UNITED STATESENVIRONMENTALPROTECTIONAGENCY OfficeofAir Quality PlanningandStandards Research TrianglePark,NorthCarolina2771 1 

## 30MAR 1994

MEMORANDUM
8 SUBJECT: Nitrogen Oxides (NOx)Questions from the Ohio EPA
FROM: G.T. Helms, Chief Ozone/Carbon (MD-15)

TO: George Czerniak, Chief Regional Air Compliance Branch EPA Region V

Thismemorandum addresses theNOx reasonably available control technology (RACT)issues raised in a November 30, 1993 memorandum from Richard Schleyer, EPA Region V, to John Silvasi. These issues were discussed and resolved by theNOx work group. Ouestion 1: Can theNOx RACT rules be made applicable only F- during the summer months since ozone is a summer problem? If not, why not?

Answer: The EPAfsRACT guidance for volatile organic compounds (VOC) states that seasonal controls are generally not allowed (EPA clarification to appendix D of the November 24, 1987 Federal Reqister, "Issues Relating toVOC Regulations Cutpoints, Deficiencies, and DeviationstWrevised January 1, 1990). As stated in theNOx Supplement to the General Preamble (57 FR 55625, November 25, 1992), theVOC RACT guidance is generally applicable toNOx RACT. Thus, the limitation on seasonal controls also applies toNOx RACT.
The EPAfsdefinition of RACT is "the lowest emission limitation that a particular source is capable of meeting by the application of control technology that is reasonably available considering technological and economic feasibilitym (44 FR 53762, September 17, 1979). Thus, RACT is not generally a function of season or other temporal factors. There are limited exceptions, however, in theVOC and NOx programs where seasonal controls are allowed. For example, EPA has developed RACT guidance for seasonal controls concerning cutback asphalt (VOC)and fuel switching (NOx)

# . Question 2: Comments have been received that a 30-day 

# - rolling average should be allowed using stack tests. The Ohio EPA is not aware of any method other than use of a continuousemissions monitor where a 30-day rolling average is possible. Is there any other possiblemethod?

Answer: This issue should be addressed in the context of the enhanced compliancemonitoring rulemaking, which is in process. guestion 3: If a source is subject to a bderallyenforceable permit to install, which requires best available control technology (BACT),would the facility have to submit a RACT study or meet any of the other requirements contained in Ohio's NOx RACT rules?

Answer: RACT requirements can, in some cases, be more stringent than the lowest achievable emission rates (LAER)or BACT (seeFebruary 28, 1990memorandum from John Calcagni to Regional Offices). Therefore,where a source has already installed BACT or LAER, the Statewould still need to complete an analysis to show that BACT or LAER is at least as stringent as RACT in that cask If RACT ismore stringent, then the RACT requirementswould apply. Question 4: Isone-source trading allowed? For example, if a source uses selective noncatalytic reduction to control NOx, ik could the source simply turn on and turn off this control device, as necessary, to comply with NOx RACT?

Answer: Once a State sets a NOx RACT emission rate limit for a source category, individual sources are generally free to meet that limit in a variety of ways. For example, where a State adopts a NOx RACT emission rate limit with a long averaging time, such as 30 days, a source with a continuous emission monitor could conceivably turn on and turn off very stringent controls on alternate days and stillmeet the RACT limit. States should, however, avoid adopting RACT rules which could result in sources maximizing their emissions on high ozone potential days, thus jeopardizing attainment. Questions 5 & 9: Will partial switching tonatural gas (cofiring gas and coal) need a State implementation plan (SIP) revision? Are site-specific SIP revisionsneeded if a source is complying with NOx RACT using fuel switching?

Answer: Individual sources that switch tonatural gas do not need source-specific SIP revisions as long as the statewide NOx RACT rules allow such switching and are consistent with EPA guidance (July30, 1993 memorandum from Michael H. Shapiro to Regional Offices on fuel switching tomeet theNOx RACTrequirements). If there is no such statewide rule, then a SIP revision would be needed tomeet the NOx RACT requirements. Question 6: Canmajor NOx sources that only operate outside the ozone season be exempt from NOx RACT?

Answer: The RACT requirement applies tomajor stationary sources, consideringpotential annual emission&. However, major NOx sources which are prohibited from operating during the ozone seasonmight qualify for an exemption from the NOx requirements under section 182(f) of the Clean Air Act. The EPA would consider a petition requesting such an exemption. Question 7: Will compliance schedule changes up toApril 1, 1996 be allowedwithout a SIP revision?

Answer: Sources that do not meet milestones contained in the State's NOx RACT rulewould be subject to enforcement actions. 

# -. Question 8: Is switching from coal to oil, or oil to natural gas allowed under the fuel-switching program? If yes, what limitswould apply in either case?

n Answer: The EPA's guidance on fuel switching tomeet NOx RACT (referencedin answer 5) is not limited to coal-to-natural gas switches. That guidance would need tobe applied in each case to determine the applicable emission limits. Question 10: Are site-specific SIP revisions needed if a source is complyingwith NOx RACT using an emissions trading program?

Answer: Individual sources that comply with NOx RACT through an emissions tradingprogram do not need source-specific SIP revisions as long as the statewideNOx RACT rules provide for such a trading program and are consistent with EPA guidance (reference forthcomingNOx trading guidance memo). If there is no such statewide rule, then a SIP revisionwould be needed to meet the NOx RACT requirements.

cc: Air Branch Chief, Regions 

### I-X NOx Work Group