Abstract View
Modeling and Interpreting the Growth of Deliquesced Ammonium Sulfate Seed Particles by α-Pinene Ozonolysis
MICHAEL S. TAYLOR, Michael J. Apsokardu, Devon Haugh, Murray Johnston, University of Delaware
Abstract Number: 235
Working Group: Aerosol Chemistry
Abstract
Particles in the Aitken mode size range (10-100 nm in diameter) often contribute the largest number fraction of particles to the air in ambient environments. Understanding the mechanisms responsible for the growth of these particles allows for cloud condensation nuclei (CCN) concentrations to be better predicted. Gas phase oxidation reactions of biogenic volatile organic compounds (BVOCs) such as α-pinene have been shown to produce low volatility organic compounds that contribute significantly to particle growth in this size range. By studying particle growth as a function of seed particle size and gas-phase mixing ratios for monoterpene ozonolysis reactions, a kinetic model can be used to explain the experimental growth. In recent work by our group, seed particle phase has been shown to affect the growth rate. For experiments performed at 60% RH, deliquesced ammonium sulfate seed particles grow about 20% faster than effloresced ammonium sulfate seed particles. For growth by α-pinene ozonolysis, the effloresced particles grow according to a condensational growth model with a highly oxidized molecule (HOM) yield of about 13% (Krasnomowitz et al., AS&T 2019). Deliquesced seed particle growth is modeled using a variety of particle phase processes that have been suggested in the literature. Our initial modeling has focused on the possibility of accretion reaction in the particle phase. By varying the volatilities and molar yields of the reactants, along with the reaction rate constant, we find that several permutations of these variables are able to explain the experimentally measured growth, but all rely on a very fast rate constant, even for highly reactive hydroperoxide functionalities. The insight gained from particle growth measurement and modeling be discussed.