United States Environmental Protection Agency

General Permit for New or Modified 

Minor Sources of Air Pollution in Indian Country

http://www.epa.gov/air/tribal/tribalnsr.html

Background Document: General Air Quality Permits for New or Modified 

True Minor Source Compression Ignition Engines and Spark Ignition 

Engines

Version 1.0

Last modified: July 2, 2014

1. Engines Source Category Definition

Engines covered by these proposed general permits

1 are stationary internal combustion engines (ICE) 

that convert heat energy into mechanical work and are not mobile. This source category does not 

include combustion turbines or nonroad2 engines (mobile ICE) such as forklifts, off-highway mobile 

cranes, bulldozers, and lawnmowers. Stationary ICE includes reciprocating ICE, rotary ICE, and other ICE, 

except combustion turbines.

These general permits also cover both non-emergency and emergency stationary ICE. Emergency 

stationary ICE include any stationary internal combustion engine whose operation is limited to 

emergency situations and required testing and maintenance. Examples include stationary ICE used to 

produce power for critical networks or equipment (including power supplied to portions of a facility) 

when electric power from the local utility (or the normal power source, if the facility runs on its own 

power production) is interrupted, or stationary ICE used to pump water in the case of fire, flood, or 

other natural disaster. Stationary ICE used to supply power to an electric grid or that supply power as 

part of a financial arrangement with another entity are not considered to be emergency engines.

3

 

This source category does not cover the manufacturers of engines. The proposed General Air Quality 

Permits for New or Modified True Minor Source Compression Ignition Engines and Spark Ignition 

Engines only cover engines that are located at true minor New Source Review (NSR) sources.

2. Source Category Characterization

There are two types of ICE: spark ignition (SI) and compression ignition (CI). A SI engine means a 

gasoline, natural gas, or any other type of engine with a spark plug (or other sparking device) and with 

operating characteristics significantly similar to the theoretical Otto combustion cycle. Spark ignition 

engines usually use a throttle to regulate intake air flow to control power during normal operation. Dualfuel engines in which a liquid fuel (typically diesel fuel) is used for CI and a gaseous fuel (typically natural 

gas) is used as the primary fuel at an annual average ratio of less than 2 parts diesel fuel to 100 parts 

total fuel on an energy equivalent basis are SI engines. A CI ICE is defined as an engine that is not a SI 

 

1 The EPA is making available for comment two proposed general permits: one for SI ICE and one for CI ICE.

2 As defined in 40 CFR 1068.30, a nonroad engine is used to propel a motor vehicle, aircraft, or a vehicle used solely 

for competition.

3 The definitions for emergency and stationary engines are adopted from the definitions in 40 CFR 60.4219.
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engine and are typically diesel engines where the heat generated from compression is enough to initiate 

the combustion process, without needing any external spark.

4

Gasoline, diesel (No.2 fuel oil), and natural gas are the three primary fuels used for engines. Most 

natural gas-fired reciprocating engines are used in the natural gas industry at pipeline compressor and 

storage stations and at gas processing plants.5 Gasoline and small diesel engines (with capacities equal 

to or less than 600 horsepower (hp)) cover a wide variety of industrial applications such as generators, 

pumps, and material handling equipment (such as conveyors). Gasoline is used primarily for mobile and 

portable engines. Diesel fuel oil is the most versatile fuel and is used in CI engines of all sizes. Substantial 

differences in engine duty cycles exist.6

Large stationary diesel engines (with capacities greater than 600 hp) are often used in oil and gas 

exploration and production. These engines, in groups of 3 to 5, supply mechanical power to operate 

drilling (rotary table), mud pumping, and hoisting equipment, and may also operate pumps or auxiliary 

power generators. Another frequent application of large stationary diesel engines is electricity 

generation for both base and standby service. Smaller uses include irrigation, hoisting, and nuclear 

power plant emergency cooling water pump operation.7

The primary criteria pollutants from engines are oxides of nitrogen (NOx), carbon monoxide (CO), and 

volatile organic compounds (VOC). The formation of NOx is exponentially related to combustion 

temperature in the engine cylinder. The other pollutants, CO and VOC, are primarily the result of 

incomplete combustion. Particulate matter (PM) emissions include trace amounts of metals, noncombustible inorganic material, and condensible, semi-volatile organics which result from volatized 

lubricating oil, engine wear, or from products of incomplete combustion. Emissions of sulfur 

compounds, mainly sulfur dioxide (SO2), are directly related to the sulfur content of the fuel.

Three generic control techniques have been developed for reciprocating engines: parametric controls 

(timing and operating at a leaner air-to-fuel ratio); combustion modifications such as advanced engine 

design for new sources or major modification to existing sources (clean-burn cylinder head designs and 

pre-stratified charge combustion for rich-burn engines); and post-combustion catalytic controls installed 

on the engine exhaust system. Post-combustion catalytic technologies include selective catalytic 

reduction for lean-burn engines, nonselective catalytic reduction for rich-burn engines, and CO oxidation 

catalysts for lean-burn engines.8

3. State NSR Minor Source Permit Programs

The U.S. Environmental Protection Agency (EPA) researched state government websites for general 

permits for this source category and examined them for applicability to a permit for Indian country. The 

EPA selected the appropriate elements for the development of the documents and regulations in the 

general permit for this source category. The EPA identified the following states and local governments 

that have specific NSR minor programs (such as general permit or general order) for engines or 

 

4 The definitions for SI and CI engines are adopted from the definitions in 40 CFR 60.4219.

5 AP-42, Chapter 3.2 – Natural Gas-fired Reciprocating Engines, http://www.epa.gov/ttn/chief/ap42/ch03/.

6 AP-42, Chapter 3.3 – Gasoline And Diesel Industrial Engines, http://www.epa.gov/ttn/chief/ap42/ch03/.

7 AP-42, Chapter 3.4 – Large Stationary Diesel And All Stationary Dual-fuel Engines, 

http://www.epa.gov/ttn/chief/ap42/ch03/.

