An official website of the United States government
Abstract. Forty years ago, lichens were identified as extraordinary biological icenucleators (INs) that enable ice formation at temperatures close to0 ∘C. By employing INs, lichens thrive in freezing environmentsthat surpass the physiological limits of other vegetation, thus making themthe majority of vegetative biomass in northern ecosystems. Aerosolizedlichen INs might further impact cloud glaciation and have the potential toalter atmospheric processes in a warming Arctic. Despite the ecologicalimportance and formidable ice nucleation activities, the abundance,diversity, sources, and role of ice nucleation in lichens remain poorlyunderstood. Here, we investigate the ice nucleation capabilities of lichenscollected from various ecosystems across Alaska. We find ice nucleatingactivity in lichen to be widespread, particularly in the coastal rainforestof southeast Alaska. Across 29 investigated lichen, all species show icenucleation temperatures above −15 ∘C, and ∼30 %initiate freezing at temperatures above −6 ∘C. Concentrationseries of lichen ice nucleation assays in combination with statisticalanalysis reveal that the lichens contain two subpopulations of INs, similarto previous observations in bacteria. However, unlike the bacterial INs, thelichen INs appear as independent subpopulations resistant to freeze–thawcycles and against temperature treatment. The ubiquity and high stability ofthe lichen INs suggest that they can impact local atmospheric processes andthat ice nucleation activity is an essential trait for their survival incold environments.
more »
« less
HUB: a method to model and extract the distribution of ice nucleation temperatures from drop-freezing experiments
The heterogeneous nucleation of ice is an importantatmospheric process facilitated by a wide range of aerosols. Drop-freezingexperiments are key for the determination of the ice nucleation activity ofbiotic and abiotic ice nucleators (INs). The results of these experimentsare reported as the fraction of frozen droplets fice(T) as a functionof decreasing temperature and the corresponding cumulative freezing spectraNm(T) computed using Gabor Vali's methodology. The differential freezingspectrum nm(T) is an approximant to the underlying distribution ofheterogeneous ice nucleation temperatures Pu(T) that represents thecharacteristic freezing temperatures of all INs in the sample. However,Nm(T) can be noisy, resulting in a differential form nm(T) that is challenging to interpret. Furthermore, there is no rigorousstatistical analysis of how many droplets and dilutions are needed to obtaina well-converged nm(T) that represents the underlying distributionPu(T). Here, we present the HUB (heterogeneousunderlying-based) method and associated Python codes thatmodel (HUB-forward code) and interpret (HUB-backward code) the results ofdrop-freezing experiments. HUB-forward predicts fice(T) and Nm(T)from a proposed distribution Pu(T) of IN temperatures, allowing itsusers to test hypotheses regarding the role of subpopulations of nuclei infreezing spectra and providing a guide for a more efficient collection offreezing data. HUB-backward uses a stochastic optimization method to computenm(T) from either Nm(T) or fice(T). The differential spectrumcomputed with HUB-backward is an analytical function that can be used toreveal and characterize the underlying number of IN subpopulations ofcomplex biological samples (e.g., ice-nucleating bacteria, fungi, pollen)and to quantify the dependence of these subpopulations on environmentalvariables. By delivering a way to compute the differential spectrum fromdrop-freezing data, and vice versa, the HUB-forward and HUB-backward codesprovide a hub to connect experiments and interpretative physical quantitiesthat can be analyzed with kinetic models and nucleation theory.
more »
« less
- Award ID(s):
- 2308172
- PAR ID:
- 10575697
- Publisher / Repository:
- Copernicus Publications
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 23
- Issue:
- 10
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 5623 to 5639
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract. From extracellular freezing to cloud glaciation, the crystallization of water is ubiquitous and shapes life as we know it. Efficient biological ice nucleators (INs) are crucial for organism survival in cold environments and, when aerosolized, serve as a significant source of atmospheric ice nuclei. Several lichen species have been identified as potent INs capable of inducing freezing at high subzero temperatures. Despite their importance, the abundance and diversity of lichen INs are still not well understood. Here, we investigate ice nucleation activity in the cyanolichen-forming genus Peltigera from across a range of ecosystems in the Arctic, the northwestern United States, and Central and South America. We find strong IN activity in all tested Peltigera species, with ice nucleation temperatures above −12 °C and 35 % of the samples initiating freezing at temperatures at or above −6.2 °C. The Peltigera INs in aqueous extract appear to be resistant to freeze–thaw cycles, suggesting that they can survive dispersal through the atmosphere and thereby potentially influence precipitation patterns. An axenic fungal culture termed L01-tf-B03, from the lichen Peltigera britannica JNU22, displays an ice nucleation temperature of −5.6 °C at 1 mg mL−1 and retains remarkably high IN activity at concentrations as low as 0.1 ng mL−1. Our analysis suggests that the INs released from this fungus in culture are 1000 times more potent than the most active bacterial INs from Pseudomonas syringae. The global distribution of Peltigera lichens, in combination with the IN activity, emphasizes their potential to act as powerful ice-nucleating agents in the atmosphere.more » « less
