Chemical Characterization of Particulate and Volatile Organic Compounds in the Rural Wintertime Atmosphere by CHARON PTR-ToF-MS

We have shown in previous work that Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) in combination with the “Chemical Analysis of Aerosol Online" (CHARON) inlet is a powerful tool for direct and online analysis of sub-µm particulate organic matter in the urban atmosphere. Herein, we report on the first CHARON PTR-ToF-MS measurements in the continental background environment, at the TROPOS Research Station in Melpitz near Leipzig (Germany) during a three week period in February 2019.

A state-of-the-art CHARON PTR-TOF 6000X2 instrument (IONICON Analytik GmbH, Austria) was used for measuring particulate organic compounds online (i.e., without filter pre-collection) and in real-time (< 1-min time resolution), at sub-ng m^-3 mass concentrations, and on an elementary composition level. Periodic switching between the standard PTR-MS gas-phase inlet and the CHARON particle inlet made it possible to comprehensively measure atmospheric organic matter in both the gaseous and particulate state at a time resolution of 10 minutes. In addition, an aerosol mass spectrometer (HR-TOF-AMS) and an aerosol chemical speciation monitor (ACSM; both Aerodyne Inc., USA) were deployed for monitoring the composition of non-refractory particulate matter. A Dual Mobility Particle Size Spectrometer (TROPOS-type T-MPSS) was used for determining the total particle size distribution. In addition, particles were collected on filters once per day and analysed offline in the laboratory.

The CHARON PTR-TOF 6000X2 instrument operated stably and reliably over the three week measurement period. Our data show that a single instrument can be used for characterizing both gaseous and particle-bound organic matter in the atmosphere at 10 minute time resolution. The obtained data agree well with ACSM, HR-TOF-AMS and T-MPSS results. A comparison with the offline results obtained from the filter samples confirmed that the CHARON PTR-ToF-MS technique accurately measures the atmospheric concentrations of selected anhydrosugars and polycyclic aromatic hydrocarbons (PAHs). We also show that CHARON PTR-ToF-MS data are useful for improving the source apportionment of particles via positive matrix factorization (PMF).

This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654109 (ACTRIS-2). F. P. has received funding through the EU's Horizon 2020 programme under grant agreement Nº674911 (IMPACT).