Sec. 249.2. Definitions

For the purpose of this regulation, the following definitions apply:

(a) Best Available Retrofit Technology or BART. An emission limitation based on the degree of reduction achievable through the application of the best system of continuous emission reduction for each visibility-impairing pollutant which is emitted by an existing stationary facility. BART for any individual source is determined by undertaking the case-by-case analysis required under section 249.3 of this Part.

(b) Deciview.

A measurement of visibility impairment. A deciview is a haze index derived from calculated light extinction, such that uniform changes in haziness correspond to uniform incremental changes in perception across the entire range of conditions, from pristine to highly impaired. The deciview haze index is calculated based on the following equation (for the purposes of calculating deciview, the atmospheric light extinction coefficient must be calculated from aerosol measurements):

HI = 10 ln (b/10)Where b = the atmospheric light extinction coefficient, expressed in inverse megameters (Mm^-1).

(c) Federal Class I Area.

A national park which exceeds 6,000 acres, national wilderness area which exceeds 5,000 acres, national memorial park which exceeds 5,000 acres, or any international park, which was in existence as of August 7, 1977.

(d) In existence.

As used in section 249.1(b)(2) of this Part, the owner or operator has obtained all necessary preconstruction approvals or permits required by Federal, State, or local air pollution emissions and air quality laws or regulations and either has:

(1) begun, or caused to begin, a continuous program of physical on-site construction of the facility; or

(2) entered into binding agreements or contractual obligations, which cannot be canceled or modified without substantial loss to the owner or operator, to undertake a program of construction of the facility to be completed in a reasonable time.

(e) Light extinction.

The process of light being absorbed or scattered as it passes through a medium, such as the atmosphere.

(f) Natural visibility conditions.

Includes naturally occurring phenomena that reduce visibility as measured in terms of light extinction, visual range, contrast, or coloration.

(g) Reconstruction.

Where the fixed capital cost of the new component exceeds 50 percent of the fixed capital cost of a comparable entirely new source. Any final decision as to whether reconstruction has occurred must be made in accordance with the provisions of 40 CFR 60.15(f)(1) through (3).

(h) Regional haze.

Visibility impairment that is caused by the emission of visibility-impairing air pollutants from numerous sources located over a wide geographic area.

(i) Visibility-impairing pollutant.

Sulfur dioxide (SO₂), nitrogen oxides (NO_x), and particulate matter less than or equal to 10 microns in diameter (PM₁₀).

(j) Visibility impairment.

Any humanly perceptible change in visibility (light extinction, visual range, contrast, coloration) from that which would have existed under natural conditions.