CMAQ Tagged Species Source Apportionment (TSSA)

1. CMAQ Tagged Species Source Apportionment (TSSA) Gail Tonnesen, Bo Wang et al., Air Quality Modeling Group University of California, Riverside WRAP Attribution of Haze Meeting, Denver, CO July 22, 2004

2. Need to understand which emissions sources contribute to haze and other pollutants. Use this information to assist in developing control strategies. Motivation

3. Chemical Mass Balance analysis Back-trajectory models Lagrangian models Sensitivity Studies Mass tracking approaches. Modeling Approaches for Source Apportionment

4. Run a model Base Case simulation. Add-in or Zero-out a particular source and run a the model again. The difference in the base case and the sensitivity case predicts the effect of changing that source on concentration at all receptor sites. Sensitivity Methods (1)

5. Advantages of Sensitivity Methods: directly related to development of control measures. Conceptually simple to apply. Problems with Sensitivity Methods: Brute force approaches (removing one species in each model run) are computationally expensive. Sensitivity results depend on the base case scenario. Sensitivities results can be non-linear and non-additive. CMAQ exhibits numerical noise in PM sensitivity runs. Sensitivity Methods (2)

6. Decoupled Direct Method is a computationally efficient sensitivity method: Calculates many sensitivities in one run. Difficult to implement in PM models. Calculates derivative – but sensitivities can be non-linear. Recommendation: Sensitivity studies are a valuable tool, but expensive to apply, and care is needed in interpretation of results. Sensitivity Methods (3)

7. Mass Tracking Algorithms Output and analyze mass flux terms and chemical reaction rates for each grid cell. Computationally prohibitive. OSAT Uses tracers to track O3 formation that was sensitive to VOC or NOx. Mass Tracking Methods

8. Use “Tagged Species” or Tracers to track chemical transformations and transport of each PM species or PM precursor . Add the tracers for key species and for defined source regions & source categories. Provides 3-D fields showing source attribution of of PM species for any grid cell in model domain. Tagged Species Approach (1)

9. Method: Add one new set of tagged species for each emissions source category or source location being tracked. Straight forward for non-reactive species: add 1 tracer for each source. Example: in each grid cell the sum of all tracers for EC equals the total (bulk) EC concentration in each cell. Each tracer is defined for all grid cells and is emitted, transported, and removed proportional to its weight of the bulk species in each grid cell. Tagged Species Approach (2)

10. More complicated for chemical reactive species and secondary particulates: Must also track the chemical reactions that convert a tracer between different gas species and from gas to PM. Model include approximately 6 forms of N species, must carry 6 additional tracers for each NOx source category to track the contributions to aerosol nitrate. SOA formation is still more complex, not included in current algorithm. SO4 and other PM species are easier and less computational expensive to treat. Tagged Species Approach (3)

11. Traced Area: WRAP Modeling Domain Source Area Mapping File: Each state is distinguished by a unique number

12. Traced Source Tags

13. Advection Calculate mass flux between grid cells to update tracers. Vertical Diffusion Apply the CMAQ diffusion algorithms to tracers. Also evaluate new algorithms to estimate actual 2-way mass transfer between layers. Update for mass flux in CLOUD & aqueous chemistry algorithm. Update tagged species for emissions and deposition terms. Check for mass conservation at each step and adjust mass if needed. Halt if large errors. Transport & Loss Terms

14. TSSA Structure Design driver.F: read tssa configuration, ptssa_init … do n = 1, nsteps tssa_couple tssa_decouple write tssa output end do • sciproc.F • Xadv • Yadv • Yadv • Xadv • Zadv • Tssa Adjadv • Hdiff • Tssa Decouple • Vdiff • Tssa Cldproc • Chem • Tssa Aero • Tssa Couple Hppm TSSA mass normalization Tssa adv update vppm Tssa hdiff update Tssa vdiff update Tssa chem update smvgear

15. NOX = reactive N family. = { NO, NO2, NO3, 2*N2O5, HONO, PNA} HNO3 PAN RNO3 ANO3J ANO3I Tagged Species for Nitrates

16. Emissions are as NOx = NO + NO2 Use integrated reaction rates at each time step to update the tagged species: NOX  PAN NOX  RNO3 NOx  HNO3 HNO3  ANO3 Chemical Transformations

17. Previously implemented in CMAQ v4.2.2. (12/03) Currently implemented in CMAQ v4.4 Programming Language: Fortran 90 Compilers: pgf90 or intel fortran compiler (ifc) Parallelism: supports multi-processor usage (MPI) Currently implemented with GEAR & QSSA chemistry solvers. Implementation in CMAQ

18. 3-d concentration field for each tagged species Each model grid cell is included as a receptor. Results can be viewed as 3-d animation of the tagged species, or layer 1 animations in PAVE Bar plots for receptor showing attribution is most useful for the receptor sites. Output files for annual simulation are too large with over 12 GB per day. Currently outputting only layer 1. Output Formats

19. Slower run time because we use GEAR or QSSA chemistry (about 4x cost of EBI solver). RAM memory is primary constraint: For many tracers we split them between 2 model runs to avoid paging memory to disk. Run Time: about 3 hours per day using 8 Opteron CPUs with 2 GB RAM. With 32 CPUs, running CMAQ in 4 seasons, takes about 2 weeks for an annual simulation. Computational Cost/Constraints

20. Animation gifs demo:

21. Test alternate treatments of HNO3 NO3 and H2SO4 SO4 equilibrium. Implement organic aerosols and ozone. Improve Graphics/Statistics Program to automate Tracer Result Evaluation. More Testing- comparisons with CAMx PSAT runs, and testing for mass conservation. Scalability in supporting other modeling domains Create corresponding source area mapping files county domains. Future Work