Environmental Engineering Reference
In-Depth Information
2. Method
In this study, we used the CAMx version 4.42 and 4.51 (Environ, 2008). We
calculated the meteorological parameters using the MM5 model (PSU/NCAR,
2004). There were three domains with resolutions of 27 × 27 km (Europe),
9 × 9 km (central Europe) and 3 × 3 km (Switzerland). We used 14
-
layers in a
terrain-following Lambert Conic Conformal coordinate system in CAMx. The
initial and boundary conditions were extracted from the output of the global model
MOZART for similar periods (Horowitz et al., 2003). The simulated episodes are
January and June 2006. The concentrations of particles smaller than 2.5 µm in
diameter were calculated using CAMx. The main changes in the new version
(4.51) are CB05 gas-phase mechanism (instead of CB4), SOA formation from
isoprene and sesquiterpenes (in addition to monoterpenes), polymerization of
anthropogenic and biogenic SOA. In addition, the saturation concentrations and
values of enthalpy of vaporization were updated as well.
σ
3. Results and Discussion
Both measurements and model results suggest that the main components of the
winter aerosols in Zurich are particulate nitrate and organic aerosols. The organic
aerosols calculated by the previous model version were mainly primary organic
aerosols whereas the measurements suggested that more than half of the parti-
culate organic mass was oxygenated organic aerosols (OOA), mostly representing
secondary organic aerosols (Lanz et al., 2008). Calculations with the new model
version improved the organic aerosol fraction by 20% mainly due to increased
SOA formation from biogenic precursors and their polymerization. Model pre-
dicted 45% of OA as secondary
(Fig. 1)
. In spite of the improvements in SOA
modeling, the predicted total organic aerosol concentrations are still lower than the
measurements (
Fig. 2)
.
Fig. 1.
Predicted organic aerosol (OA) concentrations with new model version (CAMx4.51) in
January 2006. I and III: high-wind, II and IV: low-wind periods
