Laboratory data supporting "Quantitative constraints on autoxidation and dimer formation from direct probing of monoterpene-derived peroxy radical chemistry" by Zhao, Thornton, and Pye. Abstract: Organic peroxy radicals (RO2) are key intermediates in the atmospheric degradation of organic matter and fuel combustion, but to date, few direct studies of specific RO2 in complex reaction systems exist, leading to large gaps in our understanding of their fate. We show, using direct, speciated measurements of a suite of RO2 and gas-phase dimers from O3-initiated oxidation of α-pinene that ~150 gaseous dimers (C16-20H24-34O4-13) are primarily formed through RO2 cross-reactions, with a typical rate constant of 0.75-2×10-12 cm3 molecule-1 s-1 and a lower-limit dimer formation branching ratio of 4%. These findings imply a gaseous dimer yield that varies strongly with nitric oxide (NO) concentrations, of at least 0.2-2.5% by mole (0.5-6.6% by mass) for conditions typical of forested regions with low to moderate anthropogenic influence (i.e., ≤ 50 ppt NO). Given their very low volatility, the gaseous C16-20 dimers provide a potentially important organic medium for initial particle formation, and alone can explain 5-60% of α-pinene secondary organic aerosol mass yields measured at atmospherically relevant particle mass loadings. The responses of RO2, dimers, and highly-oxygenated multifunctional compounds (HOM) to reacted α-pinene concentration and NO imply that an average ~20% of primary α-pinene RO2 from OH reaction and 10% from ozonolysis autoxidize at 3-10 s-1 and ≥ 1 s-1, respectively, confirming both oxidation pathways produce HOM efficiently, even at higher NO concentrations typical of urban areas. Thus, gas-phase dimer formation and RO2 autoxdiation are ubiquitous sources of low-volatility organic compounds capable of contributing significantly to atmospheric new particle formation and growth. This dataset is associated with the following publication: Zhao, Y., J. Thornton, and H. Pye. Quantitative constraints on autoxidation and dimer formation from direct probing of monoterpene-derived peroxy radical chemistry. PNAS (PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES). National Academy of Sciences, WASHINGTON, DC, USA, 115(48): 12142-12147, (2018).

Recently, we identified seven novel hydroxy-carboxylic acids resulting from gas-phase reactions of isoprene in the presence of nitrogen oxides (NOx), ozone (O3), and/or hydroxyl radicals (OH). In the present study, we provide evidence that hydroxy-carboxylic acids, namely methyltartaric acids (MTA) are: (1) reliable isoprene tracers, (2) likely produced via rapid peroxy radical hydrogen atom(H) shift reactions (autoxidation mechanism) and analogous alkoxy radical H shifts in low and high NOx environments respectively and (3) representative of aged ambient aerosol in the low NOx regime. Firstly, MTA are reliable tracers of isoprene aerosol because they have been identified in numerous chamber experiments involving isoprene conducted under a wide range of conditions and are absent in the oxidation of mono- and sesquiterpenes. They are also present in numerous samples of ambient aerosol collected during the past 20 years at several locations in the U.S. and Europe. Furthermore, MTA concentrations measured during a year-long field study in Research Triangle Park (RTP), NC in 2003 show a seasonal trend consistent with isoprene emissions and photochemical activity. Secondly, an analysis of chemical ionization mass spectrometer (CIMS) data of several chamber experiments in low and high NOx environments show that highly oxidized molecules (HOMs) derived from isoprene that lead to MTAs may be produced rapidly and considered as early generation isoprene oxidation products in the gas phase. Density functional theory calculations show that rapid intramolecular H shifts involving peroxy and alkoxy radicals possess low barriers for methyl-hydroxy-butenals (MHBs) that may represent precursors for MTA. From these results, a viable rapid H shift mechanism is proposed to occur that produces isoprene derived HOMs like MTA. Finally, an analysis of the mechanism shows that autoxidation-like pathways in low and high NOx may produce HOMs in a few OH oxidation steps like commonly detected methyl tetrol (MT) isoprene tracers. The ratio of MTA/MT in isoprene aerosol is also shown to be significantly greater in field versus chamber samples indicating the importance of such pathways in the atmosphere even for smaller hydrocarbons like isoprene. This dataset is associated with the following publication: Jaoui, M., I. Piletic, R. Szmigielski, K.J. Rudzinski, M. Lewandowski, T. Riedel, and T. Kleindienst. Rapid production of highly oxidized molecules in isoprene aerosol via peroxy and alkoxy radical isomerization pathways in low and high NOx environments: Combined laboratory, computational and field studies. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, NETHERLANDS, 775: 145592, (2021).

Background Previous kinetic investigations of fungal-peroxidase catalyzed oxidation of N-aryl hydroxamic acids (AHAs) and N-aryl-N-hydroxy urethanes (AHUs) revealed that the rate of reaction was independent of the formal redox potential of substrates. Moreover, the oxidation rate was 3–5 orders of magnitude less than for oxidation of physiological phenol substrates, though the redox potential was similar. Results To explain the unexpectedly low reactivity of AHAs and AHUs we made ab initio calculations of the molecular structure of the substrates following in silico docking in the active center of the enzyme. Conclusions AHAs and AHUs were docked at the distal side of heme in the sites formed by hydrophobic amino acid residues that retarded a proton transfer and finally the oxidation rate. The analogous phenol substrates were docked at different sites permitting fast proton transfer in the relay of distal His and water that helped fast substrate oxidation.

