A review of the mineralogical and chemical composition of nanoparticles associated with coal fires

This review summarizes our current knowledge on the health and environmental impact as well as the mineralogical and geochemical composition of nanoparticles (NPs) associated with coal fires. It will furthermore recommend new sampling and characterization protocols to gain a better understanding of the various types of NPs that are formed either through high‐temperature nucleation and alteration processes or via low‐temperature dissolution‐reprecipitation and weathering processes. Coal fires affect the immediate environment of coal‐producing areas and produce positive and negative feedback to climate change through the emission of carbon‐ and sulfate‐bearing gases and aerosols, respectively. Nanoparticles form during and after coal fires. They are composed of mainly soot and tar particles as well as amorphous phases, minerals, and complex mixtures of amorphous phases and minerals. It is recommended that NPs for mineralogical studies should be collected using impactors (a new generation of collectors for particulate matter, such as the TPS100 NP sampler) or that borosilicate filters at the openings of pipes and chambers be used to collect and measure gases emitted by coal fires. Furthermore, assemblages of NPs occurring at the mouths of coal fire vents should be examined using a combination of focused ion beam (FIB) technology and transmission electron microscopy (TEM), and those containing ion‐ or electron‐beam sensitive phases should be examined with the corresponding cryo‐techniques, such as cryo‐FIB, cryo‐ion mill, and cryo‐TEM. The mineralogical and chemical composition of NP‐bearing bulk samples should be examined with spectroscopy techniques such as X‐ray photoelectron spectroscopy, 13C nuclear magnetic resonance spectroscopy, or time‐of‐flight secondary ion mass spectroscopy. Core Ideas This study provides an overview of nanoparticles (NPs) associated with coal fires. It discusses major analytical techniques for the characterization of NPs. We suggest that mineralogical studies on NPs associated with coal fires should be collected in the gas phase. We propose that mineralogical studies on deposited NPs should be conducted with focused ion beam and focused ion beam.