1. Presents:/slides/greg/PSAT_11-17-03.ppt Effects of Sectional PM Distribution on PM Modeling in the Western US Ralph Morris and Bonyoung Koo ENVIRON International Corporation Novato, CA (rmorris@environcorp.com) National RPO Modeling Meeting Denver, Colorado May 24-25, 2004

2. Presents:/slides/greg/PSAT_11-17-03.ppt Outline Introduction Previous Results in SoCal WRAP 1996 Western US Modeling Conclusions

3. Presents:/slides/greg/PSAT_11-17-03.ppt CAMx4+ PM Treatment PM Size Distribution > Mechanism 4 (M4) 2-section (fine/coarse) > Sectional (N-Section, N=10, 4,…) Allows side-by-side comparisons of Sectional versus fine/coarse PM size distribution treatment in same platform Aqueous-Phase Chemistry > RADM Bulk Module > Variable Size Resolution Module (VSRM) Allows analysis of the effects of treating PM size distribution in aqueous-phase chemistry (buffering issues) Aerosol Thermodynamics > ISORROPIA PM Size Distribution > Equilibrium, Dynamic, Hybrid Secondary Organic Aerosol > SOAP

4. Presents:/slides/greg/PSAT_11-17-03.ppt Sectional vs. Fine/Coarse Comparisons in Southern California (presented previously) South Coast Air Basin (SoCAB) of Southern California October 17-19, 1995 PTEP episode > High NO3 Episode Analyze Effect of PM Size Resolution in VSRM Aqueous-phase Chemistry > CMU 1-section Bulk Module > CMU Variable Size Resolution Model (VSRM) Analyze Effects of 10-Section Versus 2-Section (Fine/Coarse) Representation on PM Size Resolution > M4 = Mechanism 4 Fine/Coarse > EQUI = 10-Section PM Representation

5. Presents:/slides/greg/PSAT_11-17-03.ppt VSRM (Multi-Section) vs. Bulk Aqueous Chemistry Percent Increase in Sulfate (%) By second day, VRSM estimates ~15-30% more sulfate across the SoCAB with > 50% increase offshore and around Long Beach

6. Presents:/slides/greg/PSAT_11-17-03.ppt VSRM (Multi-Section) vs. Bulk Aqueous Chemistry VRSM can form significantly more sulfate than the bulk 1-section aqueous-phase chemistry module

7. Presents:/slides/greg/PSAT_11-17-03.ppt 24-Hour Nitrate (  g/m 3 ) October 18, 1995 M4 peak NO 3 83  g/m 3 EQUI peak NO 3 54  g/m 3 Observed NO 3 peak at Riverside ~40  g/m 3 Differences due to assuming all nitrate is fine vs. PM nitrate represented by 10 size sections (EQUI) M4 EQUI

8. Presents:/slides/greg/PSAT_11-17-03.ppt Differences in 24-Hour Nitrate (  g/m 3 ) October 18, 1995 M4 peak NO 3 83  g/m 3 EQUI peak NO 3 54  g/m 3 EQUI 10-Section grows PM NO 3 into coarser sections where it dry deposits faster than M4 NO 3 that is assumed to be fine Result is less NO 3 in downwind Riverside area that agrees better with observations M4 M4 - EQUI

9. Presents:/slides/greg/PSAT_11-17-03.ppt WRAP/CRC Modeling Analysis 1996 36 km Western US > (Section 309 Database) Evaluate Four Models: > CMAQ V4.3 > REMSAD V7 > CAMx_M4 – Mechanism 4 Fine/Coarse > CAMx_4sec – 4-Sections, Section 4 is Coarse Use same emissions, IC/BC, vertical layers, etc. No Sea Salt or Explicit Calcium Emissions in WRAP 1996 Database How much SO4 and NO3 in Coarse Model?

10. Presents:/slides/greg/PSAT_11-17-03.ppt Example SO4 Model Performance Yellow = 1996 Annual Blue = January 1996 Red = July 1996 Fractional Bias Fractional Gross Error Winter overestimation compensates for summer underestimation results in annual bias < 10%

11. Presents:/slides/greg/PSAT_11-17-03.ppt Average 1996 PM Concentrations Across IMPROVE Monitors (Section 4 = Coarse)

12. Presents:/slides/greg/PSAT_11-17-03.ppt Conclusions Western US Sectional vs. Fine Coarse PM Distribution Representation Sectional 1996 Annual Modeling (4-Sections) Estimates that 10% of the Sulfate and 5% of the Nitrate is in the Coarse Mode (PM 2.5-10 ) SoCal Analysis Suggests: > Sectional Approach Affects Aqueous-Phase Chemistry > Biggest Effect is on Dry Deposition Rates Several Caveats Should be Mentioned: > Sea Salt was not included in the WRAP 1996 database which is known to form coarse Sodium Nitrate Important at Coastal Sites and Desert Areas > Other Soil buffering compounds (e.g., Calcium) were not explicitly treated