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Civil aviation and airports have been shown to be important sources of both Ultrafine particles (UFPs) and Volatile Organic Compounds (VOCs) in urban areas1. UFPs are a major air quality concern because their small diameter (< 100 nm) allows them to reach the lungs’ alveolar regions causing adverse health effects. The aviation emission profile from the USA’s Environmental Protection Agency includes 15 hazardous VOCs, such as benzene and numerous carcinogenic Polycyclic Aromatic Hydrocarbons (PAHs)2. To assess the impact of UFPs and VOCs emissions from aviation on nearby air quality, two intensive one-month measurement campaigns of gaseous and particulate matter were performed in November 2022 and August 2024, 1 km downwind of Zürich Airport. The results indicate that high UFP number concentrations up to 300 000 cm⁻³ originate solely from aircraft operations, as shown by the similar diurnal profiles between air traffic movements and UFPs concentrations in Fig. 1a. These emissions are either advected downwind of the airport or mixed downward during aircraft landing overpasses. Using Positive Matrix Factorisation (PMF) on the VOCUS Proton Transfer Reaction Mass Spectrometer (PTR-MS) data, a factor containing naphthalene species and several alkanes with m/z > 100 (Fig. 1 c) has been attributed to VOCs aviation-related emissions. This is further supported by the co-increase of its time series with UFPs temporal evolution (Fig 1.b). However, when the site is not downwind and under the influence of landing overpasses, only UFPs concentrations increased, rather than the VOCs aviation-related factor (Fig. 1a), highlighting landing overpasses as a major source of UFPs but not of VOCs. This contrast likely results from lower engine thrust during taxiing at the airport than during landing overpass, which produces more VOCs due to reduced combustion efficiency3. At this stage, we cannot exclude a contribution of VOC emissions from engine refuelling. Future work will investigate the formation and evolution of VOCs in aviation plumes and their potential role in UFPs formation and growth. The widespread presence of UFPs and the co- emission of VOCs poses health concerns for communities near airports that regulators should address.Figure 1: 10-minutes averaged a) Diurnal cycle of air traffic at Zürich airport, UFPs number concentration ntotalPM , and VOCs aviation emissions when the measurement site was downwind of Zürich airport during the fall 2022 measurement campaign and b) 10-days time series of the same variables. C) Factor profile of the VOCs aviation emissions determined by a source apportionment on the VOCUS PTR-MS data.This work was supported by the Swiss Federal Office of Civil Aviation (SFLV 2020-080). We acknowledge the support from ZHAW, EMPA, Frithjof Siegerist (SRTechnics), and the City of Kloten. (1) Masiol, M.; Harrison, R. M. Aircraft Engine Exhaust Emissions and Other Airport-Related Contributions to Ambient Air Pollution: A Review. Atmos. Environ. 2014, 95, 409–455. https://doi.org/10.1016/j.atmosenv.2014.05.070.(2) US EPA, O. Organic Gas Speciation Profile for Aircraft. https://www.epa.gov/regulations-emissions-vehicles-and-engines/organic-gas-speciation-profile-aircraft (accessed 2026-01-12).(3) Anderson, B. E.; Chen, G.; Blake, D. R. Hydrocarbon Emissions from a Modern Commercial Airliner. Atmos. Environ. 2006, 40 (19), 3601–3612. https://doi.org/10.1016/j.atmosenv.2005.09.072.