An economic passive sampling method to detect particulate pollutants using magnetic measurements

Is biomagnetic leaf monitoring still an effective method for monitoring the heavy metal pollution of atmospheric particulate matter in clean cities?

The development of a reasonable method for predicting heavy metals (HMs) pollution in atmospheric particulate matter (PM) remains challenging. This paper presents an elution-filtration method to collect PM from the surface of Osmanthus fragrans in a very clean area (Guiyang, China). The aim is to evaluate the effectiveness of biomagnetic leaf monitoring as a simple and rapid method for assessing HMs pollution in clean cities. For this purpose, we determined the magnetic parameters and concentrations of selected HMs in PM samples to investigate their relationships. The results showed that the magnetic minerals in PM samples were mainly low coercivity ferrimagnetic minerals, with a small amount of high coercivity minerals. The types of magnetic minerals were generally single, and the magnetic domain state was pseudo-single domain (PSD). There was a significant correlation between magnetic parameters and the heavy metal (HM) concentrations in PM. Low-field magnetic susceptibility (χ) could be used as an ideal proxy for determining anthropogenic HM pollution. Traffic emissions were the main atmospheric pollution source in urban Guiyang. Due to the incomplete traffic network and large traffic flow, traffic congestion (TC) often occurred at road intersections in the northwest and southwest corners of the city, resulting in the highest concentration of magnetic minerals and the most severe PM pollution. To mitigate atmospheric PM pollution and protect public health, it is strongly recommended that municipal authorities prioritize urban planning and traffic management to address TC. Measures should be implemented urgently to alleviate stop-and-go traffic.

A supervised machine learning approach to classify traffic-derived PM sources based on their magnetic properties

Environmental magnetism techniques are increasingly used to map the deposition of particulate pollutants on any type of accumulative surfaces. The present study is part of a collective effort that begun in recent years to evaluate the efficiency of these techniques involving a large range of measurements to trace the source signals. Here we explore the possibilities provided by the very simple but robust k-near-neighbors algorithm (kNN) for classification in a source-to-sink approach. For this purpose, in a first phase, the magnetic properties of the traffic-related sources of particulate matter (tire, brake pads, exhaust pipes, etc.) are used to parameterize and train the model. Then, the magnetic parameters measured on accumulating surfaces exposed to a polluted air as urban plant leaves and passive filters are confronted to the model. The results are very encouraging. The algorithm predicts the dominant traffic-related sources for different kinds of accumulative surfaces. The model predictions are generally consistent according to the sampling locations. Its resolution seems adequate since different dominant sources could be identified within one street. We demonstrate the possibility to trace traffic-derived pollutants from sources to sinks based only on magnetic properties, and to eventually quantify their contributions in the total magnetic signal measured. Because magnetic mapping has a high-resolution efficiency, these results open the opportunity to complement conventional methods used to measure air quality and to improve the numerical models of pollutant dispersion.

Technogenic magnetic particles from steel metallurgy and iron mining in topsoil: Indicative characteristic by magnetic parameters and Mössbauer spectra

Technogenic magnetic particles (TMPs), produced during various industrial processes, are released into the atmosphere as dust and get deposited on the surrounding topsoil. The mineralogical and structural differences of TMPs produced in different technological processes should be reflected in their magnetic properties and therefore should be indicative for industrial pollution sources. The goal of this study was to characterize the TMPs by novel methodological approach, based on combination of magnetic methods and Mössbauer spectroscopy to indicate parameters that are discriminative enough to be used as environmental indicators for iron metallurgy, steel production, and iron mining. We collected the topsoil samples in the vicinity of 4 European iron- and steelworks, located in three different countries (Poland, Norway, and Czech Republic) and operating for minimum 40 years. We sampled also topsoil close to the opencast iron mine, iron ore dressing plant, and over strongly magnetic natural background. Analysis of the hyperfine parameters of the Mössbauer spectra revealed that TMPs are "magnetite-like" minerals with low stoichiometry. It is indicated by ratio of iron ions contributions in B sites (octahedral) and A sites (tetrahedral) in magnetite spinel structure, which is much lower than 2.0 (theoretical value for stoichiometric magnetite). The characteristic feature of TMPs collected from the vicinity of old metallurgical plants (>180 years) was the high contribution of surface components probably related to the surface oxidation/maghemitization. We found that, TMPs can be easily differentiated from geogenic magnetite based on their magnetic parameters. The TMP produced by the iron and steel metallurgy had relatively narrow ranges of magnetic parameters (saturation ratio Mrs/Ms, <0.15, coercivity ratio Bcr/Bc 2.5-6.0 and saturation to susceptibility ratio Mrs/χ 3.5-15). These magnetic parameters may be indicative for TMPs emitted by these pollution sources and helpful in the study of historical pollution sources in topsoil in urban and post-industrial areas.

