The aim of this
study was to characterize the concentrations and particle mass size
distributions of water-soluble organic carbon (WSOC) in urban aerosols. The
sample collection was carried out in spring 2006 at the SMEAR III station in
Helsinki, Finland, by using a size-segregating method (MOUDI) and by collecting
sub-micrometer fraction of aerosols on the filter. During the three-month
measurement period, a major 12-day biomass burning pollution episode was
observed. Concentrations of WSOC, organic carbon, monosaccharide anhydrides,
inorganic ions and some organic acids (oxalic, succinic and malonic acid) were
analyzed from the PM₁ samples. The measured OC and WSOC
concentrations varied in ranges 0.67–15.7 µg m^–3 and 0.26–10.7 µg
m^–3, respectively. The WSOC/OC concentration ratio was between 0.30
and 0.89 with an average of 0.54. Size distributions of WSOC, inorganic ions and
total mass were determined from the MOUDI samples. WSOC had bimodal size
distributions with a clear accumulation mode below 1 µm of particle aerodynamic
diameter and minor coarse mode at sizes > 1
µm.