Identification and source attribution of organic compounds in ultrafine particles near Frankfurt International Airport

Abstract

Abstract. Analysing the composition of ambient ultrafine particles (UFPs) is a challenging task due to the low mass and chemical complexity of small particles, yet it is a prerequisite for the identification of particle sources and the assessment of potential health risks. Here, we show the molecular characterization of UFPs, based on cascade impactor (Nano-MOUDI) samples that were collected at an air quality monitoring station near one of Europe's largest airports, in Frankfurt, Germany. At this station, particle-size-distribution measurements show an enhanced number concentration of particles smaller than 50 nm during airport operating hours. We sampled the lower UFP fraction (0.010–0.018, 0.018–0.032, 0.032–0.056 µm) when the air masses arrived from the airport. We developed an optimized filter extraction procedure using ultra-high-performance liquid chromatography (UHPLC) for compound separation and a heated electrospray ionization (HESI) source with an Orbitrap high-resolution mass spectrometer (HRMS) as a detector for organic compounds. A non-target screening detected ∼200 organic compounds in the UFP fraction with sample-to-blank ratios larger than 5. We identified the largest signals as homologous series of pentaerythritol esters (PEEs) and trimethylolpropane esters (TMPEs), which are base stocks of aircraft lubrication oils. We unambiguously attribute the majority of detected compounds to jet engine lubrication oils by matching retention times, high-resolution and accurate mass measurements, and comparing tandem mass spectrometry (MS2) fragmentation patterns between both ambient samples and commercially available jet oils. For each UFP stage, we created molecular fingerprints to visualize the complex chemical composition of the organic fraction and their average carbon oxidation state. These graphs underline the presence of the homologous series of PEEs and TMPEs and the appearance of jet oil additives (e.g. tricresyl phosphate, TCP). Targeted screening of TCP confirmed the absence of the harmful tri-ortho isomer, while we identified a thermal transformation product of TMPE-based lubrication oil (trimethylolpropane phosphate, TMP-P). Even though a quantitative determination of the identified compounds is limited, the presented method enables the qualitative detection of molecular markers for jet engine lubricants in UFPs and thus strongly improves the source apportionment of UFPs near airports.

Impact of airport operations and road traffic on the particle number concentration in the vicinity of a suburban airport

“…While studies like Sun et al (2020) include a variety of predictors to analyze their contribution to air pollution, our approach shows that by focusing on these two PNC sources alone, both the contribution of each source and their combined impact can be well attributed. Ungeheuer et al (2021) include a chemical analysis of collected particles for jet oil additives to prove the origin of particles from aircraft engines, which is an alternative way to specifically identify aircraft emissions. Austin et al (2021) include the particle size as an additional observation to determine airport-derived particles, as aircraft emissions have been found to emit smaller particles with a peak PNC at ≤ 25 nm (Zhu et al, 2011;Keuken et al, 2012) in comparison to road traffic emissions that are mostly in the size range of 25-100 nm (Keuken et al, 2012).…”

An intercomparison study of four different techniques for measuring the chemical composition of nanoparticles

“…This procedure was optimized and described in detail by Ungeheuer et al (2021). The method enhances the separation of 200 organic compounds with high-resolution, and enables the determination of the accurate mass.…”

“…4. Offline analysis of filters (FILTER) using Ultra-high-performance liquid chromatography (UHPLC) and heated electrospray ionization (HESI) coupled to an Orbitrap high-resolution mass spectrometer (HRMS) (Ungeheuer et al, 2021). 100…”

Changes in Ultrafine Particle Concentrations near a Major Airport Following Reduced Transportation Activity during the COVID-19 Pandemic

“…The studies measuring or modeling UFP were short-term in nature, with the longest monitoring campaign being approximately seven weeks, and all were focused on road traffic. 12 − 14 Although UFP exposure in near-airport communities has been shown to be elevated 15 in the U.S. 16 − 18 as well as other countries 19 − 22 during normal airport operations, to date little work has been done to characterize air quality impacts due to sharp decreases in aviation activity during the pandemic.…”

“…Few studies have documented the UFP air quality impacts of the COVID-19 pandemic; a systematic review noted only two articles measuring ultrafine particles, with an additional article published more recently. The studies measuring or modeling UFP were short-term in nature, with the longest monitoring campaign being approximately seven weeks, and all were focused on road traffic. − Although UFP exposure in near-airport communities has been shown to be elevated in the U.S. − as well as other countries − during normal airport operations, to date little work has been done to characterize air quality impacts due to sharp decreases in aviation activity during the pandemic.…”