Regional Modeling of Ozone, PM and Acid Deposition

1. Regional Modeling of Ozone, PM and Acid Deposition Talat Odman, Ted Russell, Jim Wilkinson, Yueh-Jiun Yang, Jim Boylan, Alberto Mendoza School of Civil and Environmental Engineering Georgia Tech Georgia Institute of Technology

2. Overview • Wet deposition • updated results from May 95 episode • a new look at performance • Sulfur budget • effect of emission reductions • effect of initial and boundary conditions • Comparison of DDM sensitivities to brute force • Sensitivities for July 2010 • Sulfate to SO2 emissions • Ozone to NOx emissions Georgia Institute of Technology

3. Wet deposition • Precipitation inputs to URM grids larger than 12 km were being enhanced inadvertently • Corrected • Rerunning May 1995 episode • Need to rerun July 1995? • Wet deposition over the 12 km grid does not seem to be affected significantly after first 2 days • Aerosol sulfate concentrations changed significantly at the edges of the 12 km grid • therefore, aerosol concentrations as well as wet deposition may change in the 12 km grid later in the episode Georgia Institute of Technology

4. Cumulative Precipitation (2 days) Now Before Georgia Institute of Technology

5. Cumulative Sulfate Wet Deposition Before Now Georgia Institute of Technology

6. Cumulative Nitrate Wet Deposition Before Now Georgia Institute of Technology

7. Fine Sulfate Aerosols (Day 1) Before Now Georgia Institute of Technology

8. Fine Sulfate Aerosols (Day 2) Before Now Georgia Institute of Technology

9. Wet Deposition Performance • We are now calculating the best of 3x3 and 5x5 cell values around each NADP site, as well as the maximum, minimum, average and standard deviations. • We also calculate a second best value of the cumulative deposition by relaxing the time correlation • sampling ends at 7 am • accumulation of model results may continue till midnight Georgia Institute of Technology

10. SO4 Wet Deposition (July 95) Georgia Institute of Technology

11. Temporally Uncorrelated Georgia Institute of Technology

12. Sulfur Budget • Initial and final mass of sulfur was calculated along with all sulfur fluxes (emissions, deposition and boundary) • robust diagnostic of the model • yields important information on how to set initial and boundary conditions for future year simulations • URM was (is) not equipped for a sulfur budget • lateral boundary flux estimates may (still) be inaccurate • unbalanced budget should not be viewed as a mass conservation problem in the model • Performed for a single day • July 10 (second ramp-up day) Georgia Institute of Technology

13. SO2-SO4 Budget (1000 tons of S) Lateral Top Unaccounted Before After 21.2 3.8 39.7 0.1 0.1 48.0 42.5 155.5 135.0 SO2 ==> SO4 64.8 16.7 1.1 1.0 37.0 19.5 0.1 Dry Dep. Wet Dep. Emission Georgia Institute of Technology

14. Sulfur Budget (tons of S) Lateral 18,500 Top 270 Unaccounted 3,800 Before 197,500 After 183,000 Dry Dep. 17,750 Wet Dep. 38,000 Emission 19,600 Georgia Institute of Technology

15. Budget Summary • Daily sulfur emissions is 10% of the initial sulfur mass • Another 10% is coming in through lateral boundaries • Dry deposition is about 10% of the initial mass • Wet deposition is about 20% • As much as 40% of initial SO2 is converted to SO4 • Sulfur mass goes down by about 10% at the end of the day • Unaccounted mass is 2% of the initial sulfur mass Georgia Institute of Technology

16. 10% Reduction Lateral Top Unaccounted Before After 21.0 4.2 39.7 0.1 0.1 47.8 42.5 155.5 135.0 SO2 ==> SO4 64.4 16.5 1.0 1.0 37.1 17.5 0.1 Dry Dep. Wet Dep. Emission Georgia Institute of Technology

17. 10% Reduction Lateral 18,750 Top 270 Unaccounted 4,250 Before 197,500 After 182,800 Dry Dep. 17,500 Wet Dep. 38,000 Emission 17,600 Georgia Institute of Technology

18. Effects of 10% Sulfur Emission Reduction • Dry deposited SO2 decreased by 1% • SO4 leaving through the lateral boundaries decreased by about 1% • SO2 converted to SO4 decreased by less than 1% • Final SO4 mass decreased slightly • Other changes are not noticeable Georgia Institute of Technology

19. Current Sulfur Initial and Boundary Conditions • SO2 initial and boundary conditions are derived from surface data. • Data are temporally averaged for BCs, which remain constant. • Linearly interpolated in the vertical to a value of .026 ppb at 5 km. • Mixing ratio remains constant from 5 km to the domain top. • Sulfate is initially uniform at the surface: about 4.5 ug/m3 • Linearly interpolated to 0.12 ug/m3 at 5 km height. • Sulfate boundary conditions are constant: • North, West and Southwest boundary is set to 2.5 ug/m3, • Southeast and East boundary is set to 0.25 ug/m3 at surface. Georgia Institute of Technology

20. Conclusion and Recommendation for Future Year Simulations • The amount of aerosol sulfate and sulfate deposition are dominated by the amount of initial sulfur mass. • The lateral fluxes of sulfur are of the same order of magnitude as sulfur emissions. • We should reduce the initial sulfur mass by the same amount as the emission reductions: • our episodes are too short to show proper response to emission reductions • We should also consider reducing the boundary conditions for sulfur. Georgia Institute of Technology

21. Comparison of Sensitivities • We are comparing sensitivities estimated by DDM to concentration changes in actual model simulations. • July 95 is the base case: • DDM calculations are performed during the base-case simulation. • In a second simulation, we reduce SO2 emissions by 40%. • We take the difference between the base case and 40% reduction scenario and compare the results to DDM. • The results are in excellent agreement for SO2. • SO4 is similar in the beginning but the difference grows in time, which is of concern. Georgia Institute of Technology

22. Change of SO4 (ug/m3) for July 940% decrease in SO2 emissions Georgia Institute of Technology

23. Change of SO4 (ug/m3) for July 1040% decrease in SO2 emissions Georgia Institute of Technology

24. Sensitivities for July 2010 • NOx emissions for 2010 “on the books” will be updated • Sulfate to SO2 emissions and ozone to NOx • South inner, West inner subdomains • NOx from point and surface sources • Total SO2 • Entire domain • Total NOx • Total SO2 • Four sites: GSM, SNP, Shining Rock, Atlanta Georgia Institute of Technology

25. Change of SO4(ug/m3) in GSM10% decrease in SO2 emissions Georgia Institute of Technology

26. Change of SO4(ug/m3) in SNP 10% decrease in SO2 emissions Georgia Institute of Technology

27. Change of SO4(ug/m3) in SRW 10% decrease in SO2 emissions Georgia Institute of Technology

28. Change of SO4(ug/m3) in ATL 10% decrease in SO2 emissions Georgia Institute of Technology

29. Change of O3(ppb) in GSM 10% decrease in NOx emissions Georgia Institute of Technology

30. Change of O3(ppb) in SNP 10% decrease in NOx emissions Georgia Institute of Technology

31. Change of O3(ppb) in SRW 10% decrease in NOx emissions Georgia Institute of Technology

32. Change of O3(ppb) in ATL10% decrease in NOx emissions Georgia Institute of Technology