Tropospheric observations of CFC-114 and CFC-114a with a focus on long-term trends and emissions

Please use this identifier to cite or link to this item: https://ir.lib.ncu.edu.tw/handle/987654321/101951

Title:	Tropospheric observations of CFC-114 and CFC-114a with a focus on long-term trends and emissions
Authors:	王家麟;Laube, Johannes C.;Mohd Hanif, Norfazrin;Martinerie, Patricia;Gallacher, Eileen;Fraser, Paul J.;Langenfelds, Ray;Brenninkmeijer, Carl A. M.;Schwander, Jakob;Witrant, Emmanuel;Wang, Jia-Lin;Ou-Yang, Chang-Feng;Gooch, Lauren J.;Reeves, Claire E.;Sturges, William T.;Oram, David E.
Contributors:	理學院化學學系
Keywords:	Air pollution;Air sampling;Archives & records;Atmosphere;Atmospheric chemistry;Atmospheric sciences;Automatic;Calibration;Cerebral hemispheres;Chlorofluorocarbons;Climate change;Emissions;Emissions control;Engineering Sciences;Environmental science;Firn;Gases;Global temperature changes;Greenhouse effect;Greenhouse gases;Isomers;Mitigation;Mixing ratio;Montreal Protocol;Observatories;open climate campaign;Ozone;Ozone depletion;Ozone layer depletion;Radiation;Speciation;Stainless steel;Trends;Two dimensional models;Ultraviolet radiation
Date:	2016-12-09
Issue Date:	2026-04-21 14:52:22 (UTC+8)
Publisher:	European Geosciences Union;Katlenburg-Lindau: Copernicus GmbH
Abstract:	摘要： Chlorofluorocarbons (CFCs) are ozone-depleting substances as well as strong greenhouse gases, and the control of their production and use under the Montreal Protocol has had demonstrable benefits to both mitigation of increasing surface UV radiation and climate forcing. A global ban on consumption came into force in 2010, but there is evidence of continuing emissions of certain CFCs from a range of sources. One compound has received little attention in the literature, namely CFC-114 (C2Cl2F4). Of particular interest here is the differentiation between CFC-114 (CClF2CClF2) and its asymmetric isomeric form CFC-114a (CF3CCl2F) as atmospheric long-term measurements in the peer-reviewed literature to date have been assumed to represent the sum of both isomers with a time-invariant isomeric speciation. Here we report the first long-term measurements of the two isomeric forms separately, and find that they have different origins and trends in the atmosphere. Air samples collected at Cape Grim (41° S), Australia, during atmospheric background conditions since 1978, combined with samples collected from deep polar snow (firn) enable us to obtain a near-complete record of both gases since their initial production and release in the 1940s. Both isomers were present in the unpolluted atmosphere in comparably small amounts before 1960. The mixing ratio of CFC-114 doubled from 7.9 to 14.8 parts per trillion (ppt) between the start of the Cape Grim record in 1978 and the end of our record in 2014, while over the same time CFC-114a trebled from 0.35 to 1.03 ppt. Mixing ratios of both isomers are slowly decreasing by the end of this period. This is consistent with measurements of recent aircraft-based samples showing no significant interhemispheric mixing ratio gradient. We also find that the fraction of CFC-114a mixing ratio relative to that of CFC-114 increased from 4.2 to 6.9 % over the 37-year period. This contradicts the current tacit assumption used in international climate change and ozone depletion assessments that both isomers have been largely co-emitted and that their atmospheric concentration ratio has remained approximately constant in time. Complementary observations of air collected in Taiwan indicate a persisting source of CFC-114a in South East Asia which may have been contributing to the changing balance between the two isomers. In addition we present top-down global annual emission estimates of CFC-114 and CFC-114a derived from these measurements using a two-dimensional atmospheric chemistry-transport model. In general, the emissions for both compounds grew steadily during the 1980s, followed by a substantial reduction from the late 1980s onwards, which is consistent with the reduction of emission in response to the Montreal Protocol, and broadly consistent with bottom-up estimates derived by industry. However, we find that small but significant emissions of both isomers remain in 2014. Moreover the inferred changes to the ratio of emissions of the two isomers since the 1990s also indicate that the sources of the two gases are, in part, independent. 出版者： Katlenburg-Lindau: Copernicus GmbH 出版日期： 2016-12-09 出處： Atmospheric chemistry and physics, 2016-12, Vol.16 (23), p.15347-15358 資源來源： Agricultural & Environmental Science Collection 版權： COPYRIGHT 2016 Copernicus GmbH 版權： Copyright Copernicus GmbH 2016 版權： 2016. This work is published under http://creativecommons.org/licenses/by/3.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License. 版權： licence_http://creativecommons.org/publicdomain/zero 識別號： ISSN: 1680-7324 識別號： ISSN: 1680-7316 識別號： EISSN: 1680-7324 識別號： DOI: 10.5194/acp-16-15347-2016
Appears in Collections:	[Department of Chemistry] journal & Dissertation

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