Drivers of the fungal spore bioaerosol budget: observational analysis and global modeling

Abstract

Abstract. Bioaerosols are produced by biological processes and directly emitted into the atmosphere, where they contribute to ice nucleation and the formation of precipitation. Previous studies have suggested that fungal spores constitute a substantial portion of the atmospheric bioaerosol budget. However, our understanding of what controls the emission and burden of fungal spores on the global scale is limited. Here, we use a previously unexplored source of fungal spore count data from the American Academy of Allergy, Asthma, and Immunology (AAAAI) to gain insight into the drivers of their emissions. First, we derive emissions from observed concentrations at 66 stations by applying the boundary layer equilibrium assumption. We estimate an annual mean emission of 62 ± 31 m−2 s−1 across the USA. Based on these pseudo-observed emissions, we derive two models for fungal spore emissions at seasonal scales: a statistical model, which links fungal spore emissions to meteorological variables that show similar seasonal cycles (2 m specific humidity, leaf area index and friction velocity), and a population model, which describes the growth of fungi and the emission of their spores as a biological process that is driven by temperature and biomass density. Both models show better skill at reproducing the seasonal cycle in fungal spore emissions at the AAAAI stations than the model previously developed by Heald and Spracklen (2009) (referred to as HS09). We implement all three emissions models in the chemical transport model GEOS-Chem to evaluate global emissions and burden of fungal spore bioaerosol. We estimate annual global emissions of 3.7 and 3.4 Tg yr−1 for the statistical model and the population model, respectively, which is about an order of magnitude lower than the HS09 model. The global burden of the statistical and the population model is similarly an order of magnitude lower than that of the HS09 model. A comparison with independent datasets shows that the new models reproduce the seasonal cycle of fluorescent biological aerosol particle (FBAP) concentrations at two locations in Europe somewhat better than the HS09 model, although a quantitative comparison is hindered by the ambiguity in interpreting measurements of fluorescent particles. Observed vertical profiles of FBAP show that the convective transport of spores over source regions is captured well by GEOS-Chem, irrespective of which emission scheme is used. However, over the North Atlantic, far from significant spore sources, the model does not reproduce the vertical profiles. This points to the need for further exploration of the transport, cloud processing and wet removal of spores. In addition, more long-term observational datasets are needed to assess whether drivers of seasonal fungal spore emissions are similar across continents and biomes.

Ice‐Nucleating Particles That Impact Clouds and Climate: Observational and Modeling Research Needs

“…Incorporation of bacteria, fungal spore, and pollen INPs into models: Global emissions parameterizations have been developed for bacteria-bearing particles (Burrows, Butler, et al, 2009), fungal spores (Heald & Spracklen, 2009;Janssen et al, 2021), and pollen (Wozniak & Steiner, 2017). In the case of pollen, there are also a number of regional-scale emission parameterizations, but these tend to be focused on applications to human allergen forecasting and so simulate only a subset of all pollen species (e.g., Helbig et al, 2004;Prank et al, 2013Prank et al, , 2016Scheifinger et al, 2013;Sofiev et al, 2015;Zink et al, 2012).…”

“…Parameterizations of biological particle emissions have been evaluated against independently collected observational data sets with mixed results. Models may generally be able to simulate mean number and mass concentrations of biological particles within the correct order of magnitude (e.g., Burrows, Rayner, et al., 2013; Janssen et al., 2021). In some cases they have been shown to simulate seasonal cycles or regional‐scale geographic distributions that correlate with observed patterns, but tend to lack skill in reproducing day‐to‐day variability (Perring et al., 2015; Twohy et al., 2016).…”

Airborne Bioaerosol Observations Imply a Strong Terrestrial Source in the Summertime Arctic

“…The resulting emissions estimates are comparable to, or higher than, modeled summertime emissions rates of fungal spores in the continental US. (Janssen et al., 2021) This finding is especially interesting since models (which are often tied to leaf area index) would not predict strong PBA sources in the Arctic, even in the summer.…”

Seasonal Variability of the Airborne Eukaryotic Community Structure at a Coastal Site of the Central Mediterranean

“…Romano et al [ 19 ] recently provided a preliminary local database on the potential airborne pathogenic bacterial species in PM10 samples collected at the study site. Airborne fungi constitute a substantial fraction of bioaerosols in the atmosphere, as mentioned [ 31 ], and there is also a growing attention to the potential harmful effects on living organisms—mostly humans and plants—by fungal bioaerosols themselves. Among the 12 most abundant Fungi genera (mean within-sample RA ≥ 0.95%) detected in the 37 PM10 samples ( Figure 6 a), we identified 4 potential pathogenic taxa, using the American Biological Safety Association (ABSA) international database [ 32 , 33 ]; the 4 fungal genera in question were Aspergillus , Botrytis , and Fusarium —belonging to the Ascomycota phylum—and Cryptococcus , belonging to the Basidiomycota phylum.…”