Seminar Notice
 
                                    Statistical Laboratory
                                    Iowa State University
 
DATE AND TIME:       Wednesday, July 20    9:10 a.m.
 
PLACE:                          319 Snedecor Hall
 
SPEAKER:                   Cory Heilmann
 
                                                                  
TITLE: Estimation of Greenhouse Gas Emissions from a Tracer Gas Study      
 

ABSTRACT

 
The emission rate of a target gas of interest can be estimated by adding a tracer gas at a known emission rate then measuring downwind concentrations of both gases. Two methods are developed to estimate emission rates from multiple non-independent gas samples. If it is reasonable to assume that the concentrations of target and tracer gasses are proportional, a Bayesian hierarchical model accounts for measurement errors in both gases. Kriging methods can be used when gas concentrations are not proportional. Here, a ratio of kriged estimates is used to estimate the relative rate of emission. Confidence intervals can be constructed using the delta method or Fieller's theorem. When sample sizes are small, the uncertainty in the variogram parameters should be incorporated. 
 
Simulations are used to determine the performance of the Bayesian hierarchical model and kriging under various assumptions and also address the issue of spatial design. Using the delta method to construct confidence intervals of the ratio is shown to be inferior to Fieller's theorem as it produces too narrow of intervals for small sample sizes. When the model assumptions are met, coverage probabilities of the credible intervals from the Bayesian hierarchical model are good and the credible intervals are narrower than confidence intervals obtained from kriging. 
 
The methods are used to estimate the emission rate of greenhouse gases (methane, carbon dioxide, and nitrous oxides) from pig hoop structures. 
 
COFFEE:  8:45 a.m., 104 Snedecor Hall
 
Seminar schedules and abstracts are available via WWW:  http://www.stat.iastate.edu/
 
 

Denise Riker, Undergraduate Secretary
Department of Statistics
Iowa State University
320 Snedecor Hall
Ames, IA  50011
(515) 294-1076