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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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Limited Evidence for a Microbial Signal in Ground‐Level Smoke Plumes
Abstract Recent studies have suggested that microbial aerosolization in wildfire smoke is an understudied source of microbes to the atmosphere. Wildfire smoke can travel thousands of kilometers from its source with the potential to facilitate the transport of microbes, including microbes that can have far‐reaching impacts on human or ecosystem health. However, the relevance of longer‐range detection of microbes in smoke plumes remains undetermined, as previous studies have mainly focused on analyses of bioaerosols collected adjacent to or directly above wildfires. Therefore, we investigated whether wildfire smoke estimated to originate >30 km from different wildfire sources would contain detectable levels of bacterial and fungal DNA at ground level, hypothesizing that smoke‐impacted air would harbor greater amounts and a distinct composition of microbes as compared to ambient air. We used cultivation‐independent approaches to analyze 150 filters collected over time from three sampling locations in the western United States, of which 34 filters were determined to capture wildfire smoke events. Contrary to our hypothesis, smoke‐impacted samples harbored lower amounts of microbial DNA. Likewise, there was a limited signal in the composition of the microbial assemblages detected in smoke‐affected samples as compared to ambient air, but we did find that changes in humidity were associated with temporal variation in the composition of the bacterial and fungal bioaerosols. With our study design, we were unable to detect a robust and distinct microbial signal in ground‐level smoke originating from distant wildfires.
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- Award ID(s):
- 2120117
- PAR ID:
- 10509015
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 129
- Issue:
- 4
- ISSN:
- 2169-897X
- 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/10.1029/2023JD039416
