Real-time Detection of Condensed Polycyclic Aromatic Hydrocarbons (PAH) on a Molecular Composition Level at Low pg/m³ Levels by CHARON FUSION PTR-TOF 10k

MARKUS MUELLER, Markus Leiminger, Andreas Klinger, Tobias Reinecke, IONICON Analytik GmbH., Innsbruck, Austria

     Abstract Number: 101
     Working Group: Source Apportionment

Abstract
Condensed polycyclic aromatic hydrocarbons (PAHs) are highly toxic organic compounds formed naturally through incomplete combustion of organic materials but also through various anthropogenic processes. Even at lowest exposure levels, such as 1 ng m^-³ of the commonly found benzo(a)pyren, PAHs can be detrimental to human health. However, detecting these compounds can be challenging due to their semi-volatile nature and low proton affinity. Proton transfer reaction mass spectrometry (PTR-MS), a soft chemical ionization technique, is able to detect condensed PAHs at low concentrations on a molecular composition level in the gas and condensed phase.

Herein we present a new generation PTR-TOF instrument that combines a clean Fast-SRI ion source, a radio-frequency ion molecule reactor (“FUSION”) and a high resolution TOF-MS (mass resolution >10k). This FUSION PTR-TOF 10k instrument reaches unprecedented sensitivities up to 80,000 cps ppbV^-1 and limits of detection (LOD) < 1 pptV in 1 s. The original setup was successfully modified to reduce sample flow and now allows for coupling of a CHARON particle inlet including an aerodynamic lens system. Consequently, LODs are further improved by a factor 20 for particles in the size range of 100-1000 nm. This high time resolution CHARON FUSION PTR-TOF 10k allows for the real-time detection of condensed PAHs on a molecular composition level, well below harmful exposure levels with 1-min LODs down to low pg m^-3 levels.
To demonstrate the outstanding capabilities of this new instrument, we present a first characterization of ambient organic aerosol in Innsbruck, Austria. From this dataset, a series of PAHs is identified and time-series of lowest mass concentrations are determined. We found 1-min LODs for C₁₆H₁₀ (i.e. pyrene, fluoranthene) and C₂₀H₁₂ (e.g., benzo-pyrene, benzo-fluoranthene) of 70 and 25 pg m^-3, respectively. Subsequently, matrix factorization is applied, delivering insight into separate sources of PAHs.