764 Measurements and Parameterization of Ice Nuclei Concentrations at a Forested Site in Colorado: Results from the BEACHON-RoMBAS Campaign

Wednesday, 9 January 2013
Exhibit Hall 3 (Austin Convention Center)
Yutaka Tobo, Colorado State University, Fort Collins, CO; and A. J. Prenni, P. J. DeMott, E. Garcia, C. S. McCluskey, G. Tian, S. M. Kreidenweis, J. A. Huffman, C. Pöhlker, and U. Pöschl

Atmospheric ice nuclei (IN) and cloud condensation nuclei (CCN) of biological origin (e.g., bacteria, fungal spores, pollen) emitted from forested sites may play a key role in linking biogeochemical and water cycles in the semi-arid Western U.S. In this study, we examine the concentrations and compositions of IN measured during the BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics, and Nitrogen – Rocky Mountain Biogenic Aerosol Study) campaign conducted at the Manitou Forest Observatory in July-August 2011. IN number concentrations active under mixed-phase cloud conditions were obtained as a function of temperature using a continuous flow diffusion ice chamber (CFDC). We also demonstrate the first successful use of an aerosol concentrator to observe very low IN number concentrations at temperatures warmer than -20°C. Associated measurements of aerosol number-size distributions and fluorescent biological particle concentrations are used to demonstrate the sometimes strong role of biological IN emissions in such forested environments. We also use these data to develop a new parameterization to quantify IN number concentrations, in dependence on aerosol number concentrations and temperatures, at the semi-arid Western U.S. forested location. Finally, we investigate meteorological factors affecting the variation of the concentrations and compositions of IN.
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