Abstract
In this research, an analytical method was developed for simultaneous measurements of PFCs (perfluorocarbon), HFCs (hydrofluorocarbon), SF6 (sulfur hexachloride), HCFCs (hydrochlorofluorocarbon), and CFCs (chlorofluorocarbon) in the atmosphere. The analytical system is based on a cryogenic preconcentration with cryocoolers and GC/MS. Temperature programming during the cryogenic concentration and use of a molecular sieve column, have made the system free from the interference by nitrogen and carbon dioxide. Good performance was obtained for the 21 target halocarbons in this study. The relative standard deviation calculated from eight repetitive analyses of 100ppt standard gas was within 2% for most of the target compounds. Detection limits (s/n =2) were lower than 1 ppt for all the compounds except for HFC-32 (1.7ppt). The method was successfully used to study vertical distribution of the target halocarbons over Sagami Bay. The aircraft measurements in August 2003 showed significant vertical difference for HCFC-141 b, HCFC-22, HFC-134a, and CFC-12. The differences of the concentrations at 500m and at 7000m were 636ppt for HCFC-22, 440 ppt for HCFC-141b, 311 ppt for HFC-134a, and 10lppt for CFC-12. It is considered that those vertical profiles reflect the regional emissions of the halocarbons. From the 7000m measurements, the concentretions of HFC-134a and HCFC-22 concentration were found to be 25.2ppt and 157.2ppt in the free troposphere, respectively, showing their continuous increase (ex. HFC-134; 14.6ppt, HCFC-22; 143.2ppt, as of 2000, WMO Ozone Assessment 2002).
