Ethane Study Pushes Alarmist Claims on Ground-Level Ozone, Methane Emissions

For the second time in less than a month, a study on ethane emissions — a topic that has been largely ignored until recently — has come out of the woodwork.

And like the study before it, this latest ethane report has found a global rise in ethane emissions over the past five years and placed the blame on U.S. shale development. Using a decade’s worth of data from 44 remote global sampling sites, the University of Colorado (CU) and National Oceanic and Atmospheric Administration (NOAA) study estimates ethane emissions have increased 400,000 tons annually since 2009, prompting study lead author and CU associate research professor Detlev Helmig to say:

“About 60 percent of the drop we saw in ethane levels over the past 40 years has already been made up in the past five years. If this rate continues, we are on track to return to the maximum ethane levels we saw in the 1970s in only about three more years. We rarely see changes in atmospheric gases that quickly or dramatically.”

However, the study’s topline conclusion, that ethane emissions are on the rise and oil and gas is to blame, is contradicted by the actual text of the study. Likewise, the researchers’ secondary conclusions — that this will lead to spikes in ground-level ozone and that their data indicate methane emissions have been underestimated — don’t line up with the facts, either. Let’s have a look at four reasons why.

Reason #1: The researchers concede other sources could be significant contributors to rise in ethane emissions

The researchers’ contention that oil and gas development is largely to blame is based on their finding that the largest increases in ethane and propane – the latter which has a much shorter atmospheric lifespan and therefore can be attributed more accurately to regional sources – have occurred in the central and eastern U.S., areas where oil and gas development is prominent. The researchers reach this conclusion despite conceding that ethane – or “non-methane hydrocarbon (NMHC) emissions” – is also released naturally via seepage of fossil fuel deposits, volcanic activity and wildfires, as well as biomass burning.

The researchers also ultimately concede that poorly monitored areas of the world could be contributing to increases in ethane emissions:

“…This suggests yet unidentified increasing sources for NMHC emissions independent of methane or with lower methane/ethane emission ratios, or potential emission increases outside North America that cannot be well defined at present owing to the sparsity of observations in those regions (for instance, in the Middle East, Africa, and Asia).”

Oddly, the latter conclusion is one of several takeaways that seemingly contradict the researchers’ comments to the press on the study. For example, Helmig told E&E News:

“We are very, very certain that this increase in ethane is from oil and gas production. We are not aware of any other significant ethane sources in the world.”

Reason #2: Oil and gas production is not a major contributor to ground-level ozone

As EID has emphasized before, publicly available information demonstrates oil and gas production is not the significant contributor to ozone levels. Vehicle exhaust adds far more non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NOx) – both precursors to ground-level ozone – to the atmosphere than oil and gas production, as the following chart from the EPA’s 2016 Greenhouse Gas Inventory clearly demonstrates.
EPA Table NOX NMVOCs

Not only do oil and gas activities account for just 6 percent of total NOx emissions, which play more of a role in ground-level formation than VOCs, another recent NOAA report found that “The increased use of natural gas has…led to emissions reductions of NOx (40%) and SO2 (44%).”

The latest EPA data also shows that NOx emissions have declined more than 50 percent since 1990, while non-methane VOCs have declined 48 percent during that timespan.

A 1999 National Academies Press study on VOC emissions from vehicle exhaust also illustrates why ethane is not a significant contributor to tropospheric (ground-level) ozone:

“If one were to increase the total mass of VOC emissions in a city, such as Los Angeles, by 20% through additional emissions of ethane, ozone levels would increase slightly. However, if the same amount of propene were added instead, there would be a large increase in ozone. Why the big difference between the two, given that both are rather simple hydrocarbons? The primary cause of the difference is the differing rates at which these two species react in the atmosphere. Ethane has an atmospheric lifetime of weeks. Little of the ethane emitted in an urban area reacts within that area before it is transported away. Its contribution to ozone formation within the urban area is therefore very small.

“During the early years of ozone mitigation, it was recognized that there were some organics, for example ethane, that did not contribute significantly to smog formation on urban scales, whereas others, such as propene, did.”

These facts didn’t keep the researches from suggesting their finding that NMHC/ethane emissions have increased 4.2 percent annually since 2009 is contributing to spikes in ground-level ozone. In absence of significant real-world evidence, the researchers made this determination by using an atmospheric chemical transport model to forecast significant increases in ground-level ozone throughout the U.S.

But considering the two essential components for formation of ground-level ozone — NOx and NMVOCs — are both in rapid decline, the model’s assumption of constant emissions of NOx is more than a little misleading, and the researchers actually acknowledge this fact in the methodology section of the study:

“Note that these results are based on constant emissions of other precursors, including those of nitrogen oxides (NOx). Decreasing trends of NOx, over the USA and of VOCs in urban areas have led to a general decrease of ozone in many urban regions. Omissions of these effects will cause a high bias of the ozone changes that were calculated here. Consequently, these model results should be considered as preliminary results, providing an indication of the direction of ozone effects from added O&NG emissions, and taken as motivation for more in-depth modeling of the net effect resulting from these emission changes.” (emphasis added)

Also of note is the fact the study’s ozone model, “… assumed that all wells emit the same amounts of NMHC, neglecting difference in well size and leakage rate.”

In addition to these misleading one-size-fits-all methods, real-world examples demonstrate why the study’s prediction that higher ethane emissions directly correlate with elevated levels of ground-level ozone is so shaky.

