Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.509 IF 5.509
  • IF 5-year value: 5.689 IF 5-year 5.689
  • CiteScore value: 5.44 CiteScore 5.44
  • SNIP value: 1.519 SNIP 1.519
  • SJR value: 3.032 SJR 3.032
  • IPP value: 5.37 IPP 5.37
  • h5-index value: 86 h5-index 86
  • Scimago H index value: 161 Scimago H index 161
Volume 16, issue 11
Atmos. Chem. Phys., 16, 7195-7211, 2016
https://doi.org/10.5194/acp-16-7195-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 7195-7211, 2016
https://doi.org/10.5194/acp-16-7195-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Jun 2016

Research article | 10 Jun 2016

Sources of organic ice nucleating particles in soils

Tom C. J. Hill1, Paul J. DeMott1, Yutaka Tobo2,3, Janine Fröhlich-Nowoisky4, Bruce F. Moffett5, Gary D. Franc6,†, and Sonia M. Kreidenweis1 Tom C. J. Hill et al.
  • 1Department of Atmospheric Science, Colorado State University, Fort Collins, CO, 80523, USA
  • 2National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
  • 3Department of Polar Science, School of Multidisciplinary Sciences, SOKENDAI (the Graduate University for Advanced Studies), Tachikawa, Tokyo 195-8518, Japan
  • 4Multiphase Chemistry, Max Planck Institute for Chemistry, Mainz, 55020, Germany
  • 5Ocean Lab, Goodwick, SA64 0DE, UK
  • 6Plant Sciences Department, University of Wyoming, Laramie, WY, 82071, USA
  • deceased

Abstract. Soil organic matter (SOM) may be a significant source of atmospheric ice nucleating particles (INPs), especially of those active  > −15°C. However, due to both a lack of investigations and the complexity of the SOM itself, the identities of these INPs remain unknown. To more comprehensively characterize organic INPs we tested locally representative soils in Wyoming and Colorado for total organic INPs, INPs in the heat-labile fraction, ice nucleating (IN) bacteria, IN fungi, IN fulvic and humic acids, IN plant tissue, and ice nucleation by monolayers of aliphatic alcohols. All soils contained  ≈ 106 to  ≈ 5 × 107INPsg−1 dry soil active at −10°C. Removal of SOM with H2O2 removed  ≥ 99% of INPs active  > −18°C (the limit of testing), while heating of soil suspensions to 105°C showed that labile INPs increasingly predominated  > −12°C and comprised  ≥ 90% of INPs active  > −9°C. Papain protease, which inactivates IN proteins produced by the fungus Mortierella alpina, common in the region's soils, lowered INPs active at  ≥ −11°C by  ≥ 75% in two arable soils and in sagebrush shrubland soil. By contrast, lysozyme, which digests bacterial cell walls, only reduced INPs active at  ≥ −7.5 or  ≥ −6°C, depending on the soil. The known IN bacteria were not detected in any soil, using PCR for the ina gene that codes for the active protein. We directly isolated and photographed two INPs from soil, using repeated cycles of freeze testing and subdivision of droplets of dilute soil suspensions; they were complex and apparently organic entities. Ice nucleation activity was not affected by digestion of Proteinase K-susceptible proteins or the removal of entities composed of fulvic and humic acids, sterols, or aliphatic alcohol monolayers. Organic INPs active colder than −10 to −12°C were resistant to all investigations other than heat, oxidation with H2O2, and, for some, digestion with papain. They may originate from decomposing plant material, microbial biomass, and/or the humin component of the SOM. In the case of the latter then they are most likely to be a carbohydrate. Reflecting the diversity of the SOM itself, soil INPs have a range of sources which occur with differing relative abundances.

Publications Copernicus
Download
Short summary
Even though aerosols that trigger the freezing of cloud droplets are rare, they can modify cloud properties and seed precipitation. While soil organic matter is a rich source of ice nucleating particles (INPs), we know little about them. The most active INPs (freeze supercooled water > −12 °C) in Wyoming and Colorado soils were organic, sensitive to heat (105 °C), and possibly fungal proteins in several soils, but they were not known species of ice nucleating bacteria. Many may also be carbohydrates.
Even though aerosols that trigger the freezing of cloud droplets are rare, they can modify cloud...
Citation
Share