HR: 11:50h
AN: A42B-07    [Abstracts]
TI: Parameterizations for Surface Tension Effect on Equilibrium Radius of a Hygroscopic Aerosol Particle
AU: * Lewis, E R
EM: elewis@bnl.gov
AF: Environmental Chemistry Division, Atmospheric Sciences Department, Brookhaven National Laboratory, Building 815E, Upton, NY 11933 United States
AB: The equilibrium size of an atmospheric aerosol particle is a key property, affecting its light-scattering behavior, dry deposition, and the like. For a hygroscopic particle of given composition this size is determined by the particle dry mass (which can alternatively be expressed as the equivalent dry radius r_d) and the relative humidity RH. Surface tension also affects this equilibrium size (Kelvin effect) and thus the associated properties. To first order, the decrease in equilibrium particle radius at a given fractional relative humidity h (≡RH/100) resulting from the Kelvin effect depends only on relative humidity and is independent of r_d. This radius decrease is approximately Δr_d~-c·h/(1-h), where c is a constant that depends on the solute and varies only slightly with temperature. For an aqueous ammonium sulfate particle at typical temperatures c~0.25 nm; at 85% RH Δr is approximately -1.4 nm, independent of radius. This expression also yields a relationship between RH and r_d (or radius at a given RH) describing when neglect of the Kelvin effect results in a specified error in calculated particle radius. For example, for RH<95% neglect of the Kelvin effect results in less than a 5% overestimation of radius for an ammonium sulfate particle with r_d>30 nm; for RH<99% this 5% criterion requires r_d>150 nm. An expression for the equilibrium radius of an aerosol particle as a function of RH that includes the Kelvin effect and is accurate over the range of relative humidities up to and including 100% is also presented.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005