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.