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Preprints
https://doi.org/10.5194/acp-2020-569
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-569
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Jul 2020

14 Jul 2020

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This preprint is currently under review for the journal ACP.

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

Ruud H. H. Janssen1,a, Colette L. Heald1, Allison L. Steiner2, Anne E. Perring3,4, J. Alex Huffman5, Ellis S. Robinson4,b, Cynthia H. Twohy6, and Luke D. Ziemba7 Ruud H. H. Janssen et al.
  • 1Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 2Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
  • 3Department of Chemistry, Colgate University, Hamilton, NY 13346, USA
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80305, USA
  • 5Department of Chemistry and Biochemistry, University of Denver, Denver, CO 80208, USA
  • 6North West Research Associates, Redmond, WA 98052, USA
  • 7NASA Langley Research Center Hampton, VA, USA
  • anow at: TNO Climate, Air and Sustainability, Utrecht, the Netherlands
  • bnow at: John Hopkins University, Dept. of Environmental Health and Engineering, USA

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 AAAI 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 particles (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.

Ruud H. H. Janssen et al.

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Short summary
Bioaerosols are ubiquitous in the atmosphere, and have the potential to affect cloud formation, as well as human and ecosystem health. However, their emissions are not well quantified, which hinders the assessment of their role in atmospheric processes. Here, we develop two new emission schemes for fungal spores based on multi-annual datasets of spore counts. We find that our modeled global emissions and burden are an order of magnitude lower than previous estimates.
Bioaerosols are ubiquitous in the atmosphere, and have the potential to affect cloud formation,...
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