UBC Theses and Dissertations
Mixing times and phase state within secondary organic aerosol in the troposphere Maclean, Adrian Mark
Physical properties such as phase state and the mixing times of water and organic molecules within secondary organic aerosol (SOA) are critical for predicting the formation, growth, and impact of SOA in the atmosphere. In the past, it has been assumed that SOA is liquid with rapid mixing times of water and organic molecules. However, recent laboratory measurements and field studies have shown that SOA may be semi-solid or solid in the atmosphere with long mixing times for certain conditions (i.e. low temperature and low relative humidity (RH)). Despite these recent measurements, the global distributions of phase state and mixing times within SOA are not well constrained. To address this knowledge gap, this thesis presents predictions of the global distribution of phase state and mixing times within SOA for the troposphere. Global distributions of mixing times of organic molecules in SOA were predicted for the planetary boundary layer (PBL) for α-pinene SOA and sucrose-water particles based on literature viscosity data. The predicted mixing times in the PBL were fast, indicating the assumption of rapid mixing may be valid for this region of the atmosphere. The viscosities of β-caryophyllene SOA were measured as a function of RH. These viscosities were used to calculate the mixing times of organic molecules in the SOA. Mixing times increased by 3-4 orders of magnitude as the RH decreased from 50 to 0%. However, the mixing times were rapid at RH values ≥ 15%, which indicated that β-caryophyllene SOA likely mixes rapidly in the PBL. Finally, global distributions of phase states and mixing times of water and organic molecules were predicted based on room temperature viscosities for tree emission SOA and toluene SOA. Both of the SOA were predicted to be in a solid, glassy state in the upper troposphere with slow mixing times of water. Mixing times of organic molecules in SOA were predicted to be long in the middle and upper troposphere, with implications for the growth, formation. and impact of SOA in the atmosphere. The results presented here increase our knowledge of the phase state and mixing times in SOA for the troposphere.
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