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Citation: CFR 1983 ed. 618 1983 

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§ 51.2

from the ground-level elevation at the

base of the stack.

(kk) "Excessive concentrations" for

the purpose of determining good engineering practice stack height in a fluid

model or field study means a maxi- mum concentration due to downwash

wakes, or eddy effects produced by

structures or terrain features which is

at least 40 percent in excess of the

maximum concentration experienced

in the absence of such downwash,

wakes, or eddy effects.

(11) "Plume impaction" means con- centrations measured or predicted to occur when the plume interacts with

elevated terrain.

(mm) "Elevated terrain" means terrain which exceeds the elevation of

the good engineering practice stack as calculated under paragraph (ii) of this

section.

(Secs. 110, 123, 301(a), Clean Air Act as amended (42 U.S.C. 7410, 7423, 7601))

[36 FR 22398, Nov. 25, 1971, as amended at

37 FR 26311, Dec. 9, 1972; 38 FR 15195, June

8, 1973; 40 FR 7043, Feb. 18, 1975; 40 FR

46247, Oct. 6, 1975; 41 FR 18511, May 5, 1976; 43 FR 46269, Oct. 5, 1978; 47 FR 5868,

Feb. 8, 1982]

§ 51.2 Stipulations.

Nothing in this part shall be con- strued in any manner: (a) To encourage a State to prepare,

adopt, or submit a plan which does not

provide for the protection and en- hancement of air quality so as to promote the public health and welfare

and productive capacity.

(b) To encourage a State to adopt

any particular control strategy without taking into consideration the costeffectiveness of such control strategy in relation to that of alternative con- trol strategies.

(c) To preclude a State from employ- ing techniques other than those specified in this part for purposes of estimating air quality or demonstrating

the adequacy of a control strategy,

provided that such other techniques are shown to be adequate and appropriate for such purposes.

(d) To encourage a State to prepare,

adopt, or submit a plan without taking

into consideration the social and eco- nomic impact of the control strategy

set forth in such plan, including, but

not limited to, impact on availability

Title 40-Protection of Environment

of fuels, energy, transportation, and

employment.

(e) To preclude a State from preparing, adopting, or submitting a plan

which provides for attainment and

maintenance of a national standard

through the application of a control

strategy not specifically identified or described in this part.

(f) To preclude a State or political

subdivision thereof from adopting or enforcing any emission limitations or other measures or combinations thereof to attain and maintain air quality

better than that required by a national standard.

(g) To encourage a State to adopt a control strategy uniformly applicable

throughout a region unless there is no satisfactory alternative way of providing for attainment and maintenance of a national standard throughout such

region.

§ 51.3 Classification of regions.

This section establishes a classification system to categorize regions for

purposes of plan development and

evaluation. The requirements of this

part vary according to the classification of each region, in order that the

time and resources to be expended in

developing the plan for that region, as well as the substantive content of the

plan, will be commensurate with the

complexity of the air pollution problem. The classification will be based

upon measured ambient air quality,

where known, or, where not known, es- timated air quality in the area of

maximum pollutant concentration. All

regions will be classified by the Administrator after consultation with

State agencies. Each region will be

classified separately with respect to

each of the following pollutants:

Sulfur oxides, particulate matter,

carbon monoxide, nitrogen dioxide,

and ozone. (a) For sulfur oxides and particulate

matter, each region will be classified

into one of three categories, defined as Priority I, Priority II, or Priority III.

(1) (i) Ambient concentration limits,

expressed as micrograms per cubic

meter and parts per million by volume

(p.p.m. in parentheses) which define

the classification system for sulfur

oxides and particulate matter are:

618
Chapter I-Environmental Protection Agency

Priority Pollutant I-Greater than Il-From-To Ill-Less than

Sulfur oxides:

Annual arithmetic mean ...................................................... 100 (0.04) 60-100 (0.02-0.04) 60 (0.02)

24-hour maximum ................................................................ 455 (0.17) 260-455 (0.10-0,17) 260 (0.10)

3-hour maximum ................................................................................................... -- 1,300 (0.50) 1,300 (0.50)

Particulate matter:

Annual geometric mean ...................................................... 95 60-95 60

24-hour maximum ................................................................ 325 150-325 150

Any concentration above 1,300 ,g/m 3 (0.50 p.p.m.).

(ii) The more restrictive classification will be chosen where there is a

difference between the maximum

value(s) and the annual averages e.g.,

if a region is Priority I with respect to

an annual average and Priority II with

respect to a 24-hour maximum value,

the classification will be Priority I.

(2) Procedures which may be used,

where appropriate, to estimate air

quality in regions where no measured

data or inadequate data exist are described in Appendix A to this part.

(b) For carbon monoxide, nitrogen

dioxide, and ozone, each region will be

classified into one of two categories

defined as Priority I or Priority III.

(1) Ambient concentration limits

which define the classification system

are:

(i) Carbon monoxide: Priority I:

Equal to or above 55 milligrams per

cubic meter (48 p.p.m.), 1-hour maximum, or 14 milligrams per cubic meter

(12 p.p.m.), 8-hour maximum; Priority

III: Below such values.

(ii) Nitrogen dioxide: Priority I:

Equal to or above 110 micrograms per

cubic meter (0.06 p.p.m.) annual arithmetic mean; Priority III: Below such

value.

(iii) Ozone: Priority I: Equal to or

above 195 micrograms per cubic meter

(0.10 p.p.m.), 1-hour maximum; Priority III: Below such value.

(2) In the absence of measured data

to the contrary, classification with respect to carbon monoxide, ozone and

nitrogen dioxide will be based on the

following estimate of the relationship

between these pollutants and population: Any region containing an area

whose 1970 "urban place" population,

as defined in the U.S. Bureau of

Census, exceeds 200,000 will be classified Priority I. All other regions will

be classified Priority III.

(3) Where a region is classified Priority I on the basis of population, the air

quality data requirements of

§ 51.14(e)(1) shall apply. If these data

indicate the pollutant concentrations

are below the values stipulated in

paragraph (b)(1) of this section, the

region will be reclassified Priority III.

(4) Classifications with respect to

hydrocarbons will be the same as the

classifications with respect to ozone.

(c) Where a region is classified Priority I on the basis of measured or estimated air quality levels reflecting

emissions predominantly from a single

point source, it shall be further classified Priority IA. The requirements applicable to Priority IA regions shall be

the same as those for other Priority I

regions, except that the requirements

applicable to Priority II regions under

§ 51.16 shall apply. A procedure for estimating air quality levels reflecting

emissions from a single point source is

described in Appendix A to this part.

(Secs. 110, 301(a), 313, 319, Clean Air Act (42

U.S.C. 7410, 7601(a), 7613, 7619))

(36 FR 22398, Nov. 25, 1971, as amended at

44 PR 27569, May 10, 1979)

§ 51.4 Public hearings.

(a) (1) Except as otherwise provided

in paragraph (a)(2) of this section, the

State shall, prior to the adoption of

any plan or any revision thereof required by § 51.6(a) or prior to the submission to the Administrator of any

individual compliance schedule pursuant to § 51.15(a) or any revision pursuant to § 51.6(d), conduct one or more

public hearings on such plan, schedule, or revision. Separate hearings may

be held for plans to implement primary and secondary standards.

(2) No hearing shall be required for

any change to an increment of prog619

§ 51.4