The aviation industry has begun shifting to fuels derived from plants oils as a way of cutting greenhouse gas emissions. Researchers have contended that movement away from petroleum-based fuel would also cut down on emissions of ultrafine particles. According to the Dec. 21 paper by agency and university researchers, these particles are found at elevated levels around airports and can cause or exacerbate respiratory disease.

The particles are formed by nucleation in the exhaust plumes of jet engines. According to the paper, it was previously assumed that the particles were made of sulfuric and organic acids originating from fuel.

Last year, however, a team from the university analyzed particle samples that had been collected for several years by the agency at stations around the airport. University researchers found compounds indicating that a significant portion were generated from synthetic jet engine oils, which are made primarily of synthetic esters.

The researchers concluded that aviation lubes were on average responsible for between 10% and 32% of the ultrafine particles sampled around the Frankfurt airport.

“Our observations of lubrication oil emissions being an important source for [ultrafine particles] implies that this source will not be addressed by replacing traditional jet fuels with sustainable aviation fuels, and should therefore also be taken into account in the current endeavour to eliminate ultrafine particle emissions from aviation,” the paper stated.

The paper said that the number of particles can be reduced by engine design changes that optimize function of air-oil separators, ensuring that more lubricant is recovered rather than being emitted with the exhaust.

The paper is titled “Nucleation of Jet Engine Oil Vapors is a Large Source of Aviation-related Ultrafine Particles.” It was published at Nature.com and was first reported on by the university’s news website, Aktuelles.uni-frankfurt.de