The Carbon Dioxide Content of Field Air

Abstract

Equal volumes of air were drawn from each sta-tion at the rate of 100 1/hr and CO, was absorbed in standard KOH in towers which gave better than 99 % absorption at the rate of flow used. Carbonates were precipitated from the residual KOH with BaCl2 and the solution titrated to the phenolphthalein endpoint with HCl. Carbon dioxide was then calculated as mg/l at standard pressure and temperature. RESU-LTS Experiments were started in July when the corn field was tasseled and continued at intervals until October 18 when all corn plants in the area were dead and dry. Typical runs started at 3:00 A.M. and con-tinued until midnight. Various shorter runs were made to test morning and evening changes, effect of wind, etc. Figure 1 shows the type of data obtained on still days with a maximum wind velocity of 2 to 3 mph. Analyses at 1 m in the grass plot around the tower were generally not significantly different from those in the corn field. Results at 10 and 30 m on the tower tended to be intermediate between those at the lower and higher levels, with figures at 30 m rather close to those at 152. The curves of figure 1 show a build-up of CO, near the ground at night. This build-up is due to respiration of plants and soil organisms (13, 18) and develops only on a still night. It did not show at 30 m or above until after sunup, when rising currents of warm air may have caused the sudden jump of CO2 content shown at 6 A.MI. in figure 1. Fuller's results (8) suggest that a still higher concentration might have been obtained by sampling the air just above ground level. Fuller made his measurements in