EAGER: Marine Biogenic Aerosols as Cloud Condensation Nuclei over the Pacific Ocean

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This EAGER project takes advantage of a unique opportunity to piggyback important measurements of marine boundary layer atmospheric constituents on an already-organized research cruise. The primary objective of this project is to identify and quantify biogenic contributions to cloud condensation nuclei (CCN) populations over the Pacific Ocean. To meet this primary objective, observations will be conducted during a research cruise on the RV Tom Thompson. Techniques from atmospheric sciences and biological oceanography will be combined in a novel interdisciplinary approach to observe marine biogenic material near the sea surface waters and in the air above the surface, and monitor the general physical and chemical properties of the near-surface aerosol. The work will be accomplished through the following steps: CCN activity of ambient aerosols: At all points along the cruise track, direct in situ measurements will be made of the concentration of ambient aerosols and the fraction active as CCN. CCN measurements of aerosols generated from sea water: Seawater samples will be collected from the surface waters. The seawater will separated into several samples containing different size fractions of biogenic material. These will include bacteria (0.2 micrometer diameter 2.0 micrometer), viruses (0.02 micrometer diameter 0.2 micrometer), high molecular weight dissolved organic matter ( more 1000 atomic mass units, but with diameter 0.02 micrometer), and low molecular weight organic molecules ( 1000 atomic mass units). Onboard the ship, the sea water samples containing each of these fractions will be re-aerosolized individually and the aerosol sent through a CCN monitoring instrument to determine its activity. Thus the size fraction of marine biogenic material responsible for CCN activity will be assessed. Supporting measurements: Satellite images and in situ water measurements will be used to assess biological activity in the regions from which samples are obtained. Additional in situ atmospheric observations of the concentration and sizes of ambient aerosols will be collected, along with airborne particulate samples collected on filters for bulk chemical and biological analysis. Analysis of the collected aerosols, aerosol from fractionated seawater samples, and seawater samples will be used to identify key marine and non-marine compounds and to determine how their concentrations in the sea may be related to their concentrations in aerosol above the sea. To help differentiate between marine and non-marine sources of materials found in the aerosol, meteorological observations as well as meteorological back trajectory analyses will be employed.Broader Impacts: This research will identify the key components linking biological production in the ocean to marine aerosols and cloud nucleation processes. Biogenic marine aerosol may profoundly affect the spatial and temporal distribution of clouds and subsequent precipitation patterns. Limitations in knowledge concerning the radiative effects of aerosols and the clouds which form on them represent a major uncertainty in understanding the earth's radiative budget and climate change. This interdisciplinary project includes investigators from two Departments and will form the basis for continued collaboration between faculty in the Departments of Oceanography and Atmospheric Sciences. The project will provide ship-based training for a post-doctoral researcher in the Department of Atmospheric Sciences. A graduate student from the Department of Oceanography will be supported as well to participate in the research. Results will be disseminated at scientific meetings and in the peer-reviewed literature