On the trail of microscopic hazardous substances: A study from Germany shows that the ultrafine dust that whirls from airports to residential areas originates to a large extent from lubricating oils in aircraft turbines. In order to improve air quality, in addition to emissions from fuel combustion, pollution from these substances must also be reduced in a targeted manner. In addition, the possible special effects of the ultrafine dust from lubricating oils should now be examined more closely, say the researchers.
They are smaller than 100 nanometers: The tiny particles of the so-called ultra-fine dust are mainly known as by-products of combustion processes. For example, they are released when biomass is burned, and fuel combustion is also a known source of ultrafine dust. The small size makes these particles a major health problem, according to studies: they can penetrate deep into the lower respiratory tract, cross the blood-air barrier there and, depending on their composition, then cause damage in the body. In tissues, for example, they can cause inflammation and the substances are also suspected of being involved in the development of cardiovascular diseases. It has been difficult to estimate the full extent of the possible health risks.
Special airport ultrafine dust
For some time now, scientists in Frankfurt am Main have been on the trail of a special source of ultrafine dust pollution: Measurements by the Hessian State Agency for Nature Conservation, Environment and Geology have shown that significant amounts of the particles are introduced into residential areas from Frankfurt Airport. It was obvious that they came from the kerosene combustion of the aircraft - but the team of scientists at the Goethe University in Frankfurt am Main wanted to know more about it. They subjected the captured particles from the vicinity of the airport to more precise analyses.
As the scientists report, when characterizing the ultrafine dust, they came across a group of organic compounds with special chemical fingerprints that did not match kerosene. Further investigations then confirmed: A significant proportion of the particles in the ultrafine dust come from synthetic turbine lubricating oils. They were particularly strongly represented in the smallest fractions, which include 10 to 18 nanometer particles.
Through laboratory experiments, the researchers were then also able to show how the particles are formed from the lubricating oils. According to them, the basic substance can get into the exhaust gas flow of the turbine via ventilation openings in which the nanometer-sized lubricating oil droplets and oil vapors are not completely separated. The team investigated what happens next experimentally: To do this, a common turbine lubricating oil was first vaporized at around 300 degrees Celsius in a hot gas flow that simulated the turbine exhaust gases and then cooled. The researchers were then able to record and examine the particles formed.
Focus on lubricating oil emissions
It turned out: "When the vaporized lubricating oil cools down, the gaseous synthetic esters are supersaturated and form the nuclei for new particles, which can quickly grow into particles around ten nanometers in size," says senior author Alexander Vogel from Goethe University. “Our investigations suggest that these particles make up a large proportion of the ultrafine dust produced by aircraft turbines. The previous assumption that ultrafine dust is mainly formed from sulfur and aromatic compounds in kerosene is apparently not correct," says the atmospheric chemist.
The study results are therefore of considerable importance for the development of protective measures. Because the use of low-sulphur kerosene or the switch to sustainably produced fuels can only reduce part of the burden. It should therefore now be explored how the contribution from the lubricating oils can be limited. "According to our knowledge, a reduction in lubricating oil emissions has important potential for reducing ultrafine particles," says Vogel. In addition, there is a need for research on another level, the scientists write in conclusion: "The possibly special toxicological properties of lubricating oil ultrafine dust should be evaluated in order to be able to estimate their health effects," according to the research team.
Source: Goethe University Frankfurt am Main, specialist article: Communications Earth & Environment, doi: 10.1038/s43247-022-00653-w