Seasonal and meridional variations of atmospheric carbon dioxide in the lower troposphere of the northern and southern hemispheres

Systematic collection of air samples over the Pacific Ocean was begun in March 1982 on board a container ship sailing between Japan and Australia. A current picture of seasonal and meridional variations of lower tropospheric CO₂ was derived from the measurement of these samples and supplementary information from several other observational programs. It was concluded that: (1) the amplitude of the seasonal variation was about 15 ppmv in high and mid-latitudes of the northern hemisphere and decreased southward to low values of about 1 ppmv in the southern hemisphere; (2) the maximum and minimum concentrations of the seasonal variation in the mid-latitudes of the northern hemisphere appeared early in April and in mid-August, respectively, and their occurrences were delayed gradually southward and northward from that latitude; (3) the annual mean CO₂ concentration was high in the midnorthern hemisphere, decreased gradually southward to low values in the mid-southern hemisphere and increased slightly again in the Antarctic region, the concentration difference between the mid-northern hemisphere and the Antarctic region being about 3 ppmv; (4) the year-to-year changes of annual mean CO₂ concentrations in all latitudes covered by this measurement were 1.3 and 1.7 ppmv yr^-1, for 1982-1983 and 1983-1984, respectively.