(CN) – In a new study released Thursday, researchers from the Massachusetts Institute of Technology say the impact of aviation greenhouse gas emissions on the climate can be lessened, but it requires a careful balance of fuel efficiency and reduction in pollutants.
In their study published in the journal Environmental Research Letters, the MIT team address how these negative impacts can be mitigated, as well as provide comparisons for aviation emission trade-offs in regards to both air quality and climate.
"Aviation emissions are an increasingly significant contributor to anthropogenic climate change. They cause five per cent of global climate forcing,” said lead researcher Sebastian Eastham from MIT's Department of Aeronautics and Astronautics. 
Policymakers have tried addressing this issue by improving fuel efficiency, enforcing stricter emission standards, introducing market-based measures to reduce CO2 emissions, and so on.
Each of these approaches, however, present a trade off.
"We could decrease NOx emissions by designing engines with lower combustor temperatures. However, the resulting loss in thermodynamic efficiency would mean we need to burn more fuel, meaning more CO2.” Eastham said.
This study provides a solution to help decision makers to quantify the trade-offs in order to make a safe, informed decision. They comprised a set of metrics to compare the climate and air quality impacts of aviation emissions at all flight stages. They estimated the costs per unit of emitted pollutants and broke them down by each cruising, landing, and takeoff stages of a flight, as well as by the geographical region of emission.
The MIT research team used these metrics to analyze the effects of global aviation expansion based on current data, and used the results as a benchmark for three possible scenarios.
First, they considered a growth scenario with fuel efficiency increases and reductions in nitrogen oxide pollutant (NOx) emissions factors consistent with 10-year goals. Second, they evaluated the trade-offs between the climate and air quality impacts of engine-based NOx emissions reductions. Finally, they re-assessed the climate and air quality trade-offs of removing sulfur from jet fuel.
The results showed that 97% of climate and air quality damages per unit aviation fuel burn are due to three major components: air quality impacts of NOx at 58%; climate impacts of CO2 at 25%; and climate impacts of contrails at 14%. Eastham adds that it’s important to note that 86% of the NOx impacts on air quality come from the cruise portion of a flight rather than the takeoff and landing cycle.
“These components - cruise NOx emissions, CO2 emissions, and contrails - are therefore primary targets for future strategies to reduce the atmospheric impacts of aviation emissions,” Eastham said.
These results show that the best approach for the greatest net benefits would be to reduce NOx emissions during cruise, even though it reduces fuel efficiency and could cause a small but uncertain climate NOx disbenefit.
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