8 AP-42, Chapter 3.2 – Natural Gas-fired Reciprocating Engines, http://www.epa.gov/ttn/chief/ap42/ch03/.
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generators: Alaska, Arizona, Florida, New Hampshire, New Jersey, Ohio, Pennsylvania, Rhode Island, 

Virginia, Washington, and West Virginia. The requirements for the state permitting programs related to 

engines/generators are summarized in Attachment A. Permits from these states were chosen for 

examination because of characteristics they possess:

 Readily available; 

 Clear throughput limits; and 

 Organization of the regulations followed the typical form for federal NSR permits:

o Limitations and standards, and 

o Monitoring, testing, recordkeeping, and reporting requirements.

For the state permit programs reviewed, the general permits include two major types of engines: 

emergency engines and non-emergency engines. The state general permit requirements cover the 

following four areas:

 Emission Limits: Most of the state permit programs, except for the state permit program for 

Washington, contain emission limits for CO, NOX, and VOC. The emission limits for NOX range 

from 5 tons per year (tpy) to 250 tpy.

 Fuel Limits: Some state permit programs contain fuel usage limits and sulfur content limits. The 

state permit program for Virginia also includes heat content limits for fuels. 

 Operating Hour Limits: For emergency generators, most state permit programs include an 

operating hour limit of 500 hours/year. For non-emergency generators, there is no operating 

hour limit.

 Other requirements: Some state permit programs include unit capacity limits (in hp, million 

British thermal units (MMBtu)/hour, or kilowatt (KW)) and/or stack height requirements.

In addition, all of the state general permits reviewed incorporate the requirements of NSPS, Subpart IIII

(Standards of Performance for Stationary Compression Ignition Internal Combustion Engines), NSPS, 

Subpart JJJJ (Standards of Performance for Stationary Spark Ignition Internal Combustion Engines), and 

NESHAP, Subpart ZZZZ (National Emission Standards for Hazardous Air Pollutant for Reciprocating 

Internal Combustion Engines). 

4. Requirements for General Permit

4.1 Documents for General Permit

The EPA developed a standardized set of permit documents in support of a general permit for engine 

sources. These consist of the following documents: 

 Questionnaire: Assists the facility owner or operator in determining whether they are eligible for 

a General Air Quality Permit;

 Request for Coverage under the General Air Quality Permit: States the criteria for qualification, 

gathers information on the source, facility location, and source contact, and requests technical 

information on facility equipment, throughput, and attainment status;
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 Instructions: Guides the applicant in filling out the Request for Coverage under the General Air 

Quality Permit;

 General Air Quality Permit, Terms and Conditions: Contains the requirements and regulations 

with which the source must comply. The emission limitations, monitoring, recordkeeping and 

reporting requirements are in the permit, including requirements for sources located in 

nonattainment areas; and

 Potential to Emit (PTE) Calculator Spreadsheet: Allows applicants to calculate their PTE, based 

on owner inputs of the specific equipment present at their source, assuming continuous 

operation throughout the year. The PTE Calculator spreadsheet generates potential emissions, 

based on these inputs. The spreadsheet illustrates the correlation between equipment, raw 

material throughput, and emissions.

4.2 Exemption and Qualification for General Permits

Facilities applying for the proposed general permit must meet the following criteria:

 Must be a true minor NSR source; and

 Be below the emissions limitations established for the general permit.

Facilities with a PTE lower than the minor NSR thresholds specified in Table 1 of Indian Country Minor 

NSR rule (40 CFR 49.153) are exempt from the minor NSR program. The exemption thresholds for PM 

and criteria pollutants are listed in Table 1 below. Facilities applying for the proposed general permit will 

be required to calculate their PTE and may use the PTE calculator provided to determine if they are 

exempt from the minor NSR program. 

 Table 1: Minor NSR Thresholds in 40 CFR 49.153

Pollutant Attainment Area Nonattainment Area

CO 10 tpy 5 tpy

PM 10 tpy 5 tpy

PM10 5 tpy 1 tpy

PM2.5 3 tpy 0.6 tpy

SO2 10 tpy 5 tpy

NOX 10 tpy 5 tpy

VOC 5 tpy 2 tpy

Under current EPA policy, only true NSR minor sources qualify for the proposed general permit. 

Therefore, facilities will be required to compare their PTE to the NSR major source thresholds to 

determine if they qualify for the proposed general permit. The NSR major source threshold for 

attainment areas is 250 tpy for any criteria pollutant. The NSR major source thresholds for 

nonattainment areas are summarized in Table 2 below:

 Table 2: NSR Major Source Thresholds for Nonattainment Areas

Pollutant Nonattainment Classification NSR Major Source Threshold

Ozone Marginal 100 tpy of VOC or NOX

Moderate 100 tpy of VOC or NOX
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Pollutant Nonattainment Classification NSR Major Source Threshold

Serious 50 tpy of VOC or NOX

Severe 25 tpy of VOC or NOX

Extreme 10 tpy of VOC or NOX

PM10

Moderate 100 tpy

Serious 70 tpy

CO Moderate 100 tpy

Serious 50 tpy

SO2, NOx, PM2.5 No nonattainment classification 100 tpy

If the facility’s PTE is above the NSR major source threshold of 250 tpy, or above the applicable 

nonattainment area thresholds listed in Table 2 (for any pollutant), then the facility does not qualify for 

the proposed general permit. The following documents are available to assist sources in the screening 

and application process: 

 Questionnaire; and

 Request for Coverage under the General Air Quality Permit.

