Surface Ion Mobility and Deliquescence of NaCl Particles

EPA Grant Number: FP916335
Title: Surface Ion Mobility and Deliquescence of NaCl Particles
Investigators: King, Stephanie M.
Institution: Harvard University
EPA Project Officer: Boddie, Georgette
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $106,688
RFA: STAR Graduate Fellowships (2004) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Air Quality and Air Toxics , Fellowship - Atmospheric Sciences


Recent laboratory and field studies have shown that heterogeneous reactions in aqueous surface layers of salt particles can significantly affect tropospheric chemistry. The kinetics and mechanisms of these reactions, however, are not fully understood, in part because of the dependence of surface reactivity on water vapor. In particular, surface reactivity on NaCl powders has been shown previously to increase with increasing relative humidity. Although adsorbed water provides a mechanism for increased ion mobility and reactivity, relatively little is known about the details. The objective of this research focuses on characterizing ion mobility on NaCl particles and its dependence on relative humidity.


Time-resolved ion mobility measurements are made using a static mode of scanning polarization force microscopy (SPFM), which is a noncontact operation mode of atomic force microscopy that records the electrostatic (polarization) forces between a biased tip and sample surface. To determine ion mobility, the tip is held in place while a square wave voltage is applied at low frequency. The time evolution of the polarization force is recorded as solvable ions at the sample surface diffuse toward or away from the tip. The SPFM technique also will be used for noncontact imaging purposes to determine the deliquescence relative humidity of NaCl particles in the nanosize regime.

Supplemental Keywords:

fellowship, tropospheric chemistry, water vapor, salt particles, ion mobility, relative humidity, aqueous surface layer reactions,, Scientific Discipline, Air, Analytical Chemistry, Atmospheric Sciences, Ecology and Ecosystems, Engineering, Chemistry, & Physics, atmospheric measurement, environmental monitoring, aerosol particles, atmospheric particles, surface ion mobility, chemical composition, salt particles, troposphere