In full flight: making cruise emissions count

A new study that models aircraft emissions urges policymakers to consider emissions from cruising aeroplanes in air quality regulation, which currently focuses on emissions from take-off and landing only.

The researchers, based at the Massachusetts Institute of Technology in the US, show that 80 per cent of the total health impact of aircraft emissions is related to the cruise phase, equating to around 8,000 early deaths a year. ’It’s probably 100 times less than the number of people who die due to all air quality related issues,’ says lead researcher Steven Barrett. ’So it’s a small number in the grand scheme of things, but it’s important considering the size of the sector, which is a small sector in terms of emissions.’

As Barrett explains, the main culprits are those particles measuring less than 2.5?m in diameter - known as particulate matter or PM_2.5. This includes black and organic carbon, as well as aerosols formed through the reactions of nitric acid (HNO₃) and sulfuric acid (H₂SO₄). The team used a chemistry transport model combined with an emissions inventory to model the impact of aircraft cruise emissions on deaths from lung cancer, and heart and lung diseases.

If their calculations are correct, the largest burden falls on Asia, despite contributing relatively little to air traffic compared to the US, for example. ’The general vector, in a very crude sense, is from Europe at 10kms altitude towards China at ground level,’ says Barrett. In addition, the nitric acid reacts with high concentrations of ammonia - mainly from farming - in India and China leading to the formation of ammonium nitrate.

’Prior to reading this paper, I for one would have said that of course there would be emissions [from cruising] but they will be dispersed so widely that they wouldn’t have a major impact on our breathing zone emissions,’ says Frank Kelly, an environmental health expert at King’s College London, UK. ’What this paper’s tending to say is that they can in certain circumstances influence our breathing zone, and also influence the sort of atmospheric chemistry that’s going on.’ 

Kelly doesn’t believe the work will have a dramatic impact on policy. As Barrett notes, though, it does provide a stronger case for driving down total aircraft emissions. ’We used to assume that climate was due to full flight emissions and air quality was just due to the landing and take-off emissions,’ he says. ’Policymakers like to look at this in cost-benefit analysis terms and this provides an additional benefit to the mitigation of emissions.’ 

Hayley Birch