Source Attribution of Elevated Ethane Concentrations Detected by Regional Monitors in Oil and Gas Production Regions

Measurements of ambient ethane concentrations at a regional air quality monitor in the Eagle Ford oil and gas production region are compared to concentrations predicted using site-level hydrocarbon emission inventories coupled with a Gaussian puff dispersion model (CALPUFF). To account for more than half of mean concentrations due to routine emissions, sites at distances 20–50 km from the receptor site were included in the simulations. Nearly all of the highest observed concentrations were observed at night. For each night in the simulation, the location and magnitude of the maximum predicted concentration and maximum observed concentration were compared, and approximately two-thirds of the highest observed nighttime maximum concentrations were accounted for by routine emissions. In contrast, approximately a third of the highest daytime maxima could be accounted for by routine emissions. Most of the large observed maxima that are attributable to routine emissions are predicted to be caused by sources that were within 10 km of the receptor site, but sources up to 20 or more kilometers from the receptor also contributed to the predicted concentrations. A case study is provided demonstrating the potential of coupling site-level inventories of routine emissions with dispersion modeling for attributing sources of elevated hydrocarbon concentrations.

The largest hydrocarbon enhancements observed at regional monitors are due to both routine emissions and emission events from nearby and distant sources.