About
Avram Gold is a Professor at the University of North Carolina Gillings School of Global Public Health. His laboratory research covers three main areas: firstly, the synthesis of natural abundance analytical standards and internal standards labeled with stable isotopes for analyte quantitation by isotope dilution mass spectrometry, as well as structural analysis specializing in heteronuclear, multidimensional NMR. Secondly, his work has led to an interest in characterizing oxidative DNA lesions, notably being the first to characterize 2-iminohydantion, a potentially mutagenic lesion. Thirdly, his laboratory collaborates with atmospheric chemistry groups to probe the mechanisms of formation of secondary organic aerosols, focusing on the synthesis of standards, structural determinations, and elucidation of photochemical oxidation pathways, emphasizing the importance of organic epoxides as reactive intermediates.
Research topics
- Chemistry
- Environmental chemistry
- Organic chemistry
- Chromatography
- Immunology
- Biology
- Chemical engineering
- Environmental science
- Internal medicine
- Physics
- Meteorology
- Biochemistry
- Medicine
- Atmospheric sciences
Selected publications
UNC Libraries · 2026-02-11
articleOpen accessUNC Libraries · 2026-02-11
articleOpen accessThe phase states and glass transition temperatures (<em>T</em><sub>g</sub>) of secondary organic aerosol (SOA) particles are important to resolve for understanding the formation, growth, and fate of SOA as well as their cloud formation properties. Currently, there is a limited understanding of how <em>T</em><sub>g</sub> changes with the composition of organic and inorganic components of atmospheric aerosol. Using broadband dielectric spectroscopy, we measured the <em>T</em><sub>g</sub> of organic mixtures containing isoprene epoxydiol (IEPOX)-derived SOA components, including 2-methyltetrols (2-MT), 2-methyltetrol-sulfate (2-MTS), and 3-methyltetrol-sulfate (3-MTS). The results demonstrate that the <em>T</em><sub>g</sub> of mixtures depends on their composition. The Kwei equation, a modified Gordon-Taylor equation with an added quadratic term and a fitting parameter representing strong intermolecular interactions, provides a good fit for the <em>T</em><sub>g</sub>-composition relationship of complex mixtures. By combining Raman spectroscopy with geometry optimization simulations obtained using density functional theory, we demonstrate that the non-linear deviation of <em>T</em><sub>g</sub> as a function of composition may be caused by changes in the extent of hydrogen bonding in the mixture.
Efficient Isoprene Secondary Organic Aerosol Formation from a Non-IEPOX Pathway
UNC Libraries · 2026-02-12
articleOpen accessWith a large global emission rate and high reactivity, isoprene has a profound effect upon atmospheric chemistry and composition. The atmospheric pathways by which isoprene converts to secondary organic aerosol (SOA) and how anthropogenic pollutants such as nitrogen oxides and sulfur affect this process are subjects of intense research because particles affect Earth's climate and local air quality. In the absence of both nitrogen oxides and reactive aqueous seed particles, we measure SOA mass yields from isoprene photochemical oxidation of up to 15%, which are factors of 2 or more higher than those typically used in coupled chemistry climate models. SOA yield is initially constant with the addition of increasing amounts of nitric oxide (NO) but then sharply decreases for input concentrations above 50 ppbv. Online measurements of aerosol molecular composition show that the fate of second-generation RO2 radicals is key to understanding the efficient SOA formation and the NOx-dependent yields described here and in the literature. These insights allow for improved quantitative estimates of SOA formation in the preindustrial atmosphere and in biogenic-rich regions with limited anthropogenic impacts and suggest that a more-complex representation of NOx-dependent SOA yields may be important in models.
UNC Libraries · 2026-02-12
articleOpen accessOxidation of isoprene, the biogenic volatile organic compound (BVOC) with the highest emissions globally, is a large source of secondary organic aerosol (SOA) in the atmosphere. Particulate organosulfates formed from acid-driven reactions of the oxidation products isoprene epoxydiol (IEPOX) isomers are important contributors to SOA mass. Most studies have focused on organosulfate formation on ammonium sulfate particles, often at low pH. However, recent work has shown that sea spray aerosol (SSA) in the accumulation mode (∼100 nm) is quite acidic (pH ∼2) and undergoes further heterogeneous reactions with H2SO4 to form Na2SO4. Herein, we demonstrate that substantial SOA, including organosulfates, are formed on acidic sodium sulfate particles (pH = 1.4 ± 0.1) via controlled laboratory experiments. Comparable organosulfate formation was observed for acidic sodium and ammonium sulfate particles even though acidic particles with sodium versus ammonium as the primary cation formed less SOA volume. Both exhibited core-shell morphology after the reactive uptake of IEPOX; however, organosulfates were identified with Raman microspectroscopy in the core and shell of ammonium sulfate SOA particles, but only in the core for sodium sulfate SOA. Key organosulfates were also identified in ambient samples from the Galápagos Island. Our results suggest that isoprene-derived SOA formed on aged SSA is potentially an important, but underappreciated, source of SOA and organosulfates in marine and coastal regions that could modify SOA budgets.
