Aircraft measurements of tropospheric carbon dioxide over the Japanese islands

To elucidate spatial and temporal variations of the tropospheric CO2 concentrations over the Japanese Islands, air samples were collected between 26°N and 38°N latitude during the period from June 1982 to February 1985 aboard commercial jet airliners. The amplitude of the seasonal variation of upper tropospheric CO2 diminished gradually going southward with a phase delay of approximately half a month. Seasonally adjusted concentrations increased gradually in 1982, rapidly in 1983 and rather slightly in 1984 for all latitudes, and annual mean values were nearly the same for all latitudes in both 1983 and 1984.Over the southernmost part of Japan, the phase of the seasonal variation in the lower troposphere, preceded by about 15 days, those variations within the middle and upper levels of the troposphere. The peak-to-peak amplitude decreased slightly with increasing height. Annual mean values also decreased with increasing height; the concentration difference between the lowest and highest layers sampled was about 2 ppmv. The secular trend of the CO2 concentration was almost the same as at the higher latitudes.