Collaborative Research: Hygroscopic Properties of Aerosol Organics

Affiliation(s)PIProject periodFunded by
DAS Hallar, Anna Gannet 09/01/2009 - 08/31/2012 National Science Foundation

Project Description

OBJECTIVES AND METHODS Objectives 1) Determine the contribution of WSOC to hygroscopic growth under sub- and supersaturated conditions. 2) Measure the molecular composition and physical properties of WSOC. 3) Parameterize measured hygroscopic growth of water-soluble ambient aerosol using ?E-Kohler theory and represent the measurements using thermodynamic equilibrium models to determine: a) how well hygroscopic growth and CCN activity of mixed inorganic and organic aerosols can be represented; and b) to what extent structure-based models of the thermodynamics of water uptake can be constrained by the measurements of WSOC composition and compound structure. 4) Add the representations of WSOC properties developed in (3) to the web-based Extended Aerosol Inorganics Model (E-AIM) of Clegg and Wexler (E-AIM, aim.php) so that they can be used by other researchers and students. The objectives will be met by conducting the following activities: 1: Collect aerosol samples at Storm Peak Laboratory (SPL) and measure total organic carbon (OC) and WSOC concentrations in the laboratory. Separate WSOC from inorganic ions using solid phase absorbents. Conduct hygroscopic growth and CCN activity experiments on aerosols generated from total water-soluble material (WSM) and isolated WSOC. Hygroscopic growth experiments will be conducted in the laboratory using an HTDMA for 10<RH<95% and with a CCN spectrometer for supersaturations down to 0.07%. 2: Determine organic speciation of water-soluble ambient aerosols collected at SPL. Measure detailed organic composition, including empirical formula assignments and structure determination with functional groups (e.g., carboxylic, phenolic, hydroxyl, carbonyl, arylic, aliphatic, sulfate, nitrate) of integrated samples of WSOC in the laboratory. Measure the surface tension of water solutions of WSM and isolated WSOC. 3: First, represent the WSOC hygroscopic growth and CCN activity measured in the laboratory using ?E- Kohler theory of Kreidenweis and co-workers (Petters and Kreidenweis, 2007), and compare the results with those of other studies. Second, the detailed information on organic chemical functionality will be used to develop structure-based models of the equilibrium thermodynamics of the WSOC components using UNIFAC (UNIversal Functional Activity Coefficient method) (Fredenslund et al., 1975) and COSMO-SAC (COnductor-like Screening MOdel for real solvent-Segment Activity Coefficients) (Lin and Sandler, 2002; Lin et al., 2004). These will be tested in calculations of water uptake and activation for chemical systems containing inorganic and organic components, and their sensitivity to the remaining uncertainties in WSOC chemical composition will be evaluated. 4: Add the high molecular weight WSOC organic components identified in this project to the E-AIM library of organics. E-AIM users will be able to select these and other compounds from the library, in addition to the inorganic systems already built into the model, for inclusion in their aerosol thermodynamic and cloud activation calculations. These can be carried out interactively on the web site or, if needed, using a file-based version of the model.

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