UNC Libraries · 2026-02-11
articleOpen accessOrganic aerosols (OAs) may serve as ice-nucleating particles (INPs), impacting the formation and properties of cirrus clouds when their phase state and viscosity are in the semisolid to glassy range. However, there is a lack of direct parameterization between aerosol viscosity and their ice nucleation capabilities. In this study, we experimentally measured the ice nucleation rate of 2-methyltetrols (2-MT) aerosols, a key component of isoprene-epoxydiol-derived secondary organic aerosols (IEPOX-SOA), at different viscosities. These results demonstrate that the phase state has a significant impact on the ice nucleation abilities of OA under typical cirrus cloud conditions, with the ice nucleation rate increasing by 2 to 3 orders of magnitude when the phase state changes from liquid to semisolid. An innovative parametric model based on classical nucleation theory was developed to directly quantify the impact of viscosity on the heterogeneous nucleation rate. This model accurately represents our laboratory measurement and can be implemented into climate models due to its simple, equation-based form. Based on data collected from the ACRIDICON-CHUVA field campaign, our model predicts that the INP concentration from IEPOX-SOA can reach the magnitude of 1 to tens per liter in the cirrus cloud region impacted by the Amazon rainforest, consistent with recent field observations and estimations. This novel parameterization framework can also be applied in regional and global climate models to further improve representations of cirrus cloud formation and associated climate impacts.
UNC Libraries · 2026-02-12
articleOpen accessWe present measurements as part of the Southern Oxidant and Aerosol Study (SOAS) during which atmospheric aerosol particles were comprehensively characterized. We present results utilizing a Filter Inlet for Gases and AEROsol coupled to a chemical ionization mass spectrometer (CIMS). We focus on the volatility and composition of isoprene derived organic aerosol tracers and of the bulk organic aerosol. By utilizing the online volatility and molecular composition information provided by the FIGAERO-CIMS, we show that the vast majority of commonly reported molecular tracers of isoprene epoxydiol (IEPOX) derived secondary organic aerosol (SOA) is derived from thermal decomposition of accretion products or other low volatility organics having effective saturation vapor concentrations <10(-3) μg m(-3). In addition, while accounting for up to 30% of total submicrometer organic aerosol mass, the IEPOX-derived SOA has a higher volatility than the remaining bulk. That IEPOX-SOA, and more generally bulk organic aerosol in the Southeastern U.S. is comprised of effectively nonvolatile material has important implications for modeling SOA derived from isoprene, and for mechanistic interpretations of molecular tracer measurements. Our results show that partitioning theory performs well for 2-methyltetrols, once accretion product decomposition is taken into account. No significant partitioning delays due to aerosol phase or viscosity are observed, and no partitioning to particle-phase water or other unexplained mechanisms are needed to explain our results.
UNC Libraries · 2026-02-12
articleOpen accessMultiphase chemistry of isomeric isoprene epoxydiols (IEPOX) has been shown to be the dominant source of isoprene-derived secondary organic aerosol (SOA). Recent studies have reported particles composed of ammonium bisulfate (ABS) mixed with model organics exhibit slower rates of IEPOX uptake. In the present study, we investigate the effect of atmospherically relevant organic coatings of α-pinene (AP) SOA on the reactive uptake of trans-β-IEPOX onto ABS particles under different conditions and coating thicknesses. Single particle mass spectrometry was used to characterize in real-time particle size, shape, density, and quantitative composition before and after reaction with IEPOX. We find that IEPOX uptake by pure sulfate particles is a volume-controlled process, which results in particles with uniform concentration of IEPOX-derived SOA across a wide range of sizes. Aerosol acidity was shown to enhance IEPOX-derived SOA formation, consistent with recent studies. The presence of water has a weaker impact on IEPOX-derived SOA yield, but significantly enhanced formation of 2-methyltetrols, consistent with offline filter analysis. In contrast, IEPOX uptake by ABS particles coated with AP-derived SOA is lower compared to that of pure ABS particles, strongly dependent on particle composition, and therefore on particle size.
UNC Libraries · 2026-02-11
articleOpen accessAerosol acidity increases secondary organic aerosol (SOA) formed from the reactive uptake of isoprene-derived epoxydiols (IEPOX) by enhancing condensed-phase reactions within sulfate-containing submicron particles, leading to low-volatility organic products. However, the link between the initial aerosol acidity and the resulting physicochemical properties of IEPOX-derived SOA remains uncertain. Herein, we show distinct differences in the morphology, phase state, and chemical composition of individual organic-inorganic mixed particles after IEPOX uptake to ammonium sulfate particles with different initial atmospherically relevant acidities (pH = 1, 3, and 5). Physicochemical properties were characterized via atomic force microscopy coupled with photothermal infrared spectroscopy (AFM-PTIR) and Raman microspectroscopy. Compared to less acidic particles (pH 3 and 5), reactive uptake of IEPOX to the most acidic particles (pH 1) resulted in 50% more organosulfate formation, clearer phase separation (core-shell), and more irregularly shaped morphologies, suggesting that the organic phase transitioned to semisolid or solid. This study highlights that initial aerosol acidity may govern the subsequent aerosol physicochemical properties, such as viscosity and morphology, following the multiphase chemical reactions of IEPOX. These results can be used in future studies to improve model parameterizations of SOA formation from IEPOX and its properties, toward the goal of bridging predictions and atmospheric observations.
