The Effects of Car Exhaust on Plant Growth The Effects of Car Exhaust on Plant Growth Studies have shown that people living in large, polluted cities are more susceptible to many diseases and have generally lower health than people living in clean environments. I wondered: "If pollution is so harmful to humans, is it also harmful for plants or could it even kill them entirely?" My hypothesis was that pollution would be harmful to plants and inhibit their growth.
I built a germination chamber out of wood consisting of five compartments and planted 30 Mung bean seeds in each compartment. My experiment consisted of connecting a hose from a car tailpipe to the chamber's piping. I exposed each of four compartments to10, 20, 30, or 40 minutes of exhaust each day for 14 days. I also had a control compartment exposed to no exhaust. 
My results were surprising. Growth was better in the compartments with more exhaust. The compartment exposed to 40 minutes germinated fastest, had the most plants with leaves, and had the healthiest plant color. I attribute this to the mechanisms of photosynthesis.
The overall chemical equation for photosynthesis is: 6H 2O + 6CO 2 à C 6H 12O 6 + 6O 2. The plants exposed to exhaust did better than those exposed to smaller amounts or no exhaust because of the second step in photosynthesis, the light-independent process or "Calvin Cycle": C 5 + CO 2 + ATP + NADPH à C 6H 12O 6
The light-independent process takes place at night when the plant "breathes". The plant opens up pores on its leaves to let in carbon dioxide which is turned into carbohydrates for the plant to use for growth. Since the major component in car exhaust is CO 2, the exhaust actually helped the plants grow. The plants that were exposed to exhaust germinated faster, had a healthier, darker color, and had more leaves than those plants exposed to little or no exhaust.