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Understanding the trends of atmosphe...

Wang, James Shih.

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Understanding the trends of atmospheric methane in the past century.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Understanding the trends of atmospheric methane in the past century./
作者:	Wang, James Shih.
面頁冊數:	137 p.
附註:	Source: Dissertation Abstracts International, Volume: 64-09, Section: B, page: 4247.
Contained By:	Dissertation Abstracts International64-09B.
標題:	Biogeochemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3106710
ISBN:	0496542759

Understanding the trends of atmospheric methane in the past century.
Wang, James Shih.

Understanding the trends of atmospheric methane in the past century. - 137 p.

Source: Dissertation Abstracts International, Volume: 64-09, Section: B, page: 4247.

Thesis (Ph.D.)--Harvard University, 2003.

Methane (CH4), an important greenhouse gas and reactive species, has exhibited a rapid increase in concentration since pre-industrial times with a slowdown in its growth rate beginning in the 1980s. The budget of CH4 and the causes of observed trends and interannual variability are not well understood.

ISBN: 0496542759Subjects--Topical Terms:

545717
Biogeochemistry.

Understanding the trends of atmospheric methane in the past century.
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245 1 0 $a Understanding the trends of atmospheric methane in the past century.
300 $a 137 p.
500 $a Source: Dissertation Abstracts International, Volume: 64-09, Section: B, page: 4247.
500 $a Adviser: Michael B. McElroy.
502 $a Thesis (Ph.D.)--Harvard University, 2003.
520 $a Methane (CH4), an important greenhouse gas and reactive species, has exhibited a rapid increase in concentration since pre-industrial times with a slowdown in its growth rate beginning in the 1980s. The budget of CH4 and the causes of observed trends and interannual variability are not well understood.
520 $a To examine the contribution of increases in stratospheric Cl to the observed increase in delta13C of CH4 over the past century, we conducted time-dependent simulations using the Harvard 2-D stratospheric-tropospheric model of chemistry and dynamics. We present a simple framework to explain features of the atmospheric distribution of delta13C in which there are two branches of stratospheric circulation and distinct regions of high and low fractionation efficiency. We constrain the contribution of anthropogenic Cl to the 2&permil; increase in delta13C over the past century to be at most 0.54&permil;, less than the 0.7&permil; estimated by Gupta et al. [1996]. It follows that growth in the relative importance of heavier sources of CH4 (fossil fuels and/or biomass burning) has been largely responsible for the observed trend in delta13C.
520 $a We utilized the 3-D GEOS-CHEM chemical transport model accounting for interannually varying emissions, transport, and sinks to analyze trends in CH4 from 1988 to 1997. We carried out simulations of 85 Kr to verify the accuracy of the treatment of interhemispheric mixing, which is crucial for studies of long-lived tracers such as CH4. Interannual variations in CH4 sources were based on meteorological and country-level socioeconomic data. An inverse method was used to optimize the strengths of sources and sinks for the base year, 1994. Our best-guess budget suggests that the sum of emissions from animals, fossil fuels, landfills, and waste water estimated using IPCC default methodology is too high. Recent bottom-up estimates of the source from rice paddies appear to be too low. Previous top-down estimates of emissions from wetlands may be around a factor of two higher than bottom-up estimates because of possible overestimates of OH. The slowdown in the CH4 growth rate is attributed to a combination of slower growth of sources and increases in OH. The economic downturn in the former Soviet Union and Eastern Europe made a significant contribution to the decrease in growth rate of emissions. The trend in OH was driven mainly by decreases in column ozone during the period of our investigation. The 1992--1993 anomalies in CH4 growth rate can be explained by fluctuations in wetland emissions and OH in the aftermath of the eruption of Mt. Pinatubo. The results of this study suggest that the recent slowdown of CH4 may be temporary and that CH4 is likely to increase significantly in the future in the absence of systematic efforts to moderate emissions.
590 $a School code: 0084.
650 4 $a Biogeochemistry. $3 545717
650 4 $a Physics, Atmospheric Science. $3 1019431
650 4 $a Environmental Sciences. $3 676987
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710 2 0 $a Harvard University. $3 528741
773 0 $t Dissertation Abstracts International $g 64-09B.
790 1 0 $a McElroy, Michael B., $e advisor
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791 $a Ph.D.
792 $a 2003
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