UNC Libraries · 2026-02-12
articleOpen accessAtmospheric oxidation of isoprene under low-NOx conditions leads to the formation of isoprene hydroxyhydroperoxides (ISOPOOH). Subsequent oxidation of ISOPOOH largely produces isoprene epoxydiols (IEPOX), which are known secondary organic aerosol (SOA) precursors. Although SOA from IEPOX has been previously examined, systematic studies of SOA characterization through a non-IEPOX route from 1,2-ISOPOOH oxidation are lacking. In the present work, SOA formation from the oxidation of authentic 1,2-ISOPOOH under low-NOx conditions was systematically examined with varying aerosol compositions and relative humidity. High yields of highly oxidized compounds, including multifunctional organosulfates (OSs) and hydroperoxides, were chemically characterized in both laboratory-generated SOA and fine aerosol samples collected from the southeastern U.S. IEPOX-derived SOA constituents were observed in all experiments, but their concentrations were only enhanced in the presence of acidified sulfate aerosol, consistent with prior work. High-resolution aerosol mass spectrometry (HR-AMS) reveals that 1,2-ISOPOOH-derived SOA formed through non-IEPOX routes exhibits a notable mass spectrum with a characteristic fragment ion at m/z 91. This laboratory-generated mass spectrum is strongly correlated with a factor recently resolved by positive matrix factorization (PMF) of aerosol mass spectrometer data collected in areas dominated by isoprene emissions, suggesting that the non-IEPOX pathway could contribute to ambient SOA measured in the Southeastern United States.
UNC Libraries · 2026-02-11
articleOpen accessIsoprene, the most abundant biogenic volatile organic compound (BVOC) in the atmosphere, and its low-volatility oxidation products lead to secondary organic aerosol (SOA) formation. Isoprene-derived organosulfates formed from reactions of isoprene oxidation products with sulfate in the particle phase are a significant component of SOA and can hydrolyze forming polyols. Despite characterization by mass spectrometry, their basic structural and spectroscopic properties remain poorly understood. Herein, Raman microspectroscopy and density functional theory (DFT) calculations (CAM-B3LYP level of theory) were combined to analyze the vibrational modes of key organosulfates, 3-methyltetrol sulfate esters (racemic mixture of two isomers), and racemic 2-methylglyceric acid sulfate ester, and hydrolysis products, 2-methyltetrols, and 2-methylglyceric acid. Two intense vibrational modes were identified, ν(RO-SO<sub>3</sub>) (846 ± 4 cm<sup>-1</sup>) and ν<sub>s</sub>(SO<sub>3</sub>) (1065 ± 2 cm<sup>-1</sup>), along with a lower intensity δ(SO<sub>3</sub>) mode (586 ± 2 cm<sup>-1</sup>). For 2-methylglyceric acid and its sulfate esters, deprotonation of the carboxylic acid at pH values above the pK<sub>a</sub> decreased the carbonyl stretch frequency (1724 cm<sup>-1</sup>), while carboxylate modes grew in for ν<sub>s</sub>(COO<sup>-</sup>) and ν<sub>a</sub>(COO<sup>-</sup>) at 1413 and 1594 cm<sup>-1</sup>, respectively. The ν(RO-SO<sub>3</sub>) and ν<sub>s</sub>(SO<sub>3</sub>) modes were observed in individual atmospheric particles and can be used in future studies of complex SOA mixtures to distinguish organosulfates from inorganic sulfate or hydrolysis products.
Recent grants
NSF · $596k · 2020–2024
NSF · $668k · 2023–2027
NIH · $1.3M · 1998
NIH · $449k · 1993
Frequent coauthors
- 111 shared
R. Sangaiah
University of North Carolina at Chapel Hill
- 104 shared
Jason D. Surratt
University of North Carolina at Chapel Hill
- 94 shared
Zhenfa Zhang
Tianjin Medical University Cancer Institute and Hospital
- 84 shared
Louise M. Ball
University of Florida
- 51 shared
James Terner
Virginia Commonwealth University
- 50 shared
Raymond Weiss
Institut de Science et d'Ingénierie Supramoléculaires
- 49 shared
K. Jayaraj
- 41 shared
Ying‐Hsuan Lin
University of California, Riverside
Labs
Education
- 1980
Ph.D., Toxicology
University of California, Berkeley
- 1976
M.S., Toxicology
University of California, Berkeley
- 1974
B.S., Toxicology
University of California, Berkeley
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