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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.

Xiao, X, Prinn RG, Simmonds PG, Steele LP, Novelli PC, Huang J, Langenfelds RL, O'Doherty S, Krummel PB, Fraser PJ, Porter LW, Weiss RF, Salameh P, Wang RHJ.  2007.  Optimal estimation of the soil uptake rate of molecular hydrogen from the Advanced Global Atmospheric Gases Experiment and other measurements. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007241   AbstractWebsite

[1] Hydrogen (H(2)), a proposed clean energy alternative, warrants detailed investigation of its global budget and future environmental impacts. The magnitudes and seasonal cycles of the major ( presumably microbial) soil sink of hydrogen have been estimated from high-frequency in situ AGAGE H(2) observations and also from more geographically extensive but low-frequency flask measurements from CSIRO and NOAA-GMD using the Kalman filter in a two-dimensional (2-D) global transport model. Hydrogen mole fractions exhibit well-defined seasonal cycles in each hemisphere with their phase difference being only about 3 months. The global production rate of H(2) is estimated to be 103 +/- 10 Tg yr(-1) with only a small estimated interannual variation. Soil uptake ( 84 +/- 8 Tg yr(-1)) represents the major loss process for H(2) and accounts for 81% of the total destruction. Strong seasonal cycles are deduced for the soil uptake of H(2). The soil sink is a maximum over the northern extratropics in summer and peaks only 2 to 3 months earlier in the Northern Hemisphere than in the Southern Hemisphere. Oxidation by tropospheric OH (18 +/- 3 Tg yr(-1)) accounts for 17% of the destruction, with the remainder due to destruction in the stratosphere. The calculated global burden is 191 +/- 29 Tg, indicating an overall atmospheric lifetime of 1.8 +/- 0.3 years. Hydrogen in the troposphere ( 149 +/- 23 Tg burden) has a lifetime of 1.4 +/- 0.2 years.

Xiao, X, Prinn RG, Fraser PJ, Simmonds PG, Weiss RF, O'Doherty S, Miller BR, Salameh PK, Harth CM, Krummel PB, Porter LW, Muhle J, Greally BR, Cunnold D, Wang R, Montzka SA, Elkins JW, Dutton GS, Thompson TM, Butler JH, Hall BD, Reimann S, Vollmer MK, Stordal F, Lunder C, Maione M, Arduini J, Yokouchi Y.  2010.  Optimal estimation of the surface fluxes of methyl chloride using a 3-D global chemical transport model. Atmospheric Chemistry and Physics. 10:5515-5533.   10.5194/acp-10-5515-2010   AbstractWebsite

Methyl chloride (CH(3)Cl) is a chlorine-containing trace gas in the atmosphere contributing significantly to stratospheric ozone depletion. Large uncertainties in estimates of its source and sink magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of the surface fluxes of CH(3)Cl. The Model of Atmospheric Transport and Chemistry (MATCH), driven by NCEP interannually varying meteorological data, is then used to simulate CH(3)Cl mole fractions and quantify the time series of sensitivities of the mole fractions at each measurement site to the surface fluxes of various regional and global sources and sinks. We then implement the Kalman filter (with the unit pulse response method) to estimate the surface fluxes on regional/global scales with monthly resolution from January 2000 to December 2004. High frequency observations from the AGAGE, SOGE, NIES, and NOAA/ESRL HATS in situ networks and low frequency observations from the NOAA/ESRL HATS flask network are used to constrain the source and sink magnitudes. The inversion results indicate global total emissions around 4100 +/- 470 Ggyr(-1) with very large emissions of 2200 +/- 390 Gg yr(-1) from tropical plants, which turn out to be the largest single source in the CH(3)Cl budget. Relative to their a priori annual estimates, the inversion increases global annual fungal and tropical emissions, and reduces the global oceanic source. The inversion implies greater seasonal and interannual oscillations of the natural sources and sink of CH(3)Cl compared to the a priori. The inversion also reflects the strong effects of the 2002/2003 globally widespread heat waves and droughts on global emissions from tropical plants, biomass burning and salt marshes, and on the soil sink.

Xiao, X, Prinn RG, Fraser PJ, Weiss RF, Simmonds PG, O'Doherty S, Miller BR, Salameh PK, Harth CM, Krummel PB, Golombek A, Porter LW, Butler JH, Elkins JW, Dutton GS, Hall BD, Steele LP, Wang RHJ, Cunnold DM.  2010.  Atmospheric three-dimensional inverse modeling of regional industrial emissions and global oceanic uptake of carbon tetrachloride. Atmospheric Chemistry and Physics. 10:10421-10434.   10.5194/acp-10-10421-2010   AbstractWebsite

Carbon tetrachloride (CCl(4)) has substantial stratospheric ozone depletion potential and its consumption is controlled under the Montreal Protocol and its amendments. We implement a Kalman filter using atmospheric CCl(4) measurements and a 3-dimensional chemical transport model to estimate the interannual regional industrial emissions and seasonal global oceanic uptake of CCl(4) for the period of 1996-2004. The Model of Atmospheric Transport and Chemistry (MATCH), driven by offline National Center for Environmental Prediction (NCEP) reanalysis meteorological fields, is used to simulate CCl(4) mole fractions and calculate their sensitivities to regional sources and sinks using a finite difference approach. High frequency observations from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Earth System Research Laboratory (ESRL) of the National Oceanic and Atmospheric Administration (NOAA) and low frequency flask observations are together used to constrain the source and sink magnitudes, estimated as factors that multiply the a priori fluxes. Although industry data imply that the global industrial emissions were substantially declining with large interannual variations, the optimized results show only small interannual variations and a small decreasing trend. The global surface CCl(4) mole fractions were declining in this period because the CCl(4) oceanic and stratospheric sinks exceeded the industrial emissions. Compared to the a priori values, the inversion results indicate substantial increases in industrial emissions originating from the South Asian/Indian and Southeast Asian regions, and significant decreases in emissions from the European and North American regions.