Changes in the levels and variability of halocarbons and the compliance with the Montreal Protocol from an urban view

Abstract Ambient levels and variability of major atmospheric halocarbons, i.e. CFC-12, CFC-11, CFC-113, CCl 4 , CH 3 CCl 3 , C 2 HCl 3 , and C 2 Cl 4 in a major metropolis (Taipei, Taiwan) were re-investigated after fourteen years by flask sampling in 2012. Our data indicates that the variability expressed as standard deviations (SD) of CFC-113 and CCl 4 remained small (2.0 ppt and 1.9 ppt, respectively) for the 10th–90th percentile range in both sampling periods; whereas the variability of CFC-12, CFC-11, C 2 HCl 3 , and C 2 Cl 4 measured in 2012 became noticeably smaller than observed in 1998, suggesting their emissions were reduced over time. By comparing with the background data of a global network (NOAA/ESRL/GMD baseline observatories), the ambient levels and distribution of these major halocarbons in Taipei approximated those at a background site (Mauna Loa) in 2012, suggesting that the fingerprint of the major halocarbons in a used-to-be prominent source area has gradually approached to that of the background atmosphere.