On pollen and airborne virus transmission

Talib Dbouk¹, Dimitris Drikakis¹

Affiliations

PMID: 34335004
PMCID: PMC8320470
DOI: 10.1063/5.0055845

On pollen and airborne virus transmission

Talib Dbouk et al. Phys Fluids (1994). 2021 Jun.

. 2021 Jun;33(6):063313.

doi: 10.1063/5.0055845. Epub 2021 Jun 22.

Authors

Talib Dbouk¹, Dimitris Drikakis¹

Affiliation

¹ University of Nicosia, Nicosia CY-2417, Cyprus.

PMID: 34335004
PMCID: PMC8320470
DOI: 10.1063/5.0055845

Abstract

This study investigates how airborne pollen pellets (or grains) can cause severe respiratory-related problems in humans. Given that pollen pellets can capture ribonucleic acid viruses, we show that airborne pollen grains could transport airborne virus particles such as the airborne coronavirus (CoV) disease (COVID-19) or others. We consider the environmental conditions featuring the highest pollen concentration season and conduct computational multiphysics, multiscale modeling and simulations. The investigation concerns a prototype problem comprising the transport of 10⁴ airborne pollen grains dropped from a mature willow tree at a wind speed of $(U_{wind} = 4 km / h)$ . We show how pollen grains can increase the coronavirus (CoV) transmission rate in a group of people, including some infected persons. In the case of high pollen grains concentrations in the air or during pollination in the spring, the social distance of 2 m does not hold as a health safety measure for an outdoor crowd. Thus, the public authorities should revise the social distancing guidelines.

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Figures

**FIG. 1.**
(i) An example of some pollen grains of different mythologies. All the white lines at the bottom of the images are equal to 10 μm except the Opuntia, which is 25 μ. (ii) The effect of dehydration on folding pollen grains: (a) a monosulcate pollen grain of *Lilium longiflorum* in the hydrated state that witness aperture invagination in the folded state. (b) A tricolpate pollen grain of *Euphorbia milii* with the aperture that protrudes in the hydrated state but retracts completely within the pollen in the folded state. (c) Inaperturate pollen of *Aristolochia gigantea* with harmomegathy that is reduced to a mirror buckling of the pollen wall. (d) A monoporate pollen grain of maize (Zea mays). All the scale bars in (ii) correspond to 20 μm. (i) Reproduced with permission from Arizona Board of Regents/ASU Ask A Biologist, https://askabiologist.asu.edu/images/zoom/pollen-gallery-pollen-close; (ii) Reproduced with permission from Katifori *et al.*, Proc. Natl. Acad. Sci. **107**, 7635–7639 (2017). Copyright 2017 Proceedings of the National Academy of Sciences.

**FIG. 2.**
On the link between pollen maps (a) and (b) and the coronavirus infection rates per capita in the USA (c) published data on 30 April 2020. The links are highlighted by blue circles/ellipses. (a) The willow oak pollen map in the USA. Map used after permission from Ref. . The white willow (Salix Alba) pollen map in the USA. According to the pollen calendars by Lo *et al.* (2019), the highest concentrations of total allergic pollen grains in the USA and Canada (North America) are observed in the ambient air between March and May. (a) Reproduced with permission from the Biota of North America Program (BONAP) organization 2021, http://www.bonap.org/. (b) Reproduced with permission from the Early Detection and Distribution Mapping System (EDDMapS) 2021, https://www.eddmaps.org. (c) Reproduced with permission from the Big Local News COVID-19 map of 30 April 2020, https://covid19.biglocalnews.org/county-maps/index.html.

**FIG. 3.**
Top: computational modeling of a willow tree showing the trunk, stems, leaves, and the 3D tree model. Bottom: computational domain $(50 \times 20 \times 20 m^{3})$ that includes the tree model and a crowd of people (97 individual including some infected persons) illustrating the potential of airborne virus transmission through a pollen-CoV bond potential. The crowd's boundary is positioned at a distance of 20 m away from the tree's boundary. The clustering of people in the crowd respects, in general, the minimum social distance of 2 m.

