ARTICLE 6. EMISSIONS FROM EXISTING AND NEW NONPOINT SOURCES

R18-2-601. General

For purposes of this Article, any source of air contaminants which due to lack of an identifiable emission point or plume cannot be considered a point source,

shall be classified as a nonpoint source. In applying this criteria, such items as air-curtain destructors, heater-planners, and conveyor transfer points shall be

considered to have identifiable plumes. Any affected facility subject to regulation under Article 7 of this Chapter or Title 18, Chapter 2, Article 9, shall not be

subject to regulation under this Article.

Historical Note

Former Section R9-3-601 repealed, new Section R9-3-601 adopted effective May 14, 1979 (Supp. 79-1). Former Section R9-3-601 renumbered without

change as Section R18-2-601 (Supp. 87-3). Amended effective September 26, 1990 (Supp. 90-3). Former Section R18-2-601 renumbered to R18-2-

801, new Section R18-2-601 renumbered from R18-2-401 and amended effective November 15, 1993 (Supp. 93-4). Section updated to reflect

corrected citation reference (Supp. 08-1).
ARTICLE 4. PERMIT REQUIREMENTS FOR NEW MAJOR SOURCES AND MAJOR 

MODIFICATIONS TO EXISTING MAJOR SOURCES

R18-2-401. Definitions

The following definitions apply to this Article:

1. “Adverse impact on visibility” means visibility impairment that interferes with the 

management, protection, preservation, or enjoyment of the visitor’s visual experience of a 

Class I area, as determined according to R18-2-410.

2. “Baseline actual emissions” means the rate of emissions, in tons per year, of a regulated 

NSR pollutant, as determined in accordance with subsections (2)(a) through (c).

a. For any existing electric utility steam generating unit, baseline actual emissions means 

the average rate, in tons per year, at which the unit actually emitted the pollutant during 

any consecutive 24-month period selected by the owner or operator within the fiveyear period immediately preceding when the owner or operator begins actual 

construction of the project. The Director shall allow the use of a different time period 

upon a determination that it is more representative of normal source operation.

i. The average rate shall include fugitive emissions to the extent quantifiable, and 

emissions associated with startups, shutdowns, and malfunctions.

ii. The average rate shall be adjusted downward to exclude any non-compliant 

emissions that occurred while the source was operating above any emission 

limitation that was legally enforceable during the consecutive 24-month period.

iii. For a regulated NSR pollutant, when a project involves multiple emissions units, 

only one consecutive 24-month period must be used to determine the baseline 

actual emissions for the emissions units being changed. A different consecutive 24-

month period can be used for each regulated NSR pollutant.

iv. The average rate shall not be based on any consecutive 24-month period for which 

there is inadequate information for determining annual emissions, in tons per year, 

and for adjusting this amount if required by subsection (2)(a)(ii).

b. For any existing emissions unit (other than an electric utility steam generating unit), 

baseline actual emissions means the average rate, in tons per year, at which the unit 

actually emitted the pollutant during any consecutive 24-month period selected by the 

owner or operator within the 10-year period immediately preceding either the date the 

owner or operator begins actual construction of the project, or the date a complete 

permit application is received by the Administrator for a permit required under 40 CFR 

52.21 or by the Director for a permit required under the state implementation plan, 

whichever is earlier, except that the 10-year period shall not include any period earlier 

than November 15, 1990.

i. The average rate shall include fugitive emissions to the extent quantifiable, and 

emissions associated with startups, shutdowns, and malfunctions.

ii. The average rate shall be adjusted downward to exclude any non-compliant 

emissions that occurred while the source was operating above any emission 

limitation that was legally enforceable during the consecutive 24-month period. 

This provision applies to excess emissions associated with a malfunction.

iii. The average rate shall be adjusted downward to exclude any emissions that would 

have exceeded an emission limitation with which the major source must currently 

comply, had such major source been required to comply with such limitations 

during the consecutive 24-month period. However, if an emission limitation is part
of a maximum achievable control technology standard that the Administrator 

proposed or promulgated under 40 CFR 63, the baseline actual emissions need only 

be adjusted if the state of Arizona has taken credit for such emissions reductions in 

an attainment demonstration or maintenance plan submitted to the Administrator 

pursuant to section 110(a)(1) of the Act.

iv. For a regulated NSR pollutant, when a project involves multiple emissions units, 

only one consecutive 24-month period must be used to determine the baseline 

actual emissions for all existing emissions units affected by the project. A different 

consecutive 24-month period may be used for each regulated NSR pollutant.

v. The average rate shall not be based on any consecutive 24-month period for which 

there is inadequate information for determining annual emissions, in tons per year, 

and for adjusting this amount if required by subsection (2)(b)(ii) or (iii).

c. For a new emissions unit, the baseline actual emissions for purposes of determining the 

emissions increase that will result from the initial construction and operation of such 

unit shall equal zero; and thereafter, for all other purposes, shall equal the unit’s 

potential to emit.

d. For a PAL for a stationary source, the baseline actual emissions shall be calculated for 

existing electric utility steam generating units in accordance with the procedures in 

subsection (2)(a), for other existing emissions units in accordance with the procedures 

contained in subsection (2)(b), and for new emissions units in accordance with the 

procedures contained in subsection (2)(c).

