11.1.2 Annual PM2.5 NAAQS
1. Is the nonattainment problem primarily a local one, or are regional factors important?
(Surface measurements suggest that only design values in or immediately downwind
of the city violate the NAAQS. However, other nearby design values come close to the
concentration specified in the NAAQS)
2. What is the relative importance of measured primary and secondary components of PM2.5
measured at sites violating the NAAQS?
(Secondary components (i.e., SO4, NO3, OC) constitute about 80% of the measured
mass of PM2.5 . There are higher concentrations of primary PM2.5 in the core urban area
compared to the suburbs and more rural areas.)
3. What are the most prevalent components of measured PM2.5?
(The most important components in ranked order are mass associated with SO4, OC
and other primary particulate matter).
4. Does the measured mix of PM components appear to roughly agree with mix of emission
categories surrounding the monitoring sites?
(No. Relative importance of measured other primary PM2.5 (OPP) appears less than
what might be inferred from the inventory).
5. Do there appear to be any areas with large gradients of primary PM2.5 in monitored or
(Cannot really tell for sources of primary PM2.5 material until we resolve the
preceding inventory/monitoring discrepancy. There are no other obvious major sources of
primary particulate matter).
6. Is there any indication of what precursor might be limiting formation of secondary
(No indicator species analyses have been performed. Past analyses performed for
ozone-related SIP revisions suggest that ozone in this area may be limited by availability of
7. Do monitored violations occur at locations subject to mesoscale
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