Methodology for the 24-Hour NAAQS
The suggested steps outlined below assume that the attainment test has been performed using the
photochemical modeling and that the quarterly DV’s have been computed as discussed in
Section 5.2. As with the annual design value, monitoring data for 5 years are used as the basis
for the projection.
(1) Determine the local primary PM2.5 sources that are thought to be contributing to the monitor
for each of the 4 quarters60.
58Additional receptors should be placed near monitors to examine predicted concentration
gradients. Receptors should only be located in areas that are appropriate for placing FRM
monitors for comparison to the annual NAAQS (see EPA, 1997b).
59RRFs should be calculated as a ratio of the base and future mean concentrations (a ratio
of the means, not a mean of the daily ratios).
60The selection of these sources should be representative of the 5-year period used to
calculate the 5 year weighted average design values. If large emissions changes have occurred
over the 5 year period then it may be necessary to determine the local contribution of identified
(2) For each of the four representative quarters, determine the primary versus secondary
components of PM2.5 at the monitor on the 98th percentile day and all high days.
(3) Identify percentage of total primary PM2.5 at monitor due to the local sources
identified in (1). Convert the percentage to an estimated concentration in ug/m3.
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castellano: DISPER CUSTIC DESCAR RADIA italiano:
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
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