AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Global Distribution of Particle Phase State in Atmospheric Secondary Organic Aerosols
MANABU SHIRAIWA, Ying Li, Alexandra Tsimpidi, Vlassis Karydis, Thomas Berkemeier, Spyros Pandis, Jos Lelieveld, Thomas Koop, Ulrich Pöschl, University of Calfornia, Irvine
Abstract Number: 228 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA) are ubiquitous in the atmosphere. The phase state of SOA is important for their effects on climate and air quality, but its global distribution is poorly characterized. Our analysis of SOA phase state builds on the molecular corridor approach, which is a two-dimensional framework of volatility and molar mass of SOA components constrained by boundary lines of low and high molecular O:C ratio. We developed a method to estimate glass transition temperatures based on the molar mass and molecular O:C ratio of SOA components, and we used the global chemistry climate model EMAC with the organic aerosol module ORACLE to predict the phase state of atmospheric SOA. For the planetary boundary layer, global simulations indicate that SOA are mostly liquid in tropical and polar air with high relative humidity, semi-solid in the mid-latitudes, and solid over dry lands. We find that in the middle and upper troposphere SOA should be mostly in a glassy solid phase state. Thus, slow diffusion of water, oxidants, and organic molecules could kinetically limit gas-particle interactions of SOA in the free and upper troposphere, promote ice nucleation and facilitate long-range transport of reactive and toxic organic pollutants embedded in SOA.