The questionnaire and the application for the engines permits contain questions designed to limit the 

availability of this general permit to true minor source engines. For facilities not exempt from the minor 

NSR program and having a PTE below the NSR major source thresholds, the facilities will further 

evaluate if they can meet the throughput limits and operating requirements established in this general 

permit. The specific requirements for the proposed general permit are discussed in Sections 4.3, 4.4, 4.5, 

and 4.6. Section 5 provides background on the surrogate emissions limitations provided in the proposed 

engines general permit.

4.3 Specific Permit Requirements for General Permits

The terms and conditions of the proposed general permit were established according to the required 

permit content and analyses in the Indian Country Minor NSR rule. The required permit content is listed 

in 40 CFR 49.155(a) – What information must my permit include? Below we describe the basis for the 

permit conditions.

40 CFR 49.155(a)(1) – General Requirements

The rule establishes general requirements that each permit must identify: the effective date of the 

permit; the date by which the owner/operator must commence construction in order for the permit to 

remain valid; the emission units subject to the permit and their associated emission limitations; and 

monitoring, recordkeeping, and reporting requirements to assure compliance with the emission 

limitations. 

The proposed general permit contains all of this required information, except for the emission units 

subject to the permit. Because of the nature of general permits we believe it is more appropriate to 

identify the emission units covered by the general permit in the Approval of the Request for Coverage. 

The general permit incorporates the Approval of the Request for Coverage into the general permit. Each 

permit contains a separate section that specifically identifies the emission limitations and standards, 

monitoring and testing, recordkeeping, and reporting and notification requirements.
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40 CFR 49.155(a)(2) – Emission Limitations

The permit must contain the emission limitations determined by the reviewing authority under 40 CFR 

49.154(c) for each affected emissions unit. 40 CFR 49.154(c) – How will the reviewing authority 

determine the emission limitations that will be required in my permit? – identifies the case-by-case 

control technology review that must be used by the reviewing authority to determine the appropriate 

level of control. In carrying out the case-by-case control technology review, the reviewing authority 

must consider the following factors:

1. Local air quality conditions;

2. Typical control technology or other emission reduction measures used by similar sources in 

surrounding areas;

3. Anticipated economic growth in the area; and

4. Cost-effective emission reduction alternatives.

In addition, the reviewing authority must require a numerical limit on the quantity, rate or 

concentration of emissions for each regulated NSR pollutant emitted by each affected emissions unit, 

for which such a limit is technically feasible. The emission limitation required may also be included as 

pollution prevention techniques, design standards, equipment standards, work practices, operational 

standards or any combination thereof. However, the emission limitations must assure that each affected 

emission unit will comply with all requirements of 40 CFR parts 60, 61, and 63, as well as any federal or 

tribal implementation plans that apply to the unit. Finally, the emission limitations required may not rely 

on a stack height that exceeds good engineering practice or any other dispersion technique, except as 

allowed by 40 CFR 51.118(b).

To address the requirements for establishing emission limitations, the following considerations were 

used for setting the limits in the proposed general permit for engines:

1. Local air quality conditions – To address this requirement, the proposed general permits include 

more stringent engine capacity limits in nonattainment areas because limiting capacity results in 

sufficient reductions in potential emissions to ensure sources would still be below the major 

source thresholds. In addition, the CI general permit for engines is not available to sources in 

extreme or severe ozone nonattainment areas. The SI general permit for engines is not available 

to sources in serious CO nonattainment areas. The restrictions on capacity in such areas are 

necessary to keep emissions below major source levels would likely not make the general 

permits useful to owners/operators. Such facilities will need to obtain site-specific permits.

2. Typical control technology or other emission reduction measures used by similar sources in 

surrounding areas – For sources locating in attainment areas the EPA looked at the control 

requirements specified by 40 CFR parts 60, 61 and 63. These regulations establish minimum 

technology and emission limitations that must be met nationally and also meet the 

requirements of 40 CFR 49.154(c)(4) to ensure compliance with parts 60, 61, and 63. For this 

proposed general permit the EPA considered regulations that apply to engines:

a. NSPS, Subpart JJJJ – Standards of Performance for Stationary Spark Ignition Internal 

Combustion Engines;

b. 40 CFR 60 Subpart IIII – Standards of Performance for Stationary Compression Ignition 

Internal Combustion Engines;
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c. 40 CFR 63 Subpart ZZZZ – National Emission Standards for Hazardous Air Pollutions for 

Stationary Reciprocating Internal Combustion Engines; 

d. 40 CFR 89 – Control of Emissions from New and In-Use Nonroad Compression-Ignition 

Engines;

e. 40 CFR 90 – Control of Emissions from Nonroad Spark-Ignition Engines at or Below 19 

Kilowatts;

f. 40 CFR 1039 – Control of Emissions from New and In-Use Nonroad Compression-Ignition 

Engines;

g. 40 CFR 1048—Control of Emissions from New, Large Nonroad Spark-Ignition Engines; 

and

h. 40 CFR 1054 – Control of Emissions from New, Small Nonroad Spark-Ignition Engines 

and Equipment.

The General Terms and Conditions in the general permit are a standardized set of boilerplate 

conditions included with the general permits. The conditions in the Specific Terms and 

Conditions section of the general permit are developed from the NSR Rule, NSPS, NESHAP, and 

the state permit examples.

