Thermal analysis and ion mobility coupled to high-resolution mass spectrometry for organic aerosol characterization – TIMSAC

In this project, high-resolution mass spectrometry (HR-MS) either with high-resolution time-of-flight mass spectrometry (HR-TOF) or Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) are used for the description of organic aerosols at the molecular level. The unbeaten mass resolving power (> 30,000 for HR-TOF and > 500,000 for FT-ICR MS) and mass accuracy (< 1ppm) allows for a separation of highly complex organic mixtures and attribution of molecular formulae to individual molecular species without prior chromatographic separation. Consequently, so-called direct infusion assessments are most common in literature, e.g., electrospray ionization (ESI) for PM characterization for analysis of biomass burning aerosols targeting the high-polar constituents. As a matter of fact, there is still a research discrepancy for comprehensive analysis by hyphenated separation techniques and, in particular, compatible data analysis strategies. (38) However, these techniques are essential deciphering the isomeric complexity of the organic PM fraction and link results to climate and
health aspects.
Hyphenation of chromatographic technique to mass spectrometry is dominated by two principal approaches: 1) Liquid injection, and 2) Gas-phase introduction. For liquid injection techniques, such as high-performance liquid chromatography (HLPC), sample preparation is crucial, and most often, a tedious procedure, including a desalting step and the usage of multiple solvents, is essential. The high amounts of potassium and sodium exemplarily found in biomass burning particulate matter can be removed and specific organic fractions, e.g., the water-soluble fraction of organic aerosol (WSOC), are accessible.
This project focus on evolved gas analysis techniques as a complementary approach to liquid
chromatographic attempts. In brief, three different EGA approaches are commonly reported in
literature for complex mixture analysis and/or aerosol specification: Atmospheric solids analysis probe (ASAP/DIP), thermal-optical carbon analyzer (TOCA), and gas chromatography (GC) mass spectrometry hyphenation.

Heavy fuel oils for ships were analyzed with different ionization techniques in order to obtain an overview of their molecular composition and complexity. This step aims in particular to facilitate the study by Ion Mobility Spectrometry coupled to Mass Spectrometry (IMS-MS).
MALDI associated with an electron transfer matrix is particularly interesting for the selective ionization of molecules with low ionization energy such as porphyrins. Compared to LDI, ET-MALDI allows to clearly highlight petroporphyrins in fuel and particles. In addition to vanadyl porphyrins, nickel porphyrins were also observed in our samples. While the detection of these petroporphyrins in heavy fuel oils was expected, this is not the case for the particulates resulting from the combustion of these oils.
During combustion, porphyrins can be expected to be affected by combustion by transformations similar to that of PAHs. One possible chemical transformation of PAHs during combustion is dealkylation. Indeed, we observed a decrease in the relative intensity of petroporphyrins but no change in their distribution on the DBE vs C# plots suggesting that petroporphyrins were not specifically dealkylated during the combustion process but uniformly degraded.
In parallel to the mass spectrometry work, we have actively participated in the development of a FTMS (Fourier transform mass spectrometry) data processing software in partnership with the universities of Rouen, Pau and Rostock, TotalEnergies and the national high magnetic field laboratory (Maglab). The PhD student involved in this ANR project worked on the viewer part of the software which aims to facilitate the visualization of data obtained in ultra-high resolution mass spectrometry. This software allows the realization of many types of graphs and statistical studies commonly used in petroleomics and environmental science such as DBE vs C# mapping, Kendrick diagrams or principal component analysis (PCA).

The presence and fate of petroporphyrins in particulate matter from the primary exhaust of a ship engine equipped with exhaust treatment technology, i.e., a scrubber and particulate filter, motivates future studies. The fate of highly aromatic and polar petroporphyrins during these scrubbing and removal steps will be of great interest, as traces of these metals can potentially be introduced directly into the ocean.
In the near future, we will study scrubber wash waters by separating the aqueous phase from the solid phase (particulate matter) to determine the molecular complexity and to understand the effects of such a scrubbing system on ship emissions.

Anthropogenic air pollution exposes the environment to a large number of organic contaminants with severe health and climate impacts. The major impact on humankind and the tremendous molecular complexity of organic aerosols motivates the development of novel analytical instrumentation approaches.
The envisioned three-year corporate effort between the University of Rostock (Germany) and the University of Rouen-Normandy (France) primary aims to develop a set of evolved gas analysis (EGA) techniques coupled to state-of-the-art mass spectrometry (MS) platforms for the detailed chemical description of primary and secondary organic aerosols. In this respect, the shared expertise in high-resolution MS will make Fourier-transform ion cyclotron resonance (FT-ICR) and high-resolution time-of-flight MS the central analytical platforms and allow for molecular-level insights. Three main EGA approaches will be utilized for hyphenation: Atmospheric solids analysis probe (ASAP/DIP), thermal-optical carbon analyzer (TOCA), and gas chromatography (GC). Vital, ion mobility spectrometry (IMS) will serve as an additional separation technique for size and shape of the evolved constituents.
The information from the different approaches aims to reach three main achievements: 1) insights into the isomeric complexity of organic aerosols, 2) description of the chemical moieties at the molecular level, and 3) chemical comparison of primary emissions and those formed by chemical reactions (secondary, aged aerosols). Structural information is gained by the combination of GC retention time, selective ionization techniques (e.g., photoionization targeting aromatic species), fragmentation pattern (both by ASAP and tandem mass spectrometry), and ion mobility response. For this purpose, adapted data processing strategies will be developed, among others, including the theoretical computation of collision cross-sections (CCS).
Finally, this will allow us to set up a molecular repository for different types of aerosol sources, with a particular focus on shipping emissions. This molecular library is foreseen to be suitable to link human health aspects or to contribute to the understanding of the respective climate influence of particulate matter.