| Many processes influencing organic aerosols involve phase transformations. These include variation of vapor pressures with temperature, which is governed by the enthalpies of vaporization of aerosol compounds, adsorption to surfaces, often in competition with absorption into an aerosol condensed phase, and heterogeneous uptake of oxidants from the gas phase to a condensed organic phase. A confounding issue is that the relevant vapor pressures are extremely low, and there are very few data to constrain important properties. This thesis explores several facets of this theme.;Next, I address the adsorption of very low vapor pressure organics onto Teflon surfaces, which is both a potential source of error in smog-chamber experiments conducted in Teflon enclosures as well as an example of competition between surface adsorption and dissolution in a bulk condensed phase (organic aerosol). Using a Langmuir model, I find that the extent of wall adsorption is heavily dependent on the difference between DeltaHcondensation and DeltaHadsorption.;Finally, I consider the reactive uptake of ozone to alkenes condensed on an infra-red transparent window at very low temperatures, developing a novel method to employ temperature programmed reaction spectroscopy (TPRS) using real-time fourier transform infrared spectroscopy to probe the kinetics of ephemeral primary ozonides. These short lived intermediates are the first species in a complex reaction sequence initiated when ozone reacts with an alkene. Their loss pathways control the reaction mechanism, but because they are so short lived, experimental chemical studies are extremely limited. Computations with Density Functional Theory, scaled with the TPRS barrier height reveal OH yields that agree with results from previous researchers. Minimal entropic differences indicate that POZ decomposition branching is controlled purely by enthalpic variations.;First, I address the temperature dependence of saturation concentrations (C*, vapor pressures on a mass basis) by surveying and analyzing literature data on enthalpies of vaporization (DeltaHVAP) to obtain a relationship between the enthalpy of vaporization of an organic compound and its volatility. A thermodenuder model using our Delta HVAP values agrees well with observed thermal behavior. The correlation between C* and DeltaH VAP constrains a free parameter in thermodenuder data analysis. |
