New research suggests no significant reduction in total oil and natural gas emissions from 2008 to 2016 in Weld County, Colorado

June 25, 2021

Colorado oil well. Photo Credit: David Parsons | Huffington Post

New research in Elementa suggests no evident reduction in total oil and natural gas emissions and their contribution to the regional air quality from 2008 to 2016 in Weld County, in Northeastern Colorado. Samuel J. Oltmans, a scientist at Global Monitoring Laboratory and Cooperative Institute for Research in Environmental Sciences, is the lead author of this research.

The Weld County region has been in nonattainment for the surface ozone 8-hour National Ambient Air Quality Standard since 2007. From 2008 to mid-2016, oil production increased more than 7 fold and natural gas production more than tripled in the Colorado Denver-Julesburg Basin lying primarily in Weld County.

In 2019, the Environment Protection Agency reclassified the region as a serious ozone nonattainment area for the 2008 National Ambient Air Quality Standard and required new emission mitigation planning to reach attainment.

Global Monitoring Laboratory scientists and others analyzed 9-year data set of the composition of ambient air samples collected daily from the top level of the Boulder Atmospheric Observatory in Erie in southwest Weld County. These measurements documented the atmospheric concentration of various pollutants, including several volatile organic compounds mostly emitted by oil and natural gas sources.

The BAO tower compared to the Eiffel Tower. The Eiffel Tower is only 24m (78ft) taller than the BAO Tower. Air samples are taken at three different heights on the tower: 22, 100, and 300 meters above the ground.

The measurements for acetylene, a marker of combustion emissions such as traffic, did not show long-term changes. Thus, traffic emissions were not significant drivers of air quality change in this region. The measured concentration ratio of i-pentane/n-pentane showed a statistically significant trend indicating a growing influence of the relative contribution of oil and natural gas emissions on the volatile organic compounds composition in the samples at the Boulder Atmospheric Observatory.

The concentrations of methane and oil and natural gas tracer propane remained relatively constant, indicating a possible decrease in relative leakage and/or venting rate by the industry for the average unit of production.

While the most recent State inventory of volatile organic compound emissions projects an oil and natural gas emission reductions of -6.5% per year between 2011 and 2020, the best estimate of the propane emission rate of change (-1.5% per year) inferred from the measurement at the Boulder Atmospheric Observatory during 2008 to 2016 is much smaller.

These results indicate no significant reduction in levels of pollutants from oil and natural gas productions and their contribution to the regional air quality. Apparently, the reductions in emissions per well or drilling site have likely been offset by the overall growth in the number of wells and associated oil and gas operations in the basin.

Atmospheric measurements of volatile organic compounds at the Boulder Atmospheric Observatory provide an alternative method to study oil and natural gas emissions and their contributions to air quality in this region. High-quality and representative atmospheric measurements can provide useful information for policymakers and communities to evaluate the effectiveness of emission mitigation efforts.

NOAA Air Resources Laboratory provided the Hybrid Single-Particle Lagrangian Integrated Trajectory transport and dispersion model used in this publication. NOAA Physical Sciences Laboratory oversaw the operation of the Boulder Atmospheric Observatory and the tower meteorological instrumentation for many years until the tower was dismantled in 2016. The Boulder County Department of Public Health provided part of the funding for the data analysis.

Atmospheric oil and natural gas hydrocarbon trends in the Northern Colorado Front Range are notably smaller than inventory emissions reductions

Samuel J. Oltmans, Lucy C. Cheadle, Detlev Helmig, Hélène Angot, Gabrielle Pétron, Stephen A. Montzka, Edward J. Dlugokencky, Benjamin Miller, Bradley Hall, Russell C. Schnell, Jonathan Kofler, Sonja Wolter, Molly Crotwell, Carolina Siso, Pieter Tans, Arlyn Andrews

Elementa: Science of the Anthropocene (2021) 9 (1): 00136.

Abstract

From 2008 to mid-2016, there was more than a 7-fold increase in oil production and nearly a tripling of natural gas production in the Colorado Denver–Julesburg Basin (DJB). This study utilized air samples collected at the Boulder Atmospheric Observatory (BAO) tower in southwestern Weld County in the DJB to investigate atmospheric mole fraction trends of methane and volatile organic compounds (VOCs). Elevated methane and propane mole fractions and low values (<1) in the ratio of i-pentane to n-pentane at BAO were found to be associated with flow patterns that transport air from the northeast (NE) to east (E) sector to the site, the direction where the primary locations of oil and natural gas (O&NG) extraction and processing activities are located. Median mole fractions of the O&NG tracer propane at BAO were 10 times higher than background values when winds came from the NE quadrant. This contrasts with lower mole fractions of O&NG-related constituents in air parcels arriving at BAO from the south, the direction of the major urban area of Denver. None of O&NG tracers, for example, methane and propane, show statistically significant trends in mole fraction (relative to the background) over the study period in air transported from the DJB. Also, longer term acetylene mole fraction changes were not seen in NE quadrant or south sector samples. A significant decline in the mole fraction ratio of i-pentane to n-pentane in the NE sector data provides evidence of an increasing influence of O&NG on the overall composition of VOCs measured at BAO, a change not seen in measurements from the south (urban) sector. These results suggest that O&NG emissions and resulting atmospheric mole fractions have remained relatively constant over 2008–2016. The behavior in the observations is in contrast to the most recent VOC emissions inventory. While the inventory projects O&NG total VOC emission reductions between 2011 and 2020, of –6.5% per year despite the large production increases, the best estimate of the propane emission rate of change for the DJB-filtered data during 2008–2016 is much smaller, that is, –1.5% per year.

For questions or concerns, please contact Xinyi Zeng ( xinyi.zeng@noaa.gov ).