Selective characterization of petroporphyrins in shipping fuels and their corresponding emissions using electron-transfer matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry

Abstract

In the context of the global transportation of goods, shipping emissions account for a significant proportion of air pollution. Indeed, a focus has been made over recent years on this primary emission source, leading to several regulations with respect to the chemical composition of shipping fuels. However, these regulations mainly concern the fuel sulfur content (FSC) and do not consider other compound classes such as polycyclic aromatic hydrocarbons (PAHs) or metal-containing aromatics, i.e., petroporphyrins, known to be present in bunker fuels. Petroporphyrins are tetrapyrrole-based metal complexes derived from the transformation of chlorophylls through geological time scales. In contrast to PAHs, their fate in the combustion process and effects on environmental health are widely unknown. In this study, we present electron-transfer ionization in matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (ET-MALDI FTICR MS) for the characterization of vanadyl and nickel porphyrins in shipping feed fuels and primary particulate matter emissions. For the first time, these petroporphyrins could successfully be described in the heavy fuel oil (HFO) feeds but also in the particles emitted by the combustion of the respective fuel on a molecular level. Three main alkylated series of porphyrins were observed; these series can be qualified by their double bond equivalent, i.e., 17, 18, and 20, and correspond to various core structures. Our results highlight the molecular fate of the petroporphyrins through combustion and show that a significant amount of petroporphyrins is released unburned or partially dealkylated to the atmosphere. Furthermore, our results suggest that a higher amount of petroporphyrins might be released in harbors than in open sea, due to a less efficient combustion at lower engine load. This last observation motivates a future specific study on porphyrins’ health and environmental effects.