Ultrafine particles form during combustion processes, for example when wood or biomass is burned, as well as in power and industrial plants. Alongside road traffic, large airports are a major source of these ultrafine particles, which are less than 100 millionths of a millimetre (100 nanometres) in size. Because they are so small, they can penetrate deep into the lower respiratory tract, overcome the air-blood barrier and, depending on their composition, cause inflammatory reactions in the tissue, for example. What’s more, ultrafine particles are suspected of being capable of triggering cardiovascular diseases.
the particles originated to a significant degree from synthetic jet oils and were particularly prevalent in the smallest particle classes, i.e. particles 10 to 18 nanometres in size. Such lubrication oils can enter the exhaust plume of an aircraft’s engines, for example through vents where nanometre-sized oil droplets and gaseous oil vapours are not fully retained.
— source Goethe University Frankfurt | Jan 9, 2023