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Wildfire smoke, particularly particulate matter less than 2.5 microns (PM2.5), represents a major source of air pollution and a growing public health problem. PM2.5 is a general term used for any particulate < 2.5 µm; however, a wide variety of particulates with different physical and chemical properties can be formed in this size range. The health impacts of PMs are controlled by their size. Unlike larger particulates, which only enter the respiratory tract, fine PMs (<0.1 µm) can also enter the bloodstream and even pass through the blood-brain barrier. The health risks due to exposure to PM can be different for various PM phases with different physical properties, which is poorly understood. We collected wildfire smoke from more than 10 major wildfires in the Western US using active air samplers that separate particles in different size ranges (>2.5 µm - <0.25 µm). Particles were collected on filters, which are pre-weighted and loaded into the impactor. The filters were weighted and compared with the pre-weight values to calculate the mass of particles collected at each size range. Our results revealed that for all the smoke from varied wildfires, the mass of particles increased with decreasing size, with the majority (more than 50%) being less than 0.25 μm. In addition, the PM2.5 total concentration was recorded using an air quality monitor and compared to the particle size distribution in different smoke samples. The results showed that as the overall concentration of wildfire smoke decreases, the fraction of particles smaller than 0.250 microns increases even more. This suggests that these ultrafine particles not only make up the majority of PM in wildfire smoke but are also more persistent in the atmosphere, even when the total PM concentration is low. Our findings highlight the magnitude of health risks posed by PM and underscore the urgent need for effective solutions to reduce respiratory exposure in affected communities.
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Magnetic and microscopic investigation of airborne iron oxide nanoparticles in the London Underground
Abstract Particulate matter (PM) concentration levels in the London Underground (LU) are higher than London background levels and beyond World Health Organization (WHO) defined limits. Wheel, track, and brake abrasion are the primary sources of particulate matter, producing predominantly Fe-rich particles that make the LU microenvironment particularly well suited to study using environmental magnetism. Here we combine magnetic properties, high-resolution electron microscopy, and electron tomography to characterize the structure, chemistry, and morphometric properties of LU particles in three dimensions with nanoscale resolution. Our findings show that LU PM is dominated by 5–500 nm particles of maghemite, occurring as 0.1–2 μm aggregated clusters, skewing the size-fractioned concentration of PM artificially to larger sizes when measured with traditional monitors. Magnetic properties are largely independent of the PM filter size (PM 10 , PM 4 , and PM 2.5 ), and demonstrate the presence of superparamagnetic (< 30 nm), single-domain (30–70 nm), and vortex/pseudo-single domain (70–700 nm) signals only (i.e., no multi-domain particles > 1 µm). The oxidized nature of the particles suggests that PM exposure in the LU is dominated by resuspension of aged dust particles relative to freshly abraded, metallic particles from the wheel/track/brake system, suggesting that periodic removal of accumulated dust from underground tunnels might provide a cost-effective strategy for reducing exposure. The abundance of ultrafine particles identified here could have particularly adverse health impacts as their smaller size makes it possible to pass from lungs to the blood stream. Magnetic methods are shown to provide an accurate assessment of ultrafine PM characteristics, providing a robust route to monitoring, and potentially mitigating this hazard.
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- Award ID(s):
- 2153786
- PAR ID:
- 10402791
- Date Published:
- Journal Name:
- Scientific Reports
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2045-2322
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41598-022-24679-4
