CMAQ Aerosol Module Development Recent Enhancements & Future Plans

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 DevelopmentRecent 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 • 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

3. Computational Efficiency • 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(si, sj, 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

4. Computational Efficiency • 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. Aerosol module is2.3 times faster ISORROPIA takes 62% of aerosol processing Computational Efficiency

6. Numerical Stability Doubling of EC emissions in Massachusetts causes 1.7mg/m3 increase in NO3- over California! Reported by Quansong Tong, Princeton Univ. DEC DNO3-

7. 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 mg/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)

8. Numerical Stability • Identified a 2nd “family” of instabilities, resulting in ~1 mg/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

9. Code Structure & Documentation • Enhanced in-line documentation • Streamlined code structure • Removed AEROSTEP • Added HCOND3

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. Future Plans – Carbon Apportionment Diesel exhaust fraction of TCpri Biomass combustion fraction of TCpri - 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

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.