rosenbrock approach to the treatment of aqueous chemistry in cmaq

Office of Research and Development | National Exposure Research LaboratoryAtmospheric Sciences Modeling and Analysis Division |Research Triangle Park, NC

April 19, 2023

Annmarie G. Carlton, Gerald Gipson, Shawn Roselle, Rohit Mathur

Rosenbrock Approach to the Treatment of Aqueous Chemistry in CMAQ

Office of Research and Development | National Exposure Research LaboratoryAtmospheric Modeling and Analysis Division | Research Triangle Park, NC

2

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


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INTRODUCTIONEvolving 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)


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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


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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) SO4, HSO4, SO3, HSO3, CO3, HCO3, OH, NH4, HCO2, NO3, ClStart iteration and bisection (3000 iterations)Calc. final gas phase partial pressure of SO2, NH3, HNO3, HCOOH, CO2liquid conc. (mol L-1) SO4, HSO4, SO3, HSO3, CO3, HCO3, OH, NH4, HCO2, NO3, ClCheck 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


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More Processes Solved Simultaneously with ROS3

1

1 1

)(i

j

i

jjijjijni khJkyhfk

)(')())(,()()( 000000 thytytythftyhty

Rosenbrock Method

s

iiinn kbyy

11Where: J is the Jacobian

Forward Euler Method

ijijib ,, are constants


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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., 20032. Implemented ROS3 solver in CCTM with same aqueous chemical mechanism currently employed to understand solver-specific effects3. Testing:

- partitioning assumptions- expansion of the chemical mechanism


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1.) Comparison with Gear Solver in Box Model Test

ROS3

GEAR


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2.) Implementing ROS3 for CMAQ aqueous mechanism

•Gas-to-droplet partitioningCurrent assumption, instantaneous thermodynamic equilibrium according to Henry’s Law

•Oxidation Chemistry5 sulfur “family” reactions: S(IV) S(VI) via O3, H2O2, O2, MHP, PAA

2 organic reactions: GLY, MGLY + ●OH

•Wet Depostion

)()( aqAgA ii

AAi pHaqA )(

Current CMAQ Aqueous Processes


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2.) Implementing ROS3 for CMAQ aqueous mechanism


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Accumulation mode SO4 comparisons

Forward Euler Method

ROS3 Method

surface layer < ~ 34 metersμg m-3


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Differences in accumulation mode SO4

aloft layer typical of cloud base

Forward Euler Method SO4 – ROS3 Method SO4

surface layer < ~ 34 meters

μg m-3


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3.) Enhancing CMAQ Aqueous Processes: More Explicit Chemistry

13) GLY + OH(+O2) GLYAC + HO2

14) GLYAC + OH OXLAC + HO2 + H2O

15) GLYAC- + OH OXLAC- + HO2 + H2O

16) OXLAC + OH 2CO2 + 2H2O

17) OXLAC- + OH CO2 + CO2 - + 2H2O

18) OXLAC2- + OH CO2+CO2 - + OH-

19) GLYAC ↔ H+ + GLYAC-

20) OXLAC ↔ H+ + OXLAC

21) OXLAC- ↔ H+ + OXLAC2-

22) GLYAC + H2O2 HCO2H + CO2 + H2O

23) HCO2H + OH CO2 + HO2 + H2O

24) HCO2- + OH CO2

- + H2O

25) HCO2H ↔ H+ + HCO2-

1) H2O2 + hv 2OH

2) OH+ H2O2 HO2 + H2O

3) HO2 + H2O2 OH + H2O + O2

4) HO2 + HO2 H2O2 + O2

5) OH+ HO2 H2O + O2

6) OH + O2 - OH- + O2

7) HCO3- + OH CO3- +

H2O

8) CO3- + O2

- CO32- + O2

9) CO3- + HCO2

- HCO3- +

CO2-

10) CO3- + H2O2 HCO3

- + HO2

11) CO2 (+H2O) ↔ H+ + HCO3-

12) HCO3- ↔ H+ + CO3

2-

Reactions are taken from Lim et al. (2005); Carlton et al., (2008); Tan et al., (2009) and Refs. Therein.

GLY + OH ORGC

HOx chemistry Glyoxal oxidation chemistry


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3.) Enhancing CMAQ Aqueous Processes: Partitioning

HRT

AkGLkSQ

dt

dA imtimtAA

i

HRT

Ak imt

volatilization

aqueous production

sink reactions

accommodation

interfacial processes by Schwartz (1986) 12

)3

4

3(

d

g

dmt

R

D

Rk 2/1)

8(MW

RT

Theoretical maximum

Current CMAQ approachAi(g) Ai (aq)

Ai(aq) Ai (g)

imtGLk


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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


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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

rosenbrock approach to the treatment of aqueous chemistry in cmaq

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