1. STATUS REPORT “Significance” Issue Relating to Mobile Sources and Road Dust
Presented to WRAP
November 15, 2001
John Kowalczyk & Bob Neufeld
Mobile Source Forum Co-Chairs

2. Section 309 Requirement
Must determine whether mobile sources and/or road dust contribute “significantly” to visibility impairment in any of the 16 Class I Areas
No rule guidance on how to do this
Mobile Source Forum and Initiative Oversight Committee have had some discussions on this issue

3. Requirements if Mobile Source Tailpipe Emissions “Significant”
If mobile source emissions from any areas of the state are found to significantly contribute to visibility impairment at any of the 16 Class I Areas:
Set Emission Budget at Lowest Level in Period
Implement any Measures needed to achieve Budget
Establish Emissions Tracking System and Annual reporting

4. Tentative Rule Interpretations for Mobile Source Tailpipe Emissions
Mobile source tailpipe emissions should include on-road and non-road mobile sources
Analysis should examine separate contribution from major urban areas and also emissions in the remainder of each state

5. Tentative Rule Interpretations (Continued)
Emission Budgets, if needed, have no link to transportation conformity
- Should be treated as a SIP Nonattainment/
Maintenance “compliance” emission
inventory - SIP would be revised if emissions
are expected to or exceed budget
Consider doing significance determination based on average contribution to visibility impairment on 20% worst and 20% best days in a year if model runs are not excessive

6. Requirements for Paved and Unpaved Road Dust
If paved and unpaved road dust emissions in the state are found to contribute significantly at any of the 16 Class I Areas:
Implement emission management strategies as necessary and appropriate
Analysis should be based on statewide emissions

7. Visibility Impairment: How much represents a “Significant Contribution” ? A Policy Call

8. Some “Significance” Options
Prevention of Significant Deterioration Program Analogy - 4%
Federal Land Manager FLAG Report - 5%
Neither Precisely Fit Regional Haze Rule Intent
Difference in “Stringency” more than difference between 4% and 5% because percentages applied to different factors to calculate Impairment ( “extinction” )

9. PSD Analogy
Defines “Significant Contributor” to a Problem (NAAQS Violation) ~4% avg.
Would apply 4% to Human caused “extinction” to identify significant contrib.
Logic is analogous to Haze rule
Answers question: What part of problem (actual impairment at each Class I area) is significant
PSD does not Directly Address Visibility

10. FLAG Analogy Directly Applies to Visibility Concerns
Defines level of concern as 5% of Background Levels)
Logic not as analogous to Haze rule
Expresses level of concern as an amount of background, not impairment

11. Need more Work on Definition of “Significant”
Stringency difference between PSD and FLAG approach in terms of actual “extinction” amount could be substantial (factor of 3)
Need to look at actual background and impairment levels and see what the difference is between PSD and FLAG approaches
Work through Mobile Source Forum/TOC/IOC
Bring final recommendation, with modeling results, to next WRAP meeting for Approval