Chilling Out: A Cool Aqueous Environment Promotes the Formation of Gas–Surface Complexes

Abstract

SO(2), an important atmospheric pollutant, has been implicated in environmental phenomena such as acid rain, climate change, and cloud formation. In addition, SO(2) is fundamentally interesting because it forms spectroscopically identifiable complexes with water at aqueous surfaces. Vibrational sum frequency spectroscopy (VSFS) is used here to further investigate the mechanism by which SO(2) adsorbs to water at tropospherically relevant temperatures (0-23 °C). The spectral results lead to two important conclusions. SO(2) surface affinity is enhanced at colder temperatures, with nearly all of the topmost water molecules showing evidence of binding to SO(2) at 0 °C as compared to a much lower fraction at room temperature. This surface adsorption results in significant changes in water orientation at the surface, but is reversible at the temperatures examined here. Second, the SO(2) complex formation at aqueous surfaces is independent of aqueous solution acidity. One challenge in previous uptake studies was the ability to distinguish between the effects of surface adsorption as compared to bulk accommodation. The surface and vibrational specificity of these studies make this distinction possible, allowing a selective study of how the aqueous properties temperature and pH influence SO(2) surface affinity.

Regression Analyses between Recent Air Quality and Visibility Changes in Megacities at Four Haze Regions in China

“…It is worthwhile noting that, from the PM 2.5 chemical speciation data observed in the period mid-2009 to early 2010, elevated concentrations of sulfate and high ratios of sulfate: (SO 2 + sulfate) were detected in autumn and winter (Tao, J., unpublished data), which supported this hypothesis and highlighted the crucial role of secondary sulfate formation on visibility degradation at low temperatures. This result also agrees with the fact that SO 2 dissolves more readily in water and oxidizes into secondary sulfates via heterogeneous reactions at low temperatures (Ota and Richmond, 2011). A similar relationship between SO 2 and visibility impairment was also found in Hong Kong, another megacity in the PRD (Lin et al, 2012 decreases in visibility were probably due to the reduction of WS (0.75 m/s in 2005 to 0.53 m/s in 2009), although the coefficient was just 2.01 km per m/s, too low to trigger the notably decreasing trend in visibility.…”

Trimethylamine N -oxide stabilizes proteins via a distinct mechanism compared with betaine and glycine

“…Changes in the OH stretch spectra are often used to probe water structure and in particular, the water hydrogen-bonding environment (40)(41)(42)(43)(44)(45). Unfortunately, interpreting the water vibrational spectrum is not straightforward because of strong inter-/intramolecular vibrational coupling.…”

Mechanism of the Gaseous Hydrolysis Reaction of SO2: Effects of NH3 versus H2O

“…Complexes, transition states, and products for the SO 2 + nH 2 O (n = 1−5) reactions at the MP2/aug-cc-pVDZ level of theory (bond lengths in angstroms).For the hydrolysis of SO 2 with three water molecules, the reaction occurs via an eight-membered cyclic reactant complex SO 2 -3W, in which the four moieties are held together by four hydrogen bonds, (H(6) ···O S , H (3) ···O S , O (b) ···H (2) , O (c) ···H (4) ),and there is an electron donor−acceptor (EDA) type of interaction between H 2 O (a) and SO 2 . The equilibrium geometry and binding energy (18.18 kcal/mol) of SO 2 -3W are consistent with the previous results.…”