Long-term records of urban air quality are rare, yet they are essential for assessing the effectiveness of pollution-control measures and understanding risks to public health. Here we investigate multi-decadal changes in urban particulate matter, using a 44-year archive of air filter samples. Environmental magnetic measurements, supported by trace element signatures and scanning electron microscopy, are used to characterize iron-bearing particles, including magnetite/maghemite and hematite, and to constrain their dominant sources. The results show that anthropogenic magnetite/maghemite particles, primarily associated with traffic and high-temperature combustion processes, dominate the magnetic signal and exhibit marked temporal variability in concentration and composition. Magnetic concentration parameters peaked in the 1960s and decline steadily into the late 1980s, consistent with the introduction of emission regulations, cleaner fuels, and district heating. Concurrent decreases in hematite indicate a decrease in fly ash emissions. These findings demonstrate that environmental magnetic measurements provide a reliable and sensitive proxy for tracking long-term changes in urban particulate pollution and their sources. Magnetic susceptibility of particulate matter provides a powerful proxy for reconstructing past air-pollution trends, according to a long-term continuous magnetic dataset of urban aerosols from Helsinki, Finland.
Maunula et al. (Tue,) studied this question.