Preprints
https://doi.org/10.5194/egusphere-2024-876
https://doi.org/10.5194/egusphere-2024-876
03 May 2024
 | 03 May 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Can pollen affect precipitation?

Marje Prank, Juha Tonttila, Xiaoxia Shang, Sami Romakkaniemi, and Tomi Raatikainen

Abstract. Large primary bioparticles such as pollen can be abundant in the atmosphere, for example near surface pollen concentrations above 10 000 particles per cubic meter can occur during intense pollination periods. On one hand, due to their large size (10–100 micrometres), pollens can act as giant cloud condensation nuclei and enhance the collision-coalescence process in clouds that leads to drizzle formation. On the other hand, in humid conditions pollens are known to rupture and release many fine particles that can increase the cloud stability by reducing the droplet size. Additionally, both whole pollen grains and the sub-pollen particles released by pollen rupture are known to act as ice-nucleating particles (INPs). Due to these complex interactions, the role of pollen in modulating the cloud cover and precipitation remains uncertain.

We used the UCLALES-SALSA large eddy simulator for simulating birch pollen effects on liquid and mixed-phase clouds. Our simulations show that the pollen concentrations observed during the most intense pollination seasons can locally enhance precipitation from both liquid and mixed phase clouds, while more commonly encountered pollen concentrations are unlikely to cause a noticeable change. The liquid precipitation enhancement depended linearly on the emitted pollen flux in both liquid and mixed phase clouds, however, the slope of this relationship was case dependent. Ice nucleation happened at relevant degree only if the process of rupturing pollens producing large number of fine ice nucleating particles was included in the simulations. The resulting precipitation saturated for the highest INP concentrations. Secondary ice formation by rime splintering had only minor effect in the considered one-day timescale.

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Marje Prank, Juha Tonttila, Xiaoxia Shang, Sami Romakkaniemi, and Tomi Raatikainen

Status: open (until 14 Jun 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-876', Anonymous Referee #1, 06 May 2024 reply
Marje Prank, Juha Tonttila, Xiaoxia Shang, Sami Romakkaniemi, and Tomi Raatikainen

Data sets

UCLALES-SALSA model output of the experiments presented in the manuscript Marje Prank, Juha Tonttila, Xiaoxia Shang, Sami Romakkaniemi, and Tomi Raatikainen https://doi.org/10.57707/fmi-b2share.5b37722cc31d4b8c9edfeca6a8dd88f6

Model code and software

UCLALES-SALSA model code used for the presented simulations Marje Prank, Juha Tonttila, Xiaoxia Shang, Sami Romakkaniemi, and Tomi Raatikainen https://doi.org/10.57707/fmi-b2share.5b37722cc31d4b8c9edfeca6a8dd88f6

Marje Prank, Juha Tonttila, Xiaoxia Shang, Sami Romakkaniemi, and Tomi Raatikainen

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Short summary
Large primary bioparticles such as pollen can be abundant in the atmosphere. In humid conditions pollens can rupture and release a large number of fine sub-pollen particles (SPPs). The paper investigates what kind of birch pollen concentrations are needed for the pollen and SPPs to start playing a noticeable role in cloud processes and alter precipitation formation. In the studied cases only the largest observed pollen concentrations were able to noticeably alter the precipitation formation.