california air resources board1 integration of modeling results - the problem of double counting and...

California Air Resources Board 1

Integration of Modeling Results-the problem of double counting and possible

solutions

Shuming Du

August 27, 2003


RegionalModeling

Risk Assessment

Mapping andVisualization

MicroscaleModeling

Emissions andMeteorology

Modeling Framework

HARP

CHAPIS

IntegratedResults


• Overview

• Possible solutions

• Details of a new box model

• Recommendations


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


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


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


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


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


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


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


• 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


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


WVU

QC

yxzy

microscalecountdouble

|)||(|

countdoublemicroscalescaleregionaltotal CCCC

A New Box Model


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


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)


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


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


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



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


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


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


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



(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

california air resources board1 integration of modeling results - the problem of double counting and...

Documents