AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Kinetic Model for Nanoparticle Growth Relevant to New Particle Formation
MICHAEL APSOKARDU, Douglas Ridge, Murray Johnston, University of Delaware
Abstract Number: 651 Working Group: Aerosol Chemistry
Abstract Ambient measurements of the chemical composition of nanoparticles during new particle formation (NPF) show that the three main components involved in particle growth are sulfate, base (usually ammonia), and carbonaceous matter. Measurements with the nano aerosol mass spectrometer (NAMS) show that the sulfate mass fraction in the particle is adequately explained by condensation of gas phase sulfuric acid, and the mass fraction of base closely follows changes in the sulfate mass fraction. The mass fraction of carbonaceous matter varies with location and time of year, and the factors influencing its contribution to particle growth are poorly understood.
We have developed a kinetic model that iteratively calculates the volume and composition of a particle as a function of time when exposed to gas phase species. The model takes into account sulfuric acid condensation, ammonia neutralization of condensed sulfuric acid, and the condensation and/or partitioning of organic molecules including the effect of surface curvature (i.e. Kelvin effect) on these processes. The model is capable of simultaneously including a variety of organic molecular species having different physical properties (e.g. saturation vapor pressure) and gas phase concentrations. The model is being used to explore how organic molecular properties influence growth in different particle size ranges, and in particular the molecular properties required to “turn on” particle growth by carbonaceous matter in the 2-5 nm size range. Initial studies with this model will be presented.