§58.30 Special considerations for data comparisons to the NAAQS.

(a) Comparability of PM _2.5data. The primary and secondary annual and 24-hour PM _2.5 NAAQS are described in part 50 of this chapter. Monitors that follow the network technical requirements specified in §58.11 are eligible for comparison to the NAAQS subject to the additional requirements of this section. PM _2.5 measurement data from all eligible monitors are comparable to the 24-hour PM _2.5 NAAQS. PM _2.5 measurement data from all eligible monitors that are representative of area-wide air quality are comparable to the annual PM _2.5 NAAQS. Consistent with appendix D to this part, section 4.7.1, when micro- or middle-scale PM _2.5 monitoring sites collectively identify a larger region of localized high ambient PM _2.5 concentrations, such sites would be considered representative of an area-wide location and, therefore, eligible for comparison to the annual PM _2.5 NAAQS. PM _2.5 measurement data from monitors that are not representative of area-wide air quality but rather of relatively unique micro-scale, or localized hot spot, or unique middle-scale impact sites are not eligible for comparison to the annual PM _2.5 NAAQS. PM _2.5 measurement data from these monitors are eligible for comparison to the 24-hour PM _2.5 NAAQS. For example, if a micro- or middle-scale PM _2.5 monitoring site is adjacent to a unique dominating local PM _2.5 source, then the PM _2.5 measurement data from such a site would only be eligible for comparison to the 24-hour PM _2.5 NAAQS. Approval of sites that are suitable and sites that are not suitable for comparison with the annual PM _2.5 NAAQS is provided for as part of the annual monitoring network plan described in §58.10.