Removal of Carbon Monoxide by Field and Forest Soils

Abstract

AbstractThe removal of carbon monoxide from a stream of air flowing through a chamber containing soil, either from a forest or from a cultivated field, was measured in the laboratory by infrared gas analysis. The ambient CO concentration, the moisture content of the soil, and the turbulence of air above the soil modified the CO removal. The removal of CO by either soil increased with concentration between 2 and 40 ppm. Maximum rates of removal approached 0.20 mg CO dm−2 hour−1. The pattern of removal was exponential with CO concentration in moist soil and linear with CO concentration in dry soil. In the forest soil, an optimum water content for CO removal was apparent at about 55% (wt/wt). Removal of CO by the field soil increased up to about 5% water content (wt/wt), but it did not increase further as water content increased to about 15% (wt/wt). Removal of CO by the forest soil exceeded that of the field soil at all water contents when the two soils were compared at the same CO concentration. Stirring the soil enhanced the removal of CO by a crusted field soil that was dryer in the upper than in the lower part of the profile. Slowing the mixing of air over the forest soil decreased removal of CO 40 to 50% at two moisture contents. Analyzing the removal of CO by soil with a diffusion model suggests that the entry of CO into soil is opposed by a substantial diffusive resistance that varies with soil type, moisture content, turbulence of the air, and CO concentration. The measurements suggest that the soil surface of the earth removes CO at a minimum annual rate equivalent to 14% of the tropospheric inventory.