2011, Wu, Z.J., Nowak, A., Poulain, L., Herrmann, H., Wiedensohler, A.

The hygroscopic behavior of atmospherically relevant water-soluble carboxylic salts and their effects on ammonium sulfate were investigated using a hygroscopicity tandem differential mobility analyzer (H-TDMA). No hygroscopic growth is observed for disodium oxalate, while ammonium oxalate shows slight growth (growth factor = 1.05 at 90%). The growth factors at 90% RH for sodium acetate, disodium malonate, disodium succinate, disodium tartrate, diammonium tartrate, sodium pyruvate, disodium maleate, and humic acid sodium salt are 1.79, 1.78, 1.69, 1.54, 1.29, 1.70, 1.78, and 1.19, respectively. The hygroscopic growth of mixtures of organic salts with ammonium sulfate, which are prepared as surrogates of atmospheric aerosols, was determined. A clear shift in deliquescence relative humidity to lower RH with increasing organic mass fraction was observed for these mixtures. Above 80% RH, the contribution to water uptake by the organic salts was close to that of ammonium sulfate for the majority of investigated compounds. The observed hygroscopic growth of the mixed particles at RH above the deliquescence relative humidity of ammonium sulfate agreed well with that predicted using the Zdanovskii-Stokes-Robinson (ZSR) mixing rule. Mixtures of ammonium sulfate with organic salts are more hygroscopic than mixtures with organic acids, indicating that neutralization by gas-phase ammonia and/or association with cations of dicarbonxylic acids may enhance the hygroscopicity of the atmospheric particles.

2015, Alberico, E., Nielsen, M.

The possibility to implement both the exhaustive dehydrogenation of aqueous methanol to hydrogen and CO2 and the reverse reaction, the hydrogenation of CO2 to methanol and water, may pave the way to a methanol based economy as part of a promising renewable energy system. Recently, homogeneous catalytic systems have been reported which are able to promote either one or the other of the two reactions under mild conditions. Here, we review and discuss these developments.