This is a repository for all the IDL programs for the REU Ethane project with Dr. Christopher Butenhoff.
The ethane data are from NOAA, UCI, and OGI. The NOAA and OGI data are sampled every month, but the UCI data is sampled in March, June, September, and December.
This project started during the Summer 2016 and the repository was created Fall 2018.
Ethane is emitted with methane and other trace gases in the production of oil and natural gas during drilling, venting, flaring, and from infrastructure leaks during storage and distribution. Fugitive emissions from oil and gas production are one of the largest anthropogenic sources of ethane and methane and contribute significantly to global trends in their atmospheric burdens. The climate advantage of replacing coal with natural gas in energy portfolios depends critically on methane leakage rates. Because gas fluxes vary widely across production fields and distribution networks, efforts to estimate national and global rates of emissions using bottom-up accounting methods face significant challenges. Recent studies of firn and surface observations show a marked decline in global atmospheric ethane in the 1980s and 1990s which has been interpreted as a decline in fossil fuel ethane emissions. However, this conclusion is contradicted by some bottom-up emissions inventories and global inversions of isotopic methane which find fossil fuel emissions have been flat or increased during this time with a decline in biomass burning emissions. To investigate the temporal record of ethane emissions further, we used four decades (1982 – 2015) of surface air observations of ethane from three sampling networks to test competing ethane emissions scenarios evaluated with the three-dimensional atmospheric chemical–transport model GEOS-Chem. Because ethane’s main sources (fossil fuel production, biomass and biofuel burning) have different spatial footprints we hypothesize that temporal trends for each source, if they exist, will leave unique signatures in the latitudinal distribution of ethane over time. We used GEOS-Chem to predict the source latitudinal trend signatures and assess the ability of the observational ethane record to eliminate different emissions scenarios, providing insight into the recent history of fugitive emissions from fossil fuel production. Our data analysis shows that the northern hemispheric mean in the 2000s is higher than during the 1980s while the southern hemispheric mean was flat over the same time period, which causes the interhemispheric difference to increase. Since most of anthropogenic emission occurs in the northern latitudes, we infer that the increase in the interhemispheric difference is due to fossil fuel emissions. Our ethane record does not support the decline of fossil fuel emissions reported in the firn air and surface observation studies. We also confirm the emissions trends reported in the global inversions of isotopic methane study to be the best fit to the multi-decadal ethane record. In this scenario, fugitive emissions remain nearly constant from 1985 to 2000 with a rapid increase in recent years.