Researchers have long grappled with the uncertainties surrounding aerosol formation and its impact on global warming. A recent study led by Professor George Shields with undergraduates Olivia Longsworth and Conor Bready from Furman University, offers critical insights into the early stages of aerosol formation. This work, published in the journal Environmental Science: Atmospheres, investigates the interactions between common atmospheric molecules like sulfuric acid, formic acid, hydrochloric acid, ammonia, and dimethylamine.
Atmospheric aerosols significantly influence Earth’s climate by scattering, absorbing, and emitting solar radiation. Understanding how these aerosols form is essential, as their effects on climate are one of the main sources of uncertainty in current climate models. Secondary aerosols, which originate from gas-phase reactions, are particularly important as they act as cloud condensation nuclei (CCN), facilitating cloud formation.
The study focuses on the formation of prenucleation clusters, which are the precursors to larger aerosol particles. These clusters form from interactions between precursor monomers of acids, bases, and organic molecules. However, deciphering the detailed interactions responsible for prenucleation and subsequent aerosol formation has been challenging. The research team employed computational chemistry to explore these interactions, providing a comprehensive analysis of cluster formation.
By examining combinations of three acids (sulfuric acid, formic acid, hydrochloric acid) and two bases (ammonia, dimethylamine), the researchers identified the subtleties of prenucleation complex formation. They conducted an exhaustive search of the Gibbs free energy surface for these systems, utilizing high-level quantum chemical calculations. Their findings reveal that nitric acid forms stronger interactions in dry clusters compared to hydrochloric acid. However, as the clusters grow larger with hydration, hydrochloric acid becomes more favorable.
Professor Shields emphasized the significance of this work: “Our detailed study of HCl interacting with two other acids and two bases reveals the subtleties in the formation of prenucleation complexes. The hydrogen bond topology and structural interactions play a crucial role, often outweighing traditional ideas of acid or base strength.”
The study highlights that the detailed geometries of each minimum free energy cluster are more important than conventional acid/base strength for predicting which atmospheric species drive prenucleation growth. The researchers’ findings indicate that while nitric acid is more effective in dry conditions, hydrochloric acid becomes more stabilized with hydration.
Their methodology involved simulating various combinations of acids and bases with up to three water molecules. This comprehensive approach allowed them to predict the equilibrium concentrations of the sulfuric acid-formic acid-hydrochloric acid-ammonia-dimethylamine-water system. They found that different acids stabilize prenucleation clusters at different stages of growth, providing valuable insights for future research on aerosol formation.
In summary, the study underscores the complexity of aerosol formation and the critical role of specific molecular interactions. Understanding these early stages is vital for improving climate models and accurately predicting the impact of aerosols on global warming. The detailed computational analysis presented by Professor Shields, Longsworth, and Bready offers a significant step forward in unraveling the intricacies of atmospheric chemistry. This paper was the third of a series in this journal, where the Shields group investigated different combinations of acids and bases clustering with water molecules.
Journal Reference
Longsworth, Olivia M., Conor J. Bready, and George C. Shields. “The driving effects of common atmospheric molecules for formation of clusters: the case of sulfuric acid, formic acid, hydrochloric acid, ammonia, and dimethylamine.” Environmental Science: Atmospheres, 2023. DOI: https://doi.org/10.1039/D3EA00087G
Longsworth, Olivia M., Conor J. Bready, Macie S. Joines, and George C. Shields. “The Driving Effects of Common Atmospheric Molecules for Formation of Prenucleation Clusters: The Case of Sulfuric Acid, Nitric Acid, Hydrochloric Acid, Ammonia, and Dimethyl Amine” Environmental Science: Atmospheres, 2023. DOI: https://doi.org/10.1039/D3EA00118K
Longsworth, Olivia M., Conor J. Bready, Vance R. Fowler, Leah A. Juechter, Luke A. Kurfman, Grace E. Mazaleski, and George C. Shields. “The Driving Effects of Common Atmospheric Molecules for Formation of Prenucleation Clusters: The Case of Sulfuric Acid, Formic Acid, Nitric Acid, Ammonia, and Dimethyl Amine” Conor J. Bready, Vance R. Fowler, Leah A. Juechter, Luke A. Kurfman, Grace E. Mazaleski, and George C. Shields, Environmental Science: Atmospheres, 2022. DOI: https://doi.org/10.1039/D2EA00087C
About The Authors
George Shields is a professor of chemistry at Furman University, where he teaches general chemistry and physical chemistry. His research with 140+ undergraduates working in his laboratory has been widely cited. He has coauthored 116 peer-reviewed papers, including 75 papers with 70 undergraduates working in his research group. He received the American Chemical Society (ACS) Award for Research at an Undergraduate Institution in 2015, and the Research Corporation for Science Advancement Transformational Research and Excellence in Education Award in 2018. He is an elected Fellow of ACS and the American Association for the Advancement of Science. He received the Council of Undergraduate Research (CUR) Fellows Award in 2020 and the CUR-Goldwater Scholars Faculty Award in 2022. Over 90% of his undergraduate students have matriculated to graduate or professional schools. His undergraduates have received 45 national awards, including four Fulbright, 15 Goldwater, and eight Graduate Fellowships.
Conor Bready graduated from Furman in 2024. He is the recipient of a Beckman Scholar Award and a Goldwater Scholarship. He has published 8 papers working in the Shields lab. He received a Department of Energy Computational Science Graduate Fellowship, and he begins his graduate studies in theoretical chemistry at the University of California, Berkeley in August.
Olivia Longsworth is a senior at Furman and will graduate in 2025. She is the recipient of a Goldwater Scholarship. She has published three papers working in the Shields lab thus far. She plans to do attend medical school and bridge the research and clinical worlds.