For instance, the other recent NOAA ethane study claimed that the Bakken was single-handedly responsible for an upward spike in ethane emissions the past five years after more than a decade of declines.  Assuming that’s true, one would assume North Dakota would have an tropospheric ozone problem. Not so much. The authors of that study were unable to find any evidence of elevated ground-level ozone in the areas they monitored:

“Emissions of ethane, methane, and other VOCs from the Bakken have the potential to impact ozone formation on a variety of spatial scales. Local ozone enhancements observed during the Spring 2014 airborne study were relatively small due to low temperatures, large solar zenith angles, and generally high wind speeds….”

North Dakota has also regularly received strong marks from the American Lung Association for its air quality.

This new ethane study also makes reference to related studies that attempt to link oil and gas development to increased ethane levels in Baltimore and increased ozone in south Texas, Utah and Wyoming as evidence to support their claims.

But the Baltimore study that the researchers mention, which blames elevated ethane levels to Marcellus Shale development, found no correlation with elevated ground-level ozone. In fact, the Maryland Department of Environment reported, “For the first time in more than three decades, the metropolitan Baltimore area is meeting the health-based federal standard for ground-level ozone air pollution.”

Rapid population growth in metro San Antonio is actually to blame for the increased ozone found in the south Texas study that attempted to pin the problem on oil and gas development, which isn’t surprising considering the Eagle Ford Shale accounts for just three percent of both NOx and VOC emissions in 2018 projections. EID has pointed out that snow cover and weather have been the biggest contributing factors to ozone formation in Utah’s Uintah Basin, while weather has been the biggest contributor in Wyoming as well.

Speaking of the western states of Utah and Wyoming…

Reason #3: Researchers found relatively low propane emissions in high-production western states

Interestingly, the study found relatively low levels of propane emissions in Utah and Wyoming, as well as California and New Mexico. This begs the question: If oil and gas development is solely responsible for ethane emission increases, propane and ethane emissions go hand-in-hand, and ethane emissions lead to increased ozone, why is there no indication of elevated propane emissions in these high-production western states?

The reason is clear: Although fracking opponents love to suggest otherwise, there is simply no evidence that oil and gas production is a major driver in increases in ground-level ozone.

Reason #4: Detection of high levels of ethane does not necessarily correlate with high levels of methane

Considering that venting and flaring of natural gas are thought to be the primary sources of atmospheric ethane, scientists had long assumed detection of significant levels of ethane was a sure indicator of high levels of methane. But the aforementioned Bakken ethane study found the opposite to be true:

“Analyses that assume a temporally constant oil and gas production ethane: methane emission ratio lower than present in the Bakken, or other productive basins, will erroneously conclude a large fossil methane emissions increase since 2010…”

The Bakken study found that ethane accounted for nearly 50 percent of natural gas detected, while methane was closer to 20 percent.

Another recent NOAA study confirmed methane emissions from the Bakken region are much lower than previously believed, which led to scientists acknowledging that detection of higher ethane emissions does not mean that high  methane emissions are inevitable.

The actual text of the University of Colorado/NOAA ethane study appears to acknowledge this fact:

“Methane/ethane oil and natural gas emission ratios could suggest a significant increase in associated methane emissions; however this increase is inconsistent with observed leak rates in production regions and changes in methane’s global isotopic ratio.”

However, even though their study admits you can’t equate the two, a couple of the researchers’ comments posted on their respective university websites indicate that they are still clinging to the belief that high ethane measurements are clear indicators of high methane emissions. University of York professor Lucy Carpenter, who led the researchers’ NMHC measurements at the Cape Verde station, said:

“This careful study of ten years of hydrocarbon data from stations worldwide is a worrying indicator that unconventional oil and natural gas production is having a global impact. Not only will the increased hydrocarbon emissions bring higher levels of air pollution downwind of oil and natural gas production, but this study suggests that fracking could be a substantially larger emitter of methane than previously thought, with adverse affects on climate.”

Helmig has also inferred that this study indicates methane emissions are being underestimated, even though the actual study notes such is not likely the case:

“Ethane is the second most significant hydrocarbon emitted from oil and gas after methane. Other studies show on average there is about 10 times as much methane being emitted by the oil and gas industry as ethane.”

Further, the study itself is very clear that the extrapolation of ethane emissions to estimate methane emissions results in methane emission estimates that are far higher than what’s actually been detected in both bottom-up and top-down studies:

“… The cumulative increase in methane emissions implied from this approach would represent more than a doubling of O&NG-related methane USA inventory emissions and a 6.2% total increase between 2009.5 and 2014.5 of the 330 Tg yr global anthropogenic methane emission.”

“Although other recent studies have derived similar estimates for methane emission increases and associated those with increased North American O&NG emissions, most also rely on the extrapolation of NMHC results to infer methane emission changes. We note that surface and aircraft observations of methane stable isotopes from the GGGRN are inconsistent with such a large North American methane flux increase from O&NG sources. Furthermore, the methane emission implied by this analysis of NMHC data as a fraction of O&NG production is a substantially higher percentage than what has been observed in O&NG fields in North America…”

As stated earlier, the latter fact seemed to force the researchers to draw the conclusion that other than U.S. shale production could be significant contributors (which is probably why it was buried in the final paragraphs of the study).

But these factors aside, the real takeaway from the study is this: ethane emissions have largely been ignored by fracking opponents for a reason — because they are rather insignificant in the big picture. Not only is there little evidence ethane emissions have contributed to elevated ground-level ozone, it is also now clear that using ethane detection to infer high methane emissions is a faulty methodology.

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