Geologists at Jadavpur University have found that they can get a preliminary sense of the pollution in an area by collecting roadside dust and testing it with magnetic fields. The technique reveals the presence of different magnetic elements, and by tracing them back to specific sources of pollution, the researchers could tell which sources were dominating in different places.
Their study is in the area of environmental magnetism – which is “magnetism as it depicts the impact of climate change, pollution and environmental footprints on magnetic minerals present in environmental samples such as soil, dust and sediments,” Rimjhim Maity, who has completed her PhD from the Department of Geological Sciences, Jadavpur University, and is the study’s corresponding author, told The Hindu.
She and her colleagues collected roadside dust samples from 50 locations in Kolkata in 2016 using a brush and a scraper, dried them in the lab to remove all moisture, and tested them using a magnetic susceptibility meter. The extent to which a material becomes magnetised when a magnetic field is applied is its magnetic susceptibility. They also studied the shapes of the particles in each sample under an electron microscope.
Their results were published in the January 2023 edition of Current Science. They revealed “the dominance of magnetic pollutants in roadside dust in Kolkata,” Dr. Maity said. “This combined study indicated that the frequency of pollutants was higher in areas with heavy vehicular traffic and other polluting sources. However, some areas with high pollution had open spaces, indicating the dispersion of magnetic pollutants.”
For example, they found that the amount of magnetite, an iron ore, was proportional to the traffic on a given road; it is produced when fossil fuels are combusted in vehicle engines. Using the microscope, they were able to classify the particles’ surfaces as “rough and meld-like”. According to their paper, “Meld-like structure of these particles is due to the high-temperature combustion of fossil fuels”. They also wrote that “angular iron-rich particles are considered to have been emitted by vehicles having abraded and corroded vehicle parts”.
In this way, the study pieces together a coarse yet indicative map of Kolkata’s near-ground pollution.
“Broadly speaking, the method in the paper looks useful for mapping dust-loading on the roads – a very useful number for calculating road-dust resuspension emissions,” Sarath Guttikunda, founder/director of UrbanEmissions.info and an independent air-pollution researcher, said. Raj Bhagat P., senior program manager (geo-analytics) at the Sustainable Cities & Transport program at WRI India, Bengaluru, echoed him: “As a research methodology and an academic advancement, [the study] looks interesting and promising.”
But Dr. Guttikunda was concerned that it was “a manual method,” not automated like air-quality monitors.
“Although our sampling procedure required manual intervention, in this process we can easily collect samples,” Dr. Maity responded. “We don’t have to follow any lengthy process to collect data; we can collect samples like road-dust using very cost-effective tools; and the instruments used … made the sample analysis very cost-effective, less time-consuming and more constructive than chemical analysis.”
While automated monitoring is a benefit, Raj Bhagat said that “the biggest problem with continuous monitoring for our cities is not just the cost of sensors – it is about ease of operations, maintenance, logistics (who will take care of them and how), calibration for reliability, etc. At the stage of installation many sensors are well placed but in the long run, they are not calibrated, not maintained.”
Dr. Maity continued, “We are planning to do further studies to identify the usefulness of this cost-effective and less time-consuming method as a pollution proxy and apply it to detect the pollution in any environment globally,” and that it could be “very helpful for economically developing countries”.
She also said, “If each and every industry has its own environmental management team, it can easily study the level of pollution periodically and seasonally using this cost-effective method.”
Dr. Maity’s coauthors on the study were Supriya Mondal, Saurodeep Chatterjee, Debesh Gain, and Dipanjan Mazumdar.