**FIG. 4.**
The three-dimensional streaklines (colored by the velocity magnitude) at $t = 40 s$ and $t = 60 s$ . (a) and (b) for a crowd of 97 individuals. (c) and (d) for a crowd of 11 individuals. The environmental conditions are free stream air flow at $U_{wind} = 4 km / h (\approx 1.1 m / s)$ . $T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ .

**FIG. 5.**
The velocity magnitude field at different cross sections in the computational domain. (a) and (b) for a crowd of 97 individuals. (c) and (d) for a crowd of 11 individuals. The environmental conditions are free stream air flow at $U_{wind} = 4 km / h (\approx 1.1 m / s)$ . $T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ .

**FIG. 6.**
Top view of pollination of 10⁴ pollen grains detached from a willow tree at a breeze of $U_{wind} = 4 km / h$ . The airborne pollen grains penetrate a crowd of 97 individuals with clusters that respect a minimum social distance of 2 m. Computational results at $T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ . The pollen grains were scaled up by a factor of 5000 compared to their actual size. Multimedia view: https://doi.org/10.1063/5.0055845.1

**FIG. 7.**
Side view of pollination of 10⁴ pollen grains detached from a willow tree at a breeze of $U_{wind} = 4 km / h$ . The airborne pollen grains penetrate a crowd of 97 individuals with clusters that respect a minimum social distance of 2 m. Computational results at $T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ . The pollen grains were scaled up by a factor of 5000 compared to their actual size. Multimedia view: https://doi.org/10.1063/5.0055845.1

**FIG. 8.**
A zoom-in of the scene results of Fig. 7. Computational results at $T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ . The pollen grains were scaled by a factor of 5000 compared to their actual size. Multimedia view: https://doi.org/10.1063/5.0055845.2

**FIG. 9.**
Side view of pollination of 10⁴ pollen grains detached from a willow tree at a breeze of $U_{wind} = 4 km / h$ . The airborne pollen grains penetrate 11 individuals with clusters that respect a minimum social distance of 2 m. The environmental conditions are $T_{air} = 22 ° C, T_{ground} = 17 ° C$ , and $R H = 50 %$ . The pollen grains were scaled up by a factor of 5000 compared to their actual size. Multimedia view: https://doi.org/10.1063/5.0055845.3

**FIG. 10.**
Side view of pollination of 10⁴ pollen grains detached from a willow tree at a breeze of $U_{wind} = 4 km / h$ . The airborne pollen grains penetrate 11 individuals with clusters that respect a minimum social distance of 2 m. The environmental conditions are $T_{air} = 22 ° C, T_{ground} = 17 ° C$ , and $R H = 50 %$ . The pollen grains were scaled up by a factor of 5000 compared to their actual size. Multimedia view: https://doi.org/10.1063/5.0055845.4

**FIG. 11.**
Total number of airborne pollen grains as a function of time inside the volumetric zone $20 \leq x \leq 40 m; y \leq 2.5 m$ that envelop the crowd of 97 individuals, and the group of people 11 individuals. The numerous pollen grains at the ground level y = 0 are not counted. The simulations concern pollination of 10⁴ pollen grains detached from a mature willow tree at $U_{wind} = 4 km / h, T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ .

**FIG. 12.**
Total number of airborne pollen grains as a function of time inside the volumetric zone $20 \leq x \leq 40 m; y \leq 1.7 m$ that envelop the crowd of 97 individuals, and the group of people 11 individuals. The numerous pollen grains at the ground level y = 0 are not counted. The simulations concern pollination of 10⁴ pollen grains detached from a mature willow tree at $U_{wind} = 4 km / h, T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ .

**FIG. 13.**
Total number of airborne pollen grains as a function of time inside the volumetric zone $20 \leq x \leq 40 m; y \leq 1 m$ that envelop the crowd of 97 individuals, and the group of people 11 individuals. The numerous pollen grains at the ground level y = 0 are not counted. The simulations concern pollination of 10⁴ pollen grains detached from a mature willow tree at $U_{wind} = 4 km / h, T_{air} = 22 ° C, T_{ground} = 17 ° C, R H = 50 %$ .

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References

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On pollen and airborne virus transmission

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On pollen and airborne virus transmission

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