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

Integration of Modeling Results - the problem of double counting and possible solutions. Shuming Du August 27, 2003. Overview Possible solutions Details of a new box model Recommendations. Problem of ‘double-counting’.

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

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  1. Integration of Modeling Results-the problem of double counting and possible solutions Shuming Du August 27, 2003 California Air Resources Board

  2. California Air Resources Board

  3. Overview • Possible solutions • Details of a new box model • Recommendations 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 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 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 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 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 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 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 California Air Resources Board

  11. Rationale for the 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) California Air Resources Board

  12. WdC x Area • Consider a grid cell (of regional model) as a box to establish mass balance of pollutants • Turbulent diffusion is neglected |U|C x Area Wind |V|C x Area Emission California Air Resources Board

  13. A New Box Model 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 applications • The new box model • Improvement is in progress 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) California Air Resources Board

  16. CALGRID test case Red area: unit emission rate for pollutants A1, A2 … Blue area: zero emissions California Air Resources Board

  17. Comparison between CALGRID and the BOX model California Air Resources Board

  18. Comparison between CALGRID and the BOX model California Air Resources Board

  19. 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 California Air Resources Board

  21. Minimum wind speed = 0.25 m/s California Air Resources Board

  22. California Air Resources Board

  23. California Air Resources Board

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