3. “Basic design parameter” means:

a. Except as provided in subsection (3)(c), for a process unit at a steam electric generating 

facility, the owner or operator may select as its basic design parameters either 

maximum hourly heat input and maximum hourly fuel consumption rate or maximum 

hourly electric output rate and maximum steam flow rate. When establishing fuel 

consumption specifications in terms of weight or volume, the minimum fuel quality 

based on Btu content shall be used for determining the basic design parameters for a 

coal-fired electric utility steam generating unit.

b. Except as provided in subsection (3)(c), the basic design parameters for any process unit 

that is not at a steam electric generating facility are maximum rate of fuel or heat input, 

maximum rate of material input, or maximum rate of product output. Combustion 

process units will typically use maximum rate of fuel input. For sources having multiple 

end products and raw materials, the owner or operator should consider the primary 

product or primary raw material when selecting a basic design parameter.

c. If the owner or operator believes the basic design parameters in subsections (3)(a) and 

(b) are not appropriate for a specific industry or type of process unit, the owner or 

operator may propose to the Director an alternative basic design parameters for the 

source’s process unit. If the Director approves of the use of an alternative basic design 

parameters, the Director shall issue a permit that is legally enforceable that records such 

basic design parameters and requires the owner or operator to comply with such 

parameters.

d. The owner or operator shall use credible information, such as results of historic 

maximum capability tests, design information from the manufacturer, or engineering 

calculations, in establishing the magnitude of the basic design parameters specified in 

subsections (3)(a) and (b).
e. If design information is not available for a process unit, then the owner or operator shall 

determine the process unit’s basic design parameters using the maximum value 

achieved by the process unit in the five-year period immediately preceding the planned 

activity.

f. Efficiency of a process unit is not a basic design parameter.

g. The replacement activity shall not cause the process unit to exceed any emission 

limitation, or operational limitation that has the effect of constraining emissions, that 

applies to the process unit and that is legally enforceable.

4. “Complete” means, in reference to an application for a permit or permit revision, that the 

application contains all the information necessary for processing the application.

5. “Dispersion technique” means any technique that attempts to affect the concentration of a 

pollutant in the ambient air by any of the following:

a. Using that portion of a stack that exceeds good engineering practice stack height;

b. Varying the rate of emission of a pollutant according to atmospheric conditions or 

ambient concentrations of that pollutant; or

c. Increasing final exhaust gas plume rise by manipulating source process parameters, 

exhaust gas parameters, stack parameters, or combining exhaust gases from several 

existing stacks into one stack; or other selective handling of exhaust gas streams that 

increases the exhaust gas plume rise. This shall not include any of the following:

i. The reheating of a gas stream, following use of a pollution control system, for the 

purpose of returning the gas to the temperature at which it was originally discharged 

from the facility generating the gas stream.

ii. The merging of exhaust gas streams under any of the following conditions:

(1) The source owner or operator demonstrates that the facility was originally 

designed and constructed with the merged gas streams;

(2) After July 18, 1985, the merging is part of a change in operation at the facility 

that includes the installation of pollution controls and is accompanied by a net 

reduction in the allowable emissions of a pollutant, applying only to the 

emission limitation for that pollutant; or

(3) Before July 8, 1985, the merging was part of a change in operation at the facility 

that included the installation of emissions control equipment or was carried out 

for sound economic or engineering reasons. Where there was an increase in the 

emission limitation or, in the event that no emission limitation was in existence 

prior to the merging, an increase in the quantity of pollutants actually emitted 

prior to the merging, the Department shall presume that merging was 

significantly motivated by an intent to gain emissions credit for greater 

dispersion. Absent a demonstration by the source owner or operator that 

merging was not significantly motivated by such intent, the Department shall 

deny credit for the effects of the merging in calculating the allowable emissions 

for the source.

iii. Smoke management in agricultural or silvicultural prescribed burning programs.

iv. Episodic restrictions on residential woodburning and open burning.

v. Techniques that increase final exhaust gas plume rise if the resulting allowable 

emissions of sulfur dioxide from the facility do not exceed 5,000 tons per year.

