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Effects of Sectional PM Distribution on PM Modeling in the Western US

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. Outline. Introduction Previous Results in SoCal

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Effects of Sectional PM Distribution on PM Modeling in the Western US

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  1. 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 Presents:/slides/greg/PSAT_11-17-03.ppt

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

  3. 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 Presents:/slides/greg/PSAT_11-17-03.ppt

  4. 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 Presents:/slides/greg/PSAT_11-17-03.ppt

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

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

  7. 24-Hour Nitrate (g/m3) • October 18, 1995 • M4 peak NO3 83 g/m3 • EQUI peak NO3 54 g/m3 • Observed NO3 peak at Riverside ~40 g/m3 • Differences due to assuming all nitrate is fine vs. PM nitrate represented by 10 size sections (EQUI) M4 EQUI Presents:/slides/greg/PSAT_11-17-03.ppt

  8. M4 - EQUI • Differences in 24-Hour Nitrate (g/m3) • October 18, 1995 • M4 peak NO3 83 g/m3 • EQUI peak NO3 54 g/m3 • EQUI 10-Section grows PM NO3 into coarser sections where it dry deposits faster than M4 NO3 that is assumed to be fine • Result is less NO3 in downwind Riverside area that agrees better with observations M4 Presents:/slides/greg/PSAT_11-17-03.ppt

  9. 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? Presents:/slides/greg/PSAT_11-17-03.ppt

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

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

  12. 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 (PM2.5-10) • 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 Presents:/slides/greg/PSAT_11-17-03.ppt

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