| The EMEP MSC-W chemical transport model (Simpson et al., 2003) has been successfully
used for the prediction of photochemical oxidants and various inorganic aerosol components
(sulphate, nitrate, ammonium) for many years. The model generally performs well for such
species, as should be expected for compounds whose emission sources and chemistry are
fairly well know. For carbonaceous particulate matter (PCM) however the model has been
found to give very different results in different parts of Europe, with typically poor
performance in southern Europe, but rather good results in Northern Europe (Simpson et al.,
2007). Earlier comparison with the results of source-apportionment studies from the
CARBOSOL project (Gelencser et al., 2007, Simpson et al., 2007) has shown that the
poor performance in southern Europe can partly be ascribed to difficulties with
emissions from residential wood-burning, and partly due to an underestimate of the
secondary organic aerosol (SOA) component. Such difficulties are expected for
organic aerosols, a subject where the basic science is only partially understood,
and where new experimental results continually lead to revisions in existing ideas
concerning sources and formation mechanisms (e.g. Hallquist et al., 2009). In such a
situation, it is essential that model results are evaluated as thoroughly as possible, and
that where possible the various components of organic aerosol can be evaluated
separately.
A number of source-apportionment (SA) studies have recently become available in
Europe, in which data on elemental carbon (EC), organic carbon (OC), 14C, levoglucosan,
and various markers of primary organic carbon (cellulose, sugars/sugar-alcohols) have
allowed estimates of various sources of carbonaceous particulate matter (PCM). As well as
CARBOSOL, these studies include various sites in Switzerland (e.g. Lanz et al., 2008, Szidat
et al., 2006), data are available from Gothenburg in Sweden (Szidat et al., 2008) and from
southern Norway (Yttri et al., 2009).
Here we present comparisons of the EMEP model against the source-apportionment
results of all of the above studies, comparing the model’s estimates of primary, secondary,
biogenic and anthropogenic PCM against those estimated from the SA data. We also discuss
the uncertainties inherent in such SA data resulting from difficulties associated
with measurements of PCM and with the assumptions necessary to perform the
source-apportionment. Such difficulties include positive and negative artifacts due to
filter sampling, and assumptions concerning EC/OC ratios, levoglucosan/OC ratios,
etc.
References
Gelencsér, A., May, B., Simpson, D. et al., Source apportionment of PM2.5 organic aerosol
over Europe: primary/secondary, natural/anthropogenic, fossil/biogenic origin J. Geophys.
Res., 2007, 112, D23S04, doi:10.1029/2006JD008094
Hallquist, M., Wenger, J. C., Baltensperger, U. et al., The Formation, Properties and
Impact of Secondary Organic Aerosol: Current and Emerging Issues Accepted for Atmos.
Chem. Phys. Discuss., Dec 2008
Lanz, V. A., Alfarra, M. R., Baltensperger, U. et al., Source Attribution of Submicron
Organic Aerosols during Wintertime Inversions by Advanced Factor Analysis of Aerosol
Mass Spectra, Environ. Sci. Technol., 2008, 42, 214-220
Simpson, D., Fagerli, H., Jonson, J. et al., The EMEP Unified Eulerian Model. Model
Description, The Norwegian Meteorological Institute, Oslo, Norway, 2003
Simpson, D.; Yttri, K.; Klimont, Z. et al., Modeling Carbonaceous Aerosol over Europe.
Analysis of the CARBOSOL and EMEP EC/OC campaigns, J. Geophys. Res., 2007, 112,
D23S14, doi:10.1029/2006JD008158
Szidat, S., Jenk, T.M, Synal, H. et al., Contributions of fossil fuel, biomass burning, and
biogenic emissions to carbonaceous aerosols in Zürich as traced by 14C, J. Geophys. Res.,
2006, 111, 12pp
Szidat, S., Ruff, M., Wacker, L. et al., Fossil and non-fossil sources of organic carbon
(OC) and elemental carbon (EC) in Göteborg, Sweden, Atmospheric Chemistry and Physics
Discussions, 8, 16255-16289, 2008.
Yttri, K.E., Simpson, D., Dye, C. et al., Source apportionment of the carbonaceous
aerosol – Quantitative estimates based on 14C- and organic tracer analysis, to be submitted |