Capturing “real world” aircraft emissions
The hydrocarbon data, gathered from operating airplanes rather than from stationary engines, calls into question long-standing assumptions about idling aircraft emissions.
The days of watching a black plume of smoke burst out as commercial aircraft take off are long gone. Still, public fears about toxic air pollution being sprayed across nearby communities remain. While studies focusing on NOx have measured and quantified emissions at high altitude, very few studies have looked at emissions from operating airplanes on the ground.
In research described in a paper published today on ES&T’s Research ASAP website (DOI: 10.1021/es0512091), Scott Herndon, from Aerodyne Research, Inc., and colleagues used a mobile laboratory parked near the airport fence at Boston’s Logan Airport. As the plumes floated downwind across the lab’s instruments, they gathered data that result in “real world” hydrocarbon emissions from airplanes. These measurements show that such emissions may be much higher when planes are left idling on an airport tarmac than previously believed, Herndon says.
The results of this experiment will help local air-quality planners estimate airport emissions, according to researchers working on similar studies. “We have a national crisis, in effect, in that a large number of our airports are landlocked and very much need to expand,” says Phil Whitefield, researcher at the Center of Excellence for Aerospace Particulate Research at the University of Missouri. Airport expansions must be approved, and regulators will look for an environmental impact statement that estimates the impact of new emissions. “You can’t put a big bag around the airport, but we can use our emission indices and the operational aspects of the airplanes and get a very good estimate [of the emissions],” Herndon says.
The data may also lead collaborators at the International Civil Aviation Organization (ICAO) to revise the engine certification standards, says co-author Richard Miake-Lye of Aerodyne Research Inc. ICAO, which sets engine certification standards followed by aircraft engine manufacturers, last published standards for smoke and hydrocarbons, CO, and NOx in 1981. These standards were developed with data from stationary engines rather than planes operating at an airport.
The study took advantage of the Aerodyne Mobile Laboratory, a package-delivery-sized truck recently used in a project to characterize fine particulate matter in Mexico City. The lab sat for a few hours near the fence at busy Logan Airport in May 2003. Herndon, John Jayne of Aerodyne, and three graduate students intercepted over 45 plumes from specific commercial aircraft. The ambient air was continuously analyzed through a sample port located near the roof on the front of the truck, and delivered to various instruments on board.
The plumes were captured slightly less than two minutes after being emitted. Two rapid and sensitive analytical models were used to perform analyses: proton transfer reaction mass spectrometry and infrared differential absorption spectroscopy. They measured the plumes while the planes were idling, taxiing, taking off, and landing, and when the pilots started the engines.
The researchers found that hydrocarbon emissions from an idling plane engine may be greater than the emissions in the ICAO databank, by as much as 40–90%. The discrepancy can be accounted for by how the ICAO data were gathered: Engines studied for ICAO were idling at 7% of thrust. Most of the planes observed in this study had idling thrust levels below 7%; in other words, the engines studied were running at lower power levels, the researchers say. “This is really suggesting that we should think about how we model the hydrocarbon emission from idling aircraft,” Herndon says.
Herndon says that their paper is just the beginning of a flood of new data on aircraft emissions, much of it scheduled for publication in the next 6 months. “So in fact, the database of well-identified toxics that are traced to specific engine models is huge now,” Herndon says. What’s next? “The ground-service vehicles are now a big unknown,” he adds.
