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: eDocs/guidancedocs.htm eDocs/guidancedocs.htm Equation is used to estimate light scattering by particles:

“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: ndex.html ndex.html Technical document describing revised equation: 019_RevisedIMPROVEeq/RevisedIMPROVEAlgorithm3.do c 019_RevisedIMPROVEeq/RevisedIMPROVEAlgorithm3.do c Light extinction data from 2000 onward are calculated and available using old and revised equation on VIEWS: and the WRAP TSS:

“Revised” IMPROVE Light Extinction Equation Bottom line: New equation fitted to aerosol data collected 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 Scatter plot of the old IMPROVE equation estimated particle light scattering versus measured particle light scattering. Scatter plot of the revised IMPROVE equation estimated particle 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: 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 Final report soon?

“Default” Natural Conditions Estimates 20% 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 & Pitchfordpresentation 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 7 th to review monitoring data issues: iew&id=552 iew&id=552 Plan to have AoH workgroup recommend WRAP region approach