Estimation of CO₂ Concentration Distribution Using NaOH Solution in Greenhouse

Abstract

For effective CO 2 enrichment in protected horticulture, it is necessary to understand the distribution of the CO 2 concentration in a greenhouse. In this study, we used sodium hydroxide (NaOH) aqueous solution, whose pH decreases when it absorbs CO 2 to estimate the CO 2 concentration in a greenhouse. When plastic boxes with containing NaOH solutions were placed in various CO 2 concentration environments, there was a positive correlation between the CO 2 concentration and reduction the pH. Further, the pH was affected by the surface area and temperature of the aqueous solution, NaOH concentration, and CO 2 absorbing treatment time. We considered that using a hard plastic box with 50 mL of 0.004 mol・L -1 NaOH solution was suitable for measuring the pH in the greenhouse. We examined the associations among the CO 2 concentration, solution temperature, and pH in different environments using a growth chamber, and we formulated relational expressions. About 100 plastic boxes with 50 mL of 0.004 mol・L -1 NaOH solution were placed for 3 hours in a greenhouse with a CO 2 enrichment tube that was set for medium planted strawberry plants. pH changes differed depending on the location. The estimated CO 2 concentration was higher in the greenhouse than outside, and varied depending on the distance from the CO 2 enrichment tube and height from the ground in the greenhouse. The estimated CO 2 concentrations were about 100 ppm higher than the measured CO 2 concentrations, possibly affected by light and wind. We propose that using NaOH solution is a simple and effective method to estimate the distribution of the CO 2 concentration in a greenhouse. Key Words：CO