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Based on two comprehensive field studies conducted in California, background concentration (parts per trillion) of N2O (296.0 X 103), SF6 (0.16), CCI2F2 (180.8), CCI3F (103.8), CCI2FCCIF2 (16.3), CCI4 (114.2), CH3CI (952.9), CHCI3 (23.4), CH3I (2.4), CH3CCI3 (84.0), CCI2CCI2 (43.1), CHCICCI2 (14.5) and CH3Br (—) have been reported. These trace constituents were identified using retention data on eight GC columns, their electron attachment properties, and their EC thermal response. All but CHCICCI2 and CH3Br were measurable 100% of the time at both sites. Cryogenic procedures for SF6 ambient measurement were developed and successfully used. By an analysis of worldwide emissions of these trace constituents, their ambient levels, and their atmospheric lifetimes, it was possible to determine their origin (natural or anthropogenic). Our results indicate that 27% of organic chlorine contribution to the troposphere comes from fluorocarbons as opposed to a 73% contribution from the chloro-carbons. Further, the anthropogenic organic content in the troposphere was found to be about twice the natural content. Very high CHCI3 concentrations in onshore ocean waters were measured. Ambient data supporting the anthropogenic origin of CCI4 have been presented.
Singh et al. (Fri,) studied this question.