Abstract
Abstract. Assessing the environmental, health, and climate impacts of bioaerosols requires knowledge of their size and abundance. These two properties were assessed through daily measurements of chemical tracers for pollens (sucrose, fructose, and glucose), fungal spores (mannitol and glucans), and Gram-negative bacterial endotoxins in two particulate matter (PM) size modes: fine particles (< 2.5 µm) and coarse particles (2.5–10 µm) as determined by their aerodynamic diameter. Measurements were made during the spring tree pollen season (mid-April to early May) and late summer ragweed season (late August to early September) in the Midwestern US in 2013. Under dry conditions, pollen, and fungal spore tracers were primarily in coarse PM (> 75 %), as expected for particles greater than 2.5 µm. Rainfall on 2 May corresponded to maximum atmospheric pollen tracer levels and a redistribution of pollen tracers to the fine PM fraction (> 80 %). Both changes were attributed to the osmotic rupture of pollen grains that led to the suspension of fine-sized pollen fragments. Fungal spore tracers peaked in concentration following spring rain events and decreased in particle size, but to a lesser extent than pollens. A short, heavy thunderstorm in late summer corresponded to an increase in endotoxin and glucose levels, with a simultaneous shift to smaller particle sizes. Simultaneous increase in bioaerosol levels and decrease in their size have significant implications for population exposures to bioaerosols, particularly during rain events. Chemical mass balance (CMB) source apportionment modeling and regionally specific pollen profiles were used to apportion PM mass to pollens and fungal spores. Springtime pollen contributions to the mass of particles < 10 µm (PM10) ranged from 0.04 to 0.8 µg m−3 (0.2–38 %, averaging 4 %), with maxima occurring on rainy days. Fungal spore contributions to PM10 mass ranged from 0.1 to 1.5 µg m−3 (0.8–17 %, averaging 5 %), with maxima occurring after rain. Overall, this study defines changes to the fine- and coarse-mode distribution of PM, pollens, fungal spores, and endotoxins in response to rain in the Midwestern United States and advances the ability to apportion PM mass to pollens.
Highlights
Inhalable bioaerosols (< 100 μm) act as aeroallergens, triggering mild to severe allergic respiratory diseases (D’Amato et al, 2007a; Dales et al, 2003)
Fructose, and sucrose are major components of pollens; mannitol and fungal glucans are in fungal spores; and endotoxins are in bacteria
During rainy days, 62 % of pollen mass and 20 % of fungal spore mass were observed in fine particulate matter (PM). These results indicate the importance of rain altering fineand coarse-mode distribution of bioaerosols by affecting release mechanisms
Summary
Inhalable bioaerosols (< 100 μm) act as aeroallergens, triggering mild to severe allergic respiratory diseases (D’Amato et al, 2007a; Dales et al, 2003). Types of bioaerosols include viruses (< 0.3 μm), bacteria (0.25–8 μm), fungal spores (1–30 μm), and plant pollens (∼ 5–100 μm) (Jones and Harrison, 2004; Matthias-Maser and Jaenicke, 1995). Bioaerosols reach different regions of the respiratory system based on their size (Oberdörster et al, 2005; Brown et al, 2013), which is dependent on the route of breathing, age, gender, and activity level (Brown et al, 2013). Particles of 3 and 5 μm for adults and children, respectively, travel beyond the larynx (Brown et al, 2013). The human immune system produces antibodies against inhaled aeroallergens that initiate airway symptoms (e.g., cough and runny nose) and exacerbate diseases like asthma and allergic rhinitis. Allergic respiratory diseases are estimated to affect 334 million people worldwide, children
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