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).

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).

Reaction intermediates formed during the ultra-violet (UV) activation of hydrogen peroxide (H2O2) (UV-AHP) and persulfate (S2O82-) (UV-APS) include hydroxyl (•OH) and sulfate radicals (SO4•-), respectively. These radicals, used in oxidation treatment systems to degrade a broad spectrum of environmental contaminants, may also react with non-target chemical species (scavengers) that limit treatment efficiency. UV-AHP and UV-APS treatment systems were amended with solid phase alumina to assess scavenging by solid surfaces. The relative rates of reaction between the target compound, rhodamine B dye (RhB), and aqueous and solid phase scavengers was used to assess treatment performance. The overall rate of reaction and rate of radical scavenging was greater for •OH than SO4•-. Scavenging by dissolved constituents was dominated by the oxidant used (H2O2, S2O82-); and the rate of radical scavenging by alumina was greater than the rate of RhB oxidation in all cases. Treatment efficiency was lower in the UV-AHP than in the UV-APS treatment system and was attributed to greater aqueous and solid phase scavenging rates. The cost of commercially available H2O2 ($0.031 mol-1) and PS ($0.24 mol-1) was used in conjunction with the overall treatment efficiency to assess specific cost of treatment. The specific cost to treat the probe compound with UV-AHP was greater than UV-APS and was attributed to the much lower treatment efficiency with UV-AHP. The much-desired high reaction rate constants between •OH and environmental contaminants, relative to SO4•-, comes at the cost of greater combined scavenging rates, and consequently lower treatment efficiency. This dataset is associated with the following publication: Rusevova Crincoli, K., and S.G. Huling. Contrasting hydrogen peroxide- and persulfate-driven oxidation systems: Impact of radical scavenging on treatment efficiency and cost. Chemical Engineering Journal. Elsevier BV, AMSTERDAM, NETHERLANDS, 404: 1-6, (2021).

The attached extensive computational chemistry dataset was succinctly presented by Piletic et al. (Journal of Physical Chemistry A, 2017, DOI: 10.1021/acs.jpca.7b08229) and involves detailed electronic structure (density functional theory - DFT) and kinetic calculation (master equation formalism) outputs for the reactions of isoprene peroxy radical isomers with NOx. The first three tabs describe the potential energy surfaces (PESs) of the beta and delta hydroxy-peroxy isoprene isomers reacting with NO to produce NO2, HONO and organic nitrates. Microcanonical rate constants and organic nitrate yield data are presented in the fourth and fifth tabs. The PESs for the reactions of the E and Z delta hydroxy-peroxy isoprene isomers is given in the sixth tab while the seventh tab shows the PES data for the reaction of the hydroxyl radical with several organic nitrates. This dataset is associated with the following publication: Piletic, I., E. Edney, and L. Bartolotti. Barrierless Reactions with Loose Transition States Govern the Yields and Lifetimes of Organic Nitrates Derived from Isoprene. JOURNAL OF PHYSICAL CHEMISTRY A. American Chemical Society, Washington, DC, USA, 121(43): 8306-8321, (2017).

Oxidation of the monoterpene Δ3-carene (C10H16) is a potentially important and under-studied source of atmospheric secondary organic aerosol (SOA). We present chamber-based measurements of the speciated gas and particle phases during photochemical oxidation of Δ3-carene. We find evidence of highly oxidized organic molecules (HOM) in the gas phase and relatively low volatility SOA dominated by C7-C10 species. We then use computational methods to develop the first stages of a Δ3-carene photochemical oxidation mechanism and explain some of our measured compositions. We find that alkoxy bond scission of the cyclohexyl ring likely leads to efficient HOM formation, in line with previous studies. We also find a surprising role for the abstraction of primary hydrogens from methyl groups, which has been calculated to be rapid in the α-pinene system, and suggest more research is required to determine if this is more general to other systems and a feature of autoxidation. This work develops a more comprehensive view of Δ3-carene photochemical oxidation products via measurements and lays out a suggested mechanism of oxidation via computationally derived rate coefficients. This dataset is not publicly accessible because: Non-EPA data. It can be accessed through the following means: Please contact Joel Thornton at: thornton@atmos.uw.edu. Format: text files. This dataset is associated with the following publication: D'Ambro, E., N. Hyttinen, K. Møller, S. Iyer, R. Otkjær, D. Bell, J. Liu, F. Lopez-Hilfiker, S. Schobesberger, J. Shilling, A. Zelenyuk, H. Kjaergaard, J. Thornton, and T. Kurten. Pathways to highly oxidized products in the Δ3-Carene + OH system. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 56(4): 2213-2224, (2022).

