Molecular Characterization of Organosulfur Compounds in Biodiesel and Diesel Fuel Secondary Organic Aerosol.

Secondary organic aerosol (SOA), formed in the photooxidation of diesel fuel, biodiesel fuel, and 20% biodiesel fuel/80% diesel fuel mixture, are prepared under high-NOx conditions in the presence and absence of sulfur dioxide (SO2), ammonia (NH3), and relative humidity (RH). The composition of condensed-phase organic compounds in SOA is measured using several complementary techniques including aerosol mass spectrometry (AMS), high-resolution nanospray desorption electrospray ionization mass spectrometry (nano-DESI/HRMS), and ultrahigh resolution and mass accuracy 21T Fourier transform ion cyclotron resonance mass spectrometry (21T FT-ICR MS). Results demonstrate that sulfuric acid and condensed organosulfur species formed in photooxidation experiments with SO2 are present in the SOA particles. Fewer organosulfur species are formed in the high humidity experiments, performed at RH 90%, in comparison with experiments done under dry conditions. There is a strong overlap of organosulfur species observed in this study with previous field and chamber studies of SOA. Many MS peaks of organosulfates (R-OS(O)2OH) previously designated as biogenic or of unknown origin in field studies might have originated from anthropogenic sources, such as photooxidation of hydrocarbons present in diesel and biodiesel fuel.

Interaction of water vapor with the surfaces of imidazolium-based ionic liquid nanoparticles and thin films.

Understanding the interactions of humid air with ionic liquids (ILs) is critical for predicting how their physicochemical properties are affected by water. Using experimental and theoretical techniques, water vapor's interaction with aerosolized nanoparticles and thin films of [C(2)MIM][Cl] and [C(2)MIM][BF(4)] was studied. Solutions were electrosprayed to produce dry particles. Particles' hygroscopic growth was quantified using tandem nanodifferential mobility analysis as a function of relative humidity (RH). This is the first report of the interaction of water with aerosolized IL nanoparticles. The particles' small size allows true IL-water vapor equilibrium achieved quickly. Growth curves for both ILs show steady water uptake with increasing RH. Water vapor uptake by IL thin films was also examined using ATR-FTIR spectroscopy. Both experimental methods show [C(2)MIM][Cl] absorbs more water vapor than [C(2)MIM][BF(4)] over the entire RH range. Water molar fractions, calculated from growth curves, agreed well with those estimated from ATR-FTIR data. MD simulations, used to model IL-water interactions, revealed strong interactions between [Cl(-)] and water and considerably weaker interactions between [BF(4)(-)] and water. Widths and position of O-H stretching vibrations from MD simulations qualitatively reproduced ATR-FTIR results. These experimental and theoretical data provide a comprehensive picture of the behavior of absorbed water in ILs.