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Review of New IMPROVE Extinction Algorithm AoH Meeting – San Diego January 24, 2006

This review discusses proposed changes to the IMPROVE extinction algorithm, including the inclusion of sea salt, comparison of aerosol vs. measured light scattering, and the effect of splitting sulfate/nitrate/organic particles into small and large fractions.

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Review of New IMPROVE Extinction Algorithm AoH Meeting – San Diego January 24, 2006

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  1. Review of New IMPROVE Extinction AlgorithmAoH Meeting – San DiegoJanuary 24, 2006 Joe Adlhoch - Air Resource Specialists, Inc.

  2. Overview • Review of proposed changes to the IMPROVE extinction algorithm • Size fractions for sulfate/nitrate/carbon • Effect of sea salt • Comparison of aerosol vs. measured light scattering • Comparison of old and new algorithm for selected WRAP sites

  3. Old IMPROVE Algorithm • Assumptions include that • Six particle component terms plus a constant Rayleigh scattering term are sufficient for a good estimate of light extinction; • Constant dry extinction efficiency terms for each of the six particle components works adequately for all locations and times; and • Light extinction by the individual particle components can be adequately estimated as separate terms (like externally mixed components).

  4. New or Revised Terms • Variable extinction efficiencies and two additional f(RH) terms for sulfate, nitrate, and organic mass – a mixture of small and large particles is assumed • Organic Compound Mass to Organic Carbon Mass Ratio changed from 1.4 to 1.8 • Addition of Sea Salt = 1.8 x [Chloride] and has its own water growth term fSS(RH) • Rayleigh Scattering is calculated for the monitoring site elevation and annual mean temperature and integer rounded. Ranges from 8 Mm-1 at 10,000’ to 12 Mm-1 at sea level • Addition of NO2 light absorption in the visible is included for sites that have such data (not routinely available at IMPROVE sites)

  5. New IMPROVE Algorithm where and nitrate and organic are split using the same process

  6. Relative Humidity Enhancement Factors

  7. Large/Small Species Fractions • Ammonium sulfate, ammonium nitrate, and particulate organic matter are divided into “Small” and “Large” fractions: • “Small” fraction extinction efficiency less than half that of “Large” fraction • f(RH) for “Small” fraction slightly higher • “Small” fraction dominates mass up to about 5 ug/m3 • “Large” fraction dominates mass above about 12 ug/m3 • Review of WRAP data shows that while high concentrations do occur, nearly all samples of these species are below 5 ug/m3

  8. Large/Small Species Split Small fraction dominates Large fraction dominates

  9. Distribution of Sulfate Concentrations

  10. Distribution of Sulfate – Sequoia

  11. Distribution of Sulfate – Agua Tibia

  12. Distribution of Sulfate – Crater Lake

  13. Distribution of Sulfate – Jarbidge

  14. Distribution of Nitrate Concentrations

  15. Distribution of Nitrate – Sequoia

  16. Distribution of Nitrate – Agua Tibia

  17. Distribution of Nitrate – Crater Lake

  18. Distribution of Nitrate – Jarbidge

  19. Distribution of Organic Mass Conc.

  20. Distribution of OM – Sequoia

  21. Distribution of OM – Agua Tibia

  22. Distribution of OM – Crater Lake

  23. Distribution of OM – Jarbidge

  24. Review of IMPROVE Sea Salt Term • Sea salt estimated from Chloride ion measurement, Chlorine can be used as a back up • Review of 2004 data shows significant effect only at coastal sites • Review of 2000 – 2004 data timelines shows problems with Chloride measurements prior to 2004, but Chlorine appears to be a reliable back up

  25. Annual Avg. Chloride Mass, 2004

  26. Chloride/Chlorine Mass Timelines Baseline\2004: median UNC ~ 0.04\0.006; median MDL ~ 0.07\0.01 Baseline: median UNC ~ <0.001; median MDL ~ 0.001

  27. Chloride/Chlorine Mass Timelines Baseline\2004: median UNC ~ 0.04\0.006; median MDL ~ 0.07\0.01 Baseline: median UNC ~ <0.001; median MDL ~ 0.001

  28. Chloride/Chlorine Mass Timelines Baseline\2004: median UNC ~ 0.08\0.05; median MDL ~ 0.07\0.01 Baseline: median UNC ~ <0.03; median MDL ~ 0.001

  29. Estimated vs. Measured Light Scattering • Nephelometers provide a direct measurement of particle light scattering (extinction without elemental carbon absorption and Rayleigh scattering terms) • Comparison of estimated (aerosol) vs. measured (nephelometer) scattering possible at many IMPROVE sites • Typically, the Old IMPROVE equation underestimates extinction on very dirty days and overestimates extinction on very clean days • At most sites the New equation reduces this bias, though network-wide there is additional uncertainty • Change more dramatic with dirtier sites • Urban site (Phoenix) shows significant deviation from 1 to 1 line, may be due to poor characterization of urban haze, influence of NO2, or measurement errors • Following slides taken from work done by NPS

  30. Old IMPROVE Algorithm: Estimated vs. Observed Light Scattering for 21 Nephelometer Monitoring Sites

  31. New IMPROVE Algorithm: Estimated vs. Observed Light Scattering for 21 Nephelometer Monitoring Sites

  32. Site Comparison – Grand Canyon Grand Canyon ▲Old Equ. ●New Equ.

  33. Site Comparison – Gila Gila ▲Old Equ. ●New Equ.

  34. Site Comparison – Great Smoky Mtns. Great Smoky Mtns. ▲Old Equ. ●New Equ.

  35. Site Comparisons – Pacific Northwest Snoqualmie Pass Mt. Rainier Columbia River Gorge Three Sisters

  36. Site Comparisons – Southwest Sycamore Canyon Ike’s Backbone Phoenix Big Bend

  37. Site Comparisons – Central Jarbidge Lone Peak

  38. Summary of New Algorithm • The New algorithm incorporates new terms to more completely account for haze, incorporates updated information, and reduces know biases • Performance tests of the New algorithm show • it reduces bias compared to the Old algorithm at the extremes • it has as somewhat greater uncertainty that causes it to mis-select hazy days a little more frequently • little sensitivity to which algorithm is used with regards to composition on the extreme days • Following slides illustrate the difference between the 20% worst/best days calculated with the Old and New algorithm for selected sites

  39. Selected Monitoring Locations

  40. Comparison – 20% Worst Days, 2002

  41. Comparison – 20% Worst Days, 2002

  42. Comparison – 20% Best Days, 2002

  43. Comparison – 20% Best Days, 2002

  44. Implementation Steps forRegional Haze Rule Application • IMPROVE Steering Committee has approved (12/05) • Calculation of water growth functions for monthly & annual averaged conditions for each monitoring site has been completed (01/06) • Recalculation of current (5-year baseline) and natural haze levels – VIEWS – by March ??? • EPA modifies the regional haze guidance, so states can choose – 6 to 12 months • VIEWS will support both versions of the algorithm for the foreseeable future

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