152 



EHHALT 



present range of estimates for the atmospheric CH 4 turnover time spans about 

 an order of magnitude from 0.7 to 6 years. The fact that both the destruction 

 rate and Junge's rule give lower turnover times seems to indicate that the source 

 strengths in Table 2 may be underestimated or that some sources are missing 

 altogether. 



ATMOSPHERIC PROFILES OF CH 4 



Since the CH 4 sources are mainly biologic and bacterial CH 4 production is 

 strongly temperature dependent, we would expect source strengths to vary 

 with season. Consequently, since the turnover time of CH 4 is only a few years, 

 the CH 4 concentration in the atmosphere should also show a seasonal variation. 

 Such a seasonal variation could be used also to determine the tropospheric 

 turnover time of CH 4 . With this in mind we obtained a series of vertical profiles 

 of CH 4 in the troposphere up to an altitude of 9 km remote from the local sinks 

 and sources of the earth's surface. Figure 2 shows the seasonally averaged CH 4 

 profiles obtained over Scottsbluff, Nebr., during 1966 and profiles obtained over 



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CH 4 MIXING RATIO, ppM 



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Fig. 2 Seasonally averaged vertical profiles of CH 4 over the eastern Pacific and Scottsbluff, 

 Nebr. 1 8 The letters show the months over which each profile has been averaged. The 

 vertical lines represent the total average CH 4 volume-mixing ratio in the troposphere: 

 1.41 ppM. The annual averages are given at the right. 