The derivation of the surrogate emissions limitations in the general permit are discussed in 

Section 5. The minor NSR thresholds are based on provisions of the Review of New Sources and 

Modifications in Indian Country rule at 40 CFR 49.153 and are provided in Table 1.

Under the proposed permit for CI internal combustion engines, each affected non-emergency CI 

engine, excluding nonroad mobile engines, must comply with the following limitations and 

standards:

a. If using distillate fuel, use diesel or biodiesel containing no more than 15 ppm 

(parts per million) (0.0015 percent) sulfur; and

b. Each engine shall be model year 2014 or later and certified by the manufacturer to the 

applicable standards in in 40 CFR 1039.101 through 1039.104, for all pollutants, for the 

same model year and maximum engine power.

The proposed permit for CI internal combustion engines does not allow for the installation of 

non-emergency engines that do not meet Tier 4 standards. Tier 4 standards require certain nonemergency engines to be equipped with add-on controls for CO and NOX (and certified by the 

manufacturer to more stringent standards than previous model year engines). 

Non-emergency SI engines must meet certain standards provided in the permit based on the 

engine type, maximum engine power rating, and date of manufacture. The proposed permit for 

SI internal combustion engines does not allow for the installation of non-emergency engines 

that do not meet the most stringent standards in the NSPS for non-emergency engines 

manufactured after 2010 or 2011, depending on engine size.

The proposed permits for CI and SI engines allow for emergency engines to be either 

spark or CI engines. Each permit requires that each affected emergency engine shall:

a. Be equipped with a non-resettable hour meter;

b. If using distillate fuel oil, use diesel or biodiesel containing no more than 15 ppm 
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(0.0015 percent) sulfur;

c. Meet the following certification requirements for CI emergency engines:

i. For model year 2006 and later engines, the engine shall be certified 

to the applicable standards in 40 CFR part 89;

d. Meet the following certification requirements for SI emergency engines 

manufactured on or after January 1, 2009:

i. Engines greater than 50 hp and less than 130 hp shall be certified to 

the Phase I standards in 40 CFR 90.103;

ii. Engines greater than or equal to 130 hp shall be certified to the 

standards in 40 CFR 1048;

iii. All other SI emergency engines greater than 25 hp shall meet the 

standards for emergency engines in Table 1 to 40 CFR Subpart JJJJ; 

and

e. If not required to be certified to the standards in conditions c. or d. above:

i. Follow the manufacturer’s emission-related operation and 

maintenance instructions or develop your own maintenance plan 

which must provide, to the extent practicable, for the maintenance 

and operation of the engine in a manner consistent with good air 

pollution control practice for minimizing emissions;

ii. Change oil and filter and inspect every hose and belt every 500 hours 

of operation or annually, whichever comes first; and

iii. Inspect air cleaner or spark plugs, as applicable, every 1,000 hours of 

operation, or annually, whichever comes first.

3. Anticipated economic growth in the area – The Reviewing Authority may consider anticipated 

economic growth when determining whether coverage under the general permit is justifiable. 

Considering, however, that the general permit sets emission standards that are consistent with 

what is required for engines across the country in both attainment and non-attainment areas, 

we expect that this will rarely be a factor. 

4. Cost-effective emission reduction alternatives – The general permit sets emission standards that 

are consistent with what is required for engines across the country. As such, the chosen 

technologies are considered widely available and consideration of more cost-effective 

alternatives is not necessary at this time. We intend to periodically review technology costs in 

the future to determine when more stringent, cost-effective technologies become widely 

available.

40 CFR 49.155(a)(3) – Monitoring Requirements

The proposed general permit must include monitoring that is sufficient to assure compliance with the 

emission limitations that apply to the source. For CI engines, the proposed general permit requires: (1) 

monitoring of fuel use and (2) performance testing for emergency engines that are not certified by the 

manufacturer. For SI engines, the proposed permit requires: (1) monitoring of fuel use, (2) maintaining 

any air-to-fuel ratio controller, and (3) performance testing for certain engines that are not certified by 

the manufacturer

40 CFR 49.155(a)(4) – Recordkeeping Requirements

The proposed general permit must include recordkeeping that is sufficient to assure compliance with 

the emission limitations and monitoring requirements, including certain statements listed in 40 CFR 
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49.155(a)(4)(i) and (ii). In addition to the recordkeeping requirements in 40 CFR 49.155(a)(4)(i), under 

the general permit for CI engines the permittee must maintain records of: (1) the amount of fuel used 

each month for each engine; (2) for each fuel shipment, fuel supplier certification showing the sulfur 

content of fuel; (3) for each engine required to be certified or using certification, documentation from

the manufacturer that each engine is certified to the applicable standards; (4) the maintenance plan for 

each engine, including all maintenance activities conducted on a monthly basis; and (5) for emergency 

engines, maintain a log of the hours of operation, including the date, time, duration, and reason(s) for 

use. In addition, the results of each performance test must be recorded.

Under the general permit for SI engines, the permittee must maintain records of: (1) the amount of fuel 

used each month; (2) for each engine required to be certified or using certification, documentation from 

the manufacturer that each engine is certified to the applicable standards; (3) the maintenance plan for 

each engine, including all maintenance activities conducted on a monthly basis; and (4) the hours of 

operation and reason for operation for each emergency engine, on a monthly basis. In addition, the 

results of each performance test must be recorded.

40 CFR 49.155(a)(5) – Reporting Requirements

The proposed general permit includes the reporting requirements listed in 40 CFR 49.1559(a)(5)(i) and 

(ii) related to annual reports and reporting of deviations. 

