Paved and Unpaved Road Dust Bob Lebens,WESTAR Council Fall Technical Conference September 17, 2002

Monitoring Data Fine soil and coarse particles are 6-26% of the annual average light extinction Fine soil can account for 10-30% of the fine particulate mass Fine soil is almost always <10%, but can be as high as 40% for the haziest days Coarse material is usually <20%, but can be as high as 90%

GCVTC Discounted future emissions from paved and unpaved roads – due to inventory and modeling weaknesses Road Dust impacts presumed to be local Recommended voluntary measures to control dust near Class I areas

Requirement State determines, based on an assessment of the contribution of dust emissions from paved and unpaved roads on visibility conditions in Class I areas, that the contribution is either: Insignificant, or Significant

If Significant State determines the “appropriate and necessary” emission management strategies for the Class I areas.  

Appendices Modeling assessment from the Regional Modeling Center. Assessment of the impact of dust emissions from paved and unpaved roads on the visibility in Class I areas.

Appendices – If Significant Analysis of ‘necessary’ and ‘appropriate’ emission management strategies options and choices. Basis of judgment for establishing ‘significance’ levels.

Preliminary Modeling Results Smallest Cumulative Impact in 2018 0.08 deciview in Weminuche Wilderness Largest Cumulative Impact in 2018 0.31 deciview at Black Canyon of Gunnison NP (Note “Area of State” not defined – assumed to be state/reservation wide. Wind blown “natural” dust was not included in modeling and is difficult to characterize.)

Next Steps Expert Panel review of dust emissions adjustments used in Modeling Review complete by November New WRAP Dust Emissions Joint Forum Dust ‘Significance’ criteria may be the same as that selected for tailpipe emissions

Next Steps (continued) WRAP/EPA technical refinements may delay ‘necessary and appropriate’ strategies (if dust is significant) until 2008.