Contributions and limitations of environmental magnetism to characterize traffic-related particulate matter sources

The chronic exposure to particulate matter (PM) pollution causes societal and environmental issues, in particular in urban areas where most citizen are notably exposed to vehicular traffic. Since almost two decades, environmental magnetic monitoring has demonstrated its efficiency to successfully map relative concentrations of these airborne particle deposition on accumulative surfaces. A better understanding of the magnetic results requires discriminating the main traffic-related sources of the observed signal on particle collectors. To meet this objective, we investigated a sample set of exhaust and non-exhaust sources with respect to their magnetic fingerprints inferred from hysteresis cycles, first order reversal curve (FORC) diagrams, temperature dependency of initial susceptibility, and unmixing of IRM acquisition curves. The source sample set comprises 14 diesel and gasoline exhaust smoke residues, 12 abrasive-fatigue wear test pieces from worn brake-pads, brake powders, worn tire-tread, and three possible resuspension products that are asphalt concrete, street dust, and Saharan mineral dust deposited by precipitation after long-range eolian transport. Magnetic properties of the source samples were compared to those from various type of accumulative surfaces exposed to urban traffic (passive collectors, filters of facemasks for cycling, plant leaves, and tree barks). We found clear fingerprints of exhaust pipes and brake wear products on these collectors. The findings highlight the relevance of environmental magnetic tools to characterize and discriminate different traffic-related source signals.