6. “Existing emissions unit” is any emissions unit that is currently in existence and that is not 

a new emissions unit. A replacement unit is an existing emissions unit.
7. “High terrain” means any area having an elevation of 900 feet or more above the base of the 

stack of a source.

8. “Innovative control technology” means any system of air pollution control that has not been 

adequately demonstrated in practice but would have a substantial likelihood of achieving 

greater continuous emissions reduction than any control system in current practice, or of 

achieving at least comparable reductions at lower cost in terms of energy, economics, or 

nonair quality environmental impacts.

9. “Low terrain” means any area other than high terrain.

10. “Lowest achievable emission rate” (LAER) means, for any source, the more stringent rate 

of emissions based on one of the following: 

a. The most stringent emissions limitation that is contained in any implementation plan 

approved or promulgated under sections 110 or 172 of the Act for the class or category 

of stationary source, unless the owner or operator of the proposed stationary source 

demonstrates that the limitation is not achievable; or 

b. The most stringent emissions limitation that is achieved in practice by the class or 

category of stationary source. This limitation, when applied to a modification, means 

the lowest achievable emissions rate for the new or modified emissions units within the 

stationary source. The application of this term shall not permit a proposed new or 

modified stationary source to emit any pollutant in excess of the amount allowable 

under applicable standards of performance in Articles 9 and 11 of this Chapter.

11. “Major source” means:

a. Any stationary source located in a nonattainment area that emits, or has the potential to 

emit, 100 tons per year or more of any regulated NSR pollutant, except that the 

following thresholds shall apply in areas subject to subpart 2, subpart 3 or subpart 4 of 

part D, Title I of the Act:

Pollutant 

Emitted

Nonattainment

Pollutant and 

Classification

Quantity 

Threshold

tons/year or 

more

Carbon 

Monoxide (CO)

CO, Serious, if stationary sources contribute significantly to CO 

levels in the area as determined under rules issued by the 

Administrator

50 

VOC

VOC

PM10

NOx

NOx

Ozone, Serious

Ozone, Severe

PM10, Serious

Ozone, Serious

Ozone, Severe

50

25

70

50

25

b. Any stationary source located in an attainment or unclassifiable area that emits, or has 

the potential to emit, 100 tons per year or more of any regulated NSR pollutant if the 

source is classified as a Categorical Source, or 250 tons per year or more of any 

regulated NSR pollutant if the source is not classified as a Categorical Source;

c. Any stationary source that emits, or has the potential to emit, five or more tons of lead 

per year;

d. A major source that is major for VOC or nitrogen oxides shall be considered major for 

ozone; or
e. The fugitive emissions of a stationary source shall not be included in determining for 

any of the purposes of this Section whether it is a major stationary source, unless the 

source belongs to a section 302(j) category.

12. “New emissions unit” means any emissions unit which is (or will be) newly constructed 

and which has existed for less than two years from the date such emissions unit first 

operated.

13. “Plantwide applicability limitation” or “PAL” means an emission limitation that is based 

on the baseline actual emissions of all emissions units at the stationary source that emit or 

have the potential to emit the PAL pollutant, expressed in tons per year, for a pollutant at 

a major source, that is enforceable as a practical matter and established source-wide in 

accordance with this Section.

14. “PAL allowable emissions” means “allowable emissions” as defined in R18-2-101, except 

that the allowable emissions for any emissions unit shall be calculated considering any 

emission limitations that are enforceable as a practical matter on the emissions unit’s 

potential to emit.

15. PAL effective date generally means the date of issuance of the PAL permit. However, the 

PAL effective date for an increased PAL is the date any emissions unit that is part of the 

PAL major modification becomes operational and begins to emit the PAL pollutant.

16. “PAL effective period” means the period beginning with the PAL effective date and ending 

10 years later.

17. “PAL major modification” means any physical change in or change in the method of 

operation of the PAL source that causes it to emit the PAL pollutant at a level equal to or 

greater than the PAL.

18. “PAL permit” means the permit issued by the Director that establishes a PAL for a major 

source.

19. “PAL pollutant” means the pollutant for which a PAL is established at a major source.

20. “Projected actual emissions” means:

a. The maximum annual rate, in tons per year, at which an existing emissions unit is 

projected to emit a regulated NSR pollutant during any 12-month period in the 60 

calendar months following the date the unit resumes regular operation after the project, 

or in any 12-month period in the 120 calendar months following that date if the project 

involves increasing the design capacity or potential to emit of any emissions unit for 

that regulated NSR pollutant and full utilization of the unit would result in a significant 

emissions increase or a significant net emissions increase at the major source.

b. In determining the projected actual emissions before beginning actual construction, the 

owner or operator of the major source:

i. Shall consider all relevant information, including but not limited to, historical 

operational data, the company’s own representations, the company’s expected 

business activity and the company’s highest projections of business activity, the 

company’s filings with the county, state or federal regulatory authorities, and 

compliance plans under these regulations; and

ii. Shall include fugitive emissions to the extent quantifiable;

iii. Shall include emissions associated with startups and shutdowns, except emissions 

from a shutdown associated with a malfunction; and

iv. Shall exclude, only for calculating any increase in emissions that results from the 

particular project, that portion of the unit’s emissions following the project that an 
existing unit could have accommodated during the consecutive 24-month period 

used to establish the baseline actual emissions and that are also unrelated to the 

particular project, including any increased utilization due to product demand 

growth; or

c. In lieu of using the method set out subsections (20)(b)(i) through (iv), the owner or 

operator may elect to use the emissions unit’s potential to emit, in tons per year.

21. “Reconstruction” of sources located in nonattainment areas shall be presumed to have taken 

place if the fixed capital cost of the new components exceeds 50% of the fixed capital cost 

of a comparable entirely new stationary source, as determined in accordance with the 

provisions of 40 CFR 60.15(f)(1) through (3).

22. “Replacement unit” means an emissions unit for which all the criteria listed in subsections 

(22)(a) through (d) are met. No creditable emission reductions shall be generated from 

shutting down the existing emissions unit that is replaced.

a. The emissions unit is a reconstructed unit within the meaning of 40 CFR 60.15(b)(1), or 

the emissions unit completely takes the place of an existing emissions unit.

b. The emissions unit is identical to or functionally equivalent to the replaced emissions 

unit.

c. The replacement does not alter the basic design parameters of the process unit.

d. The replaced emissions unit is permanently removed from the major source, otherwise 

permanently disabled, or permanently barred from operation by a permit that is 

enforceable as a practical matter. If the replaced emissions unit is brought back into 

operation, it shall constitute a new emissions unit.

23. “Resource recovery project” means any facility at which solid waste is processed for the 

purpose of extracting, converting to energy, or otherwise separating and preparing solid 

waste for reuse. Only energy conversion facilities that utilize solid waste that provides 

more than 50% of the heat input shall be considered a resource recovery project under this 

Article.

24. “Significant emissions unit” means an emissions unit that emits or has the potential to emit 

a PAL pollutant in an amount that is equal to or greater than the significant level for that 

PAL pollutant, but less than the amount that would qualify the unit as a major emissions 

unit.

25. “Significance levels” means the following ambient concentrations for the enumerated 

pollutants:

Averaging Time 

Pollutant Annual 24-Hour 8-Hour 3-Hour 1-Hour

SO2 1 μg/m35 μg/m325 μg/m3

NO2 1 μg/m3

CO 0.5 mg/m32 mg/m3

PM10 1 μg/m35 μg/m3

PM2.5 

Class I area 0.06 μg/m3 0.07 μg/m3

PM2.5 

Class II area 0.3 μg/m3 1.2 μg/m3
PM2.5 

Class III area 0.3 μg/m3 1.2 μg/m3

Except for the annual pollutant concentrations, the Department shall deem that exceedance of 

significance levels has occurred when the ambient concentration of the above pollutant is 

exceeded more than once per year at any one location. If the concentration occurs at a specific 

location and at a time when Arizona ambient air quality standards for the pollutant are not 

violated, the significance level does not apply.

26. “Small emissions unit” means an emissions unit that emits or has the potential to emit the 

PAL pollutant in an amount less than the significant level for that PAL pollutant.

Historical Note

Adopted effective May 14, 1979 (Supp. 79-1). Amended effective October 2, 1979 (Supp. 

79-5). Former Section R9-3-401 renumbered without change as Section R18-2-401 

(Supp. 87-3). Section R18-2-401 renumbered to R18-2-601. New Section R18-2-401 

adopted effective November 15, 1993 (Supp. 93-4). Amended by final rulemaking at 5 

A.A.R. 4074, effective September 22, 1999 (Supp. 99-3). Typographical error corrected 

in R18-2-401(9)(a) (Supp. 00-4). Amended by final rulemaking at 13 A.A.R. 1134, 

effective May 5, 2007 (Supp. 07-1). Amended by final rulemaking at 18 A.A.R. 1542, 

effective August 7, 2012 (Supp. 12-2).