6. Calculate daily deciview values (from total daily extinction) and then compute the

future average mean deciviews for the worst and best days for each year. Then average

the 5 years together to get the final future mean deciview value for the worst and best


We describe each of these steps more fully below. The methodology follows the same

basic procedures outlined in the “Tracking guidance.” Further details (for steps 1 and 2) can be

found in that document. We conclude this subsection with an example illustrating the

recommended modeled uniform rate of progress analysis.

Step 1. Using monitored data, rank baseline visibility for each day with PM10, PM2.5

and speciated PM2.5 measurements within a Class I area

Ranking should be performed separately for each of the 5 years comprising the base

period77. The deciview (dv) should serve as the basis for ranking. Day-specific observations for

mass associated with SO4, NO3, OC, EC, soil, and CM, as defined in Table 6.1, should be used to

calculate bext for each day. The appropriate month- and area-specific climatological relative

humidity adjustment factor(s) (f(rh)) should be used. Total bext for all components should be

converted to deciviews for each day to get a daily deciview value.

Step 2. Calculate the average baseline deciviews for the 20% of days with worst and

the 20% days with best visibility.

For each of the 5 years in the base period, order all days considered in Step 1 from worst

(highest deciview value) to best (lowest deciview value) visibility. For each year, note the 20%

of days with worst and the 20% of days with best visibility. Calculate the arithmetic mean

deciview value for the identified 20% worst- and best visibility days in each year. Average the



n701 - n702 - n703 - n704 - n705 - n706 - n707 - n707 - n709 - n710 - n711 - n712 - n713 - n714 - n715 - n716 - n717 - n718 - n719 - n720 - n721 - n722 - n723 - n724 - n725 - n726 - n727 - n728 - n729 - n730 - n731 - n732 - n733 - n734 - n735 - n736 - n737 - n738 - n739 - n740 - n741 - n742 - n743 - n744 - n745 - n746 - n747 - n748 - n749 - n750


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