Computational Simulation of Secondary Organic Aerosol Formation in Laboratory Chambers.

In the atmosphere, certain volatile organic compounds (VOCs) undergo oxidation. Some of these oxidation products then condense into the particle phase. Oxidation products that transform into the particle phase by this route are termed secondary organic aerosol (SOA). Understanding the route by which particulate matter is formed from these reactions is a key challenge in atmospheric chemistry. The principal understanding of SOA formation is derived from studies in laboratory chambers, for which determination of the amount of SOA formed requires a rigorous, quantitative understanding of chamber phenomena. With computational simulation of the processes occurring within an environmental chamber, the extrapolation to atmospheric conditions can be assessed. Moreover, computational chamber modeling of secondary organic aerosol formation will become an integral part of experimental design and data analysis. Here, we present a comprehensive review of processes involved in laboratory chamber SOA formation with a focus on the coupling between different physicochemical processes and understanding that has recently emerged.

Unified Theory of Vapor-Wall Mass Transport in Teflon-Walled Environmental Chambers.

Secondary organic aerosol (SOA) formation is studied in laboratory chambers, in which volatile organic compounds (VOCs) are oxidized to produce low-volatility compounds that condense into the aerosol phase. It has been established that such oxidized low-volatility compounds can partition into the chamber walls, which traditionally consist of Teflon film. Several studies exist in which the rates of uptake of individual vapor compounds to the chamber walls have been measured, but a unified theory capable of describing the range of experimental measurements has been lacking. Here, a two-layer model of observed short and long vapor-wall interaction time scales in Teflon-walled environmental chambers is presented and shown to be consistent with experimental data on the rate of wall deposition of more than 90 compounds. Semiempirical relationships between key parameters in the model and vapor molecular properties are derived, which can be used to predict the fate of gas-phase vapor in the chamber under dry conditions.

Overview of ICARUS-A Curated, Open Access, Online Repository for Atmospheric Simulation Chamber Data.

Atmospheric simulation chambers continue to be indispensable tools for research in the atmospheric sciences. Insights from chamber studies are integrated into atmospheric chemical transport models, which are used for science-informed policy decisions. However, a centralized data management and access infrastructure for their scientific products had not been available in the United States and many parts of the world. ICARUS (Integrated Chamber Atmospheric data Repository for Unified Science) is an open access, searchable, web-based infrastructure for storing, sharing, discovering, and utilizing atmospheric chamber data [https://icarus.ucdavis.edu]. ICARUS has two parts: a data intake portal and a search and discovery portal. Data in ICARUS are curated, uniform, interactive, indexed on popular search engines, mirrored by other repositories, version-tracked, vocabulary-controlled, and citable. ICARUS hosts both legacy data and new data in compliance with open access data mandates. Targeted data discovery is available based on key experimental parameters, including organic reactants and mixtures that are managed using the PubChem chemical database, oxidant information, nitrogen oxide (NOx) content, alkylperoxy radical (RO2) fate, seed particle information, environmental conditions, and reaction categories. A discipline-specific repository such as ICARUS with high amounts of metadata works to support the evaluation and revision of atmospheric model mechanisms, intercomparison of data and models, and the development of new model frameworks that can have more predictive power in the current and future atmosphere. The open accessibility and interactive nature of ICARUS data may also be useful for teaching, data mining, and training machine learning models.

Transferable potentials for phase equilibria-united atom description of five- and six-membered cyclic alkanes and ethers.

While the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field has generally been successful at providing parameters that are highly transferable between different molecules, the polarity and polarizability of a given functional group can be significantly perturbed in small cyclic structures, which limits the transferability of parameters obtained for linear molecules. This has motivated us to develop a version of the TraPPE-UA force field specifically for five- and six-membered cyclic alkanes and ethers. The Lennard-Jones parameters for the methylene group obtained from cyclic alkanes are transferred to the ethers for each ring size, and those for the oxygen atom are common to all compounds for a given ring size. However, the partial charges are molecule specific and parametrized using liquid-phase dielectric constants. This model yields accurate saturated liquid densities and vapor pressures, critical temperatures and densities, normal boiling points, heat capacities, and isothermal compressibilities for the following molecules: cyclopentane, tetrahydrofuran, 1,3-dioxolane, cyclohexane, oxane, 1,4-dioxane, 1,3-dioxane, and 1,3,5-trioxane. The azeotropic behavior and separation factor for the binary mixtures of 1,3-dioxolane/cyclohexane and ethanol/1,4-dioxane are qualitively reproduced.