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California Air Resources Board 1
Integration of Modeling Results-the problem of double counting and possible
solutions
Shuming Du
August 27, 2003
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California Air Resources Board 2
RegionalModeling
Risk Assessment
Mapping andVisualization
MicroscaleModeling
Emissions andMeteorology
Modeling Framework
HARP
CHAPIS
IntegratedResults
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California Air Resources Board 3
• Overview
• Possible solutions
• Details of a new box model
• Recommendations
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California Air Resources Board 4
Problem of ‘double-counting’
• Some emission sources are included in both regional and microscale modeling
• These emissions are counted twice when integrating regional and microscale modeling results
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California Air Resources Board 5
Possible solutions (1)
• Exclude duplicate emissions from regional modeling
• Not recommended because: Fundamentally incorrect because chemistry
mechanism requires total (or actual) concentrations
Computationally not feasible for multiple (neighborhood scale) applications
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California Air Resources Board 6
Other possible solutions• Microscale modeling (usually) does not
consider chemical reactions
• Running regional model in inert mode to calculate the impact of the double-counted sources in a regional model, then deduct that impact when calculating total concentrations
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California Air Resources Board 7
Different approaches for different applications
• Statewide application for risk maps– require running regional model more one time
• Neighborhood scale applications – Several methods are being evaluated, one of
them will be discussed today
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California Air Resources Board 8
Statewide risk map - solution (2)
• For applications creating statewide risk maps, need to run regional model twice: – once with all emission sources and running the
model in reactive mode: C reactive,
– and the second time with only the emission sources that are included in the microscale modeling and running the model in inert mode: C inert
inertmicroscalereactivetotal CCCC
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California Air Resources Board 9
Neighborhood scale applications
• In principle, solution (2) could be used in neighborhood scale applications (e.g., Barrio Logan and Wilmington studies)
• Requires running regional model in inert mode for each and every neighborhood that needs to do cumulative impact assessment
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California Air Resources Board 10
Possible solution (3)
• Solution (2) is computationally demanding although much less than solution (1)
• Alternate solution: approximate calculation to replace regional scale modeling: develop a (new) simple box model
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California Air Resources Board 11
• CALGRID modeling results indicate that emission sources in (individual) neighboring cells have minor contributions
• This suggests that it is possible to use the simple box model to replace CALGRID for the purpose of calculating concentrations caused by ‘local emissions’ (i.e., neglecting contributions from neighbors)
Rationale for the box model
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California Air Resources Board 12
Wind
• Consider a grid cell (of regional model) as a box to establish mass balance of pollutants– Turbulent diffusion is neglected
Emission
|U|C x Area
|V|C x Area
WC x Area
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California Air Resources Board 13
WVU
QC
yxzy
microscalecountdouble
|)||(|
countdoublemicroscalescaleregionaltotal CCCC
A New Box Model
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California Air Resources Board 14
Summary• We have two recommendations to address the
‘double count’ problem:– Statewide applications: run regional scale model
twice
– Neighborhood scale applicationsThe new box model Improvement is in progress
inertmicroscalereactivetotal CCCC
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California Air Resources Board 15
How does the box model perform?
• Sensitivity test: run CALGRID at inert mode
• 9 grids each with unit emission rate of different pollutant, these grids cover Wilmington area where we know double counting is a problem
• Concentrations are calculated at each and every grid (87 x 67)
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California Air Resources Board 16
CALGRID test case
• (32,42) (33,42) (34,42) (35,42) (36,42)
(32,41) (33,41)C1
(34,41)C2
(35,41)C3
(36,41)
(32,40) (33,40)B1
(34,40)B2
(35,40)B3
(36,40)
(32,39) (33,39)A1
(34,39)A2
(35,39)A3
(36,39)
(32,38) (33,38) (34,38) (35,38) (36,38)
Red area: unit emission rate for pollutants A1, A2 …
Blue area: zero emissions
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California Air Resources Board 17
Comparison between CALGRID and the BOX model
Monthly averages
0.0E+00
1.0E-03
2.0E-03
3.0E-03
4.0E-03
5.0E-03
6.0E-03
A1 A2 A3 B1 B2 B3 C1 C2 C3
Pollutants
Co
nce
ntr
atio
ns
(ug
/m**
3)
CALGRID
BOX
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California Air Resources Board 18
Comparison between CALGRID and the BOX model
Hourly Concentrations of A2
0.0E+00
1.0E-02
2.0E-02
3.0E-02
4.0E-02
5.0E-02
6.0E-02
0 5 10 15 20 25 30
Time (Julian day)
Co
nce
ntr
atio
ns
(ug
/m**
3)
CALGRID
BOX
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California Air Resources Board 19
Hourly Concentrations of A2
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1.40E-02
1.60E-02
1.80E-02
2.00E-02
5 6 7 8 9 10
Time (Julian day)
Co
nce
ntr
atio
ns
(ug
/m**
3)
CALGRID
BOX
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California Air Resources Board 20
Box model overestimates?
• Yes. Why?
• Turbulent diffusion is neglected, therefore when wind speed is very low, advection will not dominate. Remedy?
• Impose a minimum wind speed (=0.25 m/s) -when wind speed is below this threshold, use it in the box model
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California Air Resources Board 21
Minimum wind speed = 0.25 m/sMonthly averages
(minimum wind speed = 0.25 m/s)
0.0E+00
1.0E-03
2.0E-03
3.0E-03
4.0E-03
5.0E-03
6.0E-03
A1 A2 A3 B1 B2 B3 C1 C2 C3
Pollutants
Co
nce
ntr
atio
ns
(ug
/m**
3)
CALGRID
BOX
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California Air Resources Board 22
Hourly Concentrations of A2(minimum wind speed = 0.25 m/s)
0.00E+00
1.00E-02
2.00E-02
3.00E-02
4.00E-02
5.00E-02
6.00E-02
0 5 10 15 20 25 30
Time (Julian day)
Co
nce
ntr
atio
ns
(ug
/m**
3)
CALGRID
BOX
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California Air Resources Board 23
Hourly Concentrations of A2
(minimum wind speed = 0.25 m/s)
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1.40E-02
1.60E-02
1.80E-02
2.00E-02
6 7 8 9 10
Time (Julian day)
Co
nce
ntr
atio
ns
(ug
/m**
3)
CALGRID
BOX