10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Size and Composition Dependent Seed Particle Growth by α-Pinene Ozonolysis
JUSTIN KRASNOMOWITZ, Michael J. Apsokardu, Chris Stangl, Shanhu Lee, Murray Johnston, University of Delaware
Abstract Number: 501 Working Group: Aerosol Chemistry
Abstract Biogenic secondary organic aerosol (BSOA) is a key contributor to particle formation and growth in the atmosphere. In principle, growth mechanisms and rates can be both seed particle size and composition dependent. This work utilizes a flow tube reactor with a 4 minute residence time to study these dependencies. Experiments performed to date were done by exposing monodispersed ammonium sulfate seed particles to varying amounts of highly oxidized molecules (HOMs) produced by α-pinene ozonolysis at low relative humidity (10%) and room temperature. Experiments were performed by first introducing monodispersed ammonium sulfate seeds (40, 60 or 80 nm in diameter) into the flow tube along with a low ozone mixing ratio. Next, α-pinene (14 ppbv) was added to begin HOM production. The ozone mixing ratio was then systematically increased from 30 to 300 ppbv during the course of the experiment to increase the average HOM mixing ratio, which caused an increasing amount of seed particle growth. Particles exiting the flow tube for each increment of ozone mixing ratio were characterized with SMPS (size distribution), NAMS (elemental composition) and ESI-HRMS (molecular composition). To a first approximation, particle growth rates were found to be independent of seed particle size and increased linearly with increasing ozone mixing ratio. The measured growth rates were consistent with a kinetic growth model based on the average HOM mixing ratio in the flow tube for each ozone increment. If anything, the kinetic model slightly underestimated the measured growth rate, suggesting that some multiphase chemistry may have occurred in addition to HOM condensation. Current and planned work will explore the effects of seed particle phase (dry vs. wet ammonium sulfate, organic vs. inorganic seed composition) as well as extend these measurements to smaller seed particle sizes.