Natural background technical review committee - Meeting V

1. Natural background technical review committee - Meeting V June 6, 2006

2. Overall Objective: • To agree on a methodology that estimates the worst and best natural conditions for each monitoring site for use with current conditions estimated by the new IMPROVE algorithm so that  Regional Haze Rule glide paths can be calculated in a consistent way for states that wish to use the new algorithm.

3. Approach • Scale current daily aerosol species mass concentrations to Trijonis east/west means and form joint dv frequency distributions that estimate natural conditions • Assumes the respective aerosol species frequency distributions have the same (geometric) shape under current and natural conditions. However, the shape of joint frequency distribution is altered for natural conditions. • Only scale mass if current species mean is greater than the natural estimate for that component. • Apply SO4, NO3, and OMC scattering efficiencies derived from current range of mass concentrations • Assumes the range of SO4, NO3 and OMC particle mass concentrations that occur under natural conditions undergo similar processing (e.g. have similar size distributions and hence scattering efficiencies) as the range of current species concentrations even though the natural mass concentrations may be significantly lower.

4. Sensitivity tests Test the sensitivity of estimated natural condition worst 20% dv to changes in the aerosol species scattering efficiencies: • Scenario N – scattering efficiencies correspond to ‘scaled’ daily natural mass concentrations • Scenario Na – OMC scattering efficiencies correspond to ‘current’ daily mass concentrations • Scenario Nb – SO4, NO3 and OMC scattering efficiencies correspond to their respective ‘current’ mass concentrations Consistency checks: • Compare estimates of worst 20% natural dv using long-term data records to establish species variability with variability derived from the 5-yr 2000 – 2004 baseline period. • Check that the best days' haze levels estimated for natural conditions are not greater than the best haze days for current conditions.

5. Scale aerosol mass frequency distributions Current 2000-2004 Hanging bars Solid - current mean Dashed - natural estimate mean • Sipsey Alabama • Each aerosol species mass concentration frequency distribution scaled to estimated natural mass concentrations • If current species mean is less than natural estimate, the that species is not scaled • Geometric shape of species distributions is unchanged Natural Estimate

6. Scaled aerosol extinction distributions Current 2000-2004 Hanging bars Solid - current mean Dashed - natural estimate mean • Sipsey Alabama • For SO4, NO3 and OMC use the current daily scattering efficiencies to calculate species extinction (scenario Nb) • Joint aerosol extinction frequency distribution shape is altered from the current distribution Natural Estimate

7. Aerosol bext and dv frequency distributions current and scenario Nb • Sipsey Alabama • Natural scenario joint distribution shape is derived from scaling current aerosol species mass concentrations to natural condition estimates • Allows estimation of worst 20% dv or aerosol species extinction

8. Worst 20% dv estimates: scenario N • Use new IMPROVE algorithm scattering efficiencies corresponding to adjusted SO4, NO3 and OMC aerosol mass concentrations

9. Worst 20% dv estimates: scenario Na • Use current OMC scattering efficiencies

10. Worst 20% dv estimates: scenario Nb • Use current SO4, NO3 and OMC scattering efficiencies

11. G90 dv sensitivity for scenarios N, Na, Nb • dv change from N to Na (adjust OMC efficiencies) • dv change from Na to Nb (adjust NO3 and SO4 efficiencies from Na) • dv change from N to Nb (adjust OMC, NO3 SO4 efficiencies) Note: G90 = Worst 20%

12. G90 dv sensitivity to scenario N, Na, NbUrban sites included • dv change from N to Na (adjust OMC efficiencies) • dv change from Na to Nb (adjust NO3 and SO4 efficiencies from Na) • dv change from N to Nb (adjust OMC, NO3 SO4 efficiencies) Note: relaxed minimum data requirement to show 170 contoured sites

13. Best 20% dv estimates - Scenario N • Use NIA scattering efficiencies on adjusted mass distributions

14. Best 20% dv estimates - Scenario Nb • Use current SO4, NO3 and OMC scattering efficiencies on adjusted mass distributions

15. 5-yr baseline vs. long-term estimatesscenario Nb Difference in worst 20% dv natural estimate 2000-2004 1988-2004

16. Glide Slopes • 2000-2004 worst 20% dv baseline: old and new IMPROVE algorithms • Worst 20% dv natural estimates: compare new approach (scenario Nb) to original default values • Worst 20% dv baseline to estimated natural condition glide slopes in dv/10yrs • Change in worst 20% dv glide slopes: new approach – default approach • Examples of aerosol species glide slopes • Note – glide slopes calculated from 5-yr baseline (mean of 3-5 annual G90 values) to natural G90 estimator (n>250 FD)

17. G90 dv 2000-2004 baseline Old IMPROVE algorithm (OIA) New IMPROVE algorithm (NIA)

18. G90 dv natural condition estimates Old ‘default approach’ using OIA ‘New approach’ using NIA (same as slide 10)

19. Glide slopes for G90 dv natural estimates Old ‘default’ approach with OIA New approach with NIA

20. Change in glide slope: new approach vs. old default approach • Values shown are (new – old) in dv/10yr for worst 20% dv natural estimates • Positive values indicate higher magnitude (steeper glide slope) for new approach

21. Aerosol species glide slopes Ammonium sulfate extinction Ammonium nitrate extinction

22. Aerosol species glide slopes Particulate organic matter extinction Light absorbing carbon extinction

23. Aerosol species glide slopes Fine soil extinction Coarse mass extinction

24. Summary • All light extinction components are scaled to estimated natural condition mean mass concentrations in a consistent manner. • Using current SO4, NO3 and OMC scattering efficiencies increases natural condition worst 20% dv estimates by 0 to 1 dv among non-urban IMPROVE sites. • We recognize that applying current particle scattering efficiencies to estimated natural aerosol mass concentrations may have conceptual flaws. For example, natural haze estimates will be elevated in regions where current levels of anthropogenic pollutants are high, producing a spatial trend that is not likely representative of natural conditions. However, we chose this approach in order to maintain consistency with the application of aerosol species scattering efficiencies in the new IMPROVE algorithm to current aerosol data. • Worst 20% dv estimated using 2000-2004 baseline data agree to within less than 1 dv natural condition estimates derived from long-term (~15 yrs) data. • In no cases are estimated natural worst 20% dv greater than current conditions. • The new approach allows calculation of species extinction on the worst 20% natural condition visibility days. This in turn allows us to estimate species specific glide slopes for RHR planning.

25. Appendix Scenarios to test the effect of scaling only aerosol species mass concentrations for components with predominantly anthropogenic sources: • N1 – only scale SO4 and NO3 to estimated natural mass concentrations • N2 – only scale SO4, NO3 and EC to estimated natural mass concentrations • Aerosol light extinction frequency distributions at SIPS1 for scenario N

26. Worst 20% dv - Scenario N1 • Control SO4, NO3 and EC

27. Worst 20% dv - Scenario N2 • Control SO4 and NO3

28. Scaled aerosol extinction frequency distributions Current 2000-2004 Hanging bars Solid - current mean Dashed - natural estimate mean • Sipsey Alabama • use adjusted daily scattering efficiencies to calculate species extinction in scenario N • Max SO4 bsp is 8.2 Mm-1, max OMC bsp is 35.5 from scenario N • Max SO4 bsp is 12.5 Mm-1, max OMC bsp is 50.6 from scenario Nb Natural Estimate