Atmospheric oxidation of natural and anthropogenic volatile organic compounds (VOCs) leads to secondary organic aerosol (SOA), which constitutes a major and often dominant component of atmospheric fine particulate matter (PM2.5). Recent work demonstrates that rapid autoxidation of organic peroxy radicals (RO2) formed during VOC oxidation results in highly oxygenated organic molecules (HOM) which efficiently form SOA. As NOx emissions decrease, the chemical regime of the atmosphere changes to one in which RO2 autoxidation becomes increasingly important, potentially increasing PM2.5, while oxidant availability driving RO2 formation rates simultaneously declines, possibly slowing regional PM2.5 formation. Using a unique suite of in situ aircraft observations and laboratory studies of HOM, together with a detailed molecular mechanism, we show that although autoxidation in an archetypal biogenic VOC system becomes more competitive as NOx decreases, absolute HOM production rates decrease due to oxidant reductions, leading to an overall positive coupling between anthropogenic NOx and localized biogenic SOA from autoxidation. This effect is observed in the Atlanta, Georgia urban plume where HOM is enhanced in the presence of elevated NO, and predictions for Guangzhou, China, where increasing HOM-RO2 production coincides with increases in NO from 1990 to 2010. These results suggest added benefits to PM2.5 abatement strategies come with NOx emission reductions and have implications for aerosol-climate interactions due to changes in global SOA resulting from NOx interactions since the pre-industrial era. Datasets include links to CMAQ, F0AM, and WAM model code as well as the SENEX aircraft campaign data archive. Files include data shown in Figure 3 (C10H18O7 HOM from SENEX), data used to construct Figure 4 and S10 (CMAQ model predictions of oxidants and intermediate species), additional supporting data in Figure S11 (SENEX C10 HOM species), and observed particle and gas composition from SOAFFEE laboratory experiments (Figure S6 and elsewhere). This dataset is associated with the following publication: Pye, H., E. D’Ambro, B. Lee, S. Schobesberger, M. Takeuchi, Y. Zhao, F. Lopez-Hilfiker, J. Liu, J. Shilling, J. Xing, R. Mathur, A. Middlebrook, J. Liao, A. Welti, M. Graus, C. Warneke, J.d. Gouw, J. Holloway, T. Ryerson, I. Pollack, and J. Thornton. Anthropogenic enhancements to production of highly oxygenated molecules from autoxidation.. PNAS (PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES). National Academy of Sciences, WASHINGTON, DC, USA, 116(14): 6641-6646, (2019).

The attached extensive computational chemistry dataset involves detailed electronic structure (density functional theory - DFT) and kinetic calculation (master equation formalism) outputs for the reactions of isoprene and first generation oxidants with the hydroxyl radical. There are a total of 9 tabs in the Excel spreadsheet. The first two tabs provide the potential energy surfaces (PESs) of the isoprene+OH and isopOOH+OH (1st generation oxidant) reactions. The PESs are zero-point energy corrected and obtained at the M062x/maug-cc-pVTZ level of DFT. The third tab provides the reaction barriers for first and second generation 1,5-hydrogen atom shifts for two different isoprene peroxy radical isomers with several different DFT methods. The fourth and fifth tabs provide microcanonical rate constants for the reactions of isoprene and isopOOH with OH respectively. The remaining tabs give the rate constants for the 1,5-H shifts for four different isoprene peroxy radicals. The rate constants are computed using the M062x density functional and an average of 4 different DFT methods given in tab 3 for comparison. The average values are reported as the final rate constants determined by computational methods. This dataset is associated with the following publication: Piletic, I., R. Howell, L. Bartolotti, T. Kleindienst, S. Kaushik, and E. Edney. Multigenerational Theoretical Study of Isoprene Peroxy Radical 1–5-Hydrogen Shift Reactions that Regenerate HOx Radicals and Produce Highly Oxidized Molecules. JOURNAL OF PHYSICAL CHEMISTRY A. American Chemical Society, Washington, DC, USA, 123(4): 906-919, (2019).

This data set is associated with an administrative report submitted to the U.S. Food and Drug Administration Center for Veterinary Medicine (CVM). The project goal was to determine the effects of hydrogen peroxide on the microflora of recirculating aquaculture systems (RAS). There are few aquaculture drugs approved for use in RAS and the CVM will evaluate findings from the study to determine if hydrogen peroxide would be safe to use in RAS.

This data set is associated with an administrative report submitted to the U.S. Food and Drug Administration Center for Veterinary Medicine (CVM). The project goal was to determine the effects of hydrogen peroxide on the microflora of recirculating aquaculture systems (RAS). There are few aquaculture drugs approved for use in RAS and the CVM will evaluate findings from the study to determine if hydrogen peroxide would be safe to use in RAS.

The dataset is supporting information containing experimental details, data, and reduced data for figures and tables presented in the journal article "Preparation of water-selective polybutadiene membranes and their use in drying alcohols by pervaporation and vapor permeation technologies" ACS Sustainable Chemistry & Engineering, 4, 4442-4450 (2016). This dataset is associated with the following publication: Vane, L., V. Namboodiri, G. Lin, M. Abar, and F. Alvarez. Preparation of Water-Selective Polybutadiene Membranes and Their Use in Drying Alcohols by Pervaporation and Vapor Permeation Technologies. SCIENCE. American Association for the Advancement of Science (AAAS), Washington, DC, USA, 4(8): 4442-4450, (2016).

Link to the paper. This dataset is associated with the following publication: Naile, J., A.W. Garrison, J. Avants, and J. Washington. Isomers/enantiomers of perfluorocarboxylic acids: Method development and detection in environmental samples. CHEMOSPHERE. Elsevier Science Ltd, New York, NY, USA, 144: 1722-1728, (2016).