Simulating the influence of primary biological aerosol particles on clouds by heterogeneous ice nucleation

Abstract

Abstract. Primary ice formation, which is an important process for mixed-phase clouds with an impact on their lifetime, radiative balance, and hence the climate, strongly depends on the availability of ice-nucleating particles (INPs). Supercooled droplets within these clouds remain liquid until an INP immersed in or colliding with the droplet reaches its activation temperature. Only a few aerosol particles are acting as INPs and the freezing efficiency varies among them. Thus, the fraction of supercooled water in the cloud depends on the specific properties and concentrations of the INPs. Primary biological aerosol particles (PBAPs) have been identified as very efficient INPs at high subzero temperatures, but their very low atmospheric concentrations make it difficult to quantify their impact on clouds. Here we use the regional atmospheric model COSMO–ART to simulate the heterogeneous ice nucleation by PBAPs during a 1-week case study on a domain covering Europe. We focus on three highly ice-nucleation-active PBAP species, Pseudomonas syringae bacteria cells and spores from the fungi Cladosporium sp. and Mortierella alpina. PBAP emissions are parameterized in order to represent the entirety of bacteria and fungal spores in the atmosphere. Thus, only parts of the simulated PBAPs are assumed to act as INPs. The ice nucleation parameterizations are specific for the three selected species and are based on a deterministic approach. The PBAP concentrations simulated in this study are within the range of previously reported results from other modeling studies and atmospheric measurements. Two regimes of PBAP INP concentrations are identified: a temperature-limited and a PBAP-limited regime, which occur at temperatures above and below a maximal concentration at around −10 ∘C, respectively. In an ensemble of control and disturbed simulations, the change in the average ice crystal concentration by biological INPs is not statistically significant, suggesting that PBAPs have no significant influence on the average state of the cloud ice phase. However, if the cloud top temperature is below −15 ∘C, PBAP can influence the cloud ice phase and produce ice crystals in the absence of other INPs. Nevertheless, the number of produced ice crystals is very low and it has no influence on the modeled number of cloud droplets and hence the cloud structure.

Bioaerosol field measurements: Challenges and perspectives in outdoor studies

“…It is also becoming clear that bio-INPs typically predominate over minerals, in terms of their numeric abundance, across a wider temperature range than previously assumed, often comprising the majority of INPs at higher temperatures and down to -23 C (Hartmann et al 2019;Suski et al 2018;McCluskey et al 2018;Petters and Wright 2015;Mason et al 2015) or even colder (Tobo et al 2014). There is a vital need for numerical modeling studies to investigate the impact of different types of bioaerosols on cloud and precipitation properties as well as climate (e.g., Hummel et al 2018;Hoose, Kristj ansson, and Burrows 2010;Sahyoun et al 2016), from regional to global scales, and by considering biogenic INPs beyond whole microbial cells.…”

Spatiotemporal patterns of microbial composition and diversity in precipitation

“…, Hummel et al. ). At temperatures warmer than −38°C, phase transition from liquid water to ice requires the presence of ice nucleating particles (INPs; Atkinson et al.…”

“…Of growing interest to ecologists are the properties of precipitation-borne microbes, particularly species and strains that may trigger precipitation through the formation of ice in clouds (i.e., bioprecipitation; Sands et al 1982, Morris et al 2014a, Hummel et al 2018. At temperatures warmer than À38°C, phase transition from liquid water to ice requires the presence of ice nucleating particles (INPs; Atkinson et al 2016, Kanji et al 2017, Knopf et al 2018.…”

Complex plant-derived organic aerosol as ice-nucleating particles – more than a sum of their parts?

“…Mineral dust particles emitted from desert areas have been identified as ubiquitous INPs which initiate ice nucleation in clouds over a wide 45 range of temperature and humidity conditions (Boose et al, 2016;Ullrich et al, 2017). Cloud-level concentrations of biological aerosol particles, in contrast, are much lower than background concentrations of mineral dust, with differences of up to 8 orders of magnitude in some cases (Hummel et al, 2018).…”