Organic particles and gaseous precursors in suburban Paris during the ACROSS campaign in summer 2022: first deployment of a PTR-ToF-MS coupled with CHARON at the SIRTA observatory

Atmospheric organic aerosols (OA) are important because of their ubiquity and significance. They are the key drivers of air quality and climate change. While the secondary fraction of OA, namely SOA, is dominant in mass (between 50 to 85%), our capability to predict SOA is still uncertain because of the influence of multiple parameters (ie. humidity, temperature, NOx, nature and vapor pressure of organic gaseous precursors). Quantifying the partitioning between the gas and particle phases of semi-volatile organic compounds (SVOCs) in real conditions is one relevant approach to better constraint the budget of SOA and to develop accurate parametrization for organic aerosol formation in climate models.

During the summer of 2022, the ACROSS field campaign (Atmospheric ChemistRy Of the Suburban foreSt) took place in the Paris region at several sites located along a southwest to northeast transect for a comprehensive characterization of the gaseous and particulate atmospheric composition. For the first time, a PTR-ToF-MS (Proton Transfer Reaction-Time of Flight Mass Spectrometry) coupled with a CHARON (Chemical Analysis of aeRosol ON-line) inlet as part of the MOCCA set-up (Mass spectrOmetry for the multiphasic Composition of the Cloudy Atmosphere) was deployed at the SIRTA observatory. SIRTA is a suburban site being part of the Aerosols, Cloud, and Trace gases Research InfraStructure (ACTRIS), where long-term monitoring of in-situ reactive gases and particles has been performed for more than a decade [Simon et al. 2022]. Such deployment is a unique opportunity to qualify and intercompare the technical performances of the CHARON-PTR-ToF-MS system with other state of the art instrumentation at the site [Petit et al. 2015/Zhang et al., 2019] (PTR-Q-MS, quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM), Scanning Mobility Particle Sizer (SMPS), Condensation Particle Counter (CPC)), or aerosol size spectrometer for PM-10 and PM-2.5 and also a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) by TROPOS institute.

In this work, I will present the technical evaluation of the CHARON-PTR-ToF-MS system with respects to other conventional mass spectrometry methods such as the ACSM, under both controlled laboratory conditions and ambient conditions. Using the unique features of the CHARON-PTR-ToF-MS system, it will consider the analysis of the temporal variability of trace gases and aerosol observations, meteorology and air mass trajectories, relevant and contrasting periods, thus, the partitioning between the particle phase and the gaseous phase could be estimated. These observations will be compared to collocated measurements of trace gases and aerosols and will be used to evaluate model predictions using equilibrium partitioning theory.

 

References :

Petit, J.-E., et al..: Two years of near real-time chemical composition of submicron aerosols in the region of Paris using an Aerosol Chemical Speciation Monitor (ACSM) and a multi-wavelength Aethalometer, Atmos. Chem. Phys., 15, 2985–3005, https://doi.org/10.5194/acp-15-2985-2015, 2015.

Simon, L., et al.: Two years of Volatile Organic Compounds online in-situ measurements at SIRTA (Paris region, France) using Proton-Transfer-Reaction Mass Spectrometry, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2022-406, in review, 2022.

Zhang, Y., et al., A.: Six-year source apportionment of submicron organic aerosols from near-continuous highly time-resolved measurements at SIRTA (Paris area, France), Atmos. Chem. Phys., 19, 14755–14776, https://doi.org/10.5194/acp-19-14755-2019, 2019.