Publications

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2017
Zhang, G, Yao B, Vollmer MK, Montzka SA, Mühle J, Weiss RF, O'Doherty S, Li Y, Fang S, Reimann S.  2017.  Ambient mixing ratios of atmospheric halogenated compounds at five background stations in China. Atmospheric Environment. 160:55-69.   10.1016/j.atmosenv.2017.04.017   AbstractWebsite

High precision measurements of three chlorofluorocarbons (CFCs), three hydrochlorofluorocarbons (HCFCs), six hydrofluorocarbons (HFCs), three perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) were made at five Chinese background stations from January 2011 to December 2012. Their station means in the background air were 239.5 ± 0.69 parts-per-trillion dry-air mole fraction mixing ratios (ppt) for CFC-11, 536.5 ± 1.49 ppt for CFC-12, 74.66 ± 0.09 ppt for CFC-113, 232.1 ± 4.77 ppt for HCFC-22, 23.78 ± 0.29 ppt for HCFC-141b, 22.92 ± 0.42 ppt for HCFC-142b, 11.75 ± 0.43 ppt for HFC-125, 71.32 ± 1.35 ppt for HFC-134a, 13.62 ± 0.43 ppt for HFC-143a, 9.10 ± 1.26 ppt for HFC-152a, 25.45 ± 0.1 ppt for HFC-23, 7.28 ± 0.48 ppt for HFC-32, 4.32 ± 0.03 ppt for PFC-116, 0.63 ± 0.04 ppt for PFC-218, 1.36 ± 0.01 ppt for PFC-318, and 7.67 ± 0.03 ppt for SF6, respectively, which were comparable with those measured at the two Northern Hemisphere (NH) AGAGE stations: Mace Head, Ireland (MHD) and Trinidad Head, California, USA (THD). Compared with our results for earlier years from in-situ measurement at SDZ, background-air mixing ratios of CFCs are now declining, while those for HCFCs, HFCs, PFCs, and SF6 are still increasing. The ratios of the number of sampling events in which measured mixing ratios were elevated above background (pollution events) relative to the total sample frequency (POL/SUM) for CFCs, HCFCs, and HFCs were found to be station dependent, generally LAN > SDZ > LFS > XGL > WLG. The enhancement (△, polluted mixing ratios minus background mixing ratios) generally show distinct patterns, with HCFCs (40.7–175.4 ppt) > HFCs (15.8–66.3 ppt)> CFCs (15.8–33.8 ppt)> PFCs (0.1–0.9 ppt) at five stations, especially for HCFC-22 ranging from 36.9 ppt to 138.2 ppt. Combining with the molecular weights, our findings imply biggest emissions of HCFCs in the regions around these Chinese sites compared to HFCs and CFCs, while the smallest of PFCs, consistent with CFCs being phased out and replaced with HCFCs in China. In addition, relative emission strengths (emission was expressed by mole fractions) of these halocarbons in China were inferred as HCFC-22 > HCFC-141b > HFC-134a > HCFC-142b for the Yangtze River Delta (YRD) and as HCFC-22 > HCFC-142b > HCFC-141b ≈ HFC-134a in the North China Plain (NCP).

2014
Xiang, B, Patra PK, Montzka SA, Miller SM, Elkins JW, Moore FL, Atlas EL, Miller BR, Weiss RF, Prinn RG, Wofsy SC.  2014.  Global emissions of refrigerants HCFC-22 and HFC-134a: Unforeseen seasonal contributions. Proceedings of the National Academy of Sciences of the United States of America. 111:17379-17384.   10.1073/pnas.1417372111   AbstractWebsite

HCFC-22 (CHClF2) and HFC-134a (CH2FCF3) are two major gases currently used worldwide in domestic and commercial refrigeration and air conditioning. HCFC-22 contributes to stratospheric ozone depletion, and both species are potent greenhouse gases. In this work, we study in situ observations of HCFC-22 and HFC-134a taken from research aircraft over the Pacific Ocean in a 3-y span [Hlaper-Pole-to-Pole Observations (HIPPO) 2009-2011] and combine these data with long-term ground observations from global surface sites [ National Oceanic and Atmospheric Administration (NOAA) and Advanced Global Atmospheric Gases Experiment (AGAGE) networks]. We find the global annual emissions of HCFC-22 and HFC-134a have increased substantially over the past two decades. Emissions of HFC-134a are consistently higher compared with the United Nations Framework Convention on Climate Change (UNFCCC) inventory since 2000, by 60% more in recent years (2009-2012). Apart from these decadal emission constraints, we also quantify recent seasonal emission patterns showing that summertime emissions of HCFC-22 and HFC-134a are two to three times higher than wintertime emissions. This unforeseen large seasonal variation indicates that unaccounted mechanisms controlling refrigerant gas emissions are missing in the existing inventory estimates. Possible mechanisms enhancing refrigerant losses in summer are (i) higher vapor pressure in the sealed compartment of the system at summer high temperatures and (ii) more frequent use and service of refrigerators and air conditioners in summer months. Our results suggest that engineering (e. g., better temperature/vibration-resistant system sealing and new system design of more compact/efficient components) and regulatory (e. g., reinforcing system service regulations) steps to improve containment of these gases from working devices could effectively reduce their release to the atmosphere.

