AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
DMA-MS based Examination of Organic Vapor Uptake by Nanometer Scale Clusters
CHENXI LI, Christopher Hogan Jr., University of Minnesota
Abstract Number: 26 Working Group: Aerosol Physics
Abstract Condensational growth of sub 2 nm particles in a supersaturated environment (CPCs) has been found to be dependent on particle material, polarity and vapor species. Vapor uptake is the first step of such processes and therefore influences subsequent particle growth. However, uptake is not well understood in the nanometer size range. In this study we utilized a differential mobility analyzer coupled with a time-of-flight mass spectrometer to examine the uptake of organic vapor molecules by nanometer scale sodium chloride cluster ions ((NaCl)x(Na+)z and (NaCl)x(Cl-)z). Chemically related (1-butanol, ethanol) and distinct (methyl ethyl ketone (MEK), toluene) vapor species were selected to observe their influence on the inverse mobility of the cluster ions. For each vapor, a similar pressure range (from 0 to several hundred Pascals) was tested. Butanol uptake results in shifts of inverse mobility of both positive and negative cluster ions by more than a factor of two. Ethanol uptake led to inverse mobility shifts that are qualitatively similar to that of butanol, though smaller at the same vapor pressure. MEK uptake led to shifts for positively charged cluster ions upwards of a factor of 1.5, while MEK exposure led to negative ion inverse mobility shifts less than a factor of 1.3. Toluene, lacking strongly polar functional groups in its molecular structure, led to shifts in inverse mobility below a factor of 1.2. In total, relative inverse mobility shifts were found to be strongly influenced by vapor molecular structure and cluster ion charge polarity. Kelvin effect based models are found inadequate to explain the observed mobility shifts, and we instead used a site-specific, Langmuir type model to fit the vapor uptake behavior by the cluster ions.