Magnetic Susceptibility of Spider Webs and Dust: Preliminary Study in Wrocław, Poland

Previous studies have proven that spider webs can be a reliable tool for magnetic biomonitoring. This study aims to present the magnetic susceptibility values of urban road dust (URD) settled indoors and outdoors, and compare these values with spider webs exposed to indoor and outdoor pollutants, and therefore to discuss their potential environmental implications. The webs of Eratigena atrica, Tegenaria ferruginea, and Agelena labyrinthica (Agelenidae) spiders from outdoor and indoor study sites were investigated, along with dust deposited on filters (indoors) and dust collected from the surrounding neighborhood (outdoors). Magnetic measurements revealed elevated levels of magnetic pollutants at all investigated sites in the city of Wrocław. The indoor/outdoor ratios of mass-specific magnetic susceptibility for the studied samples suggested a prevalence of indoor pollution sources at two of the sites (prosthetic laboratory and environmental science laboratory), whereas the third site (tenement house neighborhood) was dominated by material that presumably originated from predominantly outdoor sources. The indoor/outdoor ratios of magnetic susceptibility for the investigated matrices at the examined sites were highly comparable, which is promising for the utilization of spider webs in magnetic monitoring.

Impact of urban street canyon architecture on local atmospheric pollutant levels and magneto-chemical PM10 composition: An experimental study in Antwerp, Belgium

As real-life experimental data on natural ventilation of atmospheric pollution levels in urban street canyons is still scarce and has proven to be complex, this study, experimentally evaluated the impact of an urban street canyon opening on local atmospheric pollution levels, during a 2-week field campaign in a typical urban street canyon in Antwerp, Belgium. Besides following up on atmospheric particulate matter (PM), ultrafine particles (UFPs) and black carbon (BC) levels, the magneto-chemical PM₁₀ composition was quantified to identify contributions of specific elements in enclosed versus open street canyon sections. Results indicated no higher overall PM, UFP and BC concentrations at the enclosed site compared to the open site, but significant day-to-day variability between both monitoring locations, depending on the experienced wind conditions. On days with oblique wind regimes (4 out of 14), natural ventilation was observed at the open location while higher element contributions of Ca, Fe, Co, Ni, Cu, Zn and Sr were exhibited at the enclosed location. Magnetic properties correlated with the PM₁₀ filter loading, and elemental content of Fe, Cr, Mn and Ti. Magnetic bivariate ratios identified finel-grained magnetite carriers with grain sizes below 0.1 μm, indicating similar magnetic source contributions at both monitoring locations. Our holistic approach, combining atmospheric monitoring with magneto-chemical PM characterization has shown the complex impact of real-life wind flow regimes, different source contributions and local traffic dynamics on the resulting pollutant concentrations and contribute to a better understanding on the urban ventilation processes of atmospheric pollution.

Source apportionment of soil-contamination in Baotou City (North China) based on a combined magnetic and geochemical approach

We studied the magnetic properties and trace element concentrations (Cr, Cu, Fe, Mn, Pb, Ti, V, Zn) of urban topsoils from 111 urban sites in a large REE-Nb-Fe mining and smelting city, Baotou, Inner Mongolia, China. The results show that pseudo-single domain and multi-domain magnetite dominates the magnetic properties of the soil samples, and the magnetic concentration parameters show a large positive anomaly near the Baotou iron and steel works. The average contents of all trace metals exceeded their background level in soils in Inner Mongolia, except for Pb. The spatial distribution and correlation analysis show that magnetic parameters related to the magnetite concentration and Cr, Fe, Mn, Ti, V and Zn show similar trends of variation. In addition, the results of PCA show that Fe, Ti, and V are highly correlated with the magnetic particles derived from the Baotou iron and steel works, tailing dam, chromium plant, and cement plant. In contrast, Cr, Mn, Pb and Zn are derived from both the steel plant and traffic pollution. Using a PMF model, three potential pollution sources are identified: industrial pollution, including the steel works, tailing dam, cement plant and chromium plant, are reflected by χ_lf, χ_ARM, SIRM and SOFT, and they account for 71.2%; traffic pollution is reflected by Pb and Zn and accounts for 9.0%; and natural sources, reflected by χ_fd%, χ_ARM/χ, χ_ARM/SIRM, HARD%, S_-300, S_-100 and Ti, contribute 19.8%. The results are potentially useful for developing control measures for reducing trace metal contamination in soils in Baotou city, and in addition we conclude that a combined magnetic approach and geochemical approach is an effective means for qualitative and quantitative sources apportionment of urban surface soil pollution.

Biomagnetic Monitoring of Atmospheric Pollution: A Review of Magnetic Signatures from Biological Sensors

Biomagnetic monitoring of atmospheric pollution is a growing application in the field of environmental magnetism. Particulate matter (PM) in atmospheric pollution contains readily measurable concentrations of magnetic minerals. Biological surfaces, exposed to atmospheric pollution, accumulate magnetic particles over time, providing a record of location-specific, time-integrated air quality information. This review summarizes current knowledge of biological material ("sensors") used for biomagnetic monitoring purposes. Our work addresses the following: the range of magnetic properties reported for lichens, mosses, leaves, bark, trunk wood, insects, crustaceans, mammal and human tissues; their associations with atmospheric pollutant species (PM, NO_x, trace elements, PAHs); the pros and cons of biomagnetic monitoring of atmospheric pollution; current challenges for large-scale implementation of biomagnetic monitoring; and future perspectives. A summary table is presented, with the aim of aiding researchers and policy makers in selecting the most suitable biological sensor for their intended biomagnetic monitoring purpose.