1. 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

2. 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 N 2 O 5 heterogeneous reaction – promotes NO 3 - formation Present – CMAQ v4.4 (2004 release)  Computational Efficiency  Numerical Stability  Code Structure & Documentation Future (2005 release)  Science Upgrades  New Diagnostic Tools

3. Coagulation  CMAQv4.3 Coagulation rates for each moment calculated numerically, using Gauss-Hermite quadrature  CMAQv4.4 0 th and 3 rd moment coagulation rates solved analytically 2 nd moment coagulation rates solved using analytical expressions with tabulated correction factors ~fxn(  i,  j, D gj /D gi )  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

4. 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

5. Computational Efficiency Aerosol module is 2.3 times faster ISORROPIA takes 62% of aerosol processing

6. Doubling of EC emissions in Massachusetts causes 1.7  g/m 3 increase in NO 3 - over California! Reported by Quansong Tong, Princeton Univ. Numerical Stability  EC  NO 3 -

7. Numerical Stability Instability traced to the ISORROPIA module At low RH, infinitesimal changes in SO 4 or NH X can shift NO 3 from the gas to aerosol phase, resulting in ~10  g/m 3 changes in NO 3 - concentrations (solid line) Errors identified in (NH 4 ) 2 SO 4 activity and EX10 subprogram of ISORROPIA in CMAQ v4.3 Instability is eliminated in CMAQ v4.4 (dashed line)

8. Numerical Stability Identified a 2 nd “family” of instabilities, resulting in ~1  g/m 3 changes in NO 3 - 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

9. Code Structure & Documentation Enhanced in-line documentation Streamlined code structure  Removed AEROSTEP  Added HCOND3 AEROPROC EQL3 ISOROPIA ORGAER3 NEWT HCOND3GETCOAGS NEWPART3 _AE3

10. 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

11. - 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 Apportionment Diesel exhaust fraction of TC pri Biomass combustion fraction of TC pri

12. Future Plans – Sulfate Apportionment All scales represent the fraction of total aerosol sulfate.

13. 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.