Environmental Engineering Reference
In-Depth Information
January 2006
40
35
30
25
20
15
10
5
0
EC
NH4
N03
SO4
Org
CAMx4.42
CAMx4.51
Measurements
Fig. 2.
Predicted aerosol concentrations with two model versions (CAMx4.42 and CAMx4.51) as
well as measurements at Zurich in January 2006
The calculations for the summer episode suggested an increase in OA by 11%.
Model results indicate that SOA fraction in summer is about 70% and comes
mainly from biogenic precursors. In spite of the improvements, predicted OA con-
centrations are still lower than the measurements (
Fig. 3)
. The highest fraction of
SOA in winter is predicted to come from monoterpenes. On the other hand,
sesquiterpenes are the main source of SOA in summer.
June 2006
12
10
8
EC
NH4
NO3
SO4
Org
6
4
2
0
CAMx4.42
CAMx4.51
Measurements
Fig. 3.
Predicted aerosol concentrations with two model versions (CAMx4.42 and CAMx4.51) as
well as measurements at Payerne in June 2006
4. Conclusions
We compared the results of aerosol simulations with two CAMx versions (v4.42
and v4.51) for winter and summer episodes in Switzerland. The organic aerosols
predicted by the earlier version in winter were mainly primary, however, analysis
of AMS data suggested that about half of the particulate organic mass in winter
was oxygenated organic aerosols (OOA), mostly representing SOA. The new
version with updated SOA module led to improved SOA concentrations (20%)
due to polymerization and updated SOA parameterization. Results indicate a
similar trend about the POA and SOA fractions as measurements suggest. On the
other hand, improvement in SOA was less in summer (11%). Both model
predictions and measurements suggest that the main component of aerosols is the
