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Calculating Visibility and Natural Background

Calculating Visibility and Natural Background. VISTAS Recommendations November 15, 2005. Current and Natural Background Visibility: Policy Considerations. VISTAS assumptions must be comparable to EPA guidance and other RPOs

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Calculating Visibility and Natural Background

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  1. Calculating Visibility and Natural Background VISTAS Recommendations November 15, 2005

  2. Current and Natural Background Visibility: Policy Considerations • VISTAS assumptions must be comparable to EPA guidance and other RPOs • Retain default assumptions for calculating current and natural background visibility to retain compatibility • Report one alternative assumption for calculating current and natural background visibility • Proposed alternatives better match nephelometer data (measured light extinction) than current IMPROVE equation

  3. IMPROVE Equation for Calculating Visibility • The regional haze rules use the IMPROVE equation for calculating reconstructed extinction from IMPROVE chemical composition data: Bext = 3 * f(RH)* [Ammonium] Sulfate + 3 * f(RH)* [Ammonium] Nitrate + 4 * 1.4 x OC + 1 * SOIL Mass + 0.6 * Coarse Mass + 10 * EC + 10 (Rayleigh Scattering) • Calculate deciviews (dv): dv = 10 ln (Bext/10)

  4. IMPROVE Equation Reviewed • IMPROVE Steering Committee appointed a workgroup in July 2005 to review IMPROVE equation for calculating visibility • Workgroup: EPA, NPS, EPRI, academia, consultants • Workgroup reached consensus on alternative equation by end of Oct 2005 • Report to IMPROVE Steering Committee is being prepared (Nov 2005) • Unknown schedule for Steering Committee action or EPA response • Lots of opinions!

  5. IMPROVE Workgroup recommendations • Add seasalt (use Chlorine) • Change OC mass multiplier from 1.4 to 1.8 to reflect higher molecular weight of OC from biogenic sources • Change methods for calculating extinction efficiency for SO4, NO3, OCM to reflect greater efficiency at higher mass • New terms added for SO4, NO3, and OCM • Revise f(RH) terms for SO4, NO3, and OCM • If new equation approved, still need to develop new f(RH) curves for six components • Calculate Rayleigh scattering for elevation of IMPROVE monitor at each Class I area

  6. IMPROVE Equation for Calculating Visibility • The regional haze rules use the IMPROVE equation for calculating reconstructed extinction from IMPROVE chemical composition data: Bext = (inorg) * f(RH)new * [Ammonium Sulfate] + (inorg) * f(RH)new * [Ammonium Nitrate] + (POM) * {1.8 * [Organic Carbon]} + 1 * [SOIL] + 0.6 * [Coarse Mass] + 10 * [EC] + 1 * f(RH)new * [Sea Salt] + (Site Specific Rayleigh Scattering) Where (in Hands and Malm proposal): f(RH)new includes water below RH = 40 %, and is often higher than the older curve for corresponding RH values POM = 1.8·OC; Sea Salt = 1.8·Cl- ;αinorg= 3(0.7+.02*Mmix); αPOM= 3.63(0.7+.02*Mmix) Mmix = ([Ammonium Sulfate]+[Ammonium Nitrate]+[POM]) • Calculate deciviews (dv): dv = 10 ln (Bext/10)

  7. Comparison Between Extinction Equations 20% Worst Days* 2000 - 2003 Existing IMPROVE - left; Proposed Malm and Hand - right 250 Sea Salt 200 CM SOIL 150 Extinction (Mm-1) LAC POM 100 NH4NO3 50 (NH4)2SO4 Rayleigh 0 James River Face, VA Shenandoah Brigantine, NJ Dolly Sods *for Years with Complete Data

  8. 60 50 40 30 20 10 Comparison Between Extinction Equations 20% Best Days* 2000 - 2003 Existing IMPROVE - left; Proposed Malm and Hand - right S. Salt CM SOIL LAC Extinction (Mm-1) POM NH4NO3 (NH4)2SO4 Rayleigh 0 Mammoth Cave, KY Sipsey, AL Great Smoky Mtn., TN Cohutta, GA Linville Gorge, NC Shining Rock, NC *for Years with Complete Data

