Comparison of Near-Source BTEX Flux Measurements to Inventory Estimates for Upstream Oil and Natural Gas Operations and Identification of Specific BTEX Sources in the Northern Colorado Front Range.

Methane and the hazardous air pollutants benzene, toluene, ethylbenzene, and xylene (BTEX) are emitted from multiple oil and natural gas (O&NG) supply chain operations. In order to include these emissions in inventories, O&NG operators calculate emissions using production statistics and equipment activity factors. However, these inventory estimates need to be evaluated and some sources are not yet included in official inventories.

The University of Wyoming Mobile Laboratory, equipped with instruments to measure BTEX, CH₄, CO, CO₂ and winds at high temporal resolution, is used to investigate facility levelemissions in two basins, and the spatial distribution of O&NG emissions in a third basin. First, this study compares emission inventories to near-source flux measurements from O&NG facilities in the Uintah Basin of Utah and Upper Green River Basin of Wyoming—both of which experience high surface ozone (O₃) levels and other air quality issues due in large part to local O&NG emissions. Flux measurements were made using a point source Gaussian inversion technique during 2014 and 2015.

The third area of study is the Denver Basin in the Northern Colorado Front Range (NCFR). The region has been in nonattainment for O₃ for over ten years. Although much work has been done to quantify the contribution of O&NG emissions to O₃ formation in the region, specific activity and point sources as well as the spatial extent of pollutant pooling at the surface in various parts of the basin are still being investigated. There is also growing concern of increased exposure and health risks associated with the intermingling of O&NG operations and suburban neighborhoods. Mobile surveys of the NCFR during a variety of meteorological conditions and at different times of day and night were conducted in the fall/winter of 2017 and the summer of 2018. These surveys offer a better understanding of ambient BTEX mixing ratios and how topography, meteorology, and emissions interact in the NCFR. Mean ambient BTEX levels from O&NG basins are compared to suburban areas with and without O&NG development. Large emission sources (or hotspots) identified during mobile transects will also be discussed.