Update on IMPROVE Light Extinction Equation and Natural Conditions Estimates

Tom Moore, WRAP Technical Coordinator

May 23, 2006

OR …….

Defining Regional Haze Impacts with Aerosol Sampling Data

AND …….

Knowing the unknowable

“Old” IMPROVE Light Extinction Equation• Developed in late 1980’s – consensus light extinction

coefficients for species measured by IMPROVE aerosol sampler

• Adopted by EPA for “Tracking Progress” – regional haze monitoring guidance documents are at: http://vista.cira.colostate.edu/improve/Publications/GuidanceDocs/guidancedocs.htm

• Equation is used to estimate light scattering by particles:

10

6.0

1

10

4

)(3

)(3

MassCoarse

SoilFine

CarbonElemental

MassOrganic

NitrateRHf

SulfateRHfbext

“Revised” IMPROVE Light Extinction Equation

• Review process by IMPROVE Steering Committee and scientific community during 2005

• Findings of review prepared by Jenny Hand & Bill Malm presented and discussed at: http://www.wrapair.org/forums/aamrf/meetings/050608den/index.html

• Technical document describing revised equation: http://vista.cira.colostate.edu/improve/Publications/GrayLit/019_RevisedIMPROVEeq/RevisedIMPROVEAlgorithm3.doc

• Light extinction data from 2000 onward are calculated and available using old and revised equation on VIEWS: http://vista.cira.colostate.edu/views/ and the WRAP TSS: http://vista.cira.colostate.edu/tss/

“Revised” IMPROVE Light Extinction Equation

ppb)(NO0.33

Specific)iteS(ScatteringRayleigh

SaltSeaRH)(f1.7

MassOrganicargeL6.1MassOrganicSmall2.8

NitrateargeLRH)(f5.1NitrateSmallRH)(f2.4

SulfateargeLRH)(f4.8SulfateSmallRH)(f2.2

2

SS

LS

LS

MassCoarse

SoilFine

CarbonElemental

bext

6.0

1

10

Bottom line:

• New equation fitted to aerosol data collected 2000-04 using light extinction coefficients from research literature, to better match observed optical light scattering data

• Corrects bias but increases scatter at some sites

Light Extinction using old and revised IMPROVE Equation

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350

Measured Bsp

IMPR

OVE

Bsp

Scatter plot of the old IMPROVE equation estimatedparticle light scattering versus measured particle light

scattering.

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350

Measured Bsp

Split

Com

pone

nt M

etho

d B

sp

Scatter plot of the revised IMPROVE equation estimatedparticle light scattering versus measured particle light

scattering.

Natural Conditions Estimates

• NAPAP Visibility Report (Volume 24) [1990] authored by Trijonis, et. al.

• Based on available IMPROVE network data and other data sources

• Estimated contiguous East and West U.S. annual average natural mass loading for visibility-impairing aerosols [specified uncertainty by species]

• [Well] Known to underestimate natural carbon

• Adopted by EPA for “Estimating Natural Visibility Conditions” using “old” equation – regional haze monitoring guidance documents are at: http://vista.cira.colostate.edu/improve/Publications/GuidanceDocs/guidancedocs.htm

• Default Natural Haze Levels Sensitivity Assessment project for the 5 RPOs

• Ivar Tombach is doing the analysis

• Initial findings were presented at a June 2005 workshop http://www.wrapair.org/forums/aamrf/meetings/050608den/index.html

• Final report soon?

“Default” Natural Conditions Estimates20% Best Days (left) & 20% Worst Days (right)

What should be done [if anything] with “default” Natural Conditions Estimates?

• Knowing the unknowable – April 4, 2006 – Inter-RPO Monitoring and Data Discussion Group analysis presentation on revised natural condition estimates using the new IMPROVE algorithm and a revised statistical approach – Ames & Pitchford

• Things to think about:– Natural conditions vary continuously in space and time – do any historic data inform

better estimates for planning purposes?– The worst and best visibility days’ default natural conditions estimates are projected

from measured distributions of aerosol data – these are for total light extinction in DECIVIEWS, not for individual species – how does that line up for the WRAP region?

– How often will we see frequent large OC/EC and Dust events over the next 50 to 60 years?

– Do we need to apply the revised IMPROVE equation to natural conditions estimates?– What monitoring period of record can be used to estimate natural conditions?– Can we make a better estimate of the distributions of worst and best visibility days 58

years out, than John Trijonis did?– What are the planning implications of adjusting natural conditions estimates up and/or

down and changing the glide path for 116 Class I areas in the WRAP region, either for deciviews or individual species?

– Where does take us for “demonstrating” reasonable progress in 2018?– More questions yet to asked -

Next Steps on Natural Conditions Estimates in the WRAP Region

• Attribution of Haze workgroup conference call June 7th to review monitoring data issues: http://www.wrapair.org/cal/calendar.php?op=view&id=552

• Plan to have AoH workgroup recommend WRAP region approach

http://vista.cira.colostate.edu/tss/