Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow

Abstract

Biological ice nucleators (IN) function as catalysts for freezing at relatively warm temperatures (warmer than ؊10°C).We examined the concentration (per volume of liquid) and nature of IN in precipitation collected from Montana and Louisiana, the Alps and Pyrenees (France), Ross Island (Antarctica), and Yukon (Canada). The temperature of detectable ice-nucleating activity for more than half of the samples was > ؊5°C based on immersion freezing testing. Digestion of the samples with lysozyme (i.e., to hydrolyze bacterial cell walls) led to reductions in the frequency of freezing (0 -100%); heat treatment greatly reduced (95% average) or completely eliminated ice nucleation at the measured conditions in every sample. These behaviors were consistent with the activity being bacterial and/or proteinaceous in origin. atmosphere ͉ climate ͉ microbial dissemination ͉ biological ice nuclei A t subzero temperatures warmer than Ϫ40°C, aerosol particles in clouds initiate freezing through the heterogeneous nucleation of ice directly from water vapor or by freezing droplets via several mechanisms: deposition, condensation, contact, and immersion freezing (1). These processes lead to ice formation in clouds that can trigger precipitation. A diverse range of natural and anthropogenic particles, referred to as ice-forming nuclei or ice nucleators (IN), are capable of initiating the ice phase (2). The maximum temperature at which an IN can initiate freezing is specific to that nucleator, but they function similarly by providing templates for the aggregation of individual water molecules in the configuration of an ice embryo, resulting in a subsequent phase change and the cascade of crystal formation (3). Consequently, knowledge of the nature and sources of IN in the atmosphere is important for understanding the meteorological processes responsible for precipitation. The most active naturally occurring IN are biological in origin and have the capacity to catalyze freezing at temperatures near Ϫ2°C (4). The most widespread and well-studied biological aerosols with icenucleating activity are comprised of certain species of plantassociated bacteria (Pseudomonas syringae, Pseudomonas viridiflava, Pseudomonas fluorescens, Pantoea agglomerans, and Xanthomonas campestris), but also fungi (e.g., Fusarium avenaceum), algae such as Chlorella minutissima, and birch pollen (5). P. syringae (6 -8) and F. avenaceum (7) in particular have been detected in atmospheric aerosols and clouds. Icenucleating strains of P. syringae possess a 120-to 180-kDa ice nucleation active protein in their outer membrane comprised of contiguous repeats of a consensus octapeptide; the protein binds water molecules in an ordered arrangement, providing a nucleating template that enhances ice crystal formation (9).Based on reports of ice-nucleating bacteria at altitudes of several kilometers (6, 10) and the warm temperatures at which they function as ice nuclei (Ϫ2°C to Ϫ7°C; ref. Our previous work on snowfall collected from a variety of midand high-latitude locations...

Ice nucleation by fertile soil dusts: relative importance of mineral and biogenic components

“…The distinctive ice nucleation behaviour of our soil dusts draws interesting parallels with previous suggestions that atmospherically relevant IN, active at temperatures above around 258 K, may be exclusively biogenic Christner et al, 2008a). At similar temperatures, ice nucleation in all of the soil dusts examined during this study was dominated by active sites within the soil organic matter.…”

“…During studies of environmentally sampled ice nuclei of initially unknown composition, sensitivity to heat treatment has become a commonly employed technique to aid in classification of IN as biogenic or otherwise (Christner et al, 2008a, b;Henderson-Begg et al, 2009;Garcia et al, 2012). This straightforward test operates on the principle that known proteinaceous IN from intact bacteria and fungi are progressively lost upon heating to 363 K (Pouleur et al, 1992).…”

Atmospheric Processing and Variability of Biological Ice Nucleating Particles in Precipitation at Opme, France

“…This occurred at temperatures between −3 • C and −7.5 • C, on average over the 121 samples at −5.3 • C ± 0.7 • C ( Figure 2) (normality verified by Shapiro-Wilk test; n = 121; p = 9 × 10 −5 ); it was strongly linked with the concentration of INP measured at colder temperatures (Pearson test; p < 0.001; n = 121). Such high freezing temperatures indicate that the particles responsible for freezing were biological [4][5][6]44,45]. At −7 • C (INP −7 ), more than 90% of the samples had started freezing and INP concentration was on average 2.05 ± 2.17 mL −1 (±standard error); the concentrations measured at this temperature were used for further statistical analyses.…”

Laboratory Study of Effects of Atmospheric Pollutants on Ice Nucleation Activity of Bacteria

“…Since some kinds of bioaerosols can act as ice nuclei even at temperatures warm than -10°C (Schnell and Vali, 1972;Diehl et al, 2001;Iannone et al, 2011;Knopf et al, 2011;Morris et al, 2013;Joly et al, 2014), bioaerosols as an important component of aerosols in the atmosphere have been paid much more attentions over the past decades (Schnell and Vali, 1972;Diehl et al, 2001;Iannone et al, 2011;Knopf et al, 2011;Morris et al, 2013). Ice nucleation-active bioaerosols have widely been found in different regions and climates (Schnell and Vali, 1976;Christner et al, 2008a;Christner et al, 2008b;Pratt et al, 2009;Conen et al, 2011;Garcia et al, 2012;Burrows et al, 2013;Huffman et al, 2013;Monteil et al, 2014;O'Sullivan et al, 2014). Recent numerical studies show that ice nucleation-active bioaerosols can trigger the ice multiplication in the warmbased precipitating shallow cumulus clouds (Ariya et al, 2009;Sun et al, 2010;Sun et al, 2012).…”