40 CFR 49.155(a)(6) – Severability Clause

The proposed general permit includes a severability clause to ensure the continued validity of the other 

portions of the permit in the event of a challenge to a portion of the permit. This condition is found in 

the General Provisions of the proposed general permit.

40 CFR 49.155(a)(7) – Additional Provisions

The proposed general permit contains the additional provision required for each permit. These 

conditions are found in the General Provisions of the proposed general permit.

The questionnaire and the application for the engines permits contain questions designed to limit the 

availability of this general permit to engines that are stand alone and are not located at sources for 

which the EPA has also issued a general permit.

4.4 Requirements for Sources Located in Nonattainment Areas

The CI general permit for engines is not available to sources in extreme or severe ozone nonattainment 

areas. The SI general permit for engines is not available to sources in serious CO nonattainment areas.

4.4 Additional Permit Requirements

The proposed general permits require engines to locate at least 150 feet from the nearest property 

boundary and 1,000 feet from the nearest residence.
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4.6 Requirements of the Endangered Species Act and National Historic Preservation Act

Prior to seeking coverage under this general permit, sources must satisfactorily address the permitting 

requirements related to the Endangered Species Act and National Historic Preservation Act. Attached to 

the request for coverage document for the engines general permit, the EPA provides guidance to assist

sources in complying with these two statutes.

5. Emission Limitations9 and Surrogate Throughput Limits 

5.1 Developing the Surrogate Limits and Limitations

Capacity limits as surrogate emissions limitations were established to ensure emissions from sources of 

engines stay below the thresholds for the major NSR and Title V permitting programs. The emission 

threshold for sources located in attainment areas is 100 tpy, which is also the threshold for the Title V 

operating permit program. The emissions thresholds for facilities located in nonattainment areas are set 

at the thresholds in Table 2 for each pollutant and nonattainment status, which serve as the thresholds 

for both the major NSR and Title V permitting programs.

In general, internal combustion engines emit a multitude of pollutants, but generally CI engines emit 

NOx at levels high enough to make NOx a controlling pollutant of concern. Generally, SI engines emit CO 

at levels high enough to make CO a controlling pollutant of concern. For these reasons, we found it 

necessary to establish capacity limits as surrogate emissions limitations for the engines that are part of a

stationary source that correspond to the emissions rates for CO and NOx, as applicable, in Table 3. 

Because the major source threshold for NOx is lower in serious and above ozone nonattainment areas, 

we found it necessary to establish a lower capacity limit for CI engines at stationary sources in serious

ozone nonattainment areas. We are not making the CI general permit available for severe and extreme 

ozone nonattainment areas. Hence, we are not providing emission rates for severe and extreme ozone 

nonattainment areas.

For SI engines the capacity limits ensure emissions are below the major source thresholds in all ozone 

nonattainment areas, since the controlling pollutant is CO. The capacity limits as surrogate emissions 

limitations do not apply to nonroad engines, such as engines that operate mobile equipment (e.g., 

trucks and loaders) and portable engines that remain at one location for less than 12 months.

 Table 3: Emission Rates used to Determine Emission Limitations for Facilities with Engines

Pollutant of 

Concern

Attainment, Unclassifiable 

or Attainment/ 

Unclassifiable Areas

Nonattainment Areas

NOX 100 tpy

100 tpy

(marginal and moderate ozone areas)

50 tpy

(serious ozone areas)

CO 100 tpy 100 tpy

(moderate areas)

 

9 The definition of emission limitation used in this background document is the one provided in the Indian Country 

Minor NSR rule (described in Section 4.3) and includes requirements established by the reviewing authority that 

relate to the operation of a source, which allows for the use of production throughput limits.
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The proposed general permits include the capacity limits listed in Tables 4 and 5 below for the CI

engines and SI engines permits, respectively. The capacity limits are set at levels intended to keep the 

source’s emissions below the emissions rates in Table 3 (NOx and CO are the controlling pollutants; the 

capacity limit calculations are provided in Attachment C).

Table 4: Surrogate Capacity Limits for Internal Combustion Engines

General Permit (CI)

Capacity Limit Serious Ozone 

Nonattainment Areas Other Areas

Capacity limits for engines

and emergency engines

1100 hp for nonemergency engines 

750 hp for emergency 

engines

Option 1: 3800 hp for all 

non-emergency engines 

and 1000 hp for all 

emergency engines;10

Option 2: 1900 hp for all 

non-emergency engines 

and 2500 hp for all 

emergency engines

Table 5: Surrogate Capacity Limits for Internal Combustion Engines

General Permit (SI)

Capacity Limit All Areas

Capacity limits for engines 

and emergency engines

1750 hp for all non-emergency engines

800 hp for all emergency engines

5.2 Emission Limitations

Three considerations form the basis for the emission limitations for the general permit:

1. Are there any EPA regulation-based emission limitations?

2. What do actual emissions data from the 2011 National Emissions Inventory (NEI)11 indicate 

about the size profile of the source category? 

3. Where do state programs establish eligibility limits? 

 

10 This option is only available when a particular permitted source has non-emergency engines that are all rated 

greater than 75 hp and any non-emergency engine over 750 hp is equipped with a generator set.

11 For more information, go to: http://www.epa.gov/ttnchie1/net/2011inventory.html.
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5.2.1 EPA Regulation-Based Emissions Limitations 

Facilities in attainment areas with criteria pollutant emissions greater than 100 tpy are subject to Title V 

operating permit programs. This general permit is not intended to cover Title V major sources. 

Therefore, the emissions limitations included in the proposed permit are based on the Title V major 

source threshold of 100 tpy for each criteria pollutant for engines subject to these general permits and 

located in attainment areas. For facilities located in nonattainment areas, this general permit is not 

intended to cover NSR major sources. The NSR major source thresholds vary depending on the 

classification of the nonattainment areas and are provided in Table 2.

