1. Office of Research and Development | National Exposure Research Laboratory Atmospheric Sciences Modeling and Analysis Division |Research Triangle Park, NC February 9, 2016 Annmarie G. Carlton, Gerald Gipson, Shawn Roselle, Rohit Mathur Rosenbrock Approach to the Treatment of Aqueous Chemistry in CMAQ

2. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 1 BACKGROUND Clouds cover ~60% of the Earth’s surface –Associated convective mixing and aqueous phase processes provide a mechanism for venting atmospheric constituents from the polluted boundary layer to the free troposphere, with substantial implications for long-range pollution transport and climate

3. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 2 INTRODUCTION Evolving knowledge indicates atmospheric aqueous phase chemistry is more complex than typical model mechanisms Current aqueous mechanism designed to predict sulfate Current CMAQ aqueous chemistry module does not easily lend itself to expansion Forward Euler solver for oxidation and bisection method for pH (note linear convergence for bisection method) Stiffness induced by timescales of different orders of magnitude (e.g., ● OH reactions) ROS3 solver is a good candidate for solving atmospheric aqueous chemistry (Sandu et al., 1997; Djouad et al., 2002)

4. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 3 Multipollutant version of CMAQ Simulation with update Max=24.3 µg/m3 original simulation Max=283.4 µg/m3 Unrealistic sulfate production: -problem traced to aqueous chemistry solver technique. -Incorporated the fix into CMAQv4.7.1 Figures courtesy of P. Dolwick

5. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 4 CMAQ Aqueous Chemistry Map (aqchem.F) Molar conc. = initial amt. – amt. deposited (mol L -1 ) bisection for pH, initial guesses between 0.01 – 10 liquid conc. (mol L -1 ) SO 4, HSO 4, SO 3, HSO 3, CO 3, HCO 3, OH, NH 4, HCO 2, NO 3, Cl Start iteration and bisection (3000 iterations) Calc. final gas phase partial pressure of SO 2, NH 3, HNO 3, HCOOH, CO 2 liquid conc. (mol L -1 ) SO 4, HSO 4, SO 3, HSO 3, CO 3, HCO 3, OH, NH 4, HCO 2, NO 3, Cl Check for convergence Compute ionic strength and activity coefficient (Davies Eqn.) Calculate liquid concentrations and final gas phase concs. of oxdidants Kinetic calcs Cal. Min time step – check for large time step SIV oxidized < 0.05 of SIV oxidized since time 0, double DT Don’t let DT > TAUCLD Compute wet depositions and phase concentrations for each species TIME = TAUCLD (OR 100 iterations) Check for convergence 100 max. iterations pH partitioning oxidation deposition partitioning pH

6. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 5 More Processes Solved Simultaneously with ROS3 Rosenbrock Method Where: J is the Jacobian Forward Euler Method are constants

7. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 6 Enhance Calculation of Aqueous Chemistry in CMAQ 1. Comparison of ROS3 solver with a GEAR solver for atmospheric aqueous chemistry tested in box model used chemical mechanism described in Barth et al., 2003 2. Implemented ROS3 solver in CCTM with same aqueous chemical mechanism currently employed to understand solver-specific effects 3. Testing: - partitioning assumptions - expansion of the chemical mechanism

8. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 7 1.) Comparison with Gear Solver in Box Model Test ROS3 GEAR

9. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 8 2.) Implementing ROS3 for CMAQ aqueous mechanism Gas-to-droplet partitioning Current assumption, instantaneous thermodynamic equilibrium according to Henry’s Law Oxidation Chemistry 5 sulfur “family” reactions: S(IV)  S(VI) via O 3, H 2 O 2, O 2, MHP, PAA 2 organic reactions: GLY, MGLY + ● OH Wet Depostion Current CMAQ Aqueous Processes

10. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 9 2.) Implementing ROS3 for CMAQ aqueous mechanism

11. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 10 Accumulation mode SO 4 comparisons Forward Euler MethodROS3 Method surface layer < ~ 34 meters μ g m -3

12. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 11 Differences in accumulation mode SO 4 aloft layer typical of cloud base Forward Euler Method SO 4 – ROS3 Method SO 4 surface layer < ~ 34 meters μ g m -3

13. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 12 3.) Enhancing CMAQ Aqueous Processes: More Explicit Chemistry 13) GLY + OH(+O 2 )  GLYAC + HO 2 14) GLYAC + OH  OXLAC + HO 2 + H 2 O 15) GLYAC- + OH  OXLAC- + HO 2 + H 2 O 16) OXLAC + OH  2CO 2 + 2H 2 O 17) OXLAC- + OH  CO 2 + CO 2 - + 2H 2 O 18) OXLAC2- + OH  CO 2 +CO 2 - + OH- 19) GLYAC ↔ H + + GLYAC - 20) OXLAC ↔ H + + OXLAC 21) OXLAC- ↔ H + + OXLAC 2- 22) GLYAC + H 2 O 2  HCO 2 H + CO 2 + H 2 O 23) HCO2H + OH  CO2 + HO 2 + H 2 O 24) HCO 2 - + OH  CO 2 - + H 2 O 25) HCO 2 H ↔ H + + HCO 2 - 1) H 2 O 2 + hv  2OH 2) OH+ H 2 O 2  HO 2 + H 2 O 3) HO 2 + H 2 O 2  OH + H 2 O + O 2 4) HO 2 + HO 2  H 2 O 2 + O 2 5) OH+ HO 2  H 2 O + O 2 6) OH + O 2 -  OH - + O 2 7) HCO 3 - + OH  CO3 - + H 2 O 8) CO 3 - + O 2 -  CO 3 2- + O 2 9) CO 3 - + HCO 2 -  HCO 3 - + CO 2 - 10) CO 3 - + H 2 O 2  HCO 3 - + HO 2 11) CO 2 (+H 2 O) ↔ H + + HCO3- 12) HCO 3 - ↔ H + + CO 3 2- Reactions are taken from Lim et al. (2005); Carlton et al., (2008); Tan et al., (2009) and Refs. Therein. GLY + OH  ORGC HO x chemistry Glyoxal oxidation chemistry

14. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 13 3.) Enhancing CMAQ Aqueous Processes: Partitioning volatilization aqueous production sink reactions accommodation interfacial processes by Schwartz (1986) Theoretical maximum  Current CMAQ approach A i (g)  A i (aq) A i (aq)  A i (g)  

15. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 14 Findings and Implications In box model testing ROS3 represents a plausible technique to solve atmospheric aqueous phase chemistry –potentially more robust method than current method Successful implementation of the ROS3 solver to solve aqueous system in CMAQ –Beta version run time is slower but still optimizing

16. Office of Research and Development | National Exposure Research Laboratory Atmospheric Modeling and Analysis Division | Research Triangle Park, NC 15 Future Directions Put wet deposition back in Aqchem with ROS3 as an option in FY11 CMAQ release –Test this solver for different seasons, e.g., winter Incorporate more explicit chemistry into CMAQ –Find balance between more explicit chemistry and computational efficiency Compare with ground-base and aloft observational data –Speciated rain, cloud, deposition measurements