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 graduate students Olivia Longsworth and Conor Bready from Furman University provides fundamental insights into the early stages of aerosol formation. This work, published in the journal Environmental Science: Atmospheres, investigates the interactions between common atmospheric molecules such as 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 performed an exhaustive search of the Gibbs free energy surface for these systems, using 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 become larger with hydration, hydrochloric acid becomes more favorable.
Professor Shields highlighted the importance of this work: “Our detailed study of the interaction of HCl with two other acids and two bases reveals the subtleties of prenucleation complex formation. Hydrogen bond topology and structural interactions play a crucial role, often overriding traditional ideas about the strength of acids or bases.”
The study highlights that the detailed geometries of each minimum free energy group are more important than conventional acid/base strength in predicting which atmospheric species drive prenucleation growth. The researchers' findings indicate that while nitric acid is more effective under dry conditions, hydrochloric acid is more stabilized by 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 the prenucleation clusters at different stages of growth, providing valuable insights for future research into aerosol formation.
In summary, the study highlights the complexity of aerosol formation and the critical role of specific molecular interactions. Understanding these early stages is vital to 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 advance in unraveling the complexities of atmospheric chemistry. This paper was the third in a series in this journal, where Shields’ group investigated different combinations of acids and bases that cluster with water molecules.
Journal reference
Longsworth, Olivia M., Conor J. Bready, and George C. Shields. “The driving effects of common atmospheric molecules on cumulus cloud formation: 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 on prenucleation cluster formation: The case of sulfuric acid, nitric acid, hydrochloric acid, ammonia, and dimethylamine.” 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 on prenucleation cluster formation: The case of sulfuric acid, formic acid, nitric acid, ammonia, and dimethylamine” 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 over 140 undergraduates working in his laboratory has been widely cited. He has co-authored 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 Scientific Advancement Award for Transformational Research and Excellence in Education in 2018. He is an elected Fellow of the ACS and the American Association for the Advancement of Science. He received the Council on Undergraduate Research (CUR) Scholars Award in 2020 and the CUR-Goldwater Scholars Faculty Award in 2022. Over 90% of his undergraduates have matriculated to graduate or professional schools. Its undergraduates have received 45 national awards, including four Fulbright scholarships, 15 Goldwater scholarships, and eight graduate fellowships.
Conor Pany She graduated from Furman in 2024. She is the recipient of a Beckman Scholar Award and a Goldwater Fellowship. She has published eight papers while working in the Shields Lab. She received a graduate fellowship in Energy Computational Sciences from the Department of Energy and will begin graduate studies in theoretical chemistry at the University of California, Berkeley in August.
Olivia Longsworth She is a senior at Furman and will graduate in 2025. She received a Goldwater Scholarship. She has published three papers working in the Shields lab so far. She plans to attend medical school and bridge the worlds of research and the clinic.
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