5.2.2 Analysis of NEI Data

The EPA analyzed 2011 NEI data for certain types of existing facilities across the entire U.S. that have 

engines to evaluate the emission limitations established in the general permit. Although the NEI does 

not include potential emissions information for sources in Indian country, it reflects the actual emissions 

from facilities with engines in 50 states. In order to analyze facilities whose emissions are similar to 

those for sources potentially subject to the Indian Country Minor NSR rule, the EPA selected facilities for 

analysis with the North American Industry Classification System (NAICS) codes listed in Table 6. For 

sources with these NAICS codes, the EPA selected actual emissions12 within the ranges listed in Table 7.

 Table 6: NAICS Codes Selected for Engines

NAICS Code Description

2211** Electric Power Generation, Transmission or Distribution

622110 Medical and Surgical Hospitals

 Table 7: Emission Ranges Selected for Facilities with Engines

Criteria Pollutants

NOX CO

Attainment Area

 Min. Emissions (tpy) 10 10

 Max. Emissions (tpy) 250 250

Nonattainment Area

 Min. Emissions (tpy) 5 5

 Max. Emissions (tpy) 250 250

The EPA analyzed the emissions rates listed in Table 5 that were used to establish the surrogate 

throughput emissions limitations and selected the facilities with emission levels similar to the facilities 

potentially subject to the NSR minor program, i.e., the facilities with emissions greater than the minor 

NSR applicability thresholds in Table 1 of 40 CFR 49.153 (Indian Country Minor NSR rule) and less than 

the PSD major source threshold of 250 tpy. For purposes of this analysis, facilities located in 

nonattainment areas are defined as facilities located in counties that are designated nonattainment for 

the pollutant being analyzed. 

With the NAICS codes listed in Table 6 and the emission ranges defined in Table 7, the EPA identified 

sources of engines located in attainment and nonattainment areas for NOx, and CO. The EPA is providing 

 

12 Only point source NEI data were used for this analysis. The point source inventory does not include emissions 

from nonroad engines.
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the number of facilities (and average emissions) under the proposed emissions limitations and above 

the minor source thresholds. 

Table 8: Number of Facilities and Average Emissions for Facilities with Engines Selected

Criteria Pollutants Number of Facilities

Attainment Areas

CO

Facilities > 10 tpy and < 100 tpy 596 (22% of facilities covered)

Average Emissions (tpy) 38

Facilities > 100 tpy and < 250 tpy 245

Average Emissions (tpy) 159

NOx

Facilities >10 tpy and < 100 tpy 591 (28% of facilities covered)

Average Emissions (tpy) 38

Facilities > 100 tpy and < 250 tpy 178

Average Emissions (tpy) 156

Nonattainment Areas

CO (moderate)

Facilities > 5 tpy and < 100 tpy 133 (17% of facilities covered)

Average Emissions (tpy) 25

Facilities > 100 tpy and < 250 tpy 24

Average Emissions (tpy) 139

NOx (marginal and moderate)

Facilities >5 tpy and < 100 tpy 328 (29% of facilities covered)

Average Emissions (tpy) 25

Facilities > 100 tpy and < 250 tpy 60

Average Emissions (tpy) 154

NOx (serious)

Facilities >5 tpy and < 50 tpy 5 (36% of facilities covered)

Average Emissions (tpy) 7

Facilities > 50 tpy and < 250 tpy 0

Average Emissions (tpy) N/A

5.2.3 State Program Limits

The EPA researched similar types of permits developed by the States of Alaska, Arizona, Florida, New 

Hampshire, New Jersey, Ohio, Pennsylvania, Rhode Island, Virginia, Washington, and West Virginia. The 

requirements for each state program are summarized in Attachment A. Only the state programs for 

Arizona, New Jersey, Virginia, and Washington have capacity limits. Arizona limits the capacity of 

individual CI engines to 3000 hp. New Jersey limits the total capacity of emergency engines to less than 

80 MMBtu/hour. Virginia limits the capacity of non-emergency engines in voluntary demand response 

programs to about 59 MW for CI engines, 61 MW for SI engines and 38 MW for SI engines in 

nonattainment areas. Virginia limits the capacity of emergency engines to about 24 MW for CI engines 

and 13 MW for SI engines. Washington limits the capacity of SI emergency engines to 850 hp. . 
Page 14 of 20

5.3 Calculating the Capacity Limits

The EPA derived the capacity limits for the engines through back-calculations that yielded emissions at 

the applicability emission rates listed in Table 3. The capacity limits for non-emergency CI engines are 

based on the applicable Tier 4 emission standards in 40 CFR 1039 and AP-42 when the NSPS does not 

establish a limit for a particular pollutant. The capacity limits for non-emergency SI engines are based on 

the standards in 40 CFR 90, 40 CFR 1054, and Table 1 to 40 CFR 60 Subpart JJJJ, as applicable. AP-42 

emission factors were used when the relevant standard did not set an emission standard for a particular 

pollutant. The capacity limits for emergency engines (SI and CI) are based on AP-42 emission factors. 

