Estimation of methane and carbon dioxide surface fluxes using a 3-D global atmospheric chemical transport model

Methane (CH₄) and carbon dioxide (CO₂) are the two most radiatively important greenhouse gases attributable to human activity. Large uncertainties in their source and sink magnitudes currently exist. We estimate global methane surface emissions between 1996 and 2001, using a top-down approach that combines observed and simulated atmospheric CH₄ concentrations. As a secondary study, we describe our participation in a CO₂ inverse-modeling intercomparison. The available methane time-series data used in this work include observations from 13 high-frequency stations (in-situ) and 74 low-frequency sites (flask). We also construct an annually-repeating reference emissions field from pre-existing datasets of individual methane processes. For our forward simulations, we use the 3-D global chemical transport model MATCH driven by NCEP meteorology. A prescribed, annually-repeating OH field scaled to fit methyl chloroform observations is used as the methane sink. A total methane source of approximately 600 Tg yr⁻¹ best reproduces the methane growth rate between 1993-2001. Using the reference emissions, MATCH can reproduce the observed methane variations at many sites. Interannual variations in transport, including those associated with ENSO and the NAO, are found to be important at certain locations. We adapt the Kalman Filter to estimate methane flux magnitudes and uncertainties between 1996 and 2001. Seven seasonal processes (3 wetland, rice, and 3 biomass burning) are optimized at each month, while three aseasonal processes (animals/waste, coal, and gas) are optimized as constant emissions. These optimized emissions represent adjustments to the reference emissions. For the entire period, the inversion reduces coal and gas emissions, and

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2004

Author dc:creator

• Chen, Yu-Han, 1973-

Advisor dc:contributor.advisor

• Ronald G. Prinn.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/18068

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/18068