Title: Diurnal Variations of CO<sub>2</sub> Mixing Ratio in the Lower Atmosphere by Three Wavelength DIAL
Abstract: We have conducted the measurement of high accurate CO 2 mixing ratio profiles by measuring the temperature profiles simultaneously using the three wavelength CO 2 DIAL. The measurements of CO 2 diurnal variation in the lower atmosphere were carried out on sunny and cloudy days respectively. We find out that increasing of the CO 2 mixing ratio occurs over the altitude of about 2 km from the surface during nighttime. On the other hand, the CO 2 mixing ratio decreases over the lower atmosphere during daytime. In particular, the CO 2 mixing ratio decreases earlier on sunny days than on cloudy days after sunrise. This result suggests that CO 2 absorption by photosynthesis greatly contributes to the strength of the solar radiation.