Environmental Engineering Reference
In-Depth Information
the AURAMS15 values, while the latter are close to the observations. The small
difference between the AURAMS15 PM
1
SO
4
and PM
2.5
SO
4
suggests that most of
the PM
2.5
mass is contained within PM
1
. The GEM-MACH15 PM
2.5
SO
4
is therefore
biased high. The reason for the GEM-MACH15 PM
2.5
SO
4
positive biases is currently
under investigation and may relate to the simplified size distribution employed in
the model. The size distribution of only two bins was employed in GEM-MACH15
due to operational constraints: using a minimum number of size bins is necessary
to reduce the cpu-time required to create an operational air-quality forecast.
Ozone Comparison, Harrow Supersite
Observed Ozone at Harrow
AURAMS O3
GEM-MACH O3
180
160
140
120
100
80
60
40
20
0
6/8/2007 0:00
6/13/2007 0:00
6/18/2007 0:00
6/23/2007 0:00
6/28/2007 0:00
Time (EDT)
Fig. 1.
Ozone at Harrow, AURAMS15, GEM-MACH15, Observations
The use of only two bins for the aerosol size distribution can result in errors in
mass transfer between bins: too much PM
2.5
mass can be transferred to PM
10
.
Similarly, the two bin size distribution can result in too little mass removal due to
settling and deposition of particles. The GEM-MACH15 simulations shown here
correct for the inter-bin transfer by temporarily subdividing the two bins to a finer
resolution for both particle inter-bin growth/shrinkage, and for deposition/settling.
Sulphate At Harrow: AMS, AURAMS15, GEM-MACH15
40
AURAMS PM2.5-SO4
GEM-MACH PM2.5-SO4
AURAMS PM1-SO4
AMS - PM1 SO4
35
30
25
20
15
10
5
0
6/16/07
0:00
6/18/07
0:00
6/20/07
0:00
6/22/07
0:00
6/24/07
0:00
6/26/07
0:00
6/28/07
0:00
6/30/07
0:00
Date (Local EDT)
Fig. 2.
PM-SO4 at Harrow
