Chemical Analysis of Aerosol Nanoclusters (2-10 nm) Using a High-Flow Differential Mobility Analyzer Coupled to a Thermal Desorption Chemical Ionization Mass Spectrometer
PAULUS BAUER, Patricia M. Morris, Véronique Perraud, Barbara Finlayson-Pitts, James Smith,
University of California, Irvine Abstract Number: 473
Working Group: Instrumentation and Methods
AbstractClimate impacts of clouds are linked to cloud condensation nuclei (CCN), with the latter linked to new particle formation (NPF) and growth processes. One important phase in NPF is the transition from a fragile cluster, only consisting of several molecules, to a stable particle, with a size larger than 10 nm. The struggle for survival of this aerosol nanocluster (AN), which we define as aerosol particles in the diameter range between 2 to 10 nm, depends fundamentally on their chemical composition, e.g., acid-base ratio, organic salt formation, oxidation state and many more physicochemical properties. On one end, several measurement techniques and models exist that can probe gas-phase clusters up to ~2 nm. On the other end, there a several instruments and models that can directly assess chemical information on nanoparticles larger than 10 nm. However, examining the chemical composition of AN directly has been very challenging.
Here, we used a Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) in combination with a high-flow Differential Mobility Analyzer (DMA) to retrieve chemical information on ANs directly. The Half-Mini DMA (a high-flow DMA, J. Fernández de la Mora and J. Kozlowski, J. Aerosol Sci., 2013) has the advantage of a high resolution and a high transmission in the AN range. This is critical for collecting a high mass yield of size-selected ANs for the chemical analysis by TDCIMS. Electrospray generated salt particles were exploited as a stable and well-defined test aerosol source with a high mass output. In a further step, atmospherically relevant organic salt ANs generated via acid-base reactions in a flow tube are evaluated. This information on the highly dynamic transition from cluster to condense phase has far-reaching consequences for understanding NPF and its climatic implications.