Distribution of jet engine oil emissions in the urban surroundings of Germany's largest airport

Numerous studies have identified airports as key sources of ultrafine particles (UFPs – aerodynamic diameter <100 nm) ^{[1] [2] [3] [4]}, yet the chemical composition and formation mechanisms of these particles remain poorly understood. In a previous study we characterized the organic chemical composition of aviation-related UFPs by non-targeted screening and identified jet engine oils as a significant contributor ^[5]. Besides quantifying the mass contribution of jet oils to ambient UFPs originating from Frankfurt International Airport, we were able to show the new-particle formation ability of jet engine oils by laboratory based thermodenuder-experiments, using a common synthetic lubrication oil ^[6].

Here, we show the spatial distribution of jet engine oil emissions emerging from Frankfurt Airport, which is the largest airport in Germany.  We conducted a quantitative analysis of two different types of synthetic esters which are used as base stock in jet engine oils to monitor their prevalence in the region. Hence, we collected particles with diameters <100 nm at five different locations around the airport with varying distances to the airport grounds. We sampled UFPs on aluminium-filters using multiple 13-stage cascade impactor systems (Nano-MOUDI) in the direct vicinity of the airport runways and up to a distance of 20 km. Collection took place in summer and winter periods to observe a possible seasonal variability and at three stations in parallel to monitor the simultaneous spatial extent and wind direction dependence. In parallel to filter sampling, the particle size distribution was monitored to determine the size-resolved total particle mass. Quantitative characterization of UFPs in the size ranges 10–18 nm, 18–32 nm, 32–56 nm and 56-100 nm was performed by external calibration applying liquid chromatography (UHPLC) separation, followed by heated electrospray ionization (HESI) and mass analysis using a high-resolution Orbitrap mass spectrometer (HRMS). The two homologous ester series of pentaerythritol- (C_25-40H_44-74O₈) and trimethylolpropane (C_26-36H_48-68O₆) esters were quantified by external calibration using one ester compound (C₂₉H₅₂O₈). Since different types of Nano-MOUDI samplers (NanoMOUDI Model 115; NanoMOUDI-II 122R & 125R) were in use, we compared their sampling efficiency for each stage in order to make later corrections. Over a period of two weeks, we collected parallel filter samples at the same station and compared the collected engine oil mass accordingly. Results indicate that aircraft engine oils are detectable across the full UFP size range, with the highest concentrations observed at airport grounds in the 32-56 nm particle size fraction. Sulfate concentrations show a similar picture regarding the size distribution. To accurately account for these variations in size fractions, it is crucial to consider the differing collection efficiencies as these can vary significantly depending on the sampler model and design.

[1] Habre, R., et al. (2018) Environ. Int., 118, 48–59.

[2] Fushimi, A., et al. (2019) Atmos. Chem. Phys., 19, 6389–6399.

[3] Stacey, B., (2019) Atmos. Environ., 198, 463–477.

[4] Rivas, I., et al. (2020) Environ. Int., 135, 105345.

[5] Ungeheuer, F., et al. (2021) Atmos. Chem. Phys., 21, 3763–3775.

[6] Ungeheuer, F., et al. (2022) Commun Earth Environ 3, 319.