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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 l.jpg

Calculating Visibility and Natural Background

VISTAS Recommendations

November 15, 2005


Current and natural background visibility policy considerations l.jpg
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


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IMPROVE Equation for Calculating Visibility Considerations

  • 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)


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IMPROVE Equation Reviewed Considerations

  • 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!


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IMPROVE Workgroup recommendations Considerations

  • 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


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IMPROVE Equation for Calculating Visibility Considerations

  • 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)


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Comparison Between Extinction Equations Considerations

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


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60 Considerations

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


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50 Considerations

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


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Comparison Between Extinction Equations Considerations

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


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VISTAS Recommendations: Nov 2005 Considerations

  • 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


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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


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180% Haziest Days

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


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IMPROVE Equation for Calculating Natural Visibility Haziest Days

  • 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


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VISTAS Recommendations: Nov 2005 Haziest Days

  • 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


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VISTAS Recommendations: Nov 2005 Haziest Days

  • 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


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VISTAS Recommendations: Nov 2005 Haziest Days

  • 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