  9. 50 40 30 20 10 0 Comparison Between Extinction Equations 20% Best Days* 2000 - 2003 Existing IMPROVE - left; Proposed Malm and Hand - right S. Salt CM SOIL LAC Extinction (Mm-1) POM NH4NO3 (NH4)2SO4 Rayleigh James River Face, VA Shenandoah Brigantine, NJ Dolly Sods *for Years with Complete Data

  10. Comparison Between Extinction Equations 20% Best Days* 2000 - 2003 Existing IMPROVE - left; Proposed Malm and Hand - right 50 S. Salt 40 CM SOIL 30 Extinction (Mm-1) LAC POM 20 NH4NO3 10 (NH4)2SO4 Rayleigh 0 Swanquarter, NC Okefenokee, GA Chassahowitzka, FL Cape Romain, SC Everglades, FL St. Marks, FL *for Years with Complete Data

  11. VISTAS Recommendations: Nov 2005 • Continue to use default IMPROVE equation for VISTAS calculations of rate of progress in 2018 • For VISTAS modeling analyses, also present results for one alternative calculation • Use revised IMPROVE equation when data is available to make calculations (Jan 2006?) • Until then, continue to use alternative equation proposed by Malm and Hand in July 2005. • For SIP demonstration purposes, VISTAS will need feedback on revised IMPROVE equation from IMPROVE Steering Committee and EPA

  12. EPA Default Glidepath vs Alternative Calculations: 20% Haziest Days 20% Haziest Days Change Slope in 2018? dV Natural Background (with alternative assumptions) Natural Background (EPA default) 2000 2018 YEAR 2064

  13. 180% 1B 1Balt_c 160% 1Balt_d 140% 120% Percent of target reduction achieved 100% 80% 60% 40% JARI1 SIPS1 MING1 BRIG1 LIGO1 UPBU1 SHEN1 CHAS1 HEGL1 EVER1 SAMA1 COHU1 BRET1 SHRO1 MACA1 SWAN1 OKEF1 CACR1 GRSM1 ROMA1 DOSO1 Other Sites Mountain Sites Coastal Sites Effects of Alternative Extinction Equations on Visibility Projections – VISTAS 2018 Base D No Change in W20% Days 1B = Std IMPROVE alt_c = Ryan/EPRI alt_d = Malm/Hand Effect of alternate equations on Method 1B predictions

  14. IMPROVE Equation for Calculating Natural Visibility • The Guidance for Estimating Natural Visibility Conditions calculates the average 20% worst days as : 90th percentile = HI + 1.28 *sd Standard deviation assumed to be 3 for the east

  15. VISTAS Recommendations: Nov 2005 • To calculate natural background • Calculate 20% worst/best days from annual average natural levels in Guidance • Default Natural Visibility from Guidance • Accept assumption that days are normally distributed • While not accurate, we don’t have a better alternative. • Use 92nd percentile rather than 90th to represent 20% worst/best days • Use IMPROVE assumption of 3 for all eastern sites • Current data doesn’t support change in s 92nd percentile = HI + 1.40*sd

  16. VISTAS Recommendations: Nov 2005 • And as the alternative.. • Use revised IMPROVE equation • Include sea salt, revised terms for SO4, NO3, OC, revised extinction efficiencies, site-specific values for Rayleigh scattering • OC mass multiplier under natural conditions • Keep OC/OCM multiplier same as revised IMPROVE equation - 1.8 • Do not add additional mass for biogenic contributions: currently high uncertainty • Do not add fine soil for dust episodes

  17. VISTAS Recommendations: Nov 2005 • Inter-continental Transport does not affect the slope of the uniform rate of progress line but can be considered in defining reasonable progress for 2018 • CMAQ 36 km run underway using 2018 OTW Base D emissions, clean boundary conditions, and no Canadian and no Mexican emissions to define contribution from outside US (due Nov/Dec 2005) • Compare CMAQ results to revised GEOS-CHEM 2001 projections of contributions from outside US

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