AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Online Chemical Characterization of Sub-micron Organic Particles Using Direct Analysis in Real Time Mass Spectrometry (DART-MS)
THEODORA NAH, ManNin Chan, Stephen R. Leone, Kevin Wilson, University of California, Berkeley
Abstract Number: 689 Working Group: Instrumentation and Methods
Abstract A major fraction of atmospheric aerosols is made up of organic matter. Once airborne, organic aerosols can undergo oxidation reactions (termed “aerosol aging”) with gas phase oxidants such as ozone, nitrogen oxides, and hydroxyl radicals, resulting in changes to their chemical composition. On-line aerosol mass spectrometry (AMS) is an important tool for aerosol aging studies due to its high sensitivity and ability to analyze the chemical composition of aerosol particles in real time. Although a variety of AMSs with different ionization techniques are currently being used in field and laboratory aerosol studies, they all generally involve the complete vaporization of the particle before ionization, thus yielding a mass spectrum representative of the entire particle (i.e. bulk composition). However, there may be structural and chemical inhomogeneities within the aerosol particle that may play a significant role in controlling the oxidation rate and mechanism. Chemical reactions may also occur either at the surface or in the bulk of the particle during the aerosol aging process to produce a variety of reaction products located at different regions of the particle interface.
Direct analysis in real time mass spectrometry (DART-MS) is an ambient mass spectrometric surface characterization technique that can analyze gaseous, liquid and solid polar and non-polar samples without prior sample preparation. Here, we report the real time chemical characterization of sub-micron aerosol organic particles using DART-MS. Aerosol particles are introduced between the DART ion source and the atmospheric interface inlet of a mass spectrometer where the outermost surface layers of the aerosol particles are thermally desorbed, ionized and analyzed by a mass spectrometer. Organic particles containing molecules of different chemical functionalities are detected with reduced molecular ion fragmentation, allowing for easy identification. Measurements show that the ion signal generated by DART-MS scales with total particle surface area, thus suggesting that DART-MS is able to measure the chemical composition of the particle interfacial region. DART-MS can also be used to identify products and quantify reaction rates in aerosol aging reactions. This is demonstrated by the use of DART-MS in the ozonolysis of sub-micron oleic acid aerosol particles. Together these measurements indicate that DART-MS is a promising online chemical characterization technique for aerosol studies.