When Do Subpollen Particles Become Relevant for Ice Nucleation Processes in Clouds?. Issue 24 (14th December 2022)

• Record Type: Journal Article
• Authors: Werchner, Sven; Gute, E.; Hoose, C.; Kottmeier, Ch.; Pauling, A.; Vogel, H.; Vogel, B.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 24(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-12-14
• Subjects: subpollen particle -- SPP -- biological ice nucleation -- burst parameterization; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD036340
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: When exposed to sufficiently humid environments, pollen grains burst and release large quantities of small subpollen particles (SPPs) which carry ice nucleating macromolecules. In this study, for the first time we develop a physically based parameterization describing the bursting process of pollen by applying a turgor pressure parameterization and quantify the impact SPPs have on overall ice nucleation in clouds. SPPs are generated from simulated birch pollen emissions over Europe for a 10‐day case study in spring. We found SPP concentrations to surpass pollen grain concentrations by 4–6 orders of magnitude leading to an abundance of biological ice nuclei from SPPs in the range of 10 3 −10 4 m −3 . However, it is found that these concentrations lead to only small changes in hydrometeor number densities and precipitation. Addressing the question when SPPs become relevant for ice nucleation in clouds, we conducted a sensitivity investigation. We find that amplifying ice nucleation efficiency of biological particles by factors greater 100 increases the ice particle numbers by up to 25% ( T ≈ 268 K). Strong reductions show in cloud droplet number concentration and water vapor at these temperatures while water vapor is increasing at 600 m. Overall, we found a net reduction of water in the atmosphere as liquid and particularly water vapor density is reduced, while frozen water mass density increases above 257 K. Findings indicate an alteration of mixed‐phase cloud composition and increased precipitation (up to 6.2%) when SPPs are considered as highly efficient biological ice nuclei. Key Points: Subpollen particles (SPPs) reach freezing altitudes in large number concentrations Nucleation efficiency of SPPs affects both amplitude and sign of impact on nucleation processes Relevant impact requires greatly increased nucleation efficiency of the SPPs