Scientists show how to make airplane emissions less harmful

MIT scientists are putting wind beneath policy makers’ wings, suggesting ways to modify airplane emissions, which worsen air quality and contribute to thousands of deaths annually.

As this week’s COP25 climate change conference gains momentum, their findings could provide lift to the effort to avoid the disastrous global impacts of heat-trapping gases forecast by the UN Emissions Gap Report. The UN says countries need to quickly and drastically reduce their emission outputs.

The scientists’ study, published recently in Environmental Research Letters, breaks down how the components of plane exhaust impact the global climate and human health, and weighed the pros and cons of policies aimed at reducing the harm caused by these emissions.

“(The results of this paper) allow us to capture emission tradeoffs,” said Dr. Florian Allroggen, one of the lead researchers on the study. For example, decreasing one component of plane emissions can lead to an increase in another in order to ensure the technology performs appropriately.

The scientists found that three components of airplane emissions account for 97% of negative environmental and health impacts: nitrogen oxides, carbon dioxide and contrails, which form when water vapor condenses on emission particles.

Major airlines are already going carbon-neutral, but the researchers suggest another component may be even more important to control than carbon.

“Ninety-four percent of air quality impacts are driven by nitrogen oxides,” said Dr. Sebastian Eastham, another lead scientist on the study. “This suggests that measures aimed at reducing nitrogen oxide emissions … could lead to the greatest net benefits.”

Exposure to nitrogen oxide is associated with creating ground-level ozone, which can accelerate disease and impair lung function in humans. Two previous published studies have said air quality issues caused by pollutants from plane emissions cause about 16,000 premature deaths every year.

Aviation emissions don’t impact all areas of the globe equally. Experts highlight this fact as important in examining how to prioritize action.

“Because of atmospheric composition and emissions transport, aircraft emission impacts over Europe are significantly higher,” explained Allroggen. “One could subsequently argue that reducing aircraft emissions over Europe might be more important than over other regions of the world.”

“Both air quality and climate impacts … should be considered together if we want to bring down the environmental damages associated with flying,” Eastham said.