2008
Fine, RA, Smethie WM, Bullister JL, Rhein M, Min DH, Warner MJ, Poisson A, Weiss RF.  2008.  Decadal ventilation and mixing of Indian Ocean waters. Deep-Sea Research Part I-Oceanographic Research Papers. 55:20-37.   10.1016/j.dsr.2007.10.002   AbstractWebsite

Chlorofluorocarbon (CFC) and hydrographic data from the World Ocean Circulation Experiment (WOCE) Indian Ocean expedition are used to evaluate contributions to decadal ventilation of water masses. At a given density, CFC-derived ages increase and concentrations decrease from the south to north, with lowest concentrations and oldest ages in Bay of Bengal. Average ages for thermocline water are 0-40 years, and for intermediate water they are less than 10 years to more than 40 years. As compared with the marginal seas or throughflow, the most significant source of CFCs for the Indian Ocean south of 12 degrees N is the Southern Hemisphere. A simple calculation is used to show this is the case even at intermediate levels due to differences in gas solubilities and mixing of Antarctic Intermediate Water and Red Sea Water. Bottom water in the Australia-Antarctic Basin is higher in CFC concentrations than that to the west in the Enderby Basin, due to the shorter distance of this water to the Adelie Land coast and Ross Sea sources. However, by 40 degrees S, CFC concentrations in the bottom water of the Crozet Basin originating from the Weddell Sea are similar to those in the South Australia Basin. Independent observations, which show that bottom water undergoes elevated mixing between the Australia-Antarctic Basin and before entering the subtropics, are consistent with high CFC dilutions (3-14-fold) and a substantial concentration decrease (factor of 5) south to north of the Southeast Indian Ridge. CFC-bearing bottom waters with ages 30 years or more are transported into the subtropical South Indian Ocean by three western boundary currents, and highest concentrations are observed in the westernmost current. During WOCE, CFC-bearing bottom water reaches to about 30 degrees S in the Perth Basin, and to 20 degrees S in the Mascarene Basin. Comparing subtropical bottom water-CFC concentrations with those of the South Pacific and Atlantic oceans, at comparable latitudes, Indian Ocean bottom water-CFC concentrations are lower, consistent with its high dissipation rates from tidal mixing and current fluctuations as shown elsewhere. Thus, the generally high dilutions and low CFC concentrations in bottom water of the Indian Ocean are due to distance to the water mass source regions and the relative effectiveness of mixing. While it is not surprising that at thermocline, intermediate, and bottom levels, the significant ventilation sources on decadal time scales are all from the south, the CFCs show how local sources and mixing within the ocean affect the ventilation. (c) 2007 Elsevier Ltd. All rights reserved.

LeBel, DA, Smethie WM, Rhein M, Kieke D, Fine RA, Bullister JL, Min DH, Roether W, Weiss RF, Andrie C, Smythe-Wright D, Jones EP.  2008.  The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE. Deep-Sea Research Part I-Oceanographic Research Papers. 55:891-910.   10.1016/j.dsr.2008.03.009   AbstractWebsite

The accumulation of man-made chlorofluorocarbons (CFCs) in subsurface water masses is directly related to their formation rate, and the water mass formation rate can be calculated from its CFC inventory. CFC-11 inventories between 65 degrees N and 10 degrees S in the Atlantic Ocean have been calculated for Eighteen Degree Water (EDW) and the components of North Atlantic Deep Water (NADW) from data collected primarily between 1996 and 1998 as part of the World Ocean Circulation Experiment (WOCE). CFC-11 inventories for individual water masses are 5.4 million moles for EDW, 10.5 million moles for Upper Labrador Sea Water (ULSW) (4.6 million moles south of 42 degrees N), 23.4 million moles for Classical Labrador Sea Water (CLSW), 10.4 million moles for Iceland-Scotland Overflow Water (ISOW), and 8.3 million moles for Denmark Strait Overflow Water (DSOW). The estimated error for these inventories is about +/- 10%. The sum of the NADW components (ULSW, CLSW, ISOW, DSOW) is 53.2 million moles which is about half of the total CFC-11 inventory, 103.8 million moles, in the North Atlantic Ocean. Maps of water column inventories illustrate the formation mechanisms and spreading pathways within these water masses. The inventories directly reflect the input of newly formed water in the North Atlantic over the time scale of the CFC transient, about 3 decades. The interior regions of the North Atlantic contain most (75-80%) of the CFC-11 inventory in NADW indicating strong recirculation and mixing of newly formed NADW from the DWBC into the interior with a time scale of 2-3 decades. Average water mass formation rates between 1970 and 1997 are: 3.3Sv for EDW, 3.5Sv for ULSW (2.0Sv from the central Labrador Sea and 1.5 Sv from the southern Labrador Sea), 8.2 Sv for CLSW, 5.7 Sv for ISOW, and 2.2 Sv for DSOW. Estimated errors are +/- 20% for CLSW and +/- 16% for the other water masses. The total for NADW, which forms the deep limb of the North Atlantic Meridional Overturning Circulation, is 19.6 Sv. An extensive test of the effects of temporal variability on the average formation rate calculated from the CFC inventory indicates that the error introduced by the assumption of a constant water mass formation rate is no greater than 15% for CLSW and 10% for the other water masses. (c) 2008 Elsevier Ltd. All rights reserved.