Direct detection of condensed particulate polycyclic aromatic hydrocarbons on a molecular composition level at low pg m^-3 mass concentrations via proton-transfer-reaction mass-spectrometry

Abstract. Particle condensed polycyclic aromatic hydrocarbons (PAHs) are a group of toxic organic compounds that are produced by incomplete combustion of organic material e.g. via biomass burning or traffic emissions. Even at low long-term exposure levels, such as 1 ng m^-3 of benzo(a)pyrene, PAHs are recognized to be detrimental to human health. Therefore, a quantitative characterization of PAHs at sub-ng m^-3 levels is important to examine precise long-term exposure.

A new ultrasensitive generation of proton-transfer-reaction mass-spectrometry (PTR-MS) instruments coupled to the CHARON particle inlet is highly capable of quantitatively detecting this toxic class of compounds at a molecular composition level, while offering a high temporal resolution of < 1 min and sub-ng m^-3 limits of detection. To demonstrate the capabilities of this new CHARON FUSION PTR-TOF 10k instrument, we present a thorough characterization of summertime ambient condensed PAHs in Innsbruck, Austria. With a mass resolution of > 14 000 (m/Δm at full width half maximum) and unprecedented sensitivities of up to 40 cps ng^-1 m³, a series of 9 condensed PAHs of four (C₁₆H₁₀) to six aromatic rings (C₂₆H₁₆) are identified among a plethora of organic compounds in ambient organic aerosol. With unprecedented one-minute 3-σ limits of detection between 19 to 46 pg m^-3, quantitative time-series of these PAHs of lowermost mass concentrations are determined.

To understand the sources and processes associated with these condensed summertime PAHs in greater detail, a matrix factorization including the ~ 4 000 ionic signals detected by the CHARON FUSION PTR-TOF 10k is performed, representing the vast majority of ambient organic aerosol. A total of 10 factors and corresponding time-series can be identified. Known tracer compounds like levoglucosan, pinonic acid or nicotine consequently allow the assignment to individual organic aerosol sources and physico-chemical processes. PAH emissions from traffic are found to be minor contributors during this summertime sampling period. The highest concentrations of PAHs are identified in a mixed aged oxygenated organic aerosol, followed by a biomass-burning and a cigarette smoking organic aerosol.