Size distributions, sources and source areas of water-soluble organic carbon in urban background air H. Timonen1, S. Saarikoski1, O. Tolonen-Kivimäki1, M. Aurela1, K. Saarnio1, T. Petäjä2,3, P. P. Aalto2, M. Kulmala2, T. Pakkanen1, and R. Hillamo1 1Finnish Meteorological Institute, Air Quality, Erik Palménin Aukio 1, P.O. Box 503, 00101 Helsinki, Finland 2University of Helsinki, Department of Physical Sciences, P.O. Box 64, 00014 University of Helsinki, Finland 3Earth and Sun Systems Laboratory, Atmospheric Chemistry Division National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80305-3000, USA
Abstract. This paper represents the results of one year long measurement period of the
size distributions of water-soluble organic carbon (WSOC), inorganic ions
and gravimetric mass of particulate matter. Measurements were done at an
urban background station (SMEAR III) by using a micro-orifice uniform
deposit impactor (MOUDI). The site is located in northern European boreal
region in Helsinki, Finland. The WSOC size distribution measurements were
completed with the chemical analysis of inorganic ions, organic carbon (OC)
and monosaccharide anhydrides from the filter samples (particle aerodynamic
diameter smaller than 1 μm, PM1). Gravimetric mass concentration
varied during the MOUDI samplings between 3.4 and 55.0 μg m−3 and the
WSOC concentrations were between 0.3 and 7.4 μg m−3. On average,
water-soluble particulate organic matter (WSPOM, WSOC multiplied by 1.6 to
convert the analyzed carbon mass to organic matter mass) comprised 25±7.7%
and 7.5±3.4% of aerosol PM1 mass and the PM1–10 mass, respectively.
Inorganic ions contributed 33±12% and 28±19% of the analyzed PM1 and PM1–10 aerosol mass.
Five different aerosol categories corresponding to different sources or
source areas were identified (long-range transport aerosols, biomass burning
aerosols from wild land fires and from small-scale wood combustion, aerosols
originating from marine areas and from the clean arctic areas). Categories
were identified mainly using levoglucosan concentration level for wood
combustion and air mass backward trajectories for other groups. Clear
differences in WSOC concentrations and size distributions originating from
different sources or source areas were observed, although there are also
many other factors which might affect the results. E.g. the local conditions
and sources of volatile organic compounds (VOCs) and aerosols as well as
various transformation processes are likely to have an impact on the
measured aerosol composition. Using the source categories, it was identified
that especially the oxidation products of biogenic VOCs in summer had a
clear effect on WSOC concentrations.
Citation: Timonen, H., Saarikoski, S., Tolonen-Kivimäki, O., Aurela, M., Saarnio, K., Petäjä, T., Aalto, P. P., Kulmala, M., Pakkanen, T., and Hillamo, R.: Size distributions, sources and source areas of water-soluble organic carbon in urban background air, Atmos. Chem. Phys., 8, 5635-5647, doi:10.5194/acp-8-5635-2008, 2008.