Since 2013, we have characterized methane and other emissions from hundreds of facilities across the oil and natural gas supply chain. These include transmission compressor stations and gathering and processing facilities across the US; gas production well pads and processing facilities in the Marcellus, Uintah, and Denver-Julesburg basins; and associated gas flares in the Bakken. Methods have included direct onsite and tracer flux measurements for methane emissions; stationary downwind capture for VOCs; and airborne measurements for BC from gas flares.
In 2013, methane emissions from 45 transmission compressor stations (more than the three previous studies combined) were measured with a combination of direct onsite measurements and downwind dual tracer flux. Facility-level emission rates agreed within measurement uncertainties at most facilities, while the direct onsite measurements could not capture two super-emitters. The emissions distributions showed significant skewness with 50% of the methane attributed to 10% of the facilities, a phenomenon referred to as a “fat tail.”
In 2014 and 2015, tracer flux and other downwind techniques were used to sample methane emission rates from over 100 natural gas well pads, gathering compressor stations, and other natural gas facilities in the Marcellus shale, Denver-Julesburg, and Uintah basins. Thirteen VOCs, including benzene and toluene, were measured downwind of or near ~35 natural gas facilities in Colorado and Utah, with similar measurements to be conducted in the Marcellus Shale in late August 2015. Preliminary results show that VOC emission profiles from individual facilities vary significantly, which suggests that a single VOC profile may not characterize all natural gas production facilities. In the Marcellus, methane emissions as a function of average gas production ranged from 0.01% to 1% (median 0.09%) at unconventional production wells, and from 0.29% to over 70% (median 8.5%) at conventional wells.
In early 2014, black carbon from over 30 associated gas flares in the Bakken was measured using a single particle soot photometer (SP2) aboard the Purdue University Airborne Laboratory for Atmospheric Research (ALAR) platform. The average emission factor of 0.14 g-BC/kg-fuel is significantly lower than previous literature estimates (0.7-1.1 g-BC/kg-fuel), though several observations over 0.5 kg-BC/kg-fuel evidence a fat-tail distribution in these emissions as well.
In this talk, I shall present selected results from these different studies, and examine the distributions for different pollutants based on these measurements, which is informative for emissions inventories and a guide to emissions reduction policy.