Faculty of Graduate Studies
Graduate Programme in Chemistry
ORAL EXAMINATION PROSPECTUS
A Candidate for the Degree of
Doctor of Philosophy.
Title of Thesis: Laboratory study of hygroscopic properties of secondary organic aerosols produced from isoprene and terpenes
December 7, 2012 @ 1:00 pm – 1:45 pm
17 Petrie Science and Engineering Bldg.
York University
The hygroscopic properties of secondary organic aerosol formed by the OH-initiated oxidation of isoprene and several terpenes were investigated in the York University smog chamber facility. Pure organic particles were formed in nucleation experiments using either individual hydrocarbons or sequential oxidation of multiple hydrocarbons. In addition, to examine the interaction of organic and inorganic phases, monodisperse ammonium sulfate seed particles were allowed to undergo condensational growth due to partitioning of oxidation products from the gas phase. Humidograms (plots of the hygroscopic growth factor as function of relative humidity [RH]) were measured using a humidified tandem differential mobility analyzer (HTDMA).
The humidograms of pure organic particles formed in nucleation experiments do not show any deliquescence. As RH is raised from 10% to 90%, particles formed from β-pinene pick up water smoothly and particles formed from isoprene showed apparent diameter decrease up to 5% as RH is raised to 40% then showed similar behavior to the β-pinene SOA. The particles formed from ∆3carene also showed apparent diameter decrease up to 1% as RH is raised to 60% then showed similar behavior to the β-pinene SOA. Particles formed by oxidation of α‑pinene, limonene, and ∆3carene exhibit very little or no water uptake. The results were fitted with an empirical equation and give hygroscopicity parameters (± one standard error) of 0.0154 ± 0.0014 for β-pinene, 0.0042 ± 0.0005 for ∆3carene, 0.0031 ± 0.0002 for α-pinene, 0.0077 ± 0.0002 for limonene and 0.0401 ± 0.0011 for isoprene. These correspond to diameter growth factors of 1.031, 1.009, 1.006, 1.016 and 1.076 at 85% RH. Water uptake by multi-component secondary organic aerosols obeys the volume additivity rule.
Humidograms of mixed (inorganic/organic) aerosol particles show both smooth hygroscopic growth and deliquescence. These experimental results were fitted with a numerical model that accounts for water uptake by both phases and for the gradual dissolution of ammonium sulfate. The results show that volume additivity is a reasonable approximation for this system and that HTDMA results can be inverted to obtain the organic hygroscopicity parameter and the relative amounts of organic and inorganic material within the experimental uncertainity.