NASA - National Aeronautics and Space Administration

Water can represent a substantial fraction of the mass of tropospheric non-cloud particulate matter, and can also serve as a medium for aqueous-phase reactions in such particles. Aerosol water contents are highly dependent upon aerosol hygroscopicity and ambient relative humidities (RH). In this work we evaluate a recently proposed parameterization of composition-dependent aerosol hygroscopicity that predicts the volume of liquid water associated with a unit volume of dry aerosol. The predictions over the range 10% < RH < 99% are compared with those from a rigorous thermodynamic model and shown to predict water volumes within ∼20% for the high water contents (RH > 85%) expected to have the most significant effects on tropospheric chemistry and radiation balance. Water contents for most of the compounds studied are generally represented within experimental uncertainties over the entire range of relative humidity examined, with the exception of marine-type particles dominated by sodium chloride and sodium sulfate.