AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Hygroscopic Growth of Mixed Aerosol Particles Composed of Inorganic and Organic Compounds of Atmospheric Relevance
IDANIA ZAMORA, Mark Jacobson, Stanford University
Abstract Number: 740 Working Group: Aerosol Chemistry
Abstract The hygroscopic growth of atmospheric particles has far-reaching effects on atmospheric chemistry and Earth's climate. Water-soluble organic carbon (WSOC) constitutes a significant fraction of the dry submicron mass of atmospheric aerosols, thus affecting their water uptake properties. Although the WSOC fraction is comprised of a large amount of compounds, a set of model substances can be used to describe its behavior. For this study, mixtures of Nordic Reference fulvic acid (NRFA), with various combinations of inorganic salts (sodium chloride and ammonium sulfate) and other representative organic compounds (levoglucosan and succinic acid), were studied. We measured the equilibrium water vapor pressure over bulk solutions of these mixtures as a function of temperature and concentration. Hygroscopic growth as a function of water activity at 25$^oC was calculated from these data for particles of equivalent composition. The water vapor pressure as a function of temperature curve for a NRFA/inorganic salt solution was governed by the inorganic compound even for a solution saturated in both NRFA and salt. This effect was observed for the curves of NRFA mixtures with each salt, which mimicked the curves for the saturated pure salt solutions. While no hygroscopic growth was observed for a 2:1 NRFA/levoglucosan mass ratio mixture, a solution with a 1:3 NRFA/levoglucosan mass ratio presented a hygroscopic growth factor (G$_f) of 1.51 and 2.39 at a relative humidity (RH) of 95% and 98%, respectively. Two of the mixtures were based on chemical composition data for different aerosol types. While the solution representing organic aerosols (40% NRFA / 40% succinic acid / 20% levoglucosan) did not exhibit water uptake up to 99% RH, the solution representing biomass burning aerosols (25% NRFA / 27% succinic acid / 18% levoglucosan / 30% ammonium sulfate) had a G$_f of 1.83 and 3.33 at RH = 95% and 98%, respectively.