Oxidation of the monoterpene Δ3-carene (C10H16) is a potentially important and under-studied source of atmospheric secondary organic aerosol (SOA). We present chamber-based measurements of the speciated gas and particle phases during photochemical oxidation of Δ3-carene. We find evidence of highly oxidized organic molecules (HOM) in the gas phase and relatively low volatility SOA dominated by C7-C10 species. We then use computational methods to develop the first stages of a Δ3-carene photochemical oxidation mechanism and explain some of our measured compositions. We find that alkoxy bond scission of the cyclohexyl ring likely leads to efficient HOM formation, in line with previous studies. We also find a surprising role for the abstraction of primary hydrogens from methyl groups, which has been calculated to be rapid in the α-pinene system, and suggest more research is required to determine if this is more general to other systems and a feature of autoxidation. This work develops a more comprehensive view of Δ3-carene photochemical oxidation products via measurements and lays out a suggested mechanism of oxidation via computationally derived rate coefficients. This dataset is not publicly accessible because: Non-EPA data. It can be accessed through the following means: Please contact Joel Thornton at: thornton@atmos.uw.edu. Format: text files. This dataset is associated with the following publication: D'Ambro, E., N. Hyttinen, K. Møller, S. Iyer, R. Otkjær, D. Bell, J. Liu, F. Lopez-Hilfiker, S. Schobesberger, J. Shilling, A. Zelenyuk, H. Kjaergaard, J. Thornton, and T. Kurten. Pathways to highly oxidized products in the Δ3-Carene + OH system. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, USA, 56(4): 2213-2224, (2022).

The TROPESS Chemical Reanalysis PAN 6-Hourly 3-dimensional Product contains vertical concentrations of peroxyacetyl nitrate. The data are part of the Tropospheric Chemical Reanalysis v2 (TCR-2) for the period 2005-2021. TCR-2 uses JPL's Multi-mOdel Multi-cOnstituent Chemical (MOMO-Chem) data assimilation framework that simultaneously optimizes both concentrations and emissions of multiple species from multiple satellite sensors. The data files are written in the netCDF version 4 file format, and each file contains a year of data at 6-hourly resolution, and a spatial resolution of 1.125 x 1.125 degrees at 27 pressure levels between 1000 and 60 hPa. The principal investigator for the TCR-2 data is Miyazaki, Kazuyuki.

The TROPESS CrIS-JPSS1 L2 Peroxyacetyl Nitrate for Forward Stream, Summary Product contains the vertical distribution of the retrieved atmospheric state of peroxyacetyl nitrate (PAN), and formal uncertainties measured by the CrIS instrument on the JPSS-1 (NOAA-20) satellite. The forward stream standard product is global for the time period from 2021-04-01 to present. The NASA TRopospheric Ozone and Precursors from Earth System Sounding (TROPESS) project, uses an optimal estimation algorithm, known as the MUlti-SpEctra, MUlti-SpEcies, Multi-SEnsors (MUSES).The data files are written in the netCDF version 4 file format, and each file contains one day of data. The data have a spatial resolution of 14 km (CrIS nadir FOV), and are reported at 16 vertical levels from the surface to 0.1 hPa. The principal investigator for the TROPESS project is Kevin W. Bowman.

The TROPESS CrIS-SNPP L2 Peroxyacetyl Nitrate for Reanalysis Stream, Summary Product contains the vertical distribution of the retrieved atmospheric state of peroxyacetyl nitrate (PAN), and formal uncertainties measured by the CrIS instruments on the Suomi-NPP satellite. The reanalysis stream summary product is global for the time period from 2015-12-01 to 2023-05-18. The NASA TRopospheric Ozone and Precursors from Earth System Sounding (TROPESS) project, uses an optimal estimation algorithm, known as the MUlti-SpEctra, MUlti-SpEcies, Multi-SEnsors (MUSES).The data files are written in the netCDF version 4 file format, and each file contains one day of data. The data have a spatial resolution of 14 km (CrIS nadir FOV), and are reported at 16 vertical levels from the surface to 0.1 hPa. The principal investigator for the TROPESS project is Kevin W. Bowman.

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).