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In situ detection of biological particles in cloud ice-crystals

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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 50% of the residues and biological particles for 33%. 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.

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Figure 1: Ice-cloud microphysical properties.
Figure 2: Chemical composition of ice-crystal residues.
Figure 3: Representative chemical composition of biological and dust particles.

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  • 20 May 2009

    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.


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NSF and NCAR are acknowledged for financial support of ICE-L, as well as of A.J.H. K.A. Prather and K.A. Pratt acknowledge NSF for support of ICE-L (ATM-0650659), A-ATOFMS development (ATM-0321362) and a graduate research fellowship for K.A. Pratt. P.J.D. and A.J.P., J.R.F. and Z.W., and C.H.T. acknowledges support from NSF (ATM-0611936, ATM-0645644, and ATM-0612605, respectively). The Office of Naval Research (PE-0602435N) is acknowledged for financial support for D.L.W. Cloud probe data were provided by NCAR/EOL under sponsorship of NSF ( S. Haimov (Univ. Wyoming) processed the radar data. T. Eidhammer (NCAR) assisted with CFDC data analysis. C. Gaston (UCSD) assisted with the P. syringae A-ATOFMS data collection; J. Dixon and R. Dowen III (UCSD) provided the P. syringae cultures. S. Kreidenweis (Colorado State Univ.) is thanked for discussions. The authors acknowledge the NOAA ARL for the provision of HYSPLIT (

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Authors and Affiliations



K.A. Pratt carried out the A-ATOFMS measurements, data analysis and wrote the manuscript. P.J.D. was responsible for the CFDC measurements and contributed to writing. J.R.F. and Z.W. provided lidar and radar data. D.L.W. carried out the surface and long-range transport modelling. A.J.H. processed the cloud probe data. C.H.T. coordinated and ran the CVI during flight. A.J.P. and K.A. Prather are extra Principal Investigators of this work. All authors reviewed and commented on the paper.

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Correspondence to Paul J. DeMott or Kimberly A. Prather.

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Pratt, K., DeMott, P., French, J. et al. In situ detection of biological particles in cloud ice-crystals. Nature Geosci 2, 398–401 (2009).

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