Letter abstract

Nature Geoscience 2, 398 - 401 (2009)
Published online: 17 May 2009 | Corrected online: 20 May 2009 | doi:10.1038/ngeo521

Subject Category: Atmospheric science

In situ detection of biological particles in cloud ice-crystals

Kerri A. Pratt1, Paul J. DeMott2, Jeffrey R. French3, Zhien Wang3, Douglas L. Westphal4, Andrew J. Heymsfield5, Cynthia H. Twohy6, Anthony J. Prenni2 & Kimberly A. Prather1,7


The impact of aerosol particles on the formation and properties of clouds is one of the largest remaining sources of uncertainty in climate change projections1. Certain aerosol particles, known as ice nuclei, initiate ice-crystal formation in clouds, thereby affecting precipitation and the global hydrological cycle2. Laboratory studies suggest that some mineral dusts and primary biological particles—such as bacteria, pollen and fungi—can act as ice nuclei3. Here we use aircraft-aerosol time-of-flight spectrometry to directly measure the chemistry of individual cloud ice-crystal residues (obtained after evaporation of the ice), which were sampled at high altitude over Wyoming. We show that biological particles and mineral dust comprised most of the ice-crystal residues: mineral dust accounted for approx50% of the residues and biological particles for approx33%. Along with concurrent measurements of cloud ice-crystal and ice-nuclei concentrations, these observations suggest that certain biological and dust particles initiated ice formation in the sampled clouds. Finally, we use a global aerosol model to show long-range transport of desert dust, suggesting that biological particles can enhance the impact of desert dust storms on the formation of cloud ice.

  1. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA
  2. Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado 80523, USA
  3. Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming 82071, USA
  4. Marine Meteorology Division, Naval Research Laboratory, Monterey, California 93943, USA
  5. Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research, Boulder, Colorado 80305, USA
  6. Department of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA
  7. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA

Correspondence to: Paul J. DeMott2 e-mail: pdemott@lamar.colostate.edu

Correspondence to: Kimberly A. Prather1,7 e-mail: kprather@ucsd.edu

* In the version of this Letter initially published online, the final sentence of the penultimate paragraph in the main text was incorrect. This error has been corrected for all versions.