-
Heterogeneous ice nucleation in the atmosphere regulates cloud properties, such as phase (ice versus liquid) and lifetime. Aerosol particles of marine origin are relevant ice nucleating particle sources when marine aerosol layers are lifted over mountainous terrain and in higher latitude ocean boundary layers, distant from terrestrial aerosol sources. Among many particle compositions associated with ice nucleation by sea spray aerosols are highly saturated fatty acids. Previous studies have not demonstrated their ability to freeze dilute water droplets. This study investigates ice nucleation by monolayers at the surface of supercooled droplets and as crystalline particles at temperatures exceeding the threshold for homogeneous freezing. Results show the poor efficiency of long chain fatty acid (C16, C18) monolayers in templating freezing of pure water droplets and seawater subphase to temperatures of at least −30 °C, consistent with theory. This contrasts with freezing of fatty alcohols (C22 used here) at nearly 20 °C warmer. Evaporation of μL-sized droplets to promote structural compression of a C19 acid monolayer did not favor warmer ice formation of drops. Heterogeneous ice nucleation occurred for nL-sized droplets condensed on 5 to 100 μm crystalline particles of fatty acid (C12 to C20) at a range of temperatures below −28 °C. These experiments suggest that fatty acids nucleate ice at warmer than −36 °C only when the crystalline phase is present. Rough estimates of ice active site densities are consistent with those of marine aerosols, but require knowledge of the proportion of surface area comprised of fatty acids for application.more » « less
-
Abstract. Some biological particles, such as Snomax, are very active ice nucleating particles, inducing heterogeneous freezing in supercooled water at temperatures above −15 and up to −2 °C. Despite their exceptional freezing abilities, large uncertainties remain regarding the atmospheric abundance of biological ice nucleating particles, and their contribution to atmospheric ice nucleation. It has been suggested that small biological ice nucleating macromolecules or fragments can be carried on the surfaces of dust and other atmospheric particles. This could combine the atmospheric abundance of dust particles with the ice nucleating strength of biological material to create strongly enhanced and abundant ice nucleating surfaces in the atmosphere, with significant implications for the budget and distribution of atmospheric ice nucleating particles, and their consequent effects on cloud microphysics and mixed-phase clouds. The new critical surface area g framework that was developed by Beydoun et al. (2016) is extended to produce a heterogeneous ice nucleation mixing model that can predict the freezing behavior of multicomponent particle surfaces immersed in droplets. The model successfully predicts the immersion freezing properties of droplets containing Snomax bacterial particles across a mass concentration range of 7 orders of magnitude, by treating Snomax as comprised of two distinct distributions of heterogeneous ice nucleating activity. Furthermore, the model successfully predicts the immersion freezing behavior of a low-concentration mixture of Snomax and illite mineral particles, a proxy for the biological material–dust (bio-dust) mixtures observed in atmospheric aerosols. It is shown that even at very low Snomax concentrations in the mixture, droplet freezing at higher temperatures is still determined solely by the second less active and more abundant distribution of heterogeneous ice nucleating activity of Snomax, while freezing at lower temperatures is determined solely by the heterogeneous ice nucleating activity of pure illite. This demonstrates that in this proxy system, biological ice nucleating particles do not compromise their ice nucleating activity upon mixing with dust and no new range of intermediary freezing temperatures associated with the mixture of ice nucleating particles of differing activities is produced. The study is the first to directly examine the freezing behavior of a mixture of Snomax and illite and presents the first multicomponent ice nucleation model experimentally evaluated using a wide range of ice nucleating particle concentration mixtures in droplets.more » « less
-
null (Ed.)We generate water-rich aerosols containing 1-propanol and 1-pentanol in a supersonic nozzle to study the effects of these solutes on the freezing behavior of water. Condensation and freezing are characterized by two complementary techniques, pressure trace measurements and Fourier Transform Infrared spectroscopy. When 1-pentanol and 1-propanol are present, condensation occurs at higher temperatures because particle formation from the vapor phase is enhanced by the decrease in interfacial free energy of mixed aqueous-alcohol critical clusters relative to those of pure water. FTIR results suggest that when ∼6 nm radius droplets freeze, the tetrahedral structure of the ice is well preserved up to an overall alcohol mole fraction of 0.031 for 1-propanol and 0.043 for 1-pentanol. In this concentration range, the ice nucleation temperature decreases continuously with increasing 1-propanol concentration, whereas the onset of freezing is not significantly perturbed by 1-pentanol up to a mole fraction of 0.03. Furthermore, once freezing starts the ice nucleation rates in the aqueous-alcohol droplets are very close to those for pure water. In contrast, at the highest mole fractions of either alcohol it is not clear whether droplets freeze to form crystalline ice since the final state of the particles cannot be adequately characterized with the available experimental techniques.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-23-5623-2023