Attachment B contains example calculations showing how capacity limits in Tables 4 and 5 correspond 

to the emission rates in both ozone attainment and ozone nonattainment areas as shown in Table 3. 
Page 15 of 20

References:

40 CFR 49.151 – 40 CFR 49.173, Indian Country Air Quality Planning and Management. 

http://www.ecfr.gov/cgi-bin/text-idx?tpl=/ecfrbrowse/Title40/40cfr49_main_02.tpl

40 CFR part 60, Subpart IIII, Standards of Performance for Stationary Compression Ignition Internal 

Combustion Engines.

http://ecfr.gpoaccess.gov/cgi/t/text/textidx?c=ecfr&sid=f2c4f71bd50d2a8883adafec36732010&rgn=div6&view=text&node=40:6.0.1.1.1.98&idn

o=40

40 CFR part 60, Subpar JJJJ, Standards of Performance for Stationary Spark Ignition Internal Combustion 

Engines.

http://ecfr.gpoaccess.gov/cgi/t/text/textidx?c=ecfr&sid=f2c4f71bd50d2a8883adafec36732010&rgn=div6&view=text&node=40:6.0.1.1.1.99&idn

o=40

40 CFR part 63, Subpar ZZZZ, National Emission Standards for Hazardous Air Pollutant for Reciprocating 

Internal Combustion Engines (RICE).

http://ecfr.gpoaccess.gov/cgi/t/text/textidx?c=ecfr&rgn=div6&view=text&node=40:13.0.1.1.1.1&idno=40

AP 42, Fifth Edition, Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area 

Sources.

http://www.epa.gov/ttn/chief/ap42/index.html

Federal Register Vol. 76, No. 127, July 1, 2011, Pages 38748-38808, “Review of New Sources and 

Modifications in Indian Country; Final Rule” (Indian Country NSR Rule). 

https://www.federalregister.gov/articles/2011/07/01/2011-14981/review-of-new-sources-andmodifications-in-indian-country
Page 16 of 20

Attachment A – Summary of the State Permitting Programs for Engines

State Permit Type Emission Limits Fuel Limit Operating Hour 

Limits Other Requirements Weblink

AK

General permit 

for diesel electric 

generators.

100 tpy < NOX < 

250 tpy.

< 825,000 gallons/year of 

diesel.

N/A NSPS, Subpart IIII and

NESHAP, Subpart ZZZZ.

http://dec.alaska.gov/air

/ap/genperm.htm

AZ General permit 

for generators.

CO < 90 tpy;

NOX < 90 tpy; and

VOC < 90 tpy.

N/A N/A Each unit < 3,000 hp;

stack height requirements;

NSPS, Subpart IIII;

NSPS, Subpart JJJJ; and

NESHAP, Subpart ZZZZ.

http://www.azdeq.gov/f

unction/forms/appsair.h

tml#source

FL

General permits 

for reciprocating 

internal 

combustion 

engines.

NOX < 100 tpy and

HAP < 10/25 tpy.

< 20,000 gallons/year of 

gasoline;

< 250,000 gallons/year of 

diesel;

< 1.15 million gallons/year

of propane; and

< 40 MMcf/year of natural 

gas.

N/A NSPS, Subpart IIII

NSPS, Subpart JJJJ

NESHAP, Subpart ZZZZ

http://www.dep.state.fl.

us/air/emission/air_gp.h

tm

NH

General permit 

for emergency 

generators.

PM10 < 100 tpy;

NOX < 50 tpy;

CO < 100 tpy;

VOC < 50 tpy; and

SO2 < 100 tpy.

N/A < 500 

hours/year.

NSPS, Subpart IIII. http://des.nh.gov/organi

zation/divisions/air/peh

b/apps/permits.htm

NJ

General permit 

for emergency 

generator.

NOX < 5 tpy. No. 2 fuel, diesel, kerosene, 

natural gas-fired units only; 

and

Sulfur content limits for 

fuels.

Various 

operating hour 

limits based on 

the size of 

engines.

Total capacity < 80 MMBtu/hour. http://www.state.nj.us/

dep/aqpp/gp1list.htm

NJ General permit 

for SI engines.

NOX < 10 tpy;

CO < 33.3 tpy; and

VOC < 10 tpy.

For natural gas- and 

propane-fired units only.

N/A Total capacity < 65 MMBtu/hour;

Stack height requirements; and

NSPS, Subpart JJJJ.

http://www.state.nj.us/

dep/aqpp/gp1list.htm
Page 17 of 20

State Permit Type Emission Limits Fuel Limit Operating Hour 

Limits Other Requirements Weblink

OH

General permit 

for portable CI

diesel engines.

NOX < 74 tpy;

CO < 32.5 tpy; and

VOC < 12.33 tpy.

< 500,000 gallons/year and

Sulfur content limits.

Various 

operating hour 

limits based on 

the size of 

engines.

NSPS, Subpart IIII. http://www.epa.state.o

h.us/dapc/genpermit/cii

ce.aspx

PA

General permit 

for diesel/no. 2 

fuel engines.

NOX < 90 tpy and

NOX < 22.5 tpy

for ozone 

nonattainment 

areas

Sulfur content limits. Various 

operating hour 

limits based on 

the size and the 

location of 

engines.

Stack testing requirements. http://www.dep.state.p

a.us/dep/deputate/airw

aste/aq/permits/gp.htm

RI

General permit 

for distributed 

generators.

PTE < PSD major 

source thresholds.

N/A N/A Compliance with all applicable 

state regulations.

http://www.dem.ri.gov/

pubs/forms.htm#air

RI

General permit 

for emergency 

generators.

PTE < PSD major 

source thresholds.

N/A N/A Compliance with all applicable 

state regulations.

http://www.dem.ri.gov/

pubs/forms.htm#air

VA

General permit 

for voluntary 

demand 

response 

generators.

CO < 100 tpy;

NOX < 40 tpy 

(attainment); and

NOX < 25 tpy 

(nonattainment).

< 502,766 gallons/year of 

diesel;

< 554,230 gallons/year of 

biodiesel fuel; sulfur 

content limits and

heat content limits.

