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Factors controlling the ice nucleating abilities of α ‐pinene SOA particles
Author(s) -
Ladino L. A.,
Zhou S.,
YakobiHancock J. D.,
Aljawhary D.,
Abbatt J. P. D.
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2014jd021578
Subject(s) - ice nucleus , nucleation , aerosol , chemistry , cirrus , chemical engineering , cloud chamber , atmospheric sciences , organic chemistry , geology , physics , nuclear physics , engineering
Abstract The ice nucleation abilities of fresh, water‐soluble, internally mixed, and photochemically oxidized α ‐pinene secondary organic aerosol (SOA) particles were investigated at cirrus cloud temperatures in a continuous flow diffusion chamber. SOA sampled from a flow tube (SOA‐fresh‐FT) mimicked freshly generated particles, while the water‐soluble organic compound fraction from a FT and smog chamber (SOA‐WSOC‐FT, SOA‐WSOC‐SC) mimicked cloud‐processed particles. SOA‐fresh‐FT, SOA‐WSOC‐FT, and SOA‐WSOC‐SC particles were not highly active at nucleating ice between 233 K and 213 K, with activation onsets (i.e., 0.1% of particles forming ice) at or slightly above the theoretical homogeneous freezing line. A significant increase in the O/C of SOA‐WSOC‐SC via aqueous phase OH oxidation did not modify the ice nucleation abilities, indicating that the detailed composition of the particles is not of paramount importance to their ice nucleating abilities. Instead, precooling the SOA‐WSOC‐FT and SOA‐WSOC‐SC particles to 233 K dropped their ice nucleation onsets by up to 20% relative humidity with respect to ice, with lower temperatures likely driving the particles to be more viscous and solid‐like. However, it is possible that preactivation contributed to the reduction of the ice nucleation onsets. Particles composed of both SOA‐WSOC and ammonium sulfate (AS) were significantly less active in the deposition nucleation mode than pure, solid AS particles.