Abstract View
Modeling the Enhanced Growth by α-Pinene Ozonolysis of Wet over Dry Ammonium Sulfate Seed Particles
MICHAEL S. TAYLOR, Devon Haugh, Murray Johnston, University of Delaware
Abstract Number: 398
Working Group: Aerosol Chemistry
Abstract
Organic compounds capable of gas-particle phase condensation or partitioning are capable of contributing significantly to particle growth in the Aitken mode size range (10-100 nm). These particles often represent the largest number fractions in the air of ambient environments. Understanding the mechanisms responsible for the growth of these particles allows for cloud condensation nuclei (CCN) to be better predicted. Biogenic volatile organic compounds (BVOCs) such as α-Pinene have been shown to produce low volatility organic compounds via gas phase oxidation reactions. These products 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. Recent work by our group has shown that growth rate is affected by the phase of the seed particle. For experiments performed at 60% RH, deliquesced ammonium sulfate seed particles grow approximately 50% faster than effloresced ammonium sulfate seed particles. For growth by α-Pinene ozonolysis, effloresced particles grow according to a condensational growth model with a condensable organic vapor (COV) yield of approximately 13% (Krasnomowitz et al., AS&T 2019). This yield is somewhat larger that the yield of nonvolatile organic compounds (NVOC) reported in the literature, and one possible explanation is that semivolatile compounds react very quickly at the particle surface with NVOC. Deliquesced seed particle growth would extend these types of reactions to the particle volume as well as the surface. Deliquesced particle growth is modeled by incorporating fast accretion reactions of semi-volatile organic compounds (SVOCs) that partition into the particle phase. By varying the molar yield and volatility of SVOC along with its accretion reaction rate constant, we identify constraints on these variables that are needed in order to explain the experimentally measured particle growth. These constraints give insight into the types of reactions that contribute to enhanced growth of wet particles.