AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Nanoparticle Growth in a Tandem Flow Tube Apparatus (TANGENT)
JUSTIN KRASNOMOWITZ, Chris Stangl, Lee Tiszenkel, Qi Ouyang, Shanhu Lee, Murray Johnston, University of Delaware
Abstract Number: 770 Working Group: Aerosol Chemistry
Abstract This work uses a Tandem Aerosol Nucleation and Growth ENvironment Tube (TANGENT) apparatus to study particle growth. Freshly nucleated particles from a nucleation tube (FT-1) are sent into a growth tube (FT-2) with longer resonance time in order to study growth under varying conditions. The goal of these experiments is to elucidate mechanisms of particle growth by measuring size distributions and chemical composition of particles exiting FT-2. In our initial experiments, FT-2 is conditioned with constant mixing ratios of a-pinene (14 ppbv), sulfur dioxide (400 ppbv) and ammonia (between 160 pptv and 2 ppbv depending on the experiment), while ozone is increased in a stepwise manner over time from 10-400 ppbv. Each increment of the ozone mixing-ratio creates additional low volatility species that lead to particle growth. Elemental composition of individual nanoparticles is done using a modified version of the Nano Aerosol Mass Spectrometer (NAMS) that utilizes an aerodynamic lens assembly to focus particles in the size range of 40-100 nm. These focused particles are then intercepted by a pulsed laser and undergo Laser Induced Plasma Ionization (LIPI) to created positive multiply charged elemental ions that can then be detected using a time-of-flight mass analyzer. Information provided from NAMS gives measure of the relative importance of sulfuric acid and secondary organics in the particle growth observed. Bases such as ammonia are also present in these experiments. Analysis by NAMS allows both the degree of sulfuric acid neutralization and the relative contributions of sulfuric acid and organics to be determined. Size distributions measured by SMPS throughout the experiments aid in the determination of diameter growth rates and how they depend on the amount of a-pinene reacted.