Perfluoropropionic Acid-Driven Nucleation of Atmospheric Molecules under Ambient Conditions

A molecular-level understanding of the compositions and formation mechanism of secondary organic aerosols is important in the context of growing evidence regarding the adverse impacts of aerosols on the atmosphere and human health. The ever-growing emissions of pollutants and particulate matter in the atmosphere are a global concern. A particular class of pollutants, which are being important in this sense, are persistent organic pollutants (POPs) since they represent synthetic organic compounds with a long lifetime in the environment. Among the POPs, the perfluorinated compounds, such as perfluoroalkyl carboxylic acids (C_nF_2n+1COOH) or PFCAs, draw a lot of attention due to their adverse effect on human health. In the present work, we employ high-level density functional theory to investigate the electrostatic interaction of perfluoropropionic acid (C₂F₅COOH) or PFPA, a PFCA with n = 2, with well-known atmospheric molecules, namely, HCHO, HCOOH, CH₃OH, H₂SO₄, and CH₃SO₃H [methanesulfonic acid (MSA)]. A detailed and systematic quantum chemical calculation has been performed to analyze the structural, energetic, electrical, and spectroscopic properties of several binary clusters in the context of atmospheric nucleation process. Our analysis shows that PFPA forms very stable hydrogen-bonded binary clusters with molecules like H₂SO₄ and MSA, which widely recognized atmospheric nucleation precursors. Scattering intensities of radiation (Rayleigh activities) are found to increase many fold when PFPA forms clusters. Analyses of the cluster-binding electronic energies and the free-energy changes associated with their formation at different temperatures indicate that PFPA could participate in the initial nucleation processes and contribute effectively to the new particle formation in the atmosphere.