Prakash Bhave, Shawn Roselle, Frank Binkowski, Chris Nolte,

Shaocai Yu, Jerry Gipson, & Ken Schere

CMAS Conference – Paper #6.8

Chapel Hill, NC, October 19, 2004

CMAQ Aerosol Module Development

Recent Enhancements & Future Plans

CMAQ Aerosol Module - Overview• Past

2000 Release described by [Binkowksi & Roselle, JGR ‘03]

Major Science Upgrades (2002 & 2003 releases)• Secondary organic aerosol – reversible partitioning• Inorganic aerosol partitioning – ISORROPIA module• N2O5 heterogeneous reaction – promotes NO3

- formation

• Present – CMAQ v4.4 (2004 release) Computational Efficiency Numerical Stability Code Structure & Documentation

• Future (2005 release) Science Upgrades New Diagnostic Tools

• Coagulation CMAQv4.3

• Coagulation rates for each moment calculated numerically, using Gauss-Hermite quadrature

CMAQv4.4• 0th and 3rd moment coagulation rates solved analytically• 2nd moment coagulation rates solved using analytical expressions

with tabulated correction factors ~fxn(i, j, Dgj/Dgi)

Efficiency• New coagulation module > 60 times faster than old one

Accuracy• Resulting coagulation rates differ on the order of 1%• Insignificant effect on modeled aerosol species concentrations

Computational Efficiency

Computational Efficiency

n

j priprijjaer

iiaerisatitotiaer

mCmC

mCCCC

1 ,

,*,,,

/)/(

/

• Secondary Organic Aerosol (SOA)

CMAQv4.3• Above system solved iteratively using 50/50 initial guess

CMAQv4.4• Above system solved iteratively using initial guess based on

solution at previous time step Efficiency

• New SOA module twice as fast as old one Accuracy

• No reduction in accuracy because iterative solution is globally convergent

CMAQ4.3 CMAQ4.4

AerosolsGas ChemCloudsVert.Diff.Adv. & HDiffOther

Computational Efficiency

CMAQ4.3 CMAQ4.4

AerosolsGas ChemCloudsVert.Diff.Adv. & HDiffOther

CoagulationThermo. Eqm.SOAOther

Aerosol module is2.3 times faster

ISORROPIA takes 62% of aerosol processing

Doubling of EC emissions in Massachusetts causes 1.7g/m3 increase in NO3

- over California!

Reported by Quansong Tong, Princeton Univ.

Numerical Stability

EC NO3-

Numerical Stability• Instability traced to the

ISORROPIA module• At low RH, infinitesimal

changes in SO4 or NHX can shift NO3 from the gas to aerosol phase, resulting in ~10 g/m3 changes in NO3

- concentrations (solid line)

• Errors identified in (NH4)2SO4 activity and EX10 subprogram of ISORROPIA in CMAQ v4.3

• Instability is eliminated in CMAQ v4.4 (dashed line)

Numerical Stability• Identified a 2nd “family” of

instabilities, resulting in ~1 g/m3 changes in NO3

- concentrations

• This instability type exists in both CMAQ v4.3 (solid line) and CMAQ v4.4 (dashed line)

• All instabilities to date occur at low RH, where a solid phase should exist.

• Future version of CMAQ may allow formation of solids at low RH

Code Structure & Documentation• Enhanced in-line

documentation• Streamlined code

structure Removed AEROSTEP Added HCOND3

AEROPROC

EQL3

ISOROPIA

NEWPART3_AE3

ORGAER3 GETCOAGS

NEWT

HCOND3

Future Plans – Sea Salt• Identified best-available

parameterization of open-ocean sea-salt flux (black line)

• Fit the open-ocean flux parameterization to a sum of 2 lognormal modes (blue line)

• Next CMAQ release will have Na+ and Cl- ions treated in the aerosol thermodynamics routine

• May enhance nitrate formation and deposition in coastal areas

- CMAQ results using source apportionment capability (Aug. 1, 1999)

- Evaluations will provide direct feedback to emission inventory improvement

- Validated results can support control strategy development

Future Plans – Carbon ApportionmentDiesel exhaust fraction of TCpri Biomass combustion fraction of TCpri

Future Plans – Sulfate Apportionment

All scales represent the fraction of total aerosol sulfate.

Summary• 2004 Release

Computational Efficiency (56% speedup)• Coagulation• Secondary organic aerosol

Numerical Stability (ISORROPIA @ low RH) Code Structure & Documentation

• 2005 Release Science Upgrades

• Thermodynamics of sea-salt particles

New Diagnostic Tools• Source apportionment of primary PM• Process apportionment of aerosol sulfate

Disclaimer Notice:The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessary reflect their policies or views.