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Citation: CFR 1983 ed. 618 1983

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from the ground-level elevation at the base ofthe stack.

(kk) "Excessive concentrations" for the purpose of determining good engineering practice stack height inafluid 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, oreddyeffects.

(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 (42U.S.C. 7410,7423,7601)) [36 FR22398, Nov. 25, 1971, asamended at 37FR 26311, Dec.9, 1972;38FR 15195,June 8,1973; 40 FR 7043, Feb. 18, 1975; 40 FR 46247, Oct. 6, 1975; 41 FR 18511, May 5, 1976;43 FR46269, Oct.5, 1978;47FR 5868, Feb.8, 1982]
§51.2 Stipulations.

Nothing in this part shall be con- strued inanymanner:

(a) To encourage a State to prepare, adopt,orsubmit aplan which doesnot provide for the protection and en- hancement of air quality so as to promote the public health and welfare andproductive 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) Toprecludea State from employ- ingtechniques other thanthose 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 suchpurposes.

(d) To encourage a State to prepare, adopt,or submitaplan withouttaking 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 aState 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 inthis part.

(f) To preclude a State or political subdivision thereof from adopting or enforcing any emission limitations or other measures orcombinations 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 aregion unless there is no satisfactory alternative way ofproviding forattainment andmaintenance of

a national standard throughout such region.
§51.3 Classification ofregions.

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 forthat region, as well asthe 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 notknown, 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) Forsulfur oxides andparticulate matter, each region will be classified into one ofthree categories, defined as Priority I,Priority II,orPriority III.

(1) (i) Ambient concentration limits, expressed as micrograms per cubic meter and parts permillion by volume (p.p.m. in parentheses) which define the classification system for sulfur oxides andparticulate matterare:



### 618Chapter I-Environmental Protection Agency

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

Sulfuroxides: 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-hourmaximum

................................................................................................... -- 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 concentrationabove 1,300 ,g/m3(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 PriorityII with respect to a 24-hour maximum value, the classification willbe 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 Ato thispart.

(b) For carbon monoxide, nitrogen dioxide, andozone, each region willbe classified into one of two categories defined as Priority IorPriority 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 suchvalue.

(2) In the absence ofmeasured 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 isclassified Priority I onthe basis ofpopulation, 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 withrespect toozone.

(c) Where a region isclassified 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 singlepoint source is described in Appendix Ato thispart. (Secs. 110, 301(a), 313, 319, CleanAir Act(42 U.S.C.7410, 7601(a), 7613, 7619)) (36 FR 22398, Nov. 25, 1971, as amended at 44PR27569, May 10, 1979)

§51.4 Public hearings.

(a) (1) Except as otherwise provided in paragraph (a)(2) ofthis section, the State shall, prior to the adoption of any plan or any revision thereof required by §51.6(a) orprior 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, orrevision. 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 prog

### 619 §51.4