Harmful ozone-causing emissions are on the rise again, a new study has found.
Naturally occurring ozone in the upper atmosphere is good, protecting us from the sun’s ultra-violet rays. But ground-level ozone, formed from reactions between nitrogen oxides and non-methane hydrocarbons can be very damaging, triggering a number of health problems such as asthma and lung diseases. Ethane, a non-methane hydrocarbon, is a major precursor of ground-level ozone.
Ethane emissions peaked in 1970, but decreased steadily from 1984 to 2010. Now, ethane levels are rising again, reversing decades of decline, according to a paper published Monday in Nature Geoscience. And the major culprit is the increase in oil and natural gas production in the United States, researchers say.
To trace the changes in ethane emissions over the years, Detlev Helmig of the University of Colorado Boulder and his colleagues analysed ten years of weekly and bi-weekly ethane and propane concentrations at 44 remote stations spread all over the world.
These stations are part of the National Oceanic and Atmospheric Administration’s (NOAA) Global Greenhouse Gas Reference Network. The team also used daily continuous measurements of these hydrocarbons from five stations located in Greenland, Germany, Switzerland and Cape Verde in the Mid-Atlantic.
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About 60 per cent of the drop we saw in ethane levels over the past 40 years has already been made up in the past five years.
Detlev Helmig, researcher, University of Colorado Boulder
The results were striking — ethane concentrations seemed to have increased by three to five per cent per year in the Northern Hemisphere since 2009.
“About 60 per cent of the drop we saw in ethane levels over the past 40 years has already been made up in the past five years,” lead-author Detlev Helmig of the University of Colorado Boulder said in a statement. “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.”
The major source of this rising ethane, the team found, is the increase in oil and natural gas production in the U.S.
The team arrived at this conclusion by looking at another hydrocarbon called propane. They used propane as a proxy because most sources that emit ethane also emit propane, the authors write. Moreover, propane has a shorter lifetime in the atmosphere, and is usually detected close to its emissions source. This makes it easier to pinpoint the source.
The team’s analysis revealed that propane emissions have increased considerably only in the U.S. and downwind areas. In contrast, propane levels in central Europe, the Pacific region and the Southern Hemisphere have remained relatively stable. This rise in ethane in the U.S. coincides with the oil and natural gas boom in the country. Between 2000 and 2015, this industry — a major source of non-methane hydrocarbons — has seen a 10 to 20-fold increase in production.
“These findings suggest that the increase in ethane concentrations is due to emissions associated with a substantial increase in oil and natural gas production in the USA,” the team writes.
To demonstrate this link, the team made continuous airborne measurements of ethane over the North Dakota portion of the Bakken shale formation in spring 2014. This formation alone, they found, is responsible for emissions that is equivalent to 1 to 3 percent of global ethane emissions.
But North America is not the sole source of ethane. The study also reported high increase in propane concentrations in Tiksi, Russia.
Rising ethane levels in the atmosphere is bad news. It could result in elevated levels of ground-level ozone, particularly in the summers, the study warns, increasing health risk.
“These oil and gas operations are threatening to reverse what had been an important success story: decades of declining air pollution in North America,” Finnish meteorologists Hannele Hakola and Heidi Hellén caution in an accompanying Nature commentary.
This story was published with permission from Mongabay.
