Identification, targeted extraction and source apportionment of magnetic micro- and nanoparticles in particulate matter

• Applicants: Professor Dr. Stuart Alan Gilder; Professorin Dr. Claudia Trepmann
• Subject Area: Geophysics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 533425261

Building on our previous work on anthropogenic and natural particulate matter (PM) in and around Munich during 1999-2001, we propose a high resolution micro-magnetic and electron microscopic investigation of PM some 25 years later. We propose to develop a unique system that will allow us to extract individual micron-sized magnetic particles from dust and measure their Curie temperatures via flash calorimetry. Magnetic analyses are surprisingly rarely made in PM studies, given their comparative ease, sensitivity and cost effectiveness, combined with the fact that iron bearing particles can be a serious risk to human health. For example, in March 2022, an enormous volume of Saharan dust blew into Munich that turned the sky yellow and blanketed all surfaces. Our analyses of the dust showed surprisingly high magnetizations; Curie temperature measurements yielded a distinct signal at 770°C, signifying the presence of metallic iron. This raises the important questions: where did the iron come from, how was it transported and how long can it last in the metal phase, before oxidizing to magnetite and then hematite or maghemite? On a local level in Munich, we intend to address the following questions regarding the characteristics and occurrence of the magnetic PM: 1) How did the proportion and composition of the magnetic PM component change between 1999-2001 and 2023-2025? 2) Which sources are emitting the magnetic particles? 3) What are the transportation routes that bring magnetic particles to Munich? To identify and characterize the magnetic components in the dust, we want to further develop the so called Magnetodrome - a high resolution optical microscope surrounded by four electromagnets. We intend to compliment the Magnetodrome with an extremely precise micro-pipette extractor. The ensemble will allow us to efficiently select magnetic particles and automatically place them on SEM sample holders for subsequent microscopy or onto grids for flash calorimetry. Bulk samples will be further subjected to a suit of magnetic measurements on existing equipment to further characterize their magnetic properties, as well as non-magnetic techniques like X-ray diffraction and Mößbauer-spectroscopy. The work herein will be the basis for a doctoral thesis. Samples will be collected at regular intervals at key places in the Munich area chosen specifically to unravel anthropogenic from natural sources. Moreover, we will cooperate with experienced partners in Spain (Manuel Calvo Rathert, Uni. Burgos; Eduardo Colombo, MAGIC Telescope, La Palma) and Italy (Fabio Florindo, Uni. Rome) who will provide samples. Further analyses of dust samples from Italy, Spain and the Canary Islands should help to answer the key questions concerning the source of metallic iron, which is known to be extremely hazardous to human health. A cooperation with the Hoher Sonnblick observatory in Austria will enable us to analyze years of PM recordings.

• DFG Programme: Research Grants
• International Connection: Austria, Italy, Spain
• Co-Investigators: Dr. Kai-Uwe Hess; Professorin Dr. Anke Nölscher; Professor Dr. Nikolai Petersen
• Cooperation Partners: Professor Dr. Manuel Calvo-Rathert; Dr. Eduardo Colombo; Dr. Ramon Egli; Dr. Fabio Florindo; Professor Dr. Günther Redhammer