Wednesday, 9 January 2013
Exhibit Hall 3 (Austin Convention Center)
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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