1. Starting with an observed concentration as the base value reduces problems in

interpreting model results. If a model under (or over) predicts an observed daily maximum

concentration, the appropriate target prediction is not as clear as might be desired. For example,

if an 8-hour daily maximum ozone concentration of 120 ppb were observed and a model

predicted 100 ppb on that day, should the target for the day still be 84 ppb? In the relative

attainment test, observed data is used to define the target concentration. This has the effect of

anchoring the future concentrations to a “real” ambient value. Although good model

performance remains a prerequisite for use of a model in an attainment demonstration, problems

posed by less than ideal model performance on individual days are reduced by the new


2. The form of the 8-hour ozone and PM2.5 NAAQS necessitates such an attainment test.

The NAAQS for ozone and PM2.5 requires ambient data to be averaged over three consecutive

years. This presents difficulties using the resource-intensive Eulerian models we believe are

ozone design values by 3 ppb or PM2.5 annual design values by 0.5 ug/m3 or 24-hour PM2.5

design values by 3 ug/m3.



n601 - n602 - n603 - n604 - n605 - n606 - n607 - n608 - n609 - n610 - n611 - n612 - n613 - n614 - n615 - n616 - n617 - n618 - n619 - n620 - n621 - n622 - n623 - n624 - n625 - n626 - n627 - n628 - n629 - n630 - n631 - n632 - n633 - n634 - n635 - n636 - n637 - n638 - n639 - n640 - n641 - n642 - n643 - n644 - n645 - n646 - n647 - n648 - n649 - n650


   Flag of Portugal 


 castellano: DISPER CUSTIC DESCAR RADIA    italiano:     


 français:    português:  






deutsch: DIS CUS  DES  RAD

castellano: DIS CUS DES  RAD   english: DIS CUS DES RAD  


 português: DIS CUS DES RAD   italiano:   DIS CUS  DES RAD


français:  DIS CUS DES RAD