Abstract. Source apportionment of organic aerosols (OAs) is of great importance to
better understand the health impact and climate effects of particulate matter
air pollution. Air quality models are used as potential tools to identify
OA components and sources at high spatial and temporal resolution; however,
they generally underestimate OA concentrations, and comparisons of their
outputs with an extended set of measurements are still rare due to the lack
of long-term experimental data. In this study, we addressed such challenges
at the European level. Using the regional Comprehensive Air Quality Model
with Extensions (CAMx) and a volatility basis set (VBS) scheme which was
optimized based on recent chamber experiments with wood burning and diesel
vehicle emissions, and which contains more source-specific sets compared to
previous studies, we calculated the contribution of OA components and defined
their sources over a whole-year period (2011). We modeled separately the
primary and secondary OA contributions from old and new diesel and gasoline
vehicles, biomass burning (mostly residential wood burning and agricultural
waste burning excluding wildfires), other anthropogenic sources (mainly
shipping, industry and energy production) and biogenic sources. An important
feature of this study is that we evaluated the model results with
measurements over a longer period than in previous studies, which
strengthens our confidence in our modeled source apportionment results.
Comparison against positive matrix factorization (PMF) analyses of aerosol
mass spectrometric measurements at nine European sites suggested that the
modified VBS scheme improved the model performance for total OA as well as
the OA components, including hydrocarbon-like (HOA), biomass burning (BBOA)
and oxygenated components (OOA). By using the modified VBS scheme, the mean
bias of OOA was reduced from −1.3 to −0.4 µg m−3
corresponding to a reduction of mean fractional bias from −45 % to
−20 %. The winter OOA simulation, which was largely underestimated in
previous studies, was improved by 29 % to 42 % among the evaluated
sites compared to the default parameterization. Wood burning was the dominant
OA source in winter (61 %), while biogenic emissions contributed
∼ 55 % to OA during summer in Europe on average. In both seasons,
other anthropogenic sources comprised the second largest component (9 %
in winter and 19 % in summer as domain average), while the average
contributions of diesel and gasoline vehicles were rather small
(∼ 5 %) except for the metropolitan areas where the highest
contribution reached 31 %. The results indicate the need to improve the
emission inventory to include currently missing and highly uncertain local
emissions, as well as further improvement of VBS parameterization for winter
biomass burning. Although this study focused on Europe, it can be applied in
any other part of the globe. This study highlights the ability of long-term
measurements and source apportionment modeling to validate and improve
emission inventories, and identify sources not yet properly included in
existing inventories.
Combined passenger and parcel transportation using a mixed fleet of electric and gasoline vehicles
