Methane Emissions by the Industrial Sector Vastly Underreported

A Cornell-Environmental Defense Fund research team equipped a Google Street View car with a high-precision methane sensor and found methane emissions from ammonia fertilizer plants to be 100 times higher than the fertilizer industry's self-reported estimate.

Methane emissions produced by the industrial sector are grossly underestimated, according to a recent study conducted by a team of scientists from Cornell University and the Environmental Defense Fund.

For the study, which was recently published in Elementa, the researchers used a Google Street View vehicle fitted with a highly sensitive methane sensor to measure methane emissions in the air. They found that not only was methane emitted during ammonia fertilizer production 100 times greater than the estimate reported by the fertilizer industry, but these emissions were also significantly higher than the figure estimated by the Environmental Protection Agency (EPA) for all industrial processes across the US.

"We took one small industry that most people have never heard of and found that its methane emissions were three times higher than the EPA assumed was emitted by all industrial production in the United States," said John Albertson, professor of civil and environmental engineering and co-author of the study. "It shows us that there's a huge gap between a priori estimates and real-world measurements."

The natural gas market has recently seen a spurt in growth, boosted by more efficient gas extraction together with the perception natural gas is cleaner than fossil fuels. However, natural gas consists largely of methane, which is more potent than carbon dioxide in terms of its climate warming potential. Consequently, any significant leaks or emissions anywhere along the supply chain could mean that natural gas is contributing significantly more to climate warming than previously believed, and therefore not necessarily as clean a fuel as its made out to be.

Currently, methane emissions are assessed at a wide range of sites, including gas wells where it is extracted, power plants, and gas pipelines transporting natural gas further downstream to industrial users.

To assess methane emissions from industrial sources further downstream, the scientists focused on fertilizer producers, who use natural gas as a source of fuel as well as a primary source of urea and ammonia, both key ingredients used in fertilizer production. Only a few dozen fertilizer plants across the US produce ammonia-based fertilizer; these plants are usually sited close to a public road, making detection of emissions with mobile sensors relatively easy.

For the study, the team used a Google Street View car to travel along public roadways alongside six representative fertilizer factories in order to quantitatively evaluate rogue methane emissions inadvertently lost to the atmosphere during the manufacturing process.

When the sensors on the Google Street View vehicle detected a concentrated plume of methane downwind from a fertilizer factory, the vehicle drove around the plant dozens of times to measure the emissions.

The researchers found that typically 0.34% of the natural gas used in fertilizer factories emitted. When this emission rate is scaled up to represent the entire fertilizer industry, it suggests that the total annual methane emissions for the sector is 28 gigagrams, a figure 100 times greater than the 0.2 gigagrams reported by the fertilizer industry.

Furthermore, this figure is far higher than the 8 gigagrams of methane the EPA estimates is emitted annually by all industrial processes in the US.

"Even though a small percentage is being leaked, the fact methane is such a powerful greenhouse gas makes the small leaks very important," said Joseph Rudek, lead senior scientist at the Environmental Defense Fund and co-author of the paper. "In a 20-year timeframe, methane's global warming potential is 84 times that of carbon dioxide."

This study shows mobile sensors can provide an economical method of pinpointing significant emission sources that will in turn allow us to implement fast and efficient mitigation measures, which is essential if we hope to rapidly reduce the rate of atmospheric warming. Albertson believes mobile sensors can be applied more broadly, for example being deployed on public vehicles such as postal trucks and school buses to identify sources and monitor the rate of pollution, and possibly even help influence policymakers.

"Pollution in the air doesn't respect property boundaries, so even if you don't have access to private land, the current revolution in sensor technologies allows us a lens into the degree of cleanliness of a factory," Albertson explains. "With opportunistic sensing, pushing data to the cloud, doing the proper analysis and drawing inferences, we can build environmental policy that is based on evidence."

Journal Reference

Zhou, X., Passow, F.H., Rudek, J., von Fisher, J.C., Hamburg, S.P. and Albertson, J.D., 2019. Estimation of methane emissions from the U.S. ammonia fertilizer industry using a mobile sensing approach. Elem Sci Anth, 7(1), p.19. DOI:http://doi.org/10.1525/elementa.358

Featured Image courtesy of Cornell University