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Anchorage CO Maintenance Plan (SIP) Revisions

This presentation outlines the revisions to the Anchorage CO Maintenance Plan (SIP) in order to discontinue the I/M program while still complying with CO air quality standards. It includes steps in the development schedule, CO emission inventory, and projections, as well as a sensitivity analysis of compliance probabilities.

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Anchorage CO Maintenance Plan (SIP) Revisions

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  1. Anchorage CO Maintenance Plan (SIP) Revisions Presentation to the AMATS Air Quality Advisory Committee February 19, 2008

  2. Anchorage Assembly voted discontinue I/M on or before December 31, 2009 • Current SIP commits to continued operation of the I/M Program. • Before I/M can be lawfully discontinued, SIP must be revised to show that Anchorage will continue to comply with CO air quality standards without I/M. • EPA must approve changes to SIP.

  3. Anchorage CO Maintenance Plan / SIP Development Schedule

  4. Steps in preparation of a revised CO Maintenance Plan (SIP) • Prepare new CO emission inventory and emission projections thru 2023 • Estimate probability of continued compliance with CO air quality standards given expected changes in emission rates • Decide which CO control measures should be included in the plan. • Identify contingency measures should a violation of the air quality standard occur • Prepare a “CO emission budget” for determining conformity between future transportation plans and air quality goals outlined in the SIP  

  5. Anchorage CO Emission Inventory

  6. CO emission inventory and emission projections 2007-2023 Used recommended models from EPA or FAA to estimate CO emission rates Motor vehicles MOBILE6 Aircraft EDMS Nonroad NONROAD Area sources AP-42 Point source ADEC permit info

  7. Current and future CO emission estimates were based in part on: • Transportation model projections of vehicle travel activity (miles traveled per day, number of starts) • Current aircraft operations based on counts, future growth based on Airport Master Plan projections • Fireplace and wood stove use estimated with telephone survey data. • ISER forecasts of growth in population, households, and employment were used to help predict CO emissions through 2023.

  8. Assume that I/M will end December 2009

  9. CO Emission Inventory for Anchorage Bowl

  10. Estimated Anchorage Bowl CO Emissions in 2007 Total CO Emissions = 100.7 tpd

  11. CO emission inventory for the area surrounding the Turnagain monitoring Station.

  12. The Turnagain station measures the highest CO concentrations in Anchorage

  13. CO emissions in the Turnagain area are among the highest in the bowl.

  14. Estimated CO Emissions in Turnagain Area (2007) CO emissions in Turnagain area = 5.99 tpd

  15. Projected CO Emissions Turnagain Area (2007-2023)

  16. Estimate Probability of Compliance with CO Air Quality Standard2007-2023

  17. The EPA has recommended using a probabilistic approach to assessing long term compliance with the federal CO standard. • Need 90% or greater probability of compliance • Use statistical techniques (linear regression and prediction interval) to analyze monitoring data and compute probability of compliance • Project probability of compliance in future years based on projected CO emission trend

  18. Compliance is determined by the magnitude of the 2nd highest 8-hour concentration measured each year Second maximum 8-hour average concentration < 9 ppm

  19. Prediction Interval - In regression analysis, a range of values that estimate the value of the dependent variable for given values of one or more independent variables. where This is a one-sided prediction interval because we are interested only in the upper range of values for the dependent variable

  20. 90th Percentile Prediction Interval Computed from Turnagain 2nd Maximum

  21. The probability of complying with the standard at 2007 emission levels is estimated to be 98.1%. The probability of complying with the standard in a future year can be estimated based on whether emissions are projected to increase or decrease relative to 2007.

  22. What if we have underestimated the impact of discontinuing I/M? What if vehicle travel and wood heating grow faster than anticipated? How sensitive are our projected probabilities of compliance to changes in initial assumptions about future CO emissions ?

  23. Comparison of Original Assumptions used in Maintenance Demonstration with those used in Sensitivity Analysis

  24. Comparison of Sensitivity Analysis Assumptions with Original Emission Projections In this sensitivity analysis, by 2023, assumed CO emissions are 23% higher than the original projections

  25. Even using “worst case” assumptions in sensitivity analysis, the probability of complying with the CO standard is well above 90% every year.

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