Aviation emissions impact air quality more than climate

Researchers have found that growth in aviation is leading to poorer air quality.

Researchers at the Massachusetts Institute of Technology (MIT) evaluated the effects of a global expansion in aviation and found that the impact on air quality was two-four times higher than the climate impact.

As part of the research, which was published in IOP Publishing’s Environmental Research Letters, the team looked closely at the industry and assessed how the damage could be reduced by creating a comparative assessment of aviation emission trade-offs.

The lead researcher on the study, Dr Sebastian Eastham, from the Laboratory for Aviation and the Environment in MIT’s Department of Aeronautics and Astronautics, said:

‘Aviation emissions are an increasingly significant contributor to anthropogenic climate change. They cause 5% of global climate forcing.

‘When you consider the full flight, which includes emissions from takeoff, cruise and landing, aircraft emissions are also responsible for around 16,000 premature deaths a year from impaired air quality. This is small compared to other sectors, being only around 0.4% of the total deaths attributed annually to global air quality degradation, but is often overlooked in policy analysis.

‘The challenges for aviation sector decision-makers wanting to reduce these impacts are the trade-offs between different emission types and their impacts in different locations.’

Historically, aviation bosses have attempted to address the climate and air quality impacts of aviation by improving fuel efficiency, implementing stringent emissions standards, market-based measures to reduce CO2 emissions and the introduction of sustainable aviation fuels.

However, the study found that simply reducing one type of emission doesn’t solve the problem and can, in some cases, lead to an increase in the other.

Dr Eastham said:

‘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.

‘These are the types of trade-offs that need to be quantified, and our study offers a fast way for decision-makers to do this.’

The team then conducted further research to evaluate the effects of a global expansion in aviation on air quality and climate, which involved breaking flights down into their phases (cruise, landing and take-off) and comparing the emissions at each stage.

Dr Eastham said:

‘Our results show three components are responsible for 97% of climate and air quality damages per unit aviation fuel burn: air quality impacts of NOx at 58%; climate impacts of CO2 at 25%; and climate impacts of contrails at 14%.

‘It is important to note that around 86% of the NOx impacts on air quality are due to the emissions from cruise as opposed to the landing and takeoff 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.

‘Finally, we found the air quality impacts of aviation emissions significantly exceed the climate impacts, with air quality impacts being 1.7 to 4.4 times higher than the climate impact per unit of fuel burn.

‘This must be contrasted to ground-based industries, where post-combustion emissions control and access to cleaner fuels is widespread. For example, the climate impacts of the US power sector are of similar magnitude as the air quality impacts following significant declines in co-pollutant emissions over the past 15 years.

‘This points towards potential political and technological opportunities for reducing the atmospheric impacts of the aviation sector.’

Jenny Bates, a campaigner at Friends of the Earth, suggested government could reduce the atmospheric impacts of the aviation sector by cancelling airport expansion plans. She said:

‘Climate breakdown and air pollution are both crises that are costing lives. Aviation is an important contributor to both of these so it’s essential that the number of planes in the sky is cut down. This means putting an end to the expansion plans of airports across the country.

‘A third runway at Heathrow, in particular, would be devastating as it would not only destroy homes and cause much more noise disturbance but also unacceptably worsen air pollution and add considerably to climate emissions.’

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