Ice Formation by Laboratory Generated Amorphous SOA Coated Soot Particles
Authors
Timothy B Onasch — Aerodyne Research, Inc.
Paul Davidovits — Boston College
Douglas R Worsnop — Aerodyne Research, Inc.
Andrew Thomas Lambe — Aerodyne Research, Inc.
Daniel Knopf — Stony Brook University
Paola Massoli — Aerodyne Research, Inc.
Joseph Charnawskas — Stony Brook University
Thomas Berkemeier — Max Planck Institute for Chemistry
Manabu Shiraiwa — Max Planck Institute for Chemistry
Category
Secondary Organic Aerosol
Description
Secondary organic aerosol (SOA) particles are ubiquitous in the atmosphere and may play an important role in cloud glaciation processes. We investigate laboratory generated SOA particle systems from the reaction of volatile organic compound precursors with hydroxyl radicals for their initial water uptake and ice formation propensity as a function of temperature, T, relative humidity with respect to water, RH, and RH with respect to ice. This includes α-pinene and naphthalene SOA coated soot particles with varying O/C ratios and coating thicknesses. Micro-spectroscopic chemical imaging using scanning transmission X‐ray microscopy with near edge X‐ray absorption fine structure spectroscopy (STXM/NEXAFS) is used to characterize the mixing state of the SOA-soot particles generated in the Boston College potential aerosol mass (PAM) flow reactor in relation to their ice nucleation behavior. In addition, we employ a numerical aerosol diffusion model based on the kinetic multi-layer model for gas–particle interactions in aerosols and clouds (KM-GAP), which explicitly treats mass transport of water molecules in the gas and particle phases. This allows estimation of the partial and full deliquescence RH for amorphous α-pinene and naphthalene SOA coated soot particles with varying O/C ratios and coating thicknesses as a function of T and RH. Preliminary results indicate that naphthalene SOA coated soot particles exhibit similar ice nucleation onsets as naphthalene SOA particles. These laboratory-based investigations will improve our understanding of the effect of the organic particle phase state on prediction of atmospheric ice nucleation.
