Microhydration, structure, and climatic role of maleic acid: A computational study of MA(H2O)n clusters

Abstract

• The present work investigates the atmospheric relevance of binary clusters MA(W) n=1–8 using DFT. • The hydrate populations reveal that the dry cluster is significantly populated. • The clusters ( n = 1–3) show atmospheric relevant concentration at all RH. • Kinetic study showed that evaporation rates exceed collision rates largely, hindering cluster persistence in the atmosphere. Understanding the molecular-scale mechanisms of atmospheric new particle formation (NPF) is critical for accurately modeling aerosol-climate interactions. Maleic acid (MA), a dicarboxylic acid ubiquitous in atmospheric particulate matter, may participate in initial cluster formation. This computational study evaluates the atmospheric relevance of MA–water (W) binary clusters, MA(W) n (n = 1–8), using density functional theory (DFT). Global minimum geometries, obtained at the ωB97X-D/6-311++G(3df,3pd) level, were used to calculate binding free energies. Thermodynamic population analysis indicates a sharp decrease in cluster concentration with increasing cluster size and relative humidity (RH); only the smallest clusters (n = 1–3) maintain atmospherically relevant concentrations at moderate RH. Kinetically, evaporation rates dominate over collision rates, significantly hindering persistent cluster growth. Although the calculated cluster radiative forcing efficiencies (REs) increase with hydration (0.21–0.84 Wm −2 ppbv −1 ), these values are substantially offset by concomitant Rayleigh scattering activity. Collectively, these results suggest that binary MA-W clusters are unlikely to be stable nucleation precursors, with the MA(W) 2 cluster being particularly emphasized as a kinetic bottleneck.