Ions from Solid Particle Surfaces: Probing Particle Surface Composition with Matrix-Assisted Ionization in Vacuum - Mass Spectrometry

LISA WINGEN, Yiming Qin, Elizabeth Wingen, Cheyenne Begay, Véronique Perraud, Styliani Consta, Michelia Dam, James Smith, Barbara Finlayson-Pitts, University of California, Irvine

     Abstract Number: 95
     Working Group: Aerosol Chemistry

Abstract
Atmospheric particles impact health, visibility, and climate. Many of the processes that control these impacts begin at the air-particle interface, such as particle growth, water uptake, and heterogeneous chemistry. Analytical methods are needed to examine particle surface composition at a molecular level to improve our fundamental understanding of these processes. A surface-sensitive mass spectrometry technique is presented that provides molecular identification within solid particle surface layers in real time, but does not require the use of an external ionization source. Matrix Assisted Ionization in Vacuum - Mass Spectrometry (MAIV-MS) utilizes atomized and dried dicarboxylic acid particles from which surface ions are expelled as the particles evaporate in the inlet of a mass spectrometer. The surface sensitivity of MAIV-MS is demonstrated through particle coating experiments in which thin surface coatings of different compounds are detected, while signal from the core is relatively low in comparison. Peak intensity is shown to scale with the surface area of particles rather than their number or volume. Application of MAIV-MS to heterogeneous hydroxyl radical oxidation of solid glutaric and adipic acid particles led to the detection of organic peroxides at unexpectedly high signal intensities relative to the stable alcohol and ketone products. The online MAIV-MS particle method involves soft ionization, permitting more sensitive detection of peroxides that readily decompose using common offline analysis techniques. Insight into the ion generation mechanism from solid particles based on theoretical studies and additional applications of MAIV-MS will be discussed.