AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Growth Mechanisms of Size-Selected Ammonium Sulfate Seed Particles by Monoterpene Ozonolysis
JUSTIN KRASNOMOWITZ, Michael J. Apsokardu, Devon Haugh, Michael Taylor, Murray Johnston, University of Delaware
Abstract Number: 136 Working Group: Aerosol Chemistry
Abstract Aitken mode particles (10-100 nm in diameter) often represent the largest number fraction of particles found in the ambient environment. Understanding the processes contributing to the growth of these particles is paramount to better predict formation of cloud condensation nuclei (CCN). Low volatility organic compounds formed through gas phase oxidation of biogenic volatile organic compounds (BVOCs) such as α-pinene and limonene with low volatility have been shown to be the major source of particle growth in this size range. We have studied particle growth as a function of seed particle size and gas-phase reactant mixing ratios for α-pinene ozonolysis using a flow tube reactor and kinetic modeling. Results with dry seed particles suggest a condensational growth mechanism with a yield of condensable organic molecules of 13% from the ozonolysis reaction (Krasnomowitz et al., AS&T 2019). This yield is somewhat higher than the yield of highly oxidized molecules (HOMs) in the gas phase determined by chemical ionization. There are several reasons why the yields of condensable molecules obtained from gas- and particle- phase measurements can be different. Currently, we are investigating the effects of relative humidity on the same system. Preliminary results show that under equivalent experimental conditions including relative humidity, deliquesced ammonium sulfate particles grow much faster than dry seed particles. This effect is observed exclusively for particles below about 50 nm in diameter. Molecular composition measurements of the grown particles show that deliquesced particles contain a larger fraction of oligomers than dry particles, suggesting that particle phase chemistry contributes to the enhanced growth. Kinetic modeling to explain the particle-phase chemistry will be presented as well as particle size measurements by SMPS, molecular composition by HR-ESI-MS and single particle elemental composition by NAMS. Additional experiments focused on growth by limonene ozonolysis are underway and also will be discussed.