Time and space variations of tropospheric carbon dioxide over Japan

Aircraft measurements of atmospheric CO₂ concentration over Japan, initiated in January 1979, have been continued to the present. The average seasonal variation of atmospheric CO₂ showed maximum concentration early in April and early in May, and minimum concentration in mid-August and mid-September for the lower-most and the upper-most layers of the troposphere, respectively. The peak-to-peak amplitudes of the seasonal variation were 14.5, 9.0 and 7.8 ppmv for the lower, middle and upper tropospheres, respectively. The average rate of annual increase of the CO₂ concentration over the last 6 years was about 1.3 ppmv yr⁻¹ with considerable variation with time. The vertical profile of the annual mean value of the CO₂ concentration was almost the same from year to year; the CO₂ concentration decreased gradually with height and the concentration difference between the lowest and highest layers of the troposphere was about 2 ppmv.