08:17pm Thursday 19 October 2017

A link between air travel and deaths on the ground

Graphic: Christine Daniloff

An airplane flying at a cruise altitude of about 35,000 feet can threaten the health of people on the ground, according to a new study from MIT’s aviation research organization, the Partnership for AiR Transportation Noise and Emissions Reduction (PARTNER), that suggests that aircraft cruise emissions cause about 8,000 deaths per year — nearly half of which occur in China and India.

The research, reported online this month in Environmental Science and Technology, provides the first estimate of premature deaths attributable to aircraft emissions at cruise altitudes. Aircraft emit nitrogen oxides (NOx) and sulfur oxides (SOx), which react with gases already existing in the atmosphere to form tiny harmful particles known as “fine particulate matter.” The danger to humans comes when these particles are inhaled and trapped in the lungs, where they can then enter the bloodstream and lead to the development of cardiovascular and respiratory illnesses, including lung cancer.

Current worldwide regulations target aircraft emissions only up to 3,000 feet. That’s because regulators have assumed that anything emitted above 3,000 feet would be deposited into a part of the atmosphere that has significantly smoother air, meaning pollutants wouldn’t be affected by turbulent air that could mix them toward the ground. Thus, even though 90 percent of aircraft fuel is burned at cruise altitudes, only those pollutants emitted during takeoff and landing are regulated.

“Anything above that [altitude] really hasn’t been regulated, and the goal of this research was to determine whether that was really justified,” says lead author Steven Barrett, the Charles Stark Draper Assistant Professor of Aeronautics and Astronautics in MIT’s Department of Aeronautics and Astronautics.  

To study the effects of cruise emissions, Barrett used a computer model that combined data about plane trajectories, the amount of fuel burned during flights and the estimated emissions from those flights. He combined that with a global atmospheric model that accounts for air-circulation patterns in different parts of the globe and the effect of emissions to determine where aviation emissions might cause an increase in fine particulate matter. He then used data related to population density and risk of disease in different parts of the world to determine how the change in particulate matter over certain regions might affect people on the ground — specifically, whether the air pollutants would lead to an increased risk of death.

Analysis of these data revealed that aircraft pollution above North America and Europe — where air travel is heaviest — adversely impacts air quality in India and China. That is, even though the amount of fuel burned by aircraft over India and China accounts for only 10 percent of the estimated total amount of fuel burned by aircraft across the globe, the two countries incur nearly half — about 3,500 — of the annual deaths related to aircraft cruise emissions. The analysis also revealed that although every country in the Northern Hemisphere experienced some number of fatalities related to these emissions, almost none of the countries in the Southern Hemisphere had fatalities.

That’s because the majority of air traffic occurs in the Northern Hemisphere, where planes emit pollutants at altitudes where high-speed winds flowing eastward, such as the jet stream, spread emissions to other continents, according to the study. Part of the reason for the high percentage of premature deaths in India and China is that these regions are densely populated and also have high concentrations of ammonia in their atmosphere as a result of farming. This ammonia reacts with oxidized NOx and SOx to create fine particulate matter that people inhale on the ground.

Funded by the UK Research Councils with help from the U.S. Department of Transportation, the study recommends that cruise emissions be “explicitly considered” by international policymakers who regulate aviation engines and fuels.

contact: Patti Richards – MIT News Office
email: prichards@mit.edu
call: 617-253-8923
written by: Morgan Bettex, MIT News Office

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