N/A CI Capacity < 58,886 KW;

SI Capacity < 60,970 KW

(attainment); and

SI Capacity < 37,750 KW

(nonattainment).

http://www.deq.state.v

a.us/Programs/Air/Perm

ittingCompliance/Permit

ting/TypesofAirPermits.a

spx

VA

General permit 

for emergency 

generators.

CO < 77 tpy;

NOX < 40 tpy 

(attainment);

CO < 50 tpy; and

NOX < 25 tpy 

(nonattainment).

Sulfur content limits and

heat content limits.

< 500 

hours/year.

SI Capacity < 23,535 KW

(attainment) and

SI Capacity < 13,115 KW

(nonattainment).

http://www.deq.state.v

a.us/Programs/Air/Perm

ittingCompliance/Permit

ting/TypesofAirPermits.a

spx

WA

General order 

for gas powered 

emergency 

generators.

N/A Fuel: natural gas and 

propane.

< 500 

hours/year.

SI Capacity < 850 hp;

Stack height requirement;

NSPS, Subpart IIII; and

NESHAP, Subpart ZZZZ.

http://www.ecy.wa.gov/

programs/air/AOP_Perm

its/Boiler/GeneralOrders

.htm
Page 18 of 20

State Permit Type Emission Limits Fuel Limit Operating Hour 

Limits Other Requirements Weblink

WV

General permit 

for emergency 

generators.

CO < 10 tpy;

NOX < 10 tpy;

SO2 < 10 tpy;

VOC < 10 tpy; and

PM < 10 tpy

(attainment).

N/A < 500 

hours/year.

NSPS, Subpart IIII;

NSPS, Subpart JJJJ; and

NESHAP, Subpart ZZZZ.

http://www.dep.wv.gov

/daq/permitting/Pages/

airgeneralpermit.aspx
Page 19 of 20

Attachment B

Emissions Calculations for Capacity Limits 

SI Capacity Limits: 1750 hp for non-emergency engines and 800 hp for emergency engines 

 CO is the pollutant of concern for SI engines;

 According to the emission factors in the applicable NSPS requirements, the CO emission factor of 

6.7 g/kW-hour for landfill/digester gas represents the worst-case fuel for non-emergency SI

engines;

 For emergency engines, the AP-42 emission factor of 5.57 lb/MMBtu CO (23.72 g/kW-hour) was 

used – applicable to lean burn natural gas or LPG engines; and

 For natural gas auxiliary heaters, the AP-42 emission factor of 100 lb/MMscf CO. 

CO Emissions from Non-Emergency SI Engines

= capacity (hp) x emission factor x 8760 (hours/year) x 1 ton/2000 lb

= 1750 hp x 0.7457 kW/hp x 6.7 g CO/kW-hour x 1 lb/453.5928 g x 8760 hour/year x 

 1 ton/2000 lbs

= 84.5 tpy 

CO Emissions from Emergency Engines

= capacity (hp) x emission factor x 8760 (hours/year) x 1 ton/2000 lb

= 800 hp x 0.7457 kW/hp x 23.72 g/kW-hour x 1 lb/453.5928 g x 8760 hour/year x 

 1 ton/2000 lbs

= 7.80 tpy

CO Emissions from Natural Gas Auxiliary Heaters

= capacity (MMBtu/hour) x emission factor x heat content of fuel x 8760 (hours/year) x 

 1 ton/2000 lb

= 10 MMBtu/hour x 100 lb/MMscf x 1 scf/1020 Btu x 8760 hour/year x 1 ton/2000 lbs

= 4.3 tpy 

Total CO Emissions = 96.6 tpy (<100 tpy, the CO emission threshold for attainment areas)

CI Capacity Limits: 1900 hp for non-emergency engines and 2500 hp for emergency engines 

 Assume engines meet the requirements for Option 2 identified in Table 4 (the same calculation 

process was used for Option 1, but used different emission factors based on the applicable NSPS 

emission limits for generator sets);

 CO is the pollutant of concern for CI engines;
Page 20 of 20

 According to the emission factors in the applicable NSPS requirements, the CO emission factor of 5 

g/kW-hour for diesel engines less than 75 hp represents the worst-case emission factor for nonemergency CI engines;

 For emergency engines, the AP-42 emission factor of 5.57 lb/MMBtu CO (23.72 g/kW-hour) was 

used (applicable to lean burn natural gas or LPG engines); and

 For natural gas auxiliary heaters, the AP-42 emission factor of 100 lb/MMscf CO.

CO Emissions from Non-Emergency Ci Engines

= capacity (hp) x emission factor x 8760 (hours/year) x 1 ton/2000 lb

= 1900 hp x 0.7457 kW/hp x 5 g CO/kW-hour x 1 lb/453.5928 g x 8760 hour/year x 1 ton/2000 lbs

= 68.4 tpy 

CO Emissions from Emergency Engines

= capacity (hp) x emission factor x 8760 (hours/year) x 1 ton/2000 lb

= 2500 hp x 0.7457 kW/hp x 23.72 g/kW-hour x 1 lb/453.5928 g x 8760 hour/year x 1 ton/2000 lbs

= 24.4 tpy

CO Emissions from Natural Gas Auxiliary Heaters

= capacity (MMBtu/hour) x emission factor x heat content of fuel x 8760 (hours/year) x 

 1 ton/2000 lbs

= 10 MMBtu/hour x 100 lb/MMscf x 1 scf/1020 Btu x 8760 hour/year x 1 ton/2000 lb

= 4.3 tpy

Total CO Emissions = 97.1 tpy (<100 tpy the CO emission threshold for attainment areas)