October 23, 1997 

MEMORANDUM 

SUBJECT: Interim Implementation of New Source Review Requirements for PM2.5 

FROM: John S. Seitz, Director Office of Air Quality Planning & Standards 

(MD-10) 

TO: See Addressees 

This memorandum addresses the interim use of PM10 as a surrogate for PM2.5 in 

meeting new source review (NSR) requirements under the Clean Air Act (Act), including 

the permit programs for prevention of significant deterioration of air quality (PSD). The 

revised national ambient air quality standards (NAAQS) for particulate matter, which 

include the revised NAAQS for PM10 and new NAAQS for PM2.5, became effective on 

September 16, 1997. In view of the significant technical difficulties that now exist with 

respect to PM2.5 monitoring, emissions estimation, and modeling (described below), 

EPA believes that PM10 may properly be used as a surrogate for PM2.5 in meeting NSR 

requirements until these difficulties are resolved. The EPA's views on implementing the 

ozone and PM10 NAAQS during the interim period following the effective date of the 

new 8-hour ozone and revised PM10 NAAQS will be set forth in a separate EPA 

memorandum. 

Section 165(a)(1) of the Act provides that no new or modified major source may 

be constructed without a PSD permit. Moreover, section 165(a)(3) provides that the 

emissions from any such source may not cause or contribute to a violation of any 

NAAQS. Also, section 165(a)(4) requires best available control technology for each 

pollutant subject to regulation under the Act. The EPA's recent promulgation of the 

primary and secondary standards for PM2.5 marks the first time that EPA has specifically 

regulated fine particles--less than 2.5 microns in diameter--as a discrete indicator for 

particulate matter. Hence, this memorandum addresses how to implement PSD for PM2.5 

in light of significant technical difficulties which presently exist. 

Of specific concern is the lack of necessary tools to calculate emissions of PM2.5 

and related precursors and project ambient air quality impacts so that sources and 

permitting authorities can adequately meet the NSR requirements for PM2.5. Any 

comprehensive system for regulating PM2.5 must take into account not only the fine 

particles emitted directly by stationary sources but also the various precursors, emitted by 

certain sources, which result in secondarily-formed fine particles through chemical 

reactions in the atmosphere. Recent studies suggest that secondary particulate matter may 

account for over half of total ambient PM2.5 nationwide. Emissions factors for the fine 

particles emitted directly by stationary sources, and for some important precursors (e.g., 

ammonia), are largely unavailable at the present time. 
The EPA is in the process of developing a comprehensive modeling system which 

will be designed to include precursor emissions and account for secondary fine particle 

formation. The modeling system will also incorporate a method for nesting small local 

impacts from individual point sources within a greater modeling domain. Before this can 

be completed, it will be necessary to collect sufficient monitoring data to verify and 

validate protocol modeling results. 

Ambient monitoring for PSD purposes must be collected from appropriately 

designed monitors. Sufficient quantities of such monitors will not be available 

specifically for PSD monitoring purposes in the near future. Initially, as these monitors 

become available, they will be needed to establish the new monitoring stations for the 

national network of PM2.5 sites, including the required core PM2.5 State and local air 

monitoring stations. A high priority has been placed on the establishment of the necessary 

PM2.5 monitoring sites nationwide so that the information from these sites can be 

analyzed and evaluated in order to establish plans and priorities for implementing the 

PM2.5 NAAQS, including the promulgation of section 107 designations. 

For the reasons stated above, EPA believes that it is administratively 

impracticable at this time to require sources and State permitting authorities to attempt 

to implement PSD permitting for PM2.5. The EPA has projects underway that will 

address the current technical and informational deficiencies, but it will take 3-5 years to 

complete these projects. Until these deficiencies are corrected, EPA believes that 

sources should continue to meet PSD and NSR program requirements for controlling 

PM10 emissions (and, in the case of PM10 nonattainment areas, offsetting emissions) 

and for analyzing impacts on PM10 air quality. Meeting these measures in the interim 

will serve as a surrogate approach for reducing PM2.5 emissions and protecting air 

quality. 

This memorandum presents EPA's views on the issues associated with 

implementation of the new PM2.5 NAAQS under Federal, State and local NSR 

programs. The statements do not bind State and local governments and the public as a 

matter of law. When the technical difficulties are resolved, EPA will amend the PSD 

regulations under 40 CFR 51.166 and 52.21 to establish a PM2.5 significant emissions 

rate, and EPA will also promulgate other appropriate regulatory measures pertinent to 

PM2.5 and its precursors. Because the earliest date on which PM2.5 nonattainment areas 

will be designated is in 2002, and nonattainment NSR does not apply until after 
nonattainment designations are made, implementation of the nonattainment NSR 

requirements under part D of title I of the Act need not be addressed at this time. 

If you have any questions concerning this memorandum or wish to address any 

issues raised herein, please contact Dan deRoeck at (919) 541-5593. 

Addressees: Director, Office of Ecosystem Protection, Region I 

Director, Division of Environmental Planning and Protection, Region II 

Director, Air, Radiation, and Toxics Division, Region III 

Director, Air, Pesticides, and Toxics Management Division, Region IV 

Director, Air and Radiation Division, Region V 

Director, Multimedia Planning and Permitting Division, Region VI 

Director, Air, RCRA, and Toxics Division, Region VII 

Assistant Regional Administrator, Office of Pollution Prevention, State 

and Tribal Assistance, Region VIII 

Director, Air and Toxics Division, Region IX 

Director, Office of Air Quality, Region X 

cc: New Source Review Contacts 

Greg Foote (2344) 

Mark Kataoka (2344) 

Lydia Wegman (MD-10) 

bcc: Karen Blanchard (MD-12) 

Tom Curran (MD-12) 

Dan deRoeck (MD-12) 

Bill Hamilton (MD-15) 

Sally Shaver (MD-15)