COGA Fact Sheet: Methane and Ethane Concentrations From Oil and Gas Decreased by 52-65%
A February 2021 Ramboll report [1] of data from the Atmospheric Infrared Sounder (AIRS) sensor on NASA’s EOS/Aqua satellite shows that methane enhancements over the Front Range decreased 52% between 2013 and 2019. [2] The “enhancement” is the increase above background methane concentrations.
CDPHE’s ground-level Platteville monitoring site shows that concentrations of ethane, an indicator of oil and gas emissions, fell 65% between 2013 and 2019. [3] Platteville is surrounded by oil and gas wells.
These data sets are long-term, objective measurements by government agencies. They do not rely on reported emissions inventories -- from industry or anyone else. Ramboll’s Figure 4 shows the area of the reported satellite data and the Platteville site (the red dot). Ramboll’s Figure 10 shows the methane and ethane trends.
The AIRS and Platteville site data are corroborated by the RAQC’s 2017 and 2020 VOC emissions inventories, and by Garfield County’s 2008-2019 local air monitoring data. See the COGA/API Colorado and Weld County May 2022 AQCC briefings. Although Boulder County, Erie, Longmont, and Broomfield questioned these findings during their July 2022 Local Government AQCC presentation, their air monitoring program results do not contradict the observed methane and ethane reductions.
What This Means
1. The local governments reported local short-term emission spikes, not regional long-term trends.
Local short-term spikes can occur simultaneously with a long-term ½ to 2/3 reduction in oil and gas emissions. The only trend data reported by the local governments were (1) the 2017-2021 total ambient methane concentrations recorded at the Boulder Reservoir, which did not break out or evaluate oil and gas impacts (LG Slide 16),[4] and (2) a statement by Longmont that local methane increased faster than the global average between Q3 2020 and Q3 2021 (LG Slide 21). Longmont’s presentation glossed over the fact that methane comes from many sources. Their ethane spikes were far fewer and smaller than the methane spikes, indicating that oil and gas was not the primary source (LG Slides 20 & 22). A separate Longmont report admits that “[t]hese graphs show declines in the oil and gas tracers ethane and benzene relative to March 2020.” Longmont Regional Air Quality Study - Year 2021 Quarter 3 Report at 6-7 (Nov. 24, 2021).
2. The AIRS sensor is a proven tool for measuring methane.
The ground-level Platteville trend agrees well with the AIRS trend from about 10,000 feet. Ramboll 2021 demonstrated good correlation between the 2014 AIRS data and the 2014 “DISCOVER-AQ” aircraft data collected within the boundary layer (near ground level). Wu et al found good correlation between AIRS data and the concentrations at nine ground-level methane monitors. Ramboll at 4.
3. The large AIRS grid cell and its 20-year monitoring history are positive attributes for measuring long-term regional trends.
4. Platteville is a representative monitoring site that is closer to oil and gas development than Boulder, Broomfield, Erie, or Longmont.
The local governments’ assertion that development is slowing down near Platteville is undercut by their own LG Slide 42, which shows more planned and approved wells near Platteville than the other jurisdictions. The local governments do not dispute that Platteville experienced dense oil and gas development during the 2013 – 2019 period for which Ramboll reported sharp emission reductions. The meteorological conditions and wind patterns around Platteville make it “an ideal location for chemical speciation sampling.” CDPHE 2020 Ambient Air Monitoring Network Assessment at A-17.
5. The local governments assert that Platteville’s 6:00 – 9:00 a.m. sample collection window is an inappropriate time of day that captures only nearby emissions and misses regional conditions.
Their claim is inconsistent with Boulder County’s June 2020 Boulder Reservoir Air Monitoring Study Executive Summary which endorses the use of morning data: “morning data were chosen because concentration peaks normally occur during morning hours.” Ramboll’s back-trajectory analysis shows that the air over Platteville between 6:00 – 9:00 a.m. originates from numerous well locations in all directions at varying distances around Platteville. Ramboll Fig. 5.
6. Measuring ambient concentrations every day (by AIRS) and every six days (at Platteville) provides consistent trend data.
It is surprising that the local government presentation criticized these sampling frequencies because Erie and Broomfield also use weekly canister samples (LG Slides 29 & 34) and the Boulder Atmospheric Observatory used daily samples.
7. The local governments assert their data reveals uninventoried GHG emissions.
However, the AIRS and Platteville data are from ambient measurements, not an inventory.
8. The local governments claim that increased oil and gas production has offset the emission reductions achieved by individual sources (LG Slide 43).
However, the local governments never quantified this effect, and production has not increased quickly enough for their claim to be true. DJ Basin oil production increased by roughly a factor of three between 2013 – 2019. If individual site emissions fell by a conservative 85% during this period, [5] and the remaining 15% of 2013 baseline emissions were tripled, the 2019 emissions would be approximately 45% of the 2013 baseline. This equates to a 55% reduction, which tracks very closely with the ½ to 2/3 reduction observed by the AIRS sensor and Platteville monitor.
Sources
[1] Reddy and Taylor, “Preliminary Analysis of Northern Colorado Methane and Ethane Trends Using AIRS Satellite Data and Platteville Surface Measurements” (Feb. 4, 2021), filed as Exhibit 1 to Weld County’s Rebuttal Statement in the AQCC’s February 2021 revisions to Regulation 7.
[2] Methane enhancements fell from 39.8 ppb to 19.3 ppb, representing the mean monthly methane enhancements above background (measured at Niwot Ridge) for June-August at an elevation of 700 millibars (about 10,000 feet).
[3] Ethane concentrations fell from 277 ppb to 98 ppb, based on the annual average of canister samples taken every six days.
[4] Boulder County’s slide 16 shows total ambient methane concentrations of about 1900-2100 ppb. Ramboll reported oil and gas methane enhancements of about 20-40 ppb. The Boulder County data sheds no light on the oil and gas contribution to total methane, or how quickly oil and gas emissions are decreasing.
[5] Individual site emission reductions from 2013 – 2019 were likely well above 85%. The regulations adopted since 2014 often require operators to control emissions by 95%. To ensure compliance, operators typically use emission control devices rated at 98% or 99%. Many requirements have been imposed to ensure this level of control is achieved, such as vapor control system design standards, leak inspections, and programs to keep thief hatches closed, among others. Operators routinely “over-control” emissions pursuant to voluntary measures, agreements with local governments, and settlement agreements resulting from enforcement cases. Additional emission reductions result from new technologies and facility design, such as tankless production and non-emitting pneumatic controllers. Fleet turnover from plugging thousands of legacy wells also reduces emissions.
