Atmospheric Chemistry Program Seminar
Fates of Oxygenated Organics in Outdoor and Indoor Environments, Chemical Reactions and Partitioning by Lucas Algrim, ANYL Student, CU Boulder, Ziemann Group
"Volatile organics are emitted in indoor and outdoor environments where they are then subject to various losses such as deposition, or chemical transformation. In outdoor environments chemical reaction dominates, which will create products of higher volatility that stay in the gas phase or products of lower volatility that can partition to the particle phase to generate SOA. In indoor environments, which have lower concentrations of oxidants and greater surface area, deposition to and partitioning with surfaces are of increased relevance.
In the first section of this thesis, Chapters 2-4, we probe SOA forming potential of functionalized precursors. SOA yields were measured for OH radical-initiated reactions of the 2-6 dodecanone, 1-5 decanol, and 1-5 decyl nitrate positional isomers and also n-decane, n-dodecane and n-tetradecane in the presence of NOx. Yields decreased in the order n-tetradecane > dodecanone isomer average > n-dodecane, and the functionalized isomer yields decreased as the functional group moved toward the center of the molecule, with 6-dodecanone being an exception. Trends in the yields can be explained by the effect of carbon number and functional group presence and position on product vapor pressures, and by the isomer-specific effects of the functional group on branching ratios for the various alkoxy radical isomerizations, decompositions, and reactions with O2. Analysis of particle composition indicates within each isomer series, the SOA products are similar for each isomer. The results demonstrate that the presence of a functional group on a precursor alters gas and particle phase chemistry and provide new insights into the potential effects of molecular structure on the products of the atmospheric oxidation of volatile organic compounds.
In the second part of the thesis, Chapter 5, we parameterize the partitioning of VOCs to indoor paint films. Diffusion coefficients, Dc, of organics in a commercial paint were measured and found to correlate well with compound vapor pressures, C*. Experiments were performed by monitoring VOC partitioning in a painted flow tube. A model was constructed to replicate the VOC time traces observed during passivation and depassivation as a function of two parameters, Cw, and Dc. Modeled and measured Dc values agreed reasonably well, and modeled Cw values aligned with those calculated from the mass of paint in the flow tube. The relationship between Dc and C*, and the determination of Cw from mass of paint allow for modeling of VOC partitioning to paint films in indoor environments that indicate >50% of the VOCs with C* of 108 μg m-3 or less that contact a paint film of typical thickness, will fully permeate the paint film, regardless of emission duration."