controls

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Animation speed

CO2 setpoint

Roof vents open

Step through it

A hungry cropOn a bright morning with the vents shut, a full canopy can draw CO2 well below the outdoor level of about 400 ppm.
The burnerA clean burning heater fueled by natural gas or propane makes CO2 and some heat. Fumes must burn completely, since incomplete combustion can harm plants and people.
Enriched airRaising the canopy to about 1,000 ppm speeds photosynthesis by roughly half compared with outdoor air.
Sensor controlA CO2 sensor switches the burner or tank valve so the level stays near the setpoint during daylight hours.
Vents openWhen the house needs cooling and vents open, enriched air escapes. Growers usually lower the setpoint or stop dosing then.

A saturating curve

Photosynthesis rises quickly with CO2 at first and then levels off, like most enzyme driven processes. This model uses a simple saturating curve, rate proportional to (C minus 50) / (C minus 50 + K), with 50 ppm as the point where leaves stop gaining carbon. K is set so that 1,000 ppm gives about 50 percent more photosynthesis than 400 ppm, a common rule of thumb.

Real responses depend on light, temperature and crop, and leaves can acclimate to long enrichment. Treat the numbers as a teaching model.

Try it: slide the setpoint from 400 to 800 ppm, then from 1,100 to 1,500 ppm. The first step adds nearly 40 percent more photosynthesis; the second, an equally big jump in CO2, adds only about 12 points more, which is why growers rarely go past about 1,300 ppm.

Why vents change everything

With vents open, the house trades air with the outdoors, so the canopy drifts toward 400 ppm. The model assumes only 30 percent of the enrichment survives with vents open, a simplified assumption. Enrichment pays best in cool seasons when vents stay shut.

Sources

Carbon Dioxide Enrichment in Our Atmosphere and GreenhousesUC Cooperative Extension, Santa Cruz County
CO2 enrichment in greenhouse production: Towards a sustainable approachFrontiers in Plant Science, via PubMed Central

How to cite this model

Avid Solutions International. (2026, November 11). Why greenhouses add carbon dioxide [Interactive 3D model]. Avid Field Lab. https://avidsolutionsintl.com/explore/co2-enrichment

Last updated November 11, 2026

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