Atmospheric aerosol play a critical role climate because they scatter and absorb a portion of incoming solar radiation, can modify the optical properties, extent, and lifetime of clouds, and affect visibility. Their importance on climate is a strong function of their ability or inability to take up water in a humid atmosphere since particles that take up more water are larger and scatter and absorb more incoming radiation. The organic fraction of atmospheric aerosol is of particular importance as it may enhance or inhibit the ability of aerosol particles to absorb water and may also affect their ability to form cloud droplets. The solubility of the organic fraction can affect the hygroscopic growth and deliquescence behavior of species such as sea salt or ammonium sulfate, resulting in large uncertainties in the scattering coefficient since organic components will affect both particle refractive index and size. Organic functional group composition and solubility can be used to predict thermodynamic equilibrium based on organic composition, and the subsequently derived hygroscopic growth factors, combined with a Mie scattering model, can be used to predict scattering and absorption coefficients. Fourier transform infrared transmission spectroscopy (FTIR) of aerosol collected on stretched Teflon filters taken during the ICARTT (International Consortium for Atmospheric Research on Transport and Transformation) study of summer 2004 on Appledore Island, Maine can identify sulfate, ammonium, silicate, and organic functional groups. A simultaneous four-solvent rinsing procedure can separate these functional groups into fractions of increasing solubility. Knowledge of the solubility and optical properties and functional groups present allows model organic compounds to be chosen for further modeling of hygroscopic growth and scattering.