Dept. of Environmental Science
Oregon Graduate Center
This dissertation is divided into two parts. The first part deals primarily with the lifetime, distribution, and implications of methyl chloroform (CH3CC13) in the global environment. Part II deals with some theoretical considerations which support the calculations in Part I. The second part also contains a preliminary analysis of CHClF2 (F-22) in the atmosphere. The results of a budget analysis of CH3CCl3 imply a total global lifetime of between 7 and 10 years. The lifetime of 9 years is most consistent with the data. Similar analyses of CFCl3 (F-11) and CCl2F2 (F-12) indicate that the lifetimes of these gases are greater than 20 years. The lifetime of CH3CCl3 due to HO radical interactions is consistent with average ground level HO densities of approximately 6-7x10[superscript 5] molecules/cm3. These are used to calculate the lifetimes of many other trace gases which are, or may become, important in understanding the global atmospheric environment. Most notably, the lifetimes of CH4, F-2l, and F-22 turn out to be approximately 14, 3 and 23 years respectively. The long CH4 lifetime has a variety of implications for CO production in the atmosphere as well as the budget of CH4. The data base used for the calculations is in general different from that used in other analyses discussed in the literature. Furthermore, new equations were derived to carry out the studies discussed in this work. It was also found that the emissions history of CH3CCl3 shows cyclic fluctuations superimposed on the exponential growth. Including such fluctuations into the theory brought the observed growth of CH3CCl3 concentrations in the atmosphere in coincidence with the theoretically predicted growth rate. The observation that the ratio (R [subscript o]) of CH3CCl3 (concentration)in the northern and southern hemispheres has been changing was also properly explained by the cyclic fluctuations of the emissions. Thus in earlier years (before 1975) it is likely that there was a greater excess of CH3CCl3 in the northern hemisphere (compared to the southern hemisphere) than there is at this time. Other possible explanations of the changing ratio did not agree with observations. The theory used to study this ratio (R supscript o]) was extended to derive a simple criterion for deducing the presence of significant southern hemisphere sources of trace gases. It was found that CH=CH (acetylene), C2H6, C2H4, CO, COS, and several other relatively short-lived trace gases have southern sources. In Part II one of the studies centered around the global analysis of CHClF2 (F-22). Current global concentration of about 47 ppt was greater than could be explained by the accepted emissions estimates. Several explanations of the excess were offered. These included the possible slow conversion of F-12 to F-22 and sources other than direct F-22 emissions from the manufacture and use of this compound. Other aspects of Part II will not be discussed here. The global measurements, on which all the theoretical considerations are based, were made by R. A. Rasmussen over the past five years.
Khalil, Mohammad Aslam Khan, "Topics in the behaviour of atmospheric trace gases" (1979). Scholar Archive. 51.