Atmospheric implications of the formation of water – sulphuric acid and water – methanesulfonic acid binary clusters

Sulphuric acid (SA) and methansulfonic acid (MSA) are both gases present in the atmospheric molecular realm. The present work focuses on the atmospheric relevance of both SA and MSA cluster formations with water (W) molecules. The X3LYP/6-311++G(3df,3pd) method along with the benchmark ωB97X-D/6-311++G(3df,3pd), were performed in order to have equilibrium geometries of isomers along with their Boltzmann fraction. The binding energies per W of clusters, SA-W<i>_n</i> and MSA-W<i>_n</i> (<i>n</i> = 1–10) are almost constant for <i>n</i> = 5–10. Clusters SA-W<i>_n</i> ₌ _8–10 and MSA-W<i>_n</i> ₌ _6–10 content ion pairs. Their atmospheric concentrations are consistent with previous works and drop with the increase of W molecules. The concentration of the monohydrates SA-W₁ and MSA-W₁ are the most significant. The collision and evapouration rates were estimated for single water evapouration from clusters. The large amounts of these coefficients lead to shorter lifetimes of all the studied clusters. The estimated radiative forcing efficiency of clusters, SA-W<i>_n</i> and MSA-W<i>_n</i> grows with the size of W. The Rayleigh scattering effect of these clusters acts as the opposite effect of radiative forcing. Both radiative forcing efficiency and Rayleigh scattering effect of clusters depend on the estimated atmospheric concentrations which actually limit their effectiveness under the standard